Pediatric Clinical Pharmacology 2011
Pediatric Clinical Pharmacology 2011
Pediatric Clinical Pharmacology 2011
Volume 205
Editor-in-Chief
F.B. Hofmann, München
Editorial Board
J.A. Beavo, Seattle, WA
J.E. Barrett, Philadelphia
D. Ganten, Berlin
P. Geppetti, Florence
J.-A. Karlsson, Singapore
M.C. Michel, Ingelheim, Germany
C.P. Page, London
W. Rosenthal, Berlin
Pediatric Clinical
Pharmacology
Editors Prof. Dr. Anders Rane
Prof. em. Dr. Hannsjörg W. Seyberth Karolinska University Hospital
Klinik für Kinder- und Jugendmedizin Karolinska Institutet
Philipps-Universität Marburg Dept. Laboratory Medicine
Baldingerstraße Div. Clinical Pharmacology
35043 Marburg, Germany Stockholm
Sweden
Present address: anders.rane@ki.se
Lazarettgarten 23
76829 Landau
Germany
seyberth@staff.uni-marburg.de
v
vi Preface
pharmacotherapeutics. This has led to a widespread off label use of highly potent
but also precarious modern medicines especially in the very young and very sick
pediatric population.
The objective of this volume is to overcome in part some of these gaps by giving
an overview of the present state of the art of pediatric clinical pharmacology
including developmental physiology, pediatric-specific pathology, special tools
and methods for development of drugs for children (assessment of efficacy, toxicity,
long-term safety, etc.) as well as regulatory and ethical knowledge and skills. In the
future, structural and educational changes have to lead back to a closer cooperation
and interaction of pediatrics with (clinical) pharmacology and pharmacy. Medical
faculties and learned societies might consider establishing a tenure track system for
well-trained pediatric pharmacologists. Moreover, the young general pediatrician
needs to be better trained in the basics of pediatric drug treatment. Hopefully,
pediatric pharmacology will not end with better knowledge and medical service for
children in high-industrial countries only but will also help to improve drug
treatment especially for those children in the developing countries. Intense interna-
tional networking initiatives could be very helpful to come closer to achieve the
goal of better medicines for all children worldwide.
Truly the time should be over, in which drug treatment was everybody’s business
with the consequence that this everybody’s business is frequently nobody’s business
(Shirkey 1975).
Developmental Pharmacokinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Johannes N. van den Anker, Matthias Schwab, and Gregory L. Kearns
vii
viii Contents
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
Contributors
Joachim Boos Klinik und Poliklinik für Kinder- und Jugendmedizin, Westfälische
Wilhems-Universität, 48149 Münster, Germany
Patricia Bright U.S. Department of Health and Human Services, Food and Drug
Administration, Office of the Commissioner, Office of Pediatric Therapeutics,
Silver Spring, MD 2011, USA
ix
x Contributors
Jason Gerson U.S. Department of Health and Human Services, Food and Drug
Administration, Office of the Commissioner, Office of Pediatric Therapeutics,
Silver Spring, MD 2011, USA
Catherine S. Lee U.S. Department of Health and Human Services, Food and Drug
Administration, Office of the Commissioner, Office of Pediatric Therapeutics,
Silver Spring, MD 2011, USA
Robert M. Nelson U.S. Department of Health and Human Services, Food and
Drug Administration, Office of the Commissioner, Office of Pediatric Therapeutics,
Silver Spring, MD 2011, USA
Robert.Nelson@fda.hhs.gov
Michelle Roth-Cline U.S. Department of Health and Human Services, Food and
Drug Administration, Office of the Commissioner, Office of Pediatric Therapeutics,
Silver Spring, MD 2011, USA
Hannsj€
org W. Seyberth and Ralph E. Kauffman
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Classification of the Pediatric Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Description of the Five Relevant Periods of Development, Their Typical Features,
Common Health Problems, and the Impact on Pediatric Pharmacotherapy . . . . . . . . . . . . . . . 7
3.1 The Preterm Newborn: Period of Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 The Newborn Term Infant: Period of Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.3 The Infant and Toddler: Period of Rapid Growth and Physiological Maturation . . . 24
3.4 The Child: Period of Language, Socialization, and Continued Growth . . . . . . . . . . . . . 28
3.5 The Adolescent: Period of Final Growth and Reproductive Maturation . . . . . . . . . . . . 32
4 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1 Appropriate Tools for Assessment of Drug Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.2 Appropriate Animals and Cell Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.3 Appropriate Methods for Long-Term Safety Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Abbreviations
1 Introduction
Fig. 1 Five stages of development. The pediatric population extends from the preterm and term
newborn infant through childhood, and adolescence, or even to young adulthood. Each period of
development has its own very specific characteristics, such as period of survival, period of
adaptation, period of rapid growth and physiological maturation, period of language, socialization,
and continued growth, and period of final growth and reproductive maturation
Basics and Dynamics of Neonatal and Pediatric Pharmacology 7
Body composition correlates with both gestational and postnatal age, and it con-
tinues to change significantly during the first year of life (Ahmad et al. 2010; Ellis
2000; Fomon and Nelson 2002). High body water content and extracellular/intra-
cellular water ratio as well as very low body fat and muscle mass in the preterm
infant are important contributors to altered volumes of distribution (V(d)) of
hydrophilic and lipophilic medicines or highly tissue-bound drugs such as the
cardiac glycosides. For example, the larger total body water content of the newborn
infant (approximately 80% as compared with 60% of body weight by 5 months of
age) results in a larger mg/kg-loading dose of water-soluble medicines, such as the
aminoglycosides (Pacifici 2009).
The relatively large head circumference and cranial volume is the leading
characteristic of the body proportion from the very preterm newborn to the older
infant and toddler. Relatively large brain weight and cerebral blood flow, limited
plasma protein binding capacity, as well as increased blood–brain barrier perme-
ability all predispose the CNS to higher concentrations of administered medicines
than later in life (Strolin Benedetti et al. 2005).
Likewise, increased skin permeability needs to be considered whenever a medi-
cine is applied on the skin. Increased dermal absorption may increase risk of
adverse effects as with antibacterial agents such as alcohol and hexachlorophene
solution (Stewart and Hampton 1987) or provide an option for painless and nonin-
vasive transdermal drug delivery in preterm newborns as with caffeine for apnea
(Barrett and Rutter 1994).
The very (extremely) preterm newborn around the 22–23 weeks of gestation is
at the limit of viability because the incompletely developed complex pulmonary–
cardiovascular system is not prepared to function well in the extrauterine environ-
ment, even with intensive support. The multiple hazards are as follows:
8 H.W. Seyberth and R.E. Kauffman
At this stage, the infant is rarely in a life-threatening situation, but still is at risk for a
series of serious health problems related to immaturity of several organ systems.
These include:
– Transient tachypnea
Lack of clearance of lung fluid and relative deficiency of pulmonary surfactant
may cause transient tachypnea and RDS (Raju et al. 2006).
– Relapse into fetal circulation
Partial relapse into fetal circulation may lead to pulmonary hypertension of the
newborn. This condition may be associated with sepsis or sometimes with
maternal use of selective serotonin reuptake inhibitors (SSRIs) (Konduri and
Kim 2009; Koren and Boucher 2009; Ramachandrappa and Jain 2009).
– Temparature instability and apnea
CNS immaturity may lead to poor temperature control (Raju et al. 2006) and
failure of respiratory control with central apnea (Hunt 2006).
– Peristaltic dysfunction
Immaturity of the gastrointestinal tract may lead to feeding problems related to
peristaltic dysfunction and failure of sphincter control in the esophagus, stom-
ach, and intestines (Lebenthal and Lebenthal 1999; Neu 2007).
Basics and Dynamics of Neonatal and Pediatric Pharmacology 9
Hepatic Metabolism
Renal Elimination
At birth renal function is rather low, with a GFR down to 1 ml/min/kg, and does
not approach adult levels before the age of 6–12 months (Alcorn and McNamara
2002). Tubular secretion matures more slowly and full renal function is reached
at approximately 2–3 years of age (Fawer et al. 1979; Fettermann et al. 1965).
Delayed maturation of tubular reabsorption leads to glomerulotubular imbalance
with the risk of salt and water wasting (Alcorn and McNamara 2002; Bartelink
et al. 2006; Celsi and Aperia 1993). On the positive side, the decreased ability to
concentrate aminoglycosides in the tubular epithelium contributes to decreased
nephrotoxicity of aminoglycosides in newborns (Fleck and Br€aunlich 1995;
McCracken 1986).
Thus, it is not surprising that furosemide, which is mainly excreted as a substrate
of the PAH transport pathway unchanged in the urine, has a prolonged plasma half-
life (often exceeding 24 h) and a very low renal clearance particularly in the very
preterm newborns (Mirochnick et al. 1988; Peterson et al. 1980). Similarly, weak
organic acids such as penicillins and cephalorins, which are frequently used in
newborns, also have very low total clearances in preterm infants. The kidney almost
exclusively excretes these medicines by an active tubular organic anion transport
system, which has 20–30% of adult capacity at birth and approaches adult capacity
at approximately 7–8 months (Alcorn and McNamara 2002).
During the perinatal period many fundamental changes take place, which are
unique to the newborn and are not observed again during infancy, childhood, and
adolescence. To describe all these changes, which certainly have an impact on drug
targets, would be far beyond the scope of this subsection. Thus, only selected
aspects, where substantive progress is relevant to pediatric pharmacology, includ-
ing molecular pharmacodynamics and pharmacogenetics, are discussed.
Basics and Dynamics of Neonatal and Pediatric Pharmacology 11
Receptors/Binding Sites
– Adrenergic receptors
The ontogeny of drug–receptor interactions, particularly of the adrenergic and
cholinergic systems, has been of long-standing interest to pediatric pharmaco-
logists (Boréus 1972). However, methods for isolation of homogeneous cells
from organs of the fetus or the newborn ensuring that the cells and receptors
have not been altered during isolation and purification have not been adequately
developed (Whitsett et al. 1982). Nevertheless, there is ample direct and indirect
experimental evidence of ontogenic regulation of receptor number and function.
In the newborn rat brain, there are an increased number of b-adrenergic receptors
during the first weeks of life, while at the same time the number of a-adrenergic
receptors is declining after an initial rise in the rat brain shortly after birth
(Whitsett et al. 1982). Unfortunately, due to methodological reasons, similar
data in human tissue are often missing. Thus, more readily accessible circulating
nucleated blood cells, e.g., leukocytes, have been used with the assumption
that they may reflect the status of adrenergic receptors in the actual target
organ of interest (Fraser et al. 1981). Decreased b-adrenergic receptor sites
have been described in human cord blood neutrophils (PMN) of infants vagi-
nally delivered at term (Roan and Galant 1982). These findings may reflect
ontogenic differences between the neonatal and adult PMN. However, the effect
of increasing catecholamine secretion during the stress of delivery resulting in
downregulation of the b-adrenergic receptors cannot be ruled out.
More recent molecular pharmacology studies in the postnatal rat devoted to the
ontogenesis of b-adrenergic signaling indicate that, in contrast to the receptor
downregulation and desensitization of b-adrenergic receptors observed in the
adult, the numbers and responsiveness of b-adrenergic receptors increase in most
tissues of the immature organism in response to prolonged treatment with betami-
metics during the postnatal period. This developmental stage of the rat approxi-
mately correlates with the mid-to-late second and early third trimester of human
gestation (Slotkin et al. 2003). The process of downregulation and desensitization
are not inherent properties, but rather acquired during the above-mentioned vul-
nerable time interval when pregnant women may be treated with betamimetics for
preterm labor. Thus, intrauterine overstimulation with betamimetics during this
critical period of prenatal development can induce a permanent shift in the balance
of adrenergic-to-cholinergic tone with the risk of inducing functional and behav-
ioral teratogenesis. This is a currently offered working hypothesis in an attempt to
explain the association of prolonged (3–4 weeks) betamimetic treatment for
tocolysis and bronchodilatation of the mother with increases in functional and
behavioral disorders, including psychiatric disorders (e.g., autism), poor cognitive
and motor function, and school performance as well as changes in blood pressure
(e.g., hypertension) in the offspring (Witter et al. 2009).
– Prostanoid receptors
Prostanoids are abundantly generated throughout the perinatal period. They are
thought to be key players in the regulation of ductus arteriosus tone and in the
12 H.W. Seyberth and R.E. Kauffman
autoregulation of blood flow to the brain and retina as well as to the renal and
splanchnic vascular beds (Seyberth and K€
uhl 1988; Smith 1998; Wright et al. 2001).
The rapid changes in vascular physiology during postnatal life are not only
accomplished by rapid changes of the synthesis and metabolism of these
autacoids, but also by rapid adjustments in the turnover of prostanoid receptor
expression. This has been particularly well studied in the regulation of ductus
arteriosus tone (Smith 1998).
In utero, the main factors maintaining patency of the ductus arteriosus are
low oxygen tension and high levels of PGE2 and PGI2 (Fig. 2), which are
acting through prostanoid EP4 and IP receptors (Smith 1998; Smith and McGrath
1994; Leonhardt et al. 2003; Wright et al. 2001). Both receptors are coupled to
adenylate cyclase (Boie et al. 1994; Honda et al. 1993). cAMP generated by this
enzyme is considered to be the main intracellular second messenger involved in
smooth muscle relaxation, which is consistent with the potent vasodilator effect
PGE2 and PGI2 on the ductus. After birth, increased ductal oxygen tension and
a fall of prostanoid levels, which is accompanied by a marked reduction of
Fig. 2 Perinatal switch of ductus arteiosus from vasodilation to vasoconstriction. In utero, and to
some extent in the pretem newborn, patency of the ductus arteriosus is maintained by high levels
of PGE2 and PGI2 in addition to low oxygen tension. The potent vasodilator effect PGE2 and PGI2 on
the ductus is mediated through PGE2 and PGI2 receptors, EP4 and IP, respectively, by increasing
cAMP. cAMP is considered to be the main intracellular second messenger involved in smooth
muscle relaxation of the ductus. Postnatal increase in arterial PaO2 plays an important role in
functional closure of the ductus, which starts with oxygen-induced inhibition of O2-sensitive
potassium channels. This leads to smooth muscle cell depolarization and consequently to increased
calcium influx through voltage-dependent L-type calcium channels. In parallel with advancing
gestation, smooth muscle phosphodiesterase (PDE) isoforms in the ductus are increasingly expressed
leading to decreased intracellular cAMP, thus supporting the shift from dilatation to constriction of
the ductus arteriosus. PDE inhibitors such as milrinone, however, can prevent this shift
Basics and Dynamics of Neonatal and Pediatric Pharmacology 13
– Channel maturation and regulation of ductal tone during the perinatal period
Developmental changes of channel activities have been studied during rapid
physiological changes around birth. Besides the prostanoid system complex,
14 H.W. Seyberth and R.E. Kauffman
Fig. 3 Pharmacologic and genetic targets in transepithelial salt transport in distal tubule. Inherited
hypokalemic salt-losing tubular disorders (SLT) associated with secondary hyperaldosteronism
have common targets for mutations and pharmacological interventions such as the furosemide-
sensitive sodium-potassium-chloride cotransporter (NKCC2) and the thiazide-sensitive sodium-
chloride cotransporter (NCCT). The furosemide-like SLT is primarily a polyuric and
hypercalciuric loop disorder, while the thiazide-like SLT is a distal convoluted tubule (DCT)
disorder, which is characterized by persistent hypomagnesemia and hypocalciuria
adequate renal blood perfusion and function. The extreme low blood pressure of the
preterm infant with a mean arterial pressure of about 30 mm Hg makes an effective
filtration pressure highly dependent on the activity of vasoconstrictive angiotensin
II on the one hand and on vasodilatory renal prostanoids on the other hand (Evans
and Moorcraft 1992; Guignard 2002; Prevot et al. 2002; Seyberth et al. 1991). This
well-coordinated vasoconstriction and vasodilatation of the afferent and efferent
glomerular vasculature renders renal function oversensitive to any angiotensin-
converting enzyme (ACE) inhibitor or angiotensin receptor (ATR) antagonist and
prostanoid synthesis inhibitor. Thus, besides their intrinsic potency one cannot
expect any major differences in renal toxicity among ACE inhibitors and ATR
antagonists as well as among prostanoid synthesis inhibitors (FitzGerald and
Patrono 2001; Fr€olich 1997; Guignard 2002; Prevot et al. 2002). As long as one
avoids a prolonged ineffective circulatory volume created by extreme fluid restric-
tion, unnecessary furosemide treatment, and failure of ductal closure (all are
additional stimuli for the renin-angiotensin system), no major renal damage to the
preterm newborn is to be expected (Leonhardt et al. 2004; Seyberth et al. 1983).
Under this condition, even a 10- to 100-fold overdose of indomethacin, caused by
medication error, does not lead to significant deterioration of renal function
(Narayanan et al. 1999; Schuster et al. 1990).
(Holmstr€ om et al. 2007; Wheatley et al. 2002). ROP is a multifactorial disease of the
developing retinal vasculature under environmental, nutritional, and genetic influ-
ence. The postnatal interruption of a very vulnerable ongoing development around
26 weeks of gestation is a major trigger of this biphasic ocular disease (Hellstr€om
et al. 2009; Kermorvant-Duchemin et al. 2010). During the first ischemic phase after
birth, premature exposure of the retina to hyperoxia induces an arrest in vascular
development with a degeneration of already existing blood vessels. In the second,
vasoproliferative phase the avascular and ischemic retina triggers a compensatory
release of proangiogenic factors. This leads to abnormal, upregulated extraretinal
neovascularization, which may progress to retinal detachment and finally to blind-
ness. Basically, ROP is the result of an unbalanced activity of various proangiogenic
(such as VEGF and IGF1) and antiangiogenic (such as thrombospondin-1) factors,
interacting with protective effects of nutritional factors (such as docosahexaenoic
acid), and cytotoxic effects of oxidative and nitro-oxidative stress-dependent
mediators generated from interaction of trans-arachidonic acid with the nitrogen
dioxide radical or its precursors (Balazy and Chemtob 2008; Kermorvant-Duchemin
et al. 2010). This more complex view on the pathophysiology of ROP, however,
poses new challenges for more rational pharmacologic interventions in the future.
Presently, ROP-induced blindness in children, adolescents, and young adults has to
be considered as a major cause of all visual disorders.
Over the past 20 years, corticosteroid use in the preterm infant has fallen in and out
of favor. Steroids were introduced in the 1980s as a mode of preventing and treating
chronic (inflammatory) lung disease (CLD) in the preterm infant population. This
use has been targeted toward low birth weight infants who cannot be weaned off the
ventilator. Dose, duration, and timing of treatment with dexamethasone, the steroid
typically used in NICUs, have varied. Corticosteroids given postnatally are poten-
tially neurotoxic when given in high dose or when used in the first 96 h of life. The
mechanism by which they cause central nervous system damage is unknown, but
may be related to increased risk of periventricular leukomalacia (Levene 2007).
Unfortunately, there is still a need for long-term follow-up and reporting of late
neurological and developmental outcomes, especially among surviving infants, in
those who participated in randomized trials of early postnatal corticosteroid treat-
ment and who have already been sent to school (Doyle et al. 2010).
Body water content and extra/intracellular water ratio remain high as compared to
infants and children. However, with each week of gestational age body fat content
18 H.W. Seyberth and R.E. Kauffman
increases when compared with preterm newborns (Ahmad et al. 2010; Ellis 2000;
Fomon and Nelson 2002). Besides relatively large body surface area and head
circumference as well as high permeability of blood–brain barrier and skin, rapid
weight gain is a typical feature during this period of growth and development
(Strolin Benedetti et al. 2005). Greater vulnerability to CNS drug toxicity (e.g.,
local anesthetic agents and opioids) is in part the consequence of the decreased
blood–brain barrier (Latasch and Freye 2002)
Although the term newborn is in a much more mature stage of development than the
preterm newborn, they share several health problems with each other.
Icterus neonatorum (physiological jaundice) is certainly a safety hazard for both the
term and preterm newborn. It is the result of increased bilirubin production follow-
ing postnatal breakdown of fetal red blood cells combined with transient limitation
in the conjugation of bilirubin by the liver. Excess circulating unconjugated biliru-
bin is bound to high-affinity acidic binding sites on plasma albumin, from where it
can be displaced by highly bound acidic drugs, such as sulfisoxazole and ibuprofen,
thereby increasing the concentration of free unconjugated bilirubin that may diffuse
into the CNS. This increases the risk of kernicterus in newborn infants (Ahlfors
2004; Gal et al. 2006).
Metabolic instability during the adaptation period shortly after birth may cause
symptomatic hypoglycemia and hypocalcemia with seizures. This adaptive insta-
bility is often an endocrine/metabolic emergency situation leading to hospital
admission (No authors listed 2004). Besides prematurity and intrauterine growth
retardation, gestational diabetes is the most common cause for this neonatal com-
plication (Jain et al. 2008a, b).
In addition to the anatomical and metabolic causes of seizures, the newborn brain
is inherently prone to seizures as a consequence of incomplete neuronal matura-
tion processes. The first months of postnatal life are critical for brain development
(Ben-Ari and Holmes 2006; Dubois et al. 2008). At this age cerebral growth and
maturation are intense and are influenced by multiple external stimuli encountered
after birth. Besides dendritic growth and synaptic overproduction (in the gray
matter), which is followed by synaptic pruning, myelination in white matter is
essential for fast impulse conduction and for the structure maturation of functional
networks (Ben-Ari and Holmes 2006; Dubois et al. 2008; Holopainen 2008). It
is thought that at this stage the excitatory activity is enhanced and might contri-
bute to the developing brain’s greater capacity for activity-dependent plasticity.
Myelination is a long nonlinear process that runs from the last trimester of gestation
through the second decade of life with a peak in the first postnatal year. Besides
these structural changes, complex changes in development and function of neuro-
transmitter systems also occur including the postnatal excitatory-to-inhibitory
switch in gamma-aminobutyric acid (GABA) signaling. These functional changes
are described in more detail in “Neurotransmitters, Transporters, and Channels”.
Although parietal cells are well developed at term, the gastric pH is neutral at
birth. Decreased capacity for hydrogen ion secretion persists throughout infancy,
particularly represented by decreased acid production following pentogastrin stim-
ulation (Anderson and Lynn 2009; Stewart and Hampton 1987; Strolin Benedetti
et al. 2005). In addition, gastric contents are buffered by frequent feedings and
gastric emptying is delayed. Altogether, these factors significantly influence
the time course of drug absorption and bioavailability of acid-labile proteins and
medicines such as growth factors and penicillins, respectively (Strolin Benedetti
et al. 2005). Gastrointestinal absorption may also be facilitated for macromolecules
such as lactalbumin from human milk or for aminoglycosides in early infancy as a
consequence of the immature gastrointestinal mucosal barrier with increased per-
meability (Axelsson et al. 1989; Bhat and Meny 1984). In contrast, there are also
examples of decreased absorption, such as the absorption of fat-soluble vitamins
(vitamins D and E) in newborn infants probably because of the inadequate bile salt
concentration in the ileum (Strolin Benedetti et al. 2005) or poor lipase hydrolysis
of orally administered esters of a prodrug such as the palmitate ester of chloram-
phenicol (Shankaran and Kauffman 1984). Similarly, one step beyond intestinal
absorption and hepatic uptake, the ester prodrug oseltamivir is only partially
hydrolyzed to the active oseltamivir carboxylate by human carboxylasases. As
the activity of these enzymes is not fully developed in fetuses and young children
(Yang et al. 2009), one has to expect a low systemic bioavailability of the active
metabolite and a low efficacy of this neuraminidase inhibitor in newborn infants
and young children.
Little information regarding the clinical effects of ontogenetic changes of
cytochrome P450 enzymes and transporter proteins such as P-glycoprotein
(P-gp) in the small bowel is available (Johnson and Thomson 2008). Many oral
medicines used in pediatrics are major substrates for intestinal forms of CYP3A.
In duodenal biopsy specimens from pediatric patients aged 2 weeks to 17 years,
CYP3A4 expression and function were continuously increased with age (Johnson
et al. 2001). CYP3A4 was practically absent in the fetal duodenum and was
expressed at relatively low levels in the newborn, indicating a low first-pass
metabolism of pediatric medicines such as erythromycin (Johnson and Thomson
2008). There is also some evidence that expression of the transporter protein P-gp
is very low in the intestines of term infants as compared to young adults (Miki
et al. 2005).
Reduced expression of CYP3A and P-pg in newborns and young children can
result in increased bioavailability of medicines. For example, a study on oral
midazolam in preterm infants showed a higher bioavailability of 49% compared
to 27–36% in children (de Wildt et al. 2002; Johnson and Thomson 2008). How-
ever, the effect of reduced intestinal and hepatic first-pass metabolism on bioavail-
ability can offset several other bioavailability reducing factors such as altered gut
physiology (see above), intraluminal pH, reduced gastric emptying, or intestinal
transit time.
Basics and Dynamics of Neonatal and Pediatric Pharmacology 21
Decreased systemic clearances for most medicines are mainly related to immaturity
of hepatic and renal function (Alcorn and McNamara 2002; Rane 2005). Under
normal conditions, parturition triggers the dramatic development of hepatic
metabolism and renal function of the newborn term infant. However, there is
marked variability in the various maturation processes among the individual
drug-metabolizing enzymes and renal excretory functions, which often last over
the whole first year of life. Thus, this situation is a rapidly changing transitional
phase between the state of a newborn and that of an infant and a toddler (Alcorn and
McNamara 2002; Bartelink et al. 2006; Strolin Benedetti et al. 2005). Clearly, at
that early stage of development both genetic polymorphisms and ontogeny have a
major impact on individualized pharmacotherapy (Allegaert et al. 2007).
Receptors/Binding Sites
Opioid receptors are not fully developed in the newborn rat – one of the most
appropriate animal models to study the human species – and mature into adulthood
(Freye 1996; Latasch and Freye 2002). A phenomenal increase in opioid binding
sites occurs during maturation. Receptor density varies by brain region, with earlier
development of caudal and later development in rostral parts of the CNS. Earlier
development of opioid receptors in the medulla and pons, where the respiratory
center is located, is consistent with the clinical observations that the mean plasma
concentration of morphine that induces respiratory depression is in all pediatric age
groups including the newborns in the same range, while the mean blood level to
suppress pain is – with some overlap – about four to five times higher in newborns
and young infants as compared to older infants and children (Bouwmeester et al.
2003; Lynn et al. 1993; Olkkola et al. 1988). These pharmacological differences
of opioids in newborns, if neglected, may be a source of adverse drug reactions
22 H.W. Seyberth and R.E. Kauffman
Two examples that demonstrate the sensitivity of time windows of the brain
maturation and neuronal plasticity are presented.
Basics and Dynamics of Neonatal and Pediatric Pharmacology 23
The evidence that untreated or insufficiently treated pain in neonates and infants
results in long-term adverse consequences (e.g., hyperalgesia) stems from several
well-planned studies such as the randomized clinical trial on the effect of neonatal
circumcision with and without a topical local anesthetic on pain response during
subsequent vaccination 4–6 months later (Taddio et al. 1997). Even in extremely
preterm infants, painful procedures during intensive care and surgery have an
impact on somatosensory perception later in life (Walker et al. 2009; Hohmeister
et al. 2010). Thus, the immature CNS is a challenge when managing pain treatment
in infants with an emphasis on the need for a longer term view (Fitzgerald and
Walker 2009).
At this stage of development young children are still rapidly growing. Body weight
typically doubles by 5 months of age and triples by 1 year. By the first birthday,
body length and surface area increase by 50 and 200%, respectively. During this
period of rapid growth, accumulation of fat is remarkably rapid during the first
6 months of age. In contrast, body water content, particularly the extracellular/
intracellular ratio, continues to decrease throughout infancy (Fomon and Nelson
2002). From the drug disposition point of view, it is notable that the weight of liver
and kidney relative to total body weight reaches maximum in the 1- to 2-year-old
child, at the period of life when capacity for drug metabolism and elimination also
tends to be greatest (Kauffman 2005; Murry et al. 1995)
During the stage of intense lung growth and airway remodeling, small airway size
predisposes the child to acute obstructive lower airway diseases, e.g., bronchiolitis
(see also “Receptors/Binding Sites”), as well as to upper respiratory tract infections.
These infections probably lead to edema and dysfunction of the Eustachian tube,
which frequently contributes to middle ear infection (otitis media) (Kerschner 2007).
Postnatal maturation of the immune system is not yet complete during early
childhood, similar to the respiratory system (Holt et al. 2005). The reduced capa-
bility to express a sustained immune response predisposes young children to
infectious diseases. In addition, this concurrent maturation of immunologic and
respiratory functions may have implications for programming of long-term response
patterns to exogenous inflammatory stimuli within the immune and respiratory
systems (Holt et al. 2005).
Seizures
the highest tendency for seizure activity of anytime in life. A large number of
pathological processes may lead to seizures, including birth trauma and hypoxic–
ischemic insults immediately after birth, systemic infections and metabolic
imbalances in neonates, or fever in febrile seizures, which typically happen in
infants and young children (Ben-Ari and Holmes 2006). The high excitatory state
of the immature brain may also have some impact on the paradoxical effects of
midazolam in the very young (Tobin 2008).
Neoplastic Diseases
Frequently but not always, older infants, toddlers, and young children (see also
“Functional and Physiological Processes with Their Pathophysiology and Typical
Disorders and Their Health Problems”) exhibit the greatest overall drug clearance,
which is the result of the high metabolic and excretory function of liver and kidney.
For example, the half-life of diazepam is shortest in infants and longest in preterm
newborns and the elderly, with the magnitude of differences being more than
threefold (Coffey et al. 1983; Kauffman 2005; Mandelli et al. 1978). This “toddler
overshoot” may lead to therapeutic failure in cases where insufficient dose for age
is administered (Anderson and Lynn 2009; Chen et al. 2006; L€aer et al. 2005).
(For more clinically relevant examples, see “Major Organs of Metabolism and
Elimination”.)
Receptors/Binding Sites
is the heterogeneity of causes for infantile wheezing (Barr et al. 2000; Subbarao and
Ratjen 2006).
Mediators
More recently, another mediator system has been discussed that might be involved
in hyperresponsiveness of the tracheal–bronchial system of an infant or toddler. In a
well-established guinea pig maturational model that utilizes tracheal strips from
infant, juvenile, and adult animals, the role of airway smooth muscle in immature
airway hyperresponsiveness has been studied (Chitano et al. 2005). In contrast to
the adult, the infantile airway smooth muscle characteristically has a prostanoid-
mediated reduction of spontaneous relaxation during electric field stimulation
(Wang et al. 2008). Inhibition of prostanoid synthesis abolishes this reduced
relaxation and the age difference. A major role for leukotrienes was excluded.
Thus, it was concluded that the reduced spontaneous relaxation in immature airway
smooth muscle of the guinea pig and probably the airway hyperresponsiveness in
the young is associated with and most likely causally related to increased release of
contractile prostanoid (PGF2a, PGD2, and TXA2) (Wang et al. 2008). However,
extrapolation of the animal data to infants and toddlers with obstructive airway
disease has not yet been validated through well-designed efficacy and toxicity
studies with prostanoid synthesis inhibitors. Such well-controlled clinical studies
would be quite helpful in resolving the debate as whether ibuprofen is deleterious
or protective in children with asthma-related symptoms (Kanabar et al. 2007;
Kauffman and Lieh-Lai 2004).
Immune function
Thermoregulation
This period is characterized by slower growth rate with slender figure, increasing
muscular mass, and relative stable body habitus until the pubertal growth spurt. In
general, the various composition compartments – except the extracellular water
compartment – remain basically unchanged during this period of steady growth
(Ellis 2000; Kauffman 2005).
school (Alemzadeh and Wyatt 2007). The pathogenesis of this disorder is con-
sidered to be an autoimmune destruction of pancreatic islet b-cells, which
eventually leads to insulin deficiency.
Epilepsy
Childhood absence epilepsy is the most common form of pediatric seizures. This
benign idiopathic generalized epilepsy in an otherwise apparently healthy child is
characterized by daily frequent but brief spells. It is uncommon before the age of
5 years and typically goes into remission at the age of 10–12 years with a generally
good prognosis (Guerrini 2006).
Neoplastic Diseases
Neurobehavioral Disorders
Accidents
The child at this stage of development is intermediate between the immature infant
and the young adult (Kauffman 2005). The clearances of many hepatically
metabolized medicines, such as theophylline (Hendeles and Weinberger 1983),
omeprazole (Litalien et al. 2005), midazolam (Reed et al. 2001), and isoniazid
(McIlleron et al. 2009) are increased in children (ages 2–11 years) compared with
those of adults. This also applies to medicines, which are predominantly eliminated
by the kidney, such as sotalol (L€aer et al. 2005) and amikacin (Vogelstein et al.
1977). Consequently, higher doses are often required to achieve comparable thera-
peutic levels.
Glucose Metabolism
Coagulation System
diagnosis of hemostatic problems, reference ranges for children of all age groups
have been established. However, information on the developmental and matura-
tional changes in the pharmacodynamics of anticoagulants such as warfarin is very
limited. Apparently, Japanese children (1–11 years) with low plasma concen-
trations of vitamin K-dependent coagulation factors possess increased sensitivity
to the anticoagulant effect of warfarin (Takahashi et al. 2000). Although prepuber-
tal and adult patients showed comparable mean plasma concentrations of warfarin,
prepubertal children showed significant lower plasma concentrations of protein C
and prothrombin fragments 1 and 2 and higher INR. This augmented response to
warfarin in children, e.g., with congenital heart disease and valve replacement,
should be considered when estimating the most appropriate warfarin dose for them.
In this prepubescent pediatric population, one has primarily to consider the long-
term consequences of drug treatment of patients with chronic diseases or conditions
known as the “new pediatric morbidity” such as childhood asthma, neurodeve-
lopmental disorders, and cancer as well as obesity, arterial hypertension, and type
2 diabetes (Cox et al. 2008; Hausner et al. 2008). The latter disorders are the
consequences of “modern lifestyle” in Western as well as in emerging countries,
characterized by a decline in physical activity and an increased consumption of
“fast” processed food with high salt and caloric content. Consequently, there is a
growing need for antihypertensives, antihyperlipidemics, and type 2 antidiabetic
drugs in children (Cox et al. 2008). The long-term consequences over the whole life
span are as yet unknown.
Chemotherapy
While cancer as a cause of morbity and mortality is not new to the pediatric
population, as the survival rate has dramatically improved for a variety of neoplas-
tic diseases over the past several decades, the prevalence and duration of chemo-
therapy has increased. This success in cancer survival is not without long-term
effects on later maturation processes, such as those of the reproductive, immuno-
logical, skeletal, neural, behavioral, and cardiovascular systems. For example, the
anthracycline doxorubicin, a very effective chemotherapeutic agent for certain
childhood malignancies, is associated with a delayed serious and potentially
life-threatening cardiotoxicity. Even years after completion of medication, parti-
cularly when treatment occurred during infancy and early childhood, persistent
myocardiocyte loss, myocardial fibrosis, and failure of myocardial growth are
observed as sequelae of former doxorubicin treatment (Hausner et al. 2008). In a
more recent study, it has been shown that the relative hazard of congestive heart
failure, pericardial disease, and valvular abnormities in adult survivors of childhood
32 H.W. Seyberth and R.E. Kauffman
and adolescent cancer treated with anthracyclines increased two to five times
(Mulrooney et al. 2009).
Asthma-Controller Medication
ADHD Medication
begins between 8 and 14 years and occurs almost two years earlier in females than
males (Tanner and Davies 1985).
The main features of this maturation period are as follows: Pubertal growth
spurt, which accounts for approximately 25% of final adult height, changes in the
body habitus, and remodeling of the body over a relative short period of time with
sexual maturation. This includes feminization with more fat content in females and
masculinization with more muscular mass in males (Ellis 2000). Besides these
changes in skeletal growth and alteration in body composition, cardiorespiratory
changes take place such as doubling of the weight of the heart and rise in systolic
blood pressure primarily in boys associated with increase in lung size and vital
capacity and a drop in respiratory rate (Irwin 2003). Blood volume, red cell mass,
and hematocrit increase throughout puberty in boys, while these parameters remain
constant for girls. At the same time, dramatically increased levels of gonadal steroid
hormones, which are secreted in a pulsatile manner, are involved in regulating
plastic changes in neuronal structure and function. These modulation processes of
brain circuits at puberty can have effects on changes in social behavior, risk-taking
behaviors, and cognitive function at adolescence (Cameron 2004; Paus et al. 2008).
Thus, it is not so surprising, when these processes are suboptimal in timing and/or
magnitude that the risk of cognitive, affective, and addictive disorders increases
(see below).
Growth Retardation
Endocrine Dysfunctions
Malignancies
Malignancies, which are common in early adulthood, such as testicular and ovarian
carcinoma, Hodgkin disease, the sarcomas such as osteosarcoma, Ewing sarcoma,
and other soft-tissue sarcomas are the most common types of cancer in adolescence
(Kadan-Lottick 2007).
Emotional Instability
Sexual Behavior
Adolescents continue to initiate sexual activity early in the second decade of life.
Again age of menarche, ethnic origin, and social status may have a significant
influence on the age of first sexual intercourse; but one can assume that more than
50% of middle teen adolescents will have this experience and are prone to sexually
transmitted diseases and ectopic pregnancies (Marcell and Irwin 2003c; Dalton
2007).
– Covariation of risk behaviors
As already mentioned above, there is a close association of alcohol and uninten-
tional injury. There also appears to be a relationship between cigarette smoking
and the use of illicit substances as well as failure to use effective contraception
leading to unintended pregnancy (Marcell and Irwin 2003d). In the worst case,
the sequence of progression can be as follows: alcohol and cigarettes precede
marijuana use, which is followed by other illicit drugs (including psychedelics,
cocaine, heroin, and prescribed and nonprescribed stimulants, sedatives, and
tranquilizers), leading to a cumulative effect of all substances and sometimes to
high-risk teenage pregnancies.
Although adolescent females are more at risk for depression compared to males,
males are generally more aggressive and impulsive than females.
– Eating disorders
Anorexia nervosa (AN) and bulimia nervosa (BN) are common psychiatric
disorders in adolescents and young adults with high rates of morbidity and mor-
tality. The incidence of both disorders has increased in the general population
over the last two decades and remains eight times higher in the female than male
teenage population (Abraham and Stafford 2007).
Extreme feelings of dissatisfaction with weight and shape and fear of gaining
weight are the main causes of these disorders, leading typically to amenorrhea
and to a maintenance weight of 15% below the ideal body weight in AN. Other
clinical manifestations of eating disorders include severe malnutrition, self-
induced vomiting (particularly in BN with episodes of compulsive overeating),
and use of laxatives and/or diuretics. This may lead to dehydration, peripheral
vasoconstriction, hypothermia, bradycardia, severe electrolyte imbalance with
cardiac arrhythmia, osteopenia with stress fractures, hypoproteinemia with
peripheral edema, and decreased glomerular filtration. This complex clinical
condition is associated with severe medical and psychiatric comorbidity for
which pharmacotherapy has a limited role at the present time. Nevertheless,
the drugs mainly used in the treatment of eating disorders are antidepressants
such as SSRIs, tricyclics, and atypical antipsychotic agents (Powers and Bruty
2009). However, dosing, side-effect profile, and long-term effects of these
medications in children and adolescents are not well studied (Hausner et al.
2008).
Around the onset of puberty with increased growth hormone levels and activation
of the reproductive axis, drug-metabolizing enzyme capacity begins gradually
to decline. This decline continues throughout adolescence and concludes with
attainment of adult capacity at the completion of pubertal development (Kennedy
2008). During this period of marked hormonal changes and fluctuation, an apparent
inverse relationship between levels of growth and sex hormones and drug-
metabolizing activity can be observed. For example, a Tanner stage-dependent
decrease in CYP1A2-mediated caffeine clearance has been described in healthy
adolescents (Lambert et al. 1986). A more direct demonstration of this relationship
was observed among growth hormone-deficient prepubertal children in whom
physiological growth hormone replacement was associated with a twofold increase
in the half-life of amobarbital, a probe of hepatic microsomal drug metabolism
(Redmond et al. 1978). At least in part, changes in body composition may also have
an effect on the V(d) as illustrated by a highly significant positive correlation of
Tanner stage with theophylline elimination half-life and lean body mass and
between lean body mass and V(d) in adolescents with asthma (Cary et al. 1991).
Basics and Dynamics of Neonatal and Pediatric Pharmacology 37
Gender differences in drug disposition also become more apparent during puberty
(Beierle et al. 1999; Kennedy 2008; Lambert et al. 1986).
Thus, the effects of rapid growth, sexual maturation, and the large amount of
variability in the timing of these developmental events on pharmacokinetics must
be considered during studies with teenagers. The concept of developmental rather
than chronological age should be applied whenever it is possible (Cary et al. 1991;
Finkelstein 1994; Kennedy 2008).
These ontogenetic and pharmacokinetic changes during this stage of growth and
sexual maturation are especially important when treating common chronic illnesses
of adolescence, such as asthma, diabetes, epilepsy, and depression. This complex
hormonal and pharmacotherapeutic interplay can further be complicated by on and
off oral contraceptive therapy, teenage pregnancy, smoking, self-medication, and
illicit drug use.
With respect to renal elimination, it is of note that glomerular filtration and
tubular absorption are not influenced by sexual maturation, in contrast to tubular
secretion of medicines, e.g., tubular secretion of digoxin, which declines during
adolescence to the level seen in adults (Linday et al. 1984; Linday et al. 1981).
Methotrexate, which is excreted by the kidney via glomerular filtration and tubular
secretion, also shows reduced clearance as a function of age through adolescence
(Donelli et al. 1995).
The effects of physical growth and sexual maturation on the expression of impor-
tant drug targets, such as receptors, transporters, and channels, remain essentially
unexplored. This is in contrast to the available comprehensive knowledge about
ontogenetic differences in pharmacodynamics in the perinatal period. A major
obstacle (hurdle) may be greater difficulties in monitoring quantitatively the rele-
vant clinical end points or appropriate surrogate markers of drug action, efficacy,
and toxicity throughout the course of pubertal development and sexual maturation.
Moreover, pediatricians have relatively neglected research in the area of adolescent
medicine in the past.
Long-term safety of medicines and, even more so, the long-term consequences
of addictive substances use and drug abuse are of major concern in this pediatric
population, e.g., tobacco and alcohol consumption and doping with central
stimulants or androgens (Dwyer et al. 2009; Hausner et al. 2008; Sj€oqvist et al.
2008).
38 H.W. Seyberth and R.E. Kauffman
Psychostimulants
The long-term risk of extended use and misuse of central stimulants as perfor-
mance-enhancing drugs has already been mentioned and briefly discussed in
Basics and Dynamics of Neonatal and Pediatric Pharmacology 39
“ADHD Medication”. These risks are particularly relevant for the male teenage
population at secondary school, in which the diagnosis of ADHD is frequently
made with a prevalence of about 8% as compared to only 2% in girls (Huss et al.
2008).
4 Future Directions
There is a permanent need to fill the gaps of our knowledge about the continuous
developmental changes of therapeutic targets (e.g., enzymes, transporters,
receptors, and channels) from the fetus to young adult. These gaps include follow-
ing sections.
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Developmental Pharmacokinetics
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2 Drug Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.1 The Gastrointestinal Tract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3 The Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4 Drug Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5 Drug Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6 Phase I Enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1 CYP3A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.2 CYP1A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.3 CYP2D6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.4 CYP2C9/CYP2C19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.5 CYP2E1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
7 Drug Excretion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
8 Other Factors Influencing the Absorption, Distribution, Metabolism,
and Excretion of Drugs in Neonates and Young Infants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9 Pharmacogenomics: Impact for Pediatric Populations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
10 The Interface of Pharmacokinetics and Pharmacodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
11 Pediatric Dose Selection Based upon Pharmacokinetic Principles . . . . . . . . . . . . . . . . . . . . . . . 68
12 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
1 Introduction
adolescents (Kearns et al. 2003a; Van Den Anker and Rakhmanina 2006). The
impact of development on the pharmacokinetics of a given drug is dependent, to a
great degree, upon age-related changes in the body composition and the acquisition
of function of organs and organ systems that are important in determining drug
metabolism as well as drug transport and excretion (Edginton et al. 2006; Anderson
and Holford 2008). Although it is often convenient to classify pediatric patients
on the basis of postnatal age for the study and provision of drug therapy (e.g.,
newborn infants aged 1 month or less, infants between 1 and 24 months of age,
children between 2 and 12 years of age, and adolescents between 12 and
16–18 years of age), it is important to recognize that changes in physiology that
characterize development may not correspond to these age-defined breakpoints and
are also not linearly related to age. In fact, the most dramatic changes in drug
disposition occur during the first 12–18 months of life, when the acquisition of
organ function is most dynamic (Kearns et al. 2003a; Van Den Anker and
Rakhmanina 2006). Additionally, independent from developmental aspects, it is
important to mention that the pharmacokinetics of a given drug may be altered in
pediatric patients also due to intrinsic (e.g., genotype, inherited diseases) and/or
extrinsic (e.g., acquired diseases, diet, co-medication) factors that may occur during
the first months and years of life (Blake et al. 2006; Van Den Anker et al. 1994;
Allegaert et al. 2008; Leeder 2003; Krekels et al. 2007; Leeder et al. 2010). In
principle, however, these factors are also important for nonpediatric populations
such as adult geriatric patients. To study pediatric pharmacokinetics it is very useful
to examine the impact of development on those physiologic variables that govern
drug absorption, distribution, metabolism, and excretion (Bartelink et al. 2006;
Johnson et al. 2006; Edginton et al. 2006) which is summarized by the commonly
used term ADME.
2 Drug Absorption
The most important factors that influence drug absorption from the gastrointestinal
tract are related to the physiology of the stomach, intestine, and biliary tract. The pH
of the stomach is practically neutral at birth, decreases to around 3 within 48 h after
birth, returns to neutral over the next 24 h, and remains that way for the next 10 days
(Bartelink et al. 2006). Thereafter, it slowly declines again until it reaches adult
values at about 2 years of age. These initial changes do not occur in premature
infants, who seem to have little or no free acid during the first 14 days of life
(Bartelink et al. 2006). The time of gastric emptying is delayed in the period
immediately after birth for both full term and preterm neonates. It approaches
adult values within the first 6–8 months of life (Strolin Benedetti and Baltes
2003). Intestinal transit time is prolonged in neonates because of reduced motility
and peristalsis, but appears to be reduced in older infants as a result of increased
intestinal motility (Strolin Benedetti and Baltes 2003; Kearns 2000). Other factors
that may play a role in intestinal drug absorption are immaturity of the intestinal
mucosa leading to increased permeability, immature biliary function, high levels of
intestinal b-glucuronidase activity, reduced first-pass metabolism, maturation of
carrier mechanisms, and variable microbial colonization (Kearns 2000). These
developmental differences in the physiologic composition and function of these
organs can alter the rate and/or extent of drug absorption. Changes in intraluminal
pH can directly impact both drug stability and degree of ionization, thus influencing
the relative amount of drug available for absorption. Acid labile drugs such as
penicillin G and erythromycin are therefore more efficiently absorbed, whereas the
same changes in gastric pH (developmentally or caused by the use of proton pump
inhibitors) will result in clinically important decreases in the absorption of weak
organic acids such as phenobarbital and phenytoin, necessitating adjustment of the
amount of antiepileptic drug administered to the individual patient (Strolin
Benedetti and Baltes 2003). Additionally, the ability to solubilize and subsequently
absorb lipophilic drugs can be influenced by age-dependent changes in biliary
function. Immature conjugation and/or transport of bile salts into the intestinal
lumen results in low intraduodenal levels despite blood levels that exceed those
seen in adults. Gastric emptying time is prolonged throughout infancy and child-
hood consequent to reduced motility, which may retard drug passage into the
intestine where the majority of absorption takes place (Kearns 2000). As a conse-
quence, the rate of absorption of drugs with limited water solubility such as
phenytoin and carbamazepine can be significantly altered resulting from these
changes in gastrointestinal motility. Unfortunately, few studies have systematically
evaluated the effect of developmental changes in gastric emptying and intestinal
motility on drug absorption in infants and children. Anderson et al. showed that
the oral acetaminophen (paracetamol) absorption rate was significantly lower in
the first days of life before stabilizing 1 week after birth (Anderson et al. 2002).
Another study showed that the time to reach the maximum concentration (tmax) of
Developmental Pharmacokinetics 55
cisapride was significantly longer in preterm infants compared with term neonates
(Kearns et al. 2003b). Generally, the rate at which most drugs are absorbed is
generally slower and thus, the time to achieve maximum plasma concentrations is
prolonged in neonates and young infants relative to older infants and children.
Despite their incomplete characterization, developmental differences in the activity
of intestinal drug metabolizing enzymes and efflux transporters have the potential
to markedly alter drug bioavailability.
3 The Skin
The morphologic and functional development of the skin as well as the factors that
influence penetration of drugs into and through the skin has been reviewed (Radde
and McKercher 1985). Basically, the percutaneous absorption of a compound
is directly related to the degree of skin hydration and relative absorptive surface
area and inversely related to the thickness of the stratum corneum (Radde and
McKercher 1985). The integument of the full-term neonate possesses an intact
barrier function and is similar to that of an older child or adolescent. However, the
ratio of surface area to body weight of the full-term neonate is much higher than that
of an adult. Thus, the infant will be exposed to a relatively greater amount of drug
topically than will older infants, children, or adolescents. In contrast, data of human
skin from preterm infants indicates an inverse correlation between permeability and
gestational age (Nachman and Esterly 1980). Permeability rates were 100- to 1,000-
fold greater before 30 weeks gestation as compared with full-term neonates, with a
three to fourfold greater permeation rate seen beyond 32 weeks (Ginsberg et al.
2004). In vivo studies suggest that this increased dermal permeability in preterm
infants is a short-lived phenomenon with the permeability barrier of even the most
premature neonates similar to that of full-term neonates by 2 weeks of postnatal life
(Ginsberg et al. 2004). There are numerous reports in the literature underscoring
the importance of skin absorption in neonates primarily showing toxicity after
exposure to drugs or chemicals. These include pentachlorophenol-containing laun-
dry detergents and hydrocortisone (Armstrong et al. 1969; Feinblatt et al. 1966).
Therefore, extreme caution needs to be exercised in using topical therapy in
neonates and young infants. In contrast, the possibility of turning enhanced skin
absorption of drugs to the infant’s advantage is an interesting idea and was explored
exemplarily several years ago by using the percutaneous route to administer
theophylline in preterm infants (Evans et al. 1985). A standard dose of theophylline
gel was applied and serial theophylline levels were measured demonstrating that
therapeutic theophylline levels were achieved in 11 of 13 infants and that the
percutaneous route is a feasible method of administering theophylline in preterm
infants.
56 J.N. van den Anker et al.
4 Drug Distribution
5 Drug Metabolism
well established that infants who are barely into their second trimester of gesta-
tional life born as small as a few hundred grams (400–500 g) can survive. On the
other extreme, by the end of the first month of postnatal life, large for gestational
age infants may weigh upwards of several kilograms. Indeed, the 95th weight
percentile is approximately 5 kg. No other age groups can be defined in differences
measured logarithmically. As one might expect, there are similar tremendous
developmental changes in hepatic drug metabolizing enzymes during this time
frame. Understanding these implications is important for individualized clinical
development programs.
6 Phase I Enzymes
6.1 CYP3A
The CYP3A subfamily represents the majority of CYP total content in the liver
(Brown et al. 2008). Indeed, it has been shown that over one-half of all drugs
prescribed are metabolized by CYP3A (Zanger et al. 2008). The CYP3A subfamily
consists of CYP3A4, 3A5, 3A7, and 3A43. CYP3A43 is not known to play a
significant role in hepatic metabolism. It has been established that CYP3A4 is
the predominant CYP3A enzyme in adults, whereas CYP3A7 is the predominant
CYP3A enzyme in the fetus and infants. Moreover, there is a great deal of overlap
of specificity of ability for CYP3A4 and CYP3A7 to metabolize therapeutic agents.
In 2003, Stevens et al. published the results of examining the largest collection of
fetal and pediatric liver samples to date. The study included 212 samples. Stevens
and colleagues demonstrated that CYP3A7 is highest between 94 and 168
postconceptional days on a pmol/mg basis of total hepatic protein (Stevens et al.
2003). The level at birth is less than half that of the high prenatal value. However, it
remains higher than that of even adult CYP3A4 levels. Furthermore, these hepatic
samples demonstrated that there is minimal CYP3A4 activity prenatally that
continues to increase after birth. Nevertheless, CYP3A7 content remains higher
than CYP3A4 content until at least 6 months of age.
To date, two probe drugs have been researched extensively, which have
demonstrated the lower activity of CYP3A4 at birth and in neonates. In 2001,
De Wildt et al. published the results of midazolam metabolism given to 24 preterm
infants. Only 19 of 24 preterm infants produced detectable levels of 1-OH-
midazolam. Furthermore, these results firmly established that premature infants
had lower CYP3A4 activity than full-term infants, than did children and adults
historically. Oral cisapride has also been demonstrated to be a suitable substrate
for CYP3A4 activity (Kearns et al. 2003b). Cisapride has demonstrated a similarly
low activity for CYP3A4 in the neonatal period, as did midazolam (Kearns et al.
2003b; De Wildt et al. 2001).
60 J.N. van den Anker et al.
In conclusion, CYP3A7 activity is very high before birth and continues to have
high activity after birth and is even present into adulthood. CYP3A4 possesses very
low activity at birth and very slowly increases in the neonatal period. Thus, when
designing studies with substrates for CYP3A4 in young infants and children, great
care needs to be taken to adjust for this low activity in order to achieve the goal of
the FDA guidance that in children exposure and Cmax are not higher than that in
adults.
6.2 CYP1A2
One of the first CYP enzymes to be studied utilizing a probe drug in the first year
of life is CYP1A2. Two methylxanthines (caffeine and theophylline) have been
utilized extensively to evaluate CYP1A2 in vivo in young children (Evans et al.
1989; Erenberg et al. 2000; Lambert et al. 1986; Tateishi et al. 1999). Theophylline
and caffeine are two commonly utilized medications in neonates for the treatment
of apnea. These medications are frequently continued form the neonatal period
during the first year of life. At birth, caffeine-3-demethylation, a measure of
CYP1A2 activity, is very low. Consequently, Erenberg et al. published that the
efficacious dose of caffeine is 10 mg/kg every day (Erenberg et al. 2000). The half-
life of caffeine is 72–96 h in infants compared to approximately 5 h in older
children and adults. Similarly, 8-hydroxylation of theophylline is reduced at birth.
Nevertheless, longitudinal data indicate a rapid maturation process for CYP1A2, as
it appears to reach adult levels within the first year of life, often within the first
6 months of life. Finally, it is important to note that caffeine activity is highly
inducible by drugs, diet, and exogenous toxins such as cigarette smoke. In the adult
literature, variability in CYP1A2 activity up to 100-fold has been reported. More-
over, Blake et al. reported that caffeine elimination half-life in neonates who are
breast-fed is longer than that of formula-fed infants (Blake et al. 2006); information
which suggests that the composition of infant diet (i.e., an environmental factor)
can influence the pattern of ontogenic expression of a drug metabolizing enzyme.
In conclusion, it is evident that CYP1A2 activity is highly reduced in young
infants. Additionally, activity of the enzyme is highly inducible. Finally, maturation
of CYP1A2 activity is rapid in the first year of life. Therefore, when designing
clinical studies, which include neonates, great care must be taken to assure that
this variability in drug response is properly assessed, especially within the first
6–12 months of life.
6.3 CYP2D6
individuals are homozygous for the wild-type allele. In 1991, Treluyer et al.
published the results of liver samples from fetuses aged 17–40 weeks postconcep-
tion. These results demonstrated that the concentration of hepatic CYP2D6 protein
was very low or undetectable in these fetuses. This lack of CYP2D6 activity at birth
led to the hypothesis that birth-related events may trigger maturation of the enzyme.
In 2007, Blake et al. published in vivo results that provided further understanding of
CYP2D6 activity in the first year of life. These results came from dosing infants
with dextromethorphan at 0.5, 1, 2, 4, 6, and 12 months of age and measuring the
metabolites in urine. These dextromethorphan results demonstrate indeed that there
is low activity at birth, but that there is rapid acquisition of CYP2D6 activity in the
first year of life. Already within the first 2 weeks of life there is measurable
acquisition of CYP2D6 activity. Despite the discussion in the literature about the
fact that the increase in renal function might conceal the enzyme development
resulting in an apparent plateau of the metabolic ratio after 2 weeks (Johnson et al.
2008), very recent data show that an infant with a postmenstrual age of 52 weeks
has already mature hepatic CYP2D6 activity (Allegaert et al. 2011).
Taken together, these results demonstrate the need for careful pharmacokinetic
studies in infants and toddlers who are provided a pharmacologic agent, which is
primarily metabolized by CYP2D6 (e.g., codeine, beta-blockers, propafenone). Not
only does one need to be cognizant of potential infants who are predestined by their
genome to be poor metabolizers, but potential studies need to realize the
implications of low levels of CYP2D6 at birth and also the rapid maturation process
that occurs within the first year of life (Stevens et al. 2008).
6.4 CYP2C9/CYP2C19
Lee et al. (2002) and Koukouritaki et al. (2004) have published the most extensive
reviews to date on CYP2C activity in humans. They demonstrate that the two main
representatives of the CYP2C subfamily of enzymes (CYP2C9 and CYP2C19)
conveniently follow the CYP2C rule of 20%. Approximately 20% of hepatic CYP
content of adult livers is CYP2C and these CYP2C enzymes metabolize 20% of
pharmaceuticals developed to date.
Although not to the same extent as CYP2D6, the two main CYP2C represen-
tatives are polymorphically expressed. To date, over 30 alleles of CYP2C9 of
CYP2C9 have been identified and more than 25 alleles of CYP2C19 of CYP2C19
have been reported in the literature (Lee et al. 2002; Koukouritaki et al. 2004). Just
as with CYP2D6, some of these polymorphisms may result in poor metabolizer
status, which may confound studies in infants and young children.
The ontogeny of CYP2C9 is much better established than CYP2C19. Indeed,
hepatic liver samples have shown that CYP2C9 activity is functionally very low
just prior to birth. However, much like CYP2D6, this activity increases quickly in
the first year of life. The classic example of the effects of this very low level of
CYP2C9 activity at birth can be seen with phenytoin (Suzuki et al. 1994). Indeed,
62 J.N. van den Anker et al.
6.5 CYP2E1
331(neonates/preterms)
1000 333(1-11 months)
334(1-11 yrs)
337 (12-16 yrs)
100
10
0.1
0.0 0.2 0.4 0.6 0.8 1.0 4.0 8.0 12.0 16.0
AGE (years)
Fig. 1 Aggregate apparent oral clearance (CL/F) data for pantoprazole obtained from four
pediatric clinical pharmacokinetic studies of the drug (study numbers 331, 333, 334, and 337)
performed as part of pediatric labeling studies conducted under a written request from the U.S.
Food and Drug Administration. All studies involved administration of a single oral dose of
pantoprazole given as the proprietary drug formulation. To illustrate the association of develop-
ment with pantoprazole pharmacokinetics, the value of CL/F has been normalized to a “standard”
adult weight of 70 kg
and ethanol) (Jimenez-Lopez and Cederbaum 2005). However, only in the last
5 years has the developmental pattern of this important enzyme been well under-
stood (Johnsrud et al. 2003). Nevertheless, human hepatic CYP2E1 developmental
expression is difficult to appreciate due to the multiple levels of regulation in its
activity. For example, CYP2E1 is known to be elevated in individuals who have
high levels of ethanol consumption, in individuals who are obese, and finally in
individuals who have type 2 diabetes (Caro and Cederbaum 2004). Finally, an
increasing number of genetic polymorphisms, which lead to lower CYP2E1 protein
concentration, have been demonstrated in the literature (Hanioka et al. 2003).
To date, Johnsrud et al. have published the largest study of the activity of fetal
and pediatric liver samples to determine the ontogeny of CYP2E1 (Johnsrud et al.
2003). Measurable CYP2E1 activity was demonstrated in 18 of 49 second trimester
livers and 12 of 15 third trimester samples. Moreover, measurements of mean
concentrations of CYP2E1 protein as part of total milligrams of microsomal protein
found that second trimester infants averaged 0.35 pmol/mg, third trimester
64 J.N. van den Anker et al.
infants 6.7 pmol/mg, newborns 8.8 pmol/mg and older infants aged 30–90 days
23.8 pmol/mg, and finally children aged 90 days to 18 years 41.4 pmol/mg. Thus,
this implies a rapid maturation starting in late fetal life and continuing through early
infancy in CYP2E1 activity. It would appear that these data demonstrate that
careful attention would be required in studies of new CYP2E1 substrates in infants
under the age of 90 days.
7 Drug Excretion
The kidney is the primary organ responsible for the excretion of drugs and their
metabolites. Maturation of renal function is a dynamic process that begins early
during fetal organogenesis and is complete by early childhood (Rhodin et al. 2009;
Chen et al. 2006). The developmental increase in glomerular filtration rate (GFR)
involves active nephrogenesis, a process that begins at 9 weeks and is complete by
36 weeks of gestation, followed by postnatal changes in renal and intrarenal blood
flow. Following birth, the GFR is approximately 2–4 ml/min/kg in term neonates
and as low as 0.6–0.8 ml/min/kg in preterm neonates (Van den Anker et al. 1995a).
GFR increases rapidly during the first 2 weeks of life followed by a steady rise until
adult values are reached by 8–12 months. This increase in GFR in the first weeks of
life is mainly because of an increase in renal blood flow. Similarly, tubular
secretory pathways are immature at birth and gain adult capacity during the first
year of life.
There is a clear controversy regarding the use of serum creatinine to predict renal
function in children (Filler and Lepage 2003). Serum creatinine depends on many
factors and residual maternally derived creatinine interferes with the assay in the
first days of life in neonates (Capparelli et al. 2001). In addition, factors that have a
negative influence on the use of plasma creatinine to predict renal function are renal
tubule integrity issues and GFR values of less than 20 mL/min/1.73 m2. In these
individuals, GFR is probably overestimated. If creatinine is measured with the Jaffé
reaction ketoacids, serum bilirubin and cephalosporins interfere with the reaction
and therefore the use of an enzymatic method should be advised because of less
interference as compared to the Jaffé method (Van den Anker et al. 1995c). A more
direct approach to estimate the GFR is to use a marker that is freely permeable
across the glomerular capillary and neither secreted nor reabsorbed by the tubulus.
Markers that have been mentioned to measure the GFR are inulin, polyfructosan S,
cystatin C, 51Cr-EDTA, 125I-iothalamate, or mannitol (Filler and Lepage 2003;
Hayton 2002). A marker to estimate the active tubular secretion in children is
p-aminohippuric acid (Hayton 2002).
However, a comparison between serum creatinine with inulin clearance in
preterm infants showed a good and clinical useful correlation and supported
serum creatinine as an appropriate measure of GFR in preterm infants already on
day 3 of life (Van Den Anker et al. 1995c).
Developmental Pharmacokinetics 65
In addition to growth and development, there are several other major variables that
will influence the pharmacokinetic parameters of drugs such as inborn or acquired
diseases, environmental influences such as body cooling, and pharmacogenomics.
It is outside the scope of this chapter to provide extensive information on these
important variables but a few will be highlighted here.
Hypoxic–ischemic events are encountered regularly in sick neonates and these
events might result in a decrease in the rate and amount of drug absorption as well
as impaired renal function. There are data to show that after perinatal asphyxia the
GFR in neonates is 50% less as compared to neonates born without asphyxia,
resulting in a decreased clearance of renally cleared drugs (Van den Anker et al.
1995b). The persistence and/or closure of a patent ductus arteriosus has a major
impact on both the volume of distribution and elimination of frequently used drugs
in the newborn (Van den Anker et al. 1995d). This has been shown for drugs such as
ceftazidime where the existence of a patent ductus and or the exposure to indo-
methacin to close this ductus was associated with a decreased GFR and a larger
volume of distribution of ceftazidime, a solely renally cleared drug. In another
study investigating ibuprofen, there was a significant increase in the clearance of
ibuprofen after closure of the ductus (Van Overmeire et al. 2001). Finally, total
body cooling is a new treatment modality that is being used to improve the
neurological outcome of neonates who suffered from perinatal asphyxia. In a
66 J.N. van den Anker et al.
pH change
9
8
7
6
pH Change
5
4
3
2
1
0
0 4 8 12 16 20 24
Time (hours)
exposure of drug from given dose with the consequence of producing less or more
drug being available at the receptor(s) consequent to whether drug clearance is
decreased or increased relative to values in adults. The resultant alteration in the
dose–concentration profile may result in an attenuated (ineffective) or exagge-
rated (toxicity) pharmacodynamic response in an infant or child, a situation
which is especially relevant for drugs with a narrow therapeutic index (e.g.,
aminoglycoside antibiotics, digoxin, antiarrhythmic agents). Thus, in some
circumstances, apparent developmental differences in drug response/effect may
be simply explained on pharmacokinetic basis. This is illustrated by the H 2
antagonist famotidine where consequent to a marked reduction in plasma clear-
ance (i.e., renal elimination), a single intravenous dose produced a sustained
increase in the intragastric pH in neonates for a 24-h postdose period (Fig. 2)
(James et al. 1998).
Most current age-specific dosing requirements are based on the known influence of
ontogeny on drug disposition. Current gaps in our knowledge (e.g., incomplete
developmental profiles for hepatic and extrahepatic drug metabolizing enzymes,
lack of knowledge with regard to expression of drug transporters that may influence
drug clearance and/or bioavailability) prevent the use of simple formulas and/or
allometric scaling for effective pediatric dose prediction; a fact especially true in
very young infants where the relationship between body size and the maturation of
Developmental Pharmacokinetics 69
pathways predominantly responsible for drug clearance are not linear (Holford
2010). Such approaches (e.g., allometric scaling) may have some potential clinical
utility in children older than 3 years of age and adolescents whose organ function
and body composition approximates that of young adults.
Age-specific dosing regimens for selected commonly used drugs where
developmental differences in the dose–concentration profile have been well
characterized serve to illustrate this point. For drugs whose plasma concentrations
are routinely measured clinically (e.g., aminoglycosides, digoxin, caffeine, phenyt-
oin, phenobarbital, carbamazepine, methotrexate, cyclosporine, tacrolimus,
mycophenolate mofetil), or for whom pharmacokinetic characteristics were defined
in pediatric patients during the drug development process, individualization of
treatment based on patient-derived and in selected instances, population-estimated
pharmacokinetic parameters is easily achieved. However, in the absence of such
pharmacokinetic data and/or established pediatric dosing guidelines, alternate
methods for dose selection must be used.
As discussed previously, the majority of age-adjusted pediatric drug dosing
regimens utilize either body weight or surface area as surrogates to reflect the
developmental determinants of drug disposition. Dose selection based on body
weight or body surface areas will generally produce similar plasma concentration
profiles except for those drugs whose apparent volume of distribution (Vd)
corresponds to the extracellular fluid pool (i.e., Vd < 0.3 L/kg), where a body
surface area based approach is preferable. In contrast, for drugs whose apparent
Vd exceeds the extracellular fluid space (i.e., >0.3 L/kg), a body weight based
approach for dose selection is preferable and as a result is the most frequently used
approach for dosing in pediatrics.
When the pediatric dose for a given drug is not known these principles can be
used to best approximate a proper dose for the initiation of treatment. Ritschel and
Kearns (2009) have described an approach to determine dose in infants that is
illustrated by the following equations:
Infant dose ðif Vd < 0:3 L/kgÞ ¼ ðinfant BSA in m2 =1:73 m2 Þ adult dose,
Infant dose ðif Vd 0:3 L/kgÞ ¼ ðinfant BW in kg=70 kgÞ adult dose:
This approach is only useful for selection of dose size, and does not offer
information regarding dosing interval since the equations contain no specific
variable that describes potential age-associated differences in drug clearance. It is
also important to note that this approach assumes that the body height and weight of
a given child are appropriate (i.e., normal) for age and there are no abnormalities in
body composition (e.g., edema, ascites) that can be produced by disease.
In neonates and young infants, the dosing interval for drugs with significant
(i.e., >50%) renal elimination by glomerular filtration can be approximated by
estimation of the apparent elimination half-life (t1/2) of the drug at a given point in
development by using the following equations:
70 J.N. van den Anker et al.
where kel represents the average terminal apparent terminal elimination rate con-
stant, GFR is an estimate of the glomerular filtration rate (which can be obtained
from either a creatinine clearance determination or age-related normal values), and
Fel is the fraction of drug excreted unchanged in the urine.
Alternatively, projection of pediatric dose requirement can be performed using
in silico techniques (e.g., whole body physiologically based pharmacokinetic/
pharmacodynamic models, population-based simulation, PK-Sim Packages, Simcyp
Pediatric ADME Simulator) (Johnson and Rostami-Hodjegan 2011). The success
of these approaches (i.e., prediction accuracy) is based upon the availability and
reliability of parameter estimates (either pharmacokinetic, pharmacodynamic, or
pharmacogenomic) and their prior knowledge in the specific subpopulation being
used for dose projection (Espie et al. 2009). These caveats are especially important
during early infancy where dynamic changes in drug disposition and action are
likely consequent to ontogeny and developmental maturity in drug clearance
pathways has not yet been attained.
12 Conclusions
Acknowledgements Johannes van den Anker is supported in part by FP7 grants TINN (223614),
TINN2 (260908), and NEUROSIS (223060), and Matthias Schwab is supported in part by the FP7
grant NEUROSIS (223060).
Developmental Pharmacokinetics 71
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Developmental Pharmacokinetics 75
Contents
1 Therapeutic Drug Monitoring: Definition, Which Drug to Measure? . . . . . . . . . . . . . . . . . . . . . . 78
2 Pharmacological Differences Between Adults and Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3 TDM in Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.1 Timing of Sampling for TDM in Children (Table 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.2 Technical Aspects of TDM: Sample Collection, Analytical Methods . . . . . . . . . . . . . . . 81
3.3 Which Samples to Analyze: Blood or Saliva, Dried Blood Spot? . . . . . . . . . . . . . . . . . . . 82
4 New Approaches for TDM: Population Pharmacokinetics and Bayesian Estimator . . . . . . 84
4.1 Bayesian Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5 Pharmacodynamic Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Although criteria for TDM pertain to both adults and children, children are
more likely to benefit from TDM, as in contrast to the adult situation, validated
dosage recommendations are limited for many drugs prescribed in children.
Indeed, approximately 70% of drugs prescribed to children, and more than 93%
to critically ill neonates, are unlicensed or used in an off-label manner (‘t Jong
et al. 2000, 2002; Conroy et al. 2000). As growth and development are a contin-
uum, with continuous changes in physiological parameters during childhood,
marked differences in the pharmacokinetic and pharmacodynamic behavior of
many drugs are reported between children and adults. All pharmacokinetic phases
are involved (Kearns et al. 2003): in such situations, pediatric dosage is empirical.
As a result, therapeutic failures, adverse events, and even fatalities may occur
(Ince et al. 2009).
Oral absorption may be altered by changes in gastroenterological physiology
with age. During the neonatal period, intragastric pH is relatively high (greater than
4), as both basal acid output and the total volume of gastric secretions are limited.
As a consequence, the bioavailability of acid labile compounds is increased
Table 1 Requirements to set up TDM for a given drug (Touw et al. 2005; Soldin and Soldin 2002)
• A relationship exists between drug plasma (blood) concentration and effect and is stronger than
between drug dosage and effect
• The drug has a narrow therapeutic index, i.e., small difference between the therapeutic and toxic
concentrations, between the low concentration, without effect and the high concentration,
associated with toxicity
• The concentrations resulting from a given dose are unpredictable as a result of inter- and
intra-individual variability
• The clinical effects are not easily measurable
• A rapid and reliable analytical method is validated to determine drug and metabolites
concentrations
In addition, TDM can also be useful:
• If toxicity is suspected
• In the absence of drug response when subtherapeutic concentrations are suspected or compliance
is questionable
• When dose adjustment is required as a result of drug interactions or changes in clinical state
Principles of Therapeutic Drug Monitoring 79
compared to older children (Agunod et al. 1969; Rodbro et al. 1967). Furthermore,
in infants younger than 6 months, gastric emptying is much slower, which probably
prolongs the time required to achieve maximal plasma levels. Most of these
physiological variables affecting oral absorption are immature, reaching adult
values, between 5 and 10 years of age. Percutaneous absorption is enhanced in
infants, which may be partly accounted by the presence of a thinner stratum
corneum in the preterm neonate (Rutter 1987) and by the relatively greater extent
of cutaneous perfusion and hydration of the epidermis throughout childhood (Okah
et al. 1995; Fluhr et al. 2000). Rectal absorption may also be enhanced in neonates
and infants (Kearns et al. 2003). Intramuscular absorption depends on several
physiological factors: reduced skeletal-muscle blood flow and inefficient muscular
contractions may reduce the rate of intramuscular drug absorption. On the other
hand, the relatively higher density of skeletal-muscle capillaries in infants may
increase absorption (Greenblatt and Koch-Weser 1976; Carry et al. 1986).
Distribution may be altered by the differences in body composition. In
neonates and infants, the relatively larger total body water (70–75% in neonates
versus 50–55% in adults) and extracellular water component (40% in neonates
versus 20% in adults) and lower fat tissue (15% in infants versus 20% in adults)
affect the distribution of drugs which are mainly distributed in body water and to a
lesser extent of lipophilic drugs (Koren 1997). In addition, the lower protein
binding in neonates and infant increases the free fraction of drugs highly bound
in older children and adults.
Metabolism is influenced by numerous factors and primarily by age. In the
neonate, the hepatic microsomal enzyme system is immature. Drug-metabolizing
activities by cytochrome P450 oxidases (CYP, phase I enzymes) and conjugating
enzymes (phase II enzymes) are substantially lower and vary extensively between
patients (See Chapter: Pharmacokinetics and maturation/development). This
explains why the variability of pharmacokinetic parameters such as clearance or
elimination half-life is much higher in children than in adults. TDM is therefore
very useful during this period, because of the lack of validated dosage regimens and
the rapid change of enzyme activities.
Renal elimination. The glomerular filtration rate (GFR) is much lower in
neonates than in older infants, children, or adults. GFR matures during infancy
and approaches an adult rate by 6–12 months postnatal age. The maturation process
of renal structure and function includes prolongation and maturation of renal
tubules, increase in renal blood flow, and improvement of filtration efficiency. In
addition, blood flow is shifted from the deeper to the more superficial nephrons
(Koren 1997).
Pharmacodynamic differences also exist between the pediatric and adult
populations. Indeed, children do not always respond to drug treatment similarly
to adults. One of the examples is warfarin. Developmental changes in the phar-
macokinetics and pharmacodynamics of warfarin enantiomers were studied in
prepubertal, pubertal, and adult patients given long-term warfarin therapy.
The results showed that the patients from these three age groups had comparable
mean plasma concentrations of unbound warfarin enantiomers. However, the
80 W. Zhao and E. Jacqz-Aigrain
3 TDM in Practice
Drugs are usually administered at repeated doses with a constant dosage interval,
either orally or intravenously. Blood or plasma concentrations rise and fall in each
inter-dose interval, from peak to trough. For drugs with linear elimination given at
a fixed dosage regimen, drug concentrations reach steady-state conditions after
4–5 half-lives. Approximated steady-state concentrations may be reached earlier if
a loading dose is given. This estimation does not apply to drugs with saturable
elimination when given at the usual dose, i.e., phenytoin and theophylline. In such
cases of dose dependant kinetics, the drug concentrations increase disproportion-
ately. During continuous infusion, no fluctuations are expected in blood/plasma
concentrations at steady state. In some situations, drugs should be monitored before
steady-state levels are reached to ensure the efficacy and avoid toxicity (1) when the
half-live is long, in order to detect overdosing before steady state; (2) in individuals
with impaired metabolism or renal clearance; and (3) in case of potential drug
interactions. In all cases, detailed information on patient’s disease and clinical
conditions, biological parameters of interest, drug, dosage regimen and associated
therapies, and time of sampling relative to the time of drug administration are
essential to interpret the results (Gross 2001).
Table 2 Technical aspects of Delay between start of treatment and time of sampling
TDM; sample collection,
Sampling time (peak or trough?)
analytical methods
Number of samples
Conditions of sampling
Type of sample (blood, plasma, saliva, dried spot, etc.)
Volume of each sample
Appropriate collecting tube
Validated analytical method
Principles of Therapeutic Drug Monitoring 81
The influence of the blood collecting tube on the concentrations measured should be
taken into consideration. Indeed, several studies have reported that inappropriate
tubes containing serum separator gels can significantly affect the determination of
phenytoin (Dasgupta et al. 1994; Quattrocchi et al. 1983) or ribavirin, the latter
being more stable in gel-containing tubes than in dry or ethylenediaminetetra-acetic
acid tubes (Marquet et al. 2010). Therefore, it is strongly recommended to evaluate
the matrix effect of blood collecting tubes when validating a new analytic method
for TDM. Another important issue in pediatric TDM is for techniques validated for
very small sample volumes, especially in neonates, with low total blood volume
(40 mL for a preterm infant of 500 g). Moreover, as hematocrit is higher in young
infants, more blood has to be drawn to obtain a similar volume of plasma. To
optimize TDM, a TDM laboratory has to develop analytical methods adapted to
the age of the patients, particularly for neonates. In addition, all laboratories should
make analytical procedures available to clinicians that include for each drug the
optimal sampling time and sampling volume required, the type of blood collecting
tubes, clinical and biological parameters required to interpret the measured concen-
tration (Koren 1997). Differences between analytical methods may have a major
impact on the results. Monitoring of immunosuppressants is taken here as an
example. Because of their high inter- and intra-individual variability and narrow
therapeutic index, TDM of immunosuppressants is mandatory both in children and
in adults whatever the indication, but primarily to prevent transplant rejection and
toxicity in organ transplanted children. Immunoassay techniques are widely used for
TDM as they are easy to perform and are less time consuming than chromatographic
methods. However, although often regarded as “specific” for the parent drug, the
antibody may cross-react with other compounds, including metabolites of the drug.
Therefore, the concentrations are often overestimated as compared with chro-
matographic assays. Due to the cross reactivity of mycophenolic acid (MPA) with
its acyl-glucuronide metabolite (AcMPAG) in enzyme-multiplied immunoassay
technique (EMIT), the concentrations of MPA determined by EMIT were systemat-
ically higher than by high-performance liquid chromatography with ultraviolet
(HPLC-UV) method, with an average positive bias of 15% in pediatric transplant
recipients (Irtan et al. 2008). In general, these differences do not affect significantly
the clinical value of TDM, although they have an impact on the target concentration
and contribute to the variability of drug concentrations reported in the literature.
However, in defined clinical conditions where the concentrations of metabolites
contribute significantly to the measured drug concentration, the differences between
analytical assays should be taken into account to interpret the results. This is the
case, for example, in liver transplanted patients immediately posttransplant receiving
mycophenolate mofetil (MMF) the prodrug of MPA, where overestimation of MPA
concentration may occur and be misleading (Sch€ utz et al. 1998).
82 W. Zhao and E. Jacqz-Aigrain
detection may not be suitable, the reference method being HPLC coupled with
tandem mass spectrometry (MS/MS) used in most publications on DBS analysis.
The interpretation of drug concentrations measured during monitoring should
take into account all the aspect and conditions of monitoring (including dose and
dosage schedule, the type of biological sample, analytical technique used, start of
treatment, potential drug interactions, etc.) and use reference concentrations to
draw recommendations for dosage adaptation (Table 3).
stating that the posterior probability density p(P/C) of the pharmacokinetic param-
eter P, given the measured concentration C in a given patient, is proportional to the
product of the likelihood of the data p(C/P) with the prior probability density of the
parameters p(P) in the population to which the patient belongs. The likelihood
Principles of Therapeutic Drug Monitoring 85
5 Pharmacodynamic Monitoring
The current TDM approach determines drug concentrations (or other pharmacoki-
netic parameters) in extracellular or whole blood fractions. It is used as a surrogate
marker of effect, but in some cases it may be hampered by the absence of correla-
tion between exposure and effect. In recent years, it was shown that the assessment
of pharmacodynamic effects provides a mean to improve and individualize drug
therapy. Numerous attempts have been made to develop biomarkers that would
complete TDM, e.g., pharmacodynamic monitoring of immunosuppressive ther-
apy, which is considered as a new strategy to tailor immunosuppressive therapy
(Oellerich et al. 2006; Sommerer et al. 2009).
However, immunosuppressive effect is complex and involves drug-independent
mediators, such as immunophilins for activity of cyclosporine and tacrolimus
(calcineurin inhibitors, CNI). Concentrations based TDM is limited in its ability
to measure drug effectiveness at its immunosuppressive site of action. As a result,
measured concentrations within the therapeutic range do not guarantee absence of
rejection or avoidance of toxicity in all patients and at all times. Pharmacodynamic
approaches are designed to address this issue (van Rossum et al. 2010). Numerous
tools have been developed for pharmacodynamic monitoring of CNI therapy, such
as calcineurin inhibition, IL-2 production, expression of genes encoding cytokines,
intra-lymphocyte ATP concentrations in CD4+ cells, and T-cell cytometric and
functional assays as markers of the degree of CNI-induced immunosuppression (de
Jonge et al. 2009). Preliminary reports also show associations between the different
pharmacodynamic markers and outcome as well as CNI pharmacokinetics (Fukudo
et al. 2005; Sanquer et al. 2004; Brunet et al. 2007). However, the routinely clinical
use of these pharmacodynamic markets remains to be validated in order to be
implemented in clinical practice. Studies in larger patient populations are needed
to evaluate the clinical value of these promising approaches.
Pharmacodynamic monitoring is not supposed to replace current concentrations
based TDM rather a complementary combination of TDM and pharmacodynamic
monitoring, which could help to improve pharmacotherapy for more effective and
safe results in individual patients.
Principles of Therapeutic Drug Monitoring 87
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Drug Delivery and Formulations
Contents
1 Administration Routes and Drug Dosage Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
1.1 Peroral Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
1.2 Oromucosal Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
1.3 Rectal Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
1.4 Topical/Transdermal Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
1.5 Parenteral Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
1.6 Intranasal Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
1.7 Pulmonary Drug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
2 Excipients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
2.1 Exposure and Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
2.2 Impurities in Medicinal Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3 Compliance Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
J. Breitkreutz (*)
Institut f€ur Pharmazeutische Technologie und Biopharmazie, Heinrich-Heine-Universit€at
D€usseldorf, Universit€atsstraße 1, 40225 D€
usseldorf, Germany
e-mail: joerg.breitkreutz@uni-duesseldorf.de
J. Boos
Klinik und Poliklinik f€
ur Kinder- und Jugendmedizin, Westf€alische Wilhems-Universit€at, 48149
M€ unster, Germany
and oral thin strips (buccal wafers), and multiparticulate dosage forms based on
mini-tabletting or pelletization technologies. Parenteral administration is likely to
remain the first choice for children in the neonatal period and for emergency cases.
Alternative routes of administration include transdermal, pulmonary and nasal drug
delivery systems. A few products are already available on the market, but others
still need further investigations and clinical proof of concept.
Abbreviations
Choice for the Paediatric Population released by the European Medicines Agency
(EMA), the central regulatory office for medicinal products in the European Union,
a matrix on the acceptability of administration routes and dosage forms in relation
to age is provided (EMA 2006). The table is extremely helpful to elaborate a rough
idea on the opportunities and challenges of drug administration, but is not legally
binding. The source data of the matrix were expert opinions only and not scientifi-
cally derived results. However, when submitting the Paediatric Investigational Plan
(PIP) to the EMA, which is now general requirement in the drug license procedure
in Europe (Breitkreutz 2008), the provided table might be of additional benefit for
preparing the regulatory discussions. However, recent advances in pharmaceutical
technologies such as new drug dosage forms and novel functional excipients
urgently require a general revision of the present reflection paper (Krause and
Breitkreutz 2008).
160
140
120
% of labelled claim
100
80
60
40
20
0
Pipette Spoon 1/2 Spoon 1/4 Spoon
Amoxicillin Erythromycin
Fig. 1 Dosing errors when using measuring spoons in medicinal products (modified from
Breitkreutz et al. 1999). Percentage shows the actually measured dose in relation to the labelled
claim in all amoxicillin and erythromycin products available on the German market (top). The
deviating volumes are due to the inadequate calibration of the spoons provided in the package
(bottom: precisely measured 2.5 ml liquid, but graduation is still visible and hence, causes
overdosing)
Fig. 2 Multifunctional tablet for paediatric use: Coartem® (Novartis). The tablet can be dissolved
in glass or a small volume of liquid on a spoon prior to administration. The formulation is speci-
fically designed for malaria treatment of children in developing countries with high temperatures
and humidity
Solid preparations which spontaneously disperse in the oral cavity (e.g. orodis-
persible tablets, thin film strips, oral lyophilisates) stand also on the periphery of
Drug Delivery and Formulations 97
solids and liquids. There are exciting new opportunities and recent advances in this
area. Oral lyophilisates, e.g. based on the Zydis® technology, have been introduced
some years ago offering fast-disintegrating wafers instantaneously forming a drug
solution within a few seconds (Seager 1998). As the production of the lyophilisates
is quite energy and cost-consuming their use was limited to niche markets, e.g.
for antiemetic drugs in high-dose cancer therapy. By introducing new functional
excipients, such as ready-to-use powder mixtures for direct tabletting, new
opportunities arise. By these excipients, mostly composed of co-processed man-
nitol, binders and super-disintegrants, orally disintegrating tablets (ODTs) can be
developed offering almost the same disintegration profiles as oral lyophilisates, but
produced on conventional tabletting equipment (Brown 2003). An interesting new
approach has been recently introduced by combining the mini-tablet and the ODT
concept (Fig. 3). These orodispersible mini-tablets dissolve within a few seconds in
the mouth releasing the drug substance. In the best case only 2.5 mg drug can be
loaded into a 2-mm mini-tablet, so that multiple dosing might be necessary. An
unpleasant taste of the API may be another issue and could require taste-masking
measures which would further reduce the dose loading. Oral film strips are another
alternative in paediatrics and the first medicinal products, e.g. with antiemetic drugs
or cough medication, have been introduced (Garsuch and Breitkreutz 2010).
Depending on drug substance, the film area and height up to 70 mg, but usually
only 15–25 mg API can be included in an oral film piece. The limitation of the
orodispersible formulations in general is the poor drug load when maintaining
the fast-dissolving properties. However, in paediatric medicines numerous drug
molecules are used at low doses and are therefore potential candidates for oromu-
cosal drug preparations. Another challenge is that only few excipients are available
to improve medication’s palatability and that using these excipients might cause a
reduction of the maximum drug load. Moreover, it is to be noted that few studies
have been performed to assess appropriate age, stage of development, and dosage
form of choice regarding applicability, acceptability, and preference. Further it has
to be considered that the absorption profile may be complicated as some molecules
may be absorbed directly through the oral mucosa, but an uncertain ration of the
dose is absorbed after swallowing.
0s 4s 6s 8s 10s
Fig. 3 Orally disintegrating mini-tablet (diameter: 2 mm) rapidly losing shape and partly
dissolving in artificial saliva
98 J. Breitkreutz and J. Boos
The rectal administration route can be used for local (e.g. laxative or anti-
inflammatory) or systemic (e.g. antipyretic or anticonvulsive) treatment. The
administration of drugs by rectal formulations (e.g. suppositories, solution, soft
capsules or ointments) can result in a wide variability in the rate and extent of
absorption in children. The rectal administration of suppositories or enemas for
systemic effects may nevertheless be chosen because the patient cannot take
medication orally, because the oral dosage form is rejected as a result of palatability
issues or because immediate absorption is required in emergency cases such as
grand-mal seizures. However, the use of rectal preparations has major drawbacks.
When administering rectal preparations, there is always the danger of premature
expulsion. The rectal bioavailability is limited for a broad range of drug molecules
(e.g. levodopa, phenytoin and penicillins), compared with oral or intestinal absorp-
tion (Krause and Breitkreutz 2008). Last but not least, the rectal route is poorly
accepted by a number of patients and caregivers in certain countries and cultures.
The development of the stratum corneum, the most prominent absorption barrier of
human skin, is complete at birth but is more perfused and hydrated than in older
children or adults. Therefore, neonates and infants have an underdeveloped epider-
mal barrier and are subject to excessive absorption of potentially toxic ingredients
from topically applied products. Only few transdermal products (e.g. contraceptive
drugs, caffeine, fentanyl, scopolamine, nicotine and methylphenidate) have been
tested or marketed for use in the paediatric population and predominantly have
targeted the elder children. Scopolamine is licensed only for children aged 14 years
or more because accidental overdoses in younger patients resulted in hallucinogenic
reactions. But still, the development of transdermal products in paediatric doses
could be beneficial for children who are unable to tolerate or accept oral
medications. The need for several sizes of patches to cover different doses might
be a further limitation. Sometimes adult patches are cut into pieces to obtain the
required size and dose. It is important to note that this is only possible with matrix-
type patches and, even then, the release kinetic may be modified and may cause
accidental overdosing.
This drug delivery into the nose provides fast and direct access to systemic cir-
culation without first-pass metabolism. Administration is not easy especially with
uncooperative children, but small volumes involved, rapidity of execution, feasi-
bility at home has made it more attractive, particularly for no-needle approach to
acute illnesses. Aerosols with an appropriate device can avoid swallowing and
is more precise in terms of dose. APIs such as benzodiazepines, fentanyl,
diamorphine, midazolame and ketamine have been used successfully via this
route. The key issue is to guarantee the released dose from a single actuation
from the device, especially for children as the dose is low and small deviations
from the intended dose may critically harm the patients.
particles deposit more peripherically and less in the upper airways whereas large
particles mostly stay in the mouth or throat by impaction to the endothelial cells. In
the case of dry powder inhalers (DPI) with interactive powder mixtures the outer
deposition of large particles made from carriers like lactose is intended, but the
smaller drug particles should enter the lung. In this particular case drug deposition
in the lung is a function of breathing abilities (to release the total dose, to separate
drug and excipients and to enable the direct flow of micronized drug particles into
the lung), of the formulation (which excipients, which drug crystals) and of the
device (breathing resistance, actuation, mouth adapter). It might be possible that
various devices and formulations would be needed for the same drug to suit the
requirements and properties of different age groups.
Pressured metered-dose inhalers (pMDI) have been sometimes successfully
employed in the paediatric population. These products are designed to deliver a
unit dose at high velocity with small particle size. However, self-administration is
difficult for younger patients with reduced coordination abilities and less compli-
ance consciousness.
To decrease oropharyngeal impaction and optimize utilization, various spacers
can be used. Face masks enable the use of pMDI for very young infants whereas
DPIs are only suitable for children with enough inspiratory flow to trigger particles’
release and transport the particles deep in the lung. Nebulizers are applicable for all
ages but very few are portable yet. Guidance for use of different inhaler types (i.e.
nebulizers, pMDI and DPI) has been established by the Global Initiative on Asthma
(GINA), a panel of clinical experts who look at the various inhaler types, their
features, and patient experience. Their guidance has been incorporated in national
regulatory guidance throughout the world. The most appropriate device should be
selected for each child. Children younger than 4 years should use a pMDI plus a
spacer with face mask or a nebulizer with face mask. Children aged 4–6 years should
use a pMDI plus a spacer with mouthpiece, a DPI, or, if necessary, a nebulizer with
face mask. For children using spacers, the spacer must fit the inhaler, and particular
attention should be paid to ensure that the spacer fits the child’s face. Children of any
age older than 6 years who have difficulty using pMDIs should use a pMDI with a
spacer, breath-actuated inhaler, DPI, or nebulizer. Particularly among children
younger than 5 years, inhaler techniques may be poor and should be monitored
closely. In order to improve devices and formulations, the development of in-vitro
models fully reflecting the physiological conditions at different age groups of
children are under development in our working group. The aim is to improve today’s
deposition rates by taking the differences in airways and capabilities into account.
2 Excipients
Table 2 Some excipients with elevated toxicological risk and severe outcome in children
reported in the literature
Excipient Patients at risk Administration Adverse reactions
Benzyl alcohol <6 months Oral, parenteral Neurotoxicity, metabolic
acidosis, >100 deaths
Polyethylene glycol <6 months Parenteral Metabolic acidosis
(Macrogol)
Aluminium salts <6 months Oral, parenteral Encephalopathy, microcytic
anaemia, osteodystrophy
Propylene glycol <12 months Oral, parenteral Neurotoxicity, seizures,
hyperosmolarity, death
Menthol <12 months Oral, nasal, dermal Bronchoconstriction, death
application to
face or breast
Diethylene glycol <18 years, all ages Oral Metabolic acidosis,
hyperosmolarity, >500
deaths
Benzalkonium Hypersensitive Oral, nasal, ocular Bronchoconstriction in
chloride patients, all ages hypersensitive patients,
loss of microvili function
Parabens <18 years, all ages Oral, parenteral, Allergies, contact dermatitis,
ocular, topical carcinogenic potential
Sulfites, bisulfites Hypersensitive Oral, parenteral Anaphylactic reactions
patients, all ages
The risk of children exposed to pharmaceutical excipients is linked to their age and
thereby, the maturation of organs and functions of the metabolic systems. The
Drug Delivery and Formulations 103
excipients may maintain for longer period in the juvenile body due to reduced meta-
bolic capacity or minor renal elimination. They can easily enter the brain as the
blood–brain barrier is more permeable than in adults. They can activate the immune
system of the maturing organism and may induce allergies or anaphylactic reactions.
Excipients with an elevated risk in paediatrics linked to the pharmacokinetic
properties are benzyl alcohol, ethanol, propylene glycol, polyethylene glycol and
aluminium salts (such as aluminium stearate or aluminium hydroxides). Benzyl
alcohol caused the “gasping syndrome” first described in 1981 by the accumulation
of metabolites such as benzaldehyde and benzoic acid in blood (metabolic acidosis)
and brain (neurotoxicity) causing more than 100 deaths worldwide (Gershanik et al.
1981). Metabolic acidosis is also a problem associated with high intake of polyethyl-
ene glycol and propylene glycol. Propylene glycol is regarded as very safe in the adult
population. There is no limit to be considered when using propylene glycol in
adulthood. In syrups for oral use it is often used as solvent, co-solvent or as a
replacement for a preservative at very high concentrations. There have never been
any reports on neurotoxic effects in adolescents and school-children. But in neonates,
especially in low-weight newborns and pre-term babies, numerous deaths, severe
brain damage and life-long handicaps have been reported (American Academy of
Pediatrics 1997; MacDonald et al. 1987). Propylene glycol and its metabolites may
enter the brain and may cause seizure and other neurotoxicological effect.
The neurotoxic potency of ethanol is well known, but the long-term effects of
low ethanol doses are still under discussion. Ethanol levels in pre-term neonates or
neonates with low birth weight have been recently investigated and raise concerns
(Whittacker et al. 2009). In some paediatric patients, even lower limits must be
considered, e.g. in children with liver and kidney malfunctions. In paediatric
dialysis patients the use of propylene glycol, polyethylene glycols and aluminium
salts should be completely prohibited. Hypersensitive patients may adversely react
on allergen presented in the formulation such as parabens, benzalkonium chloride,
colourants (azo dyes), sulfites, starches (glutens) or wool wax (Breitkreutz and
Boos 2007). For parabens agonistic activity at hormone receptors is discussed and
propyl paraben has been recently deleted from the list of permitted food additives in
the EU. In some cases, the immune system will cause anaphylactic reaction which
may be severe and live-threatening (dextran, sodium bisulfite, macrogolglycerol-
ricinoleate). Moreover, it has to be considered that some children may suffer from
rare diseases such as phenylketonuria, hereditary fructose intolerance and lactose
intolerance. In phenylketonuria, the use of aspartame must be prohibited as it is a
phenylalanine source. In fructose intolerance, the intake of the excipients fructose,
sucrose and sorbitol should be avoided.
some more potential contaminants have been identified in materials derived from
mammalian species with transmissible spongiform encephalitis (TSE), excipients
with potential viral load, and substances with potential endotoxin and pyrogen
load.
Some excipients in medicinal products are not labelled as they are only present
in traces. Residual solvents, for instance, are used in the manufacturing process
to solve a drug substance, a film former or a granulation binder. Residuals of
catalysts from the synthesis of the compounds and salts from heavy metals from
synthesis or packaging materials may be contained. Plasticizers from plastic
containers may migrate into the liquid phase (see section “Parenteral Drug
Delivery”). The residual burden of solvents is a good example, how difficult a
risk assessment in paediatric is: The amount of residuals of organic solutes in a
finished product is limited by the Permitted Daily Exposure (PDE). The organic
solvents are categorized into three classes by the toxic potency. Solvents with
highest toxicity are listed in class I, the less problematic solvents in class III.
However, both the categorization and the fixed limits have been derived from risk
assessment for adults, namely a woman with 50 kg body weight. It is not probable
that these limits match the paediatric situation. Therefore, for the PIP procedure
and for the market licensing procedure it is recommended to reduce the burden of
potential contaminants as far as possible. Alternative manufacturing technologies
such as aqueous film coating, dry powder coating, lipid coating and aqueous or
solvent-free granulation methods are highly demanded and should be applied for
paediatric medicines whenever possible.
3 Compliance Issues
4 Conclusions
Drug delivery to children is still a major challenge. Key issues are age-appropriate
formulations, safety of excipients, suitability of drug delivery devices and therapy
compliance. Some improvements have been made recently. The most promising
in oral drug delivery are orodispersible mini-tablets and thin film strips. In
parenteral drug delivery age-adapted devices and profound knowledge on the
preparation of extemporaneous or enabling formulations are of major importance.
In pulmonary drug delivery new in vitro deposition models, adapted to physio-
logical properties of children, may lead to better formulations and delivery
devices. The new EU formulation will stimulate the research and development
in paediatric medicines. Hopefully we will be able to match the unmet needs of
paediatric patients soon.
106 J. Breitkreutz and J. Boos
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Part II
Development of Pediatric Medicines
Development of Paediatric Medicines: Concepts
and Principles
Contents
1 Evolution of Paediatric Drug Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
2 Challenges in the Transition from Retrospective to Prospective Assessment
of Medicines for Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
3 Priorities and Unmet Needs in Paediatric Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
3.1 Essentials in Paediatric Clinical Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
4 Incentives and Rewards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5 A New Role for Regulatory Authorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
6 Strategy for a Paediatric Development Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
7 Limitations of Paediatric Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
8 Future Perspectives in Regulatory Affairs and Public Health Policies . . . . . . . . . . . . . . . . . . 122
9 Foreseeable and Unforeseeable Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
K. Rose (*)
klausrose Consulting, Pediatric Drug Development & More, Birsstrasse 16, 4052 Basel,
Switzerland
e-mail: rose@granzer.biz
O. Della Pasqua
Division of Pharmacology, Amsterdam Center for Drug Research, Leiden University, Einsteinweg
55, P.O. Box 9503, 2300 RA Leiden, The Netherlands
Clinical Pharmacology & Discovery Medicine, GlaxoSmithKline R&D, Stockley Park, Uxbridge
UB11 1BT, United Kingdom
e-mail: odp72514@gsk.com
trials. Today pharmaceutical progress is so obvious and well established that the
discrepancy between its benefit for adults as compared to children started to be
perceived by champions in different institutions. There is an increased under-
standing of the child’s physiology during developmental growth, of the matura-
tion of enzyme systems, of the pharmacokinetics and pharmacodynamics and of
the differences in disease processes. The involved institutions include legislators,
government, regulatory authorities, academic scientists, pharmaceutical com-
panies, the WHO, to name just the most prominent ones, but there are many
more. Driving forces for the improvement of medicines for children include
societal priorities, the involvement of science, the mission of regulatory authori-
ties the role of clinical pharmacologists, paediatricians, and the characteristics of
our market-driven economy with its chaotic, contradictory and lively elements.
We do not live in an ideal world, but there is progress, and children are likely to
benefit from it.
Since its earliest origins, mankind, adults and children were challenged by
accidents, diseases and hazards that required medical treatment. Until less than a
century ago, women used to get pregnant at a very young age and usually gave birth
to several children. The death rate of these children was horrific by today’s
standards, as was the frequency of mothers dying at childbirth. This situation
occurred despite health care providers being available during all these millennia
and centuries. Based on current medical knowledge little of what they could deliver
was helpful, albeit state-of-the-art at the time. And these professionals had an
amazingly high social reputation, with a status between priests and physicians. In
parallel to the evolvement of modern medicines, the principles of professional
health care practice and the criteria for the recognition of effective treatments
also changed dramatically over the last centuries, with an ever accelerating speed
of change. To a great extent, scientific principles have replaced common belief,
tradition and superstition, all of which pervaded therapeutics over the centuries.
The reputation of a member of the medical community has today something to do
with his or her actual knowledge and therapeutic skills.
On the other hand, there is today an increasingly complex layer between the
patient receiving treatment and the health care professional dispensing it. Thera-
peutics is based on an intricate process that we will define here as evidence
synthesis. To assess the efficacy of a new drug, clinical trials are performed in
hundreds or thousands of patients. The implementation and execution of these
Development of Paediatric Medicines: Concepts and Principles 113
trials may involve multiple clinical research centres, which can be thousands of
miles away, in another country, in another continent, or spread worldwide. To
ensure that such trials adhere to the state-of-the art standards and procedures,
a network of regulation exists that is recognised by national authorities and
professionals worldwide (ICH 2010). In addition, regulatory authorities have
established a comprehensive mechanism of monitoring and auditing. A clinical
trial performed in China, India and Latin America may be audited by the FDA
(2010), the EMA (2010), or even jointly by these two agencies. All the informa-
tion gathered in a trial will at the end be processed, analysed and reported. The
submission of such evidence to regulatory authorities triggers an evaluation
process that may lead to approval or rejection of the proposed treatment or
therapy. If the evaluation is positive, the evidence from clinical trial results
becomes part of the label or summary of product characteristics (SPC) and of
the patient information leaflet. In contrast to long gone times, none of the infor-
mation regarding the indication, efficacy and safety of a treatment originates from
the medical doctor who prescribes it. Instead, it is the result of pharmaceutical
physicians, clinical scientists and other professionals who contribute to drug
development. In this chapter, we try to grasp how this layer between patient and
caregiver is being adapted to the specific needs of children.
The advent of industrialisation in combination with the awakening of medical
sciences towards the end of the nineteenth century resulted in the identification and
subsequent availability of new, efficacious medicines. This process has since then
yielded powerful medications (e.g. antibiotics or steroids) for the treatment of
adults. These drugs have been subsequently brought into paediatrics based on
empiricism, an approach which has prevailed until recently.
Despite the development of pharmacology and clinical pharmacology as
disciplines with increasing understanding of the mode of action of available
drugs, including the requirements to demonstrate their efficacy, the formal assess-
ment of treatment effects in children has remained limited due to cultural,
practical and ethical reasons. In addition, the tools for the evaluation of efficacy
and safety in children have been historically questionable by current standards in
clinical research. Drugs developed early in the last century showed strong effi-
cacy, but had also the potential for serious side-effects and adverse events. The
first major tragedies (Taussig 1962; Wax 1995), leading to multiple deaths and
malformations resulted in the mandate for manufacturers in the USA to yield
proof of safety (1936) and efficacy (1960s, Kefauver-Harris amendments) (Hilts
2003; Rose and van den Anker 2010; Stoetter 2007). Since then, therapeutic
claims have to be demonstrated by properly designed clinical trials and other
measures. The requirement for data supporting product claims represented the
beginning of the modern drug labelling system. The initial deep, nearly blind
confidence in modern medications was in this way replaced by the need to impose
control. In the United States, the Food and Drug Administration (FDA) became
responsible for the assessment of the scientific and quality aspects of drug
development. Comparable legislation followed in Europe, with some variations
in the implementation in different individual countries.
114 K. Rose and O. Della Pasqua
It has not become yet evident to the international community that the current
European legislation has introduced an unprecedented revolution. It forces phar-
maceutical industry and researchers across all therapeutic areas to consider the
future paediatric use of new chemical or biological entities, which are neither on
the market, nor available to the adult population yet. This poses another important
challenge: informal benchmarking from prior therapeutic utilisation in adults
will not be available at the time a new drug or biological is first administered to
children. The long-lasting arguments that in the past supported the empiricism
used by paediatricians and paediatric pharmacologists will have less and less
space in the years to come. Off-label use will not be supported by evidence of
safety and efficacy in adults at the same extent post-launch data have provided in
the past.
In contrast to the retrospective evaluation of a drug’s pharmacokinetics, phar-
macodynamics or clinical profile, which has been driven by academic research,
considerations about the clinical development of new medicines and future use of a
new compound in children will require direct involvement of the pharmaceutical
industry and potentially other sponsors. The need to establish partnerships, to foster
critical mass in academia and to enable effective public–private partnerships or
other collaborative efforts has, however, not been defined by the law. This repre-
sents the single most important challenge to the success of this new era in paediatric
drug development.
In summary, the evidence supporting paediatric drug utilisation is evolving from
a rather simple research activity within the realms of academic expert groups to a
global multidisciplinary effort where relevant stakeholders must work together.
However, modern society is complex and cooperation cannot be taken for granted,
particularly when different interests are at stake. Collaboration is not the result of
logical thinking nor is it based on effective use of resources and expertise towards a
common goal. It is imposed by a framework created by the paediatric legislation,
the results of which are just beginning to become visible.
Priorities and unmet medical needs vary across geographic regions not only
because of biological, clinical and demographic reasons, but also due to political,
economical and social differences in the perception of the implications of disease
on child health and well-being. Let’s take as example two diseases which are
currently the focus of various research efforts: attention-deficit hyperactivity dis-
order (ADHD) and malaria. In the United States, ADHD is perceived as a develop-
mental disorder that requires pharmaceutical treatment to facilitate school
116 K. Rose and O. Della Pasqua
advancement of children, reducing the burden of parents and teachers. The same
disorder is perceived differently in Europe. On the other hand, malaria pervades the
lives of millions of children in Africa. Which of these two diseases should be
prioritised in terms of R&D efforts and health care policies? Many voices may
advocate malaria, but the answer to this question is complex and remains a social
and ethical dilemma as long as the priorities of the major players depend primarily
upon return-of-investment (RoI).
The majority of organisations in a market economy will have to consider direct
or indirect return of investment to fulfil their social and economic role. Serious non-
profit organisations and private–public partnerships, such as Drugs for Neglected
Diseases Initiative (DNDi 2010) and Medicines against Malaria Venture (MMV
2010) have a research agenda and predefined targets to meet. Many more stake-
holders can be found by web search engines, including charities, African govern-
ments, the United Nations, the World Health Organisation (WHO 2010) and the
Bill and Melinda Gates foundation (Gates Foundation 2010), all of which have their
own agenda.
The aforementioned issues are not addressed by the legislation on medicines for
children. In market-driven drug development, it is the management of individual
companies that decides which therapeutic targets will be included into the R&D
portfolio. A company has to aim for long-term survival, irrespective of the ethos
and social responsibilities it may endorse. To survive in a global economy,
enterprises must be able to maintain revenue. However, it is also true that there
are millions of children on this planet that have diseases that could be treated with
medications that are already available, but not accessible to the patients in need.
There is no single solution to this and many other dilemmas. A different, joint
public–private partnership model might be considered which would be recognised
beyond the regulatory and geographical borders of single countries. Without an
integrated, long-term action plan, it is unlikely that the needs of vulnerable popu-
lations, whether ADHD patients in the United States or malaria-infected children
in Africa, will be duly addressed.
There are key elements where most scientists will agree are necessary in drug
development if children are to be considered as integral part of it. Among other
things, an assessment must be performed for each disease which delineates unmet
medical needs and ongoing efforts in basic and applied research (e.g. understand-
ing of disease processes, target identification). Another critical factor under-
pinning a more effective approach to paediatric drug research is the ability to
access and share data on disease, safety and treatment outcome across organi-
sations. Currently, regulatory authorities are the only stakeholders who have the
privilege to access, to review and to mine preclinical and clinical research data
Development of Paediatric Medicines: Concepts and Principles 117
across a wide range of diseases. It could be argued that such valuable data should
not remain obscure to the wider scientific community, that the benefits from
sharing disease and treatment-related information represent an opportunity to
every stakeholder, and that mechanisms could be implemented to protect com-
mercial and patent interests without dismissing the impact that further integra-
tion of information can have on therapeutics. This discussion will go on for a
long time.
Concerted efforts are also required to ensure optimal implementation of clini-
cal development plans for each drug that reaches development stage. Unfortu-
nately, little attention has been paid so far to the implementation of paediatric
trials. The ethical, practical and financial burden associated with gathering evi-
dence from pharmacokinetics, efficacy and safety in children remains irrespective
of the therapeutic indication. In addition, lack of consensus exists in areas such as
(1) accepted age-matched normal range for laboratory measurements (e.g., for
haematology, biochemistry, urinanalysis), (2) requirements for the validation of
clinical endpoints for the assessment of efficacy and safety, and (3) standards for
long-term safety monitoring and pharmacovigilance. Moreover, guidelines and
policies for paediatric drug development are still highly regulated on a regional
base, despite the availability of a worldwide framework by ICH. Considerable
differences remain between regions and personal views seem to dictate imple-
mentation policies. In contrast, the decision regarding which therapeutic area to
invest is entirely up to local decision-makers usually from private companies.
Investment choices from non-profit organisations such as the Bill Gates founda-
tion (USA) or governmental institutes such as Institute Pasteur (France) and
Fiocruz Institute (Brazil) are minority examples of a different modus operandi
in R&D. Despite evidence for effective results, they have not had the impact on
market drivers which individual companies have had so far. Channelling the
debate on unmet medical needs and on the requirements for the level of evidence
through non-profit organisations may represent an opportunity to further find
common ground between private interests (patient advocacy groups, pharmaceu-
tical companies) and public health policies.
The future of paediatric development will ultimately depend on decision-
makers. However, fundamental modifications are required in the way decisions
are made about medicines for children. One thinkable scenario would be a joint
international governmental programme to reimburse new drugs with proven clini-
cal benefit based on health outcome, comparable to the approach that has evolved
over the last decades for vaccination and immunisation programmes across the
world. Various rare diseases and therapeutic niches exist which would benefit from
a similar framework. Entrepreneurial efforts could lead to start-up companies
which can rely on return of investment. This mechanism would trigger oppor-
tunities for identifying investors and clinical development venture capital. New
charities and research organisations with clear focus might evolve. In this
public–private partnership paradigm, profit margins can be defined by consensus
of all relevant stakeholders, rather than by shareholders.
118 K. Rose and O. Della Pasqua
One of the main changes in the way drugs have been approved for paediatric use is
the requirement for formal evidence of efficacy and safety as needed for adult
indications. Historically, the implementation of paediatric legislation in the United
States from 1997 to 2007 [FDA Modernization Act (FDAMA), Pediatric Research
Equity Act (PREA), Best Pharmaceuticals for Children Act (BPCA), FDA Amend-
ment Acts (FDAAA)] (2010) has driven paediatric product development without
explicit timing for the generation of such evidence. The absence of a milestone for
the implementation of paediatric plans has caused a major gap in R&D. Given that
most clinical studies were phase IV commitments, poor integration of the clinical
plans has become common practice for indications which include adults and
children. Despite the controversy, this system has improved the off-label use of
most licensed medicines.
The introduction of the paediatric legislation in the EU has added an important
element to paediatric research. It defines the timing at which a paediatric plan
120 K. Rose and O. Della Pasqua
should be in place. The regulation has changed the R&D landscape by introducing a
milestone for the implementation of a proposal, the paediatric investigational plan,
which could even occur in parallel to the development of the adult indication, where
applicable.
A detailed description of the requirements for a paediatric development plan is
out of the scope of this chapter, but the new EU legislation is triggering a profound
review of strategy and key processes in adult and paediatric drug development.
There are various challenges from a clinical and scientific perspective, including
establishing the rationale for dose selection in clinical trials in children, identifica-
tion and validation of primary endpoints for paediatric diseases and the assessment
of long-term safety in paediatric trials. From a theoretical perspective, one impor-
tant challenge is how to distinguish the influence of developmental growth and
other external factors from drug-related effects. Of particular interest is the role of
co-morbidities specific to childhood which may become important confounders
of drug response in children. On the other hand, the shift in paradigm also poses a
challenge to clinical practice, which will have to abandon informal, off-label
prescription as the basis of therapeutic innovation. Paediatricians and clinical
researchers have to face the requirements for the generation of formal evidence.
This is and may remain a major cultural hurdle throughout the next generation.
Paediatric prescription has been dominated by empiricism and myths about how to
best treat children. This problem is compounded by the lack of scientific and
technical training in paediatric clinical pharmacology, which would provide
paediatricians with the appropriate set of skills to design better trials and accurately
interpret findings from randomised clinical trials.
As indicated above, for the first time in the history of paediatric medicine, the
assessment of risk–benefit ratio is becoming a prospective exercise. The dialogue
between industry, academia, professional networks, regulators and patient organi-
sations will be critical to ensure paediatric needs are prioritised and complexities
understood accordingly.
Conceptually, the development of a paediatric strategy must account for a
number of aspects, which can be categorised as follows:
1. Level of evidence. Arguments to support the need to generate efficacy data vs.
using indirect inferences from extrapolation and bridging studies.
2. Disease. Understanding of differences or similarities in aetiology, epidemiol-
ogy, symptoms and signs across populations. This includes the availability of
common endpoints for the assessment of efficacy and safety in children of
different ages vs. adults.
3. Dosing rationale. Understanding of the requirements for the dosing rationale
which should be based on exposure–response relationships, rather than empiri-
cally defined by differences in body size. These considerations apply equally to
efficacy and safety.
4. Drug delivery. Understanding of the implications of changes in dosage form
and route of administration, taking into account the need for age-suitable
formulations.
Development of Paediatric Medicines: Concepts and Principles 121
The paediatric legislation in force in both the United States and European Union has
and will have long-lasting implications for the development of medicines for
children. Paediatric legislation will evolve further and will certainly not cease
to exist in either region. They have introduced processes and procedures which
will become an integral part of the drug development pursuit. Companies and
organisations that dismiss this shift in paradigm will have to face penalties imposed
not only by regulatory authorities on the file-ability of a market authorisation
application, but also by the resulting change in medical culture and market percep-
tion, which will disfavour off-label use of medicines in children. Most importantly,
this change may have consequences to the liability of sponsors and paediatricians to
legal action.
It is also important to consider that public understanding of drug development is
limited at present. Some facts are well known, e.g. increased life expectancy in
Western countries and the role modern pharmaceutical treatment plays in this.
Other facts remain unclear, particularly in Europe. There remains a quasi-mystical
belief in the medical wisdom and in the role of medical training. The appreciation
of the value of clinical trials as a key pillar of therapeutics is much less established.
This is exacerbated by media speculation and by the belief that children should not
be the subject of clinical experimentation. In general terms, this attitude reflects
cultural and historical differences between nations. U.S. citizens, on the other hand,
have a stronger scepticism towards authority and are more prepared to tread new
paths. Irrespective of these differences, the importance of gathering evidence on
efficacy and safety based on controlled, randomised clinical trials will become
obvious to parents, society and to many other stakeholders.
The debate will go on with defenders and contenders of governmental con-
trol and of entrepreneurial freedom. Albeit difficult to predict what will happen
Development of Paediatric Medicines: Concepts and Principles 123
10 Conclusions
Drug development is not a linear process which can be easily directed by guide-
lines and policies. It involves numerous, complex iterations, many of which do
not depend solely on logical, scientific judgement or criteria. It also depends on
medical, economical, ethical and political considerations. Given the nature of the
latter factors, consensus in health care priorities, medical needs and reimbursement
will remain an additional challenge for all stakeholders in R&D. Society, and in
particular children and adolescents, will continue to develop and behave differently
from today. They will face other lifestyle challenges and will have access to
different therapeutic options than today’s generation. In any case, the current
regulatory framework shows that legislation will continue to determine or at least
influence the directions and future of public health care. The right of access to safe
and effective medicines is certainly an achievement which cannot be overturned.
References
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Study Design and Simulation Approach
Stephanie L€
aer and Bernd Meibohm
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
2.1 Computer-Based Modeling and Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
2.2 Models for Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
2.3 Clinical Trial Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
2.4 Virtual World Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
3 Improving Dosing Strategies by Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
3.1 Examples of “Top Down” Simulations for Deriving Dosing Recommendations . . 138
3.2 Examples of “Bottom Up” Simulations for Deriving Dosing Recommendations . 141
4 Improving Clinical Trial Design by Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
4.1 Fastening Timelines of Clinical Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
4.2 Optimizing Sample Size and Selection of Pharmacokinetic Sampling Time
Points for Pediatric Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
S. L€aer (*)
Department of Clinical Pharmacy and Pharmacotherapy, Heinrich-Heine-University of
D€usseldorf, Universit€atsstrasse 1, 40225 D€
usseldorf, Germany
e-mail: stephanie.laeer@uni-duesseldorf.de
B. Meibohm
College of Pharmacy, University of Tennessee Health Science Center, 874 Union Avenue, Rm. 5p,
Memphis, TN 38163, USA
“bottom up” approach, as well as the term “virtual world simulation.” The
illustrated examples in this chapter from pediatric clinical trials will help to
understand and demonstrate these key elements. The importance of the understand-
ing of developmental physiology and pharmacokinetics will become visible when
explaining novel “bottom up” approaches like physiologically based pharmacoki-
netic simulations which also bridge to current research tools from other areas such
as systems biology using mathematical models to describe biological systems.
Abbreviations
1 Introduction
leverage knowledge from adult clinical trials enabling efficient data collection by
providing dosing schedules, optimizing and/or minimizing the number of plasma
samples required for pharmacokinetic and pharmacodynamic investigations and
even minimizing the number of infants and children required in clinical trials.
In this chapter, the principles and methods of modeling and simulation
approaches using computers and computer software are explained. The illustrated
examples from pediatric clinical trials should help to understand and demonstrate
the key elements of classical and novel modeling and simulation tools for pediatric
drug development. The specific topics will:
– define the terms deterministic simulation and Monte Carlo simulation.
– describe the classical “top down” and the novel “bottom up” approach of
modeling and simulation.
– describe virtual world simulation.
– provide a portfolio of examples of simulations to illustrate the benefits and
limitations of simulations.
2 Methods
Fig. 1 Modeling and simulation as one of the three pillars of facilitating the solution to
pharmacotherapeutic problems, along with theoretical reasoning and hypothesis building and
clinical experimentation. The modeling and simulation process visualizes and optimizes the
clinical experiment and thus helps fastening the process and even reducing the number of
experiments needed to be performed. From Laer et al. (2009)
usually known, and thus patients with even similar known covariates will exhibit a
distribution of different parameters, which will subsequently result in variability in
drug exposure and/or response. The deterministic modeling approach neglects this
uncertainty of the parameter point estimates.
a b
c d PLASMA LUNG
10 10
1 1
0.1 0.1
0.01 0.01
10 10
LIVER KIDNEY
1 1
0.1 0.1
0.01 0.01
10
Concentration [µg/ml]
10 MUSCLE BONE
1 1
0.1 0.1
0.01 0.01
10 10
SKIN FAT
1 1
0.1 0.1
0.01 0.01
1 10
BRAIN TESTES
0.1 1
0.01 0.1
0.001 0.01
0 2 4 6 8 10 0 2 4 6 8 10
Time [h]
Fig. 2 Illustration of the concept for building a physiologically based pharmacokinetic model
modified according to Willmann et al. (2003). (a) Organisms, e.g., human beings of different ages
or populations are the basis for the model. (b) The organism is divided into a number of
compartments, each representing a single organ. To describe the distribution of compounds in
the body the organs are connected via their arteries and veins to the arterial and venous blood pool.
Inter-compartmental mass transport occurs via organ-specific blood flow rates. The organs are
mathematically connected. (c) Division of each organ into three sub-compartments representing
the vascular (with blood cells), interstitial, and cellular space. The interstitial space is assumed to
be in direct contact with the plasma. The exchange of substances between the cellular and
interstitial compartment can occur by permeation across the membranes via passive diffusion as
well as active influx and efflux transport processes by saturable Michaelis–Menten (MM) kinetics
(parameters: Vmax, Km). Metabolization of substances (Meta1, Meta2) occurs via active enzymes
(MM-kinetics). Finally, the model consists of a large number of coupled differential equations. (d)
Output of the model: Concentration time curves for the substances. Shown are simulated and
observed ciprofloxacin concentrations in various organs after intravenously applied ciprofloxacin
5 mg/kg to a rat
Study Design and Simulation Approach 133
Table 1 Body and tissue weights (kg), cardiac output (L/min) as function of age according to
Bj€orkman (2004)
Tissue Neonate 6 months 1 year 2 years 5 years 10 years 15 years Adult
Body 3.55 8.03 10.2 12.6 19.7 31.4 56.7 73.0
Lung 0.06 0.12 0.16 0.24 0.34 0.43 0.90 1.20
Liver 0.12 0.27 0.36 0.48 0.59 0.87 1.35 1.80
Kidney 0.03 0.05 0.06 0.09 0.11 0.18 0.25 0.31
Gut 0.05 0.09 0.14 0.19 0.34 0.58 0.82 1.02
Muscle 0.80 1.35 1.90 2.83 5.60 11.0 24.0 29.0
Adipose 0.89 2.97 3.64 3.76 5.0 7.50 9.50 14.5
CO 0.58 1.35 1.68 2.06 2.88 3.90 5.77 6.79
QH 0.22 0.38 0.45 0.53 0.72 1.04 1.55 1.72
CO cardiac output, QH total hepatic blood flow
Fig. 3 Changes in liver volume (LV) (a) and liver blood flow (b) as function of age according to
Johnson et al. (2006)
2006), the fraction of vascular and interstitial space, changes in total body water and
adipose tissue content, plasma protein concentration especially of albumin and
alpha glycoprotein, and renal and hepatic elimination.
There are numerous reports about developmental changes in metabolizing
enzymes from birth to adolescence (van der Marel et al. 2003; Bouwmeester
et al. 2004; see also Table 2). Nearly each CYP450 isoform shows a different pattern
of maturation, and might influence the drug clearance with respect to specific age
134 S. L€aer and B. Meibohm
Table 2 Enzyme activities (expressed as fraction of adult values) as function of age Edginton
et al. (2006)
Enzyme Neonate 1 month 3 months 6 months 1 years 10 years
Cyp3A4 0.24 0.5 0.7 1.1 1.3 1
Cyp1A2 0.1 0.2 0.25 0.29 0.35 1
Cyp2E1 0.32 0.4 0.46 0.46 1 1
UGT2B7 0.064 0.1 0.3 0.7 1 1
groups. The most abundant hepatic CYP450, the CYPs 3A4 and 3A7, which belong
to the subfamily CYP3A, show a different evolution with time: CYP3A7 is the
major active isoform in neonates and young infants but there is a progressive shift
from CYP3A7 toward CYP3A4 in the first weeks of life. And, although these
enzymes share at least 85% sequence identity, they exhibit large differences in
substrate specificity and catalytic activities (Hines 2008).
Similar to enzyme systems, the integration of the maturation of renal excretion
in a PBPK model is highly relevant because of its impact on the pharmacokinetics
of compounds with renal clearance as major elimination pathway (Alcorn and
McNamara 2003; Morselli et al. 1980; Yared and Ichikara 1994). Both, glomerular
filtration rate and tubular secretion, undergo developmental changes (Arant 1978).
Glomerular filtration rate increases rapidly in the first weeks to reach adult values
between 2 and 6 months because of an increase in cardiac blood flow, a decrease in
arteriolar resistance and an increase in the surface area and the pore size of the
glomerular membrane. The tubular secretion increases at a slower rate than the
glomerular filtration rate (GFR), particularly because of the delay in the maturation
of active transporters, but also due to the smaller size of the tubulus and a smaller
mass of functioning tubular cells in children. The maturation of tubular secretion
takes about 1 year.
a
Total clearance
12 Contribution of CYP3A4
Contribution of CYP2C9
10
Predicted clearance
(ml/min/kg)
0
0 2 4 6 8 10 12 14 16 18
Age (years)
b
dose mg/kg
0.5
(ng •h/ml)
2000
1500
0−∞
Simulated AUC
1000
500
0
0.25 0.5 0.75 1 1.5 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Adults
Age (year)
Fig. 4 Simulation results of a PBPK model for sildenafil for children using the PK-Sim®.software
module (Hsien 2010). (a) Predicted age-dependent sildenafil hepatic clearance across the different
pediatric ages based on the clearance scaling module in PK-Sim®. (b) Age-related doses for oral
sildenafil in children depending on the simulated age-related exposure (not shown) of sildenafil in
a virtual pediatric population and the estimated exposure of the estimated doses of sildenafil in
children between 3 months and 18 years of age. Potential pediatric doses on the basis of the
simulations for sildenafil in order to achieve adult exposure: Infants and younger children from
3 months to 4 years: 0.8 mg/kg, children from 5 to 8 years 0.5 mg/kg and children older than
8 years 0.35 mg/kg similar than in adults. Box plots represent median, 25th and 75th percentiles
(box), 5th and 95th percentiles (error bar) and maximum and minimum values (x) of AUC
01 from 1,000 simulations in each age
Study Design and Simulation Approach 137
children data on the ontogeny of these parameters are not always available and/or
they are not available from only one source. This may lead to some confusion and to
a problem in establishing a reliable source of accurate and consistent information.
In addition, some gaps may be present in fully or accurately describing some
physiological process especially in young children, which in turn may lead to an
inability of the model to successfully describe the pharmacokinetics of certain
drugs in this age group.
Clinical trial simulation is one of the more complex current applications of M&S
techniques and is an example that frequently combines model components derived
through inductive as well as deductive analysis approaches (Bonate 2000). Trial
simulation uses numerical simulation techniques to assess in silico how a clinical
study is likely to perform based on simulation of the behavior of its individual
participants and prior knowledge and assumptions for underlying distributions and
mechanisms (Girard 2005). As such, trial simulations may include a variety of sub-
models. It does not only include a structural dose–exposure–response/toxicity
relationship (PK/PD-model) that was derived using the “top-down” or “bottom-
up” approach, but also includes model components that capture access to patient
populations including patient demographics, study design, enrolment criteria,
natural progression of the disease, response to placebo, adherence to the
pharmacotherapeutic regimen, and drop-outs from the study. Each of these model
components contains one of multiple deterministic as well as stochastic elements.
With these model components, clinical trial simulation is able to run many virtual
repetitions of a trial. The multiple stochastic elements may affect trial outcome
differently in each repetition. With hundreds or thousands of virtual repetitions for
the trial execution, clinical trial simulation allows establishing a likelihood profile
of trial outcomes that provides the investigator information about the chance of
achieving the primary outcome of a study given a specific study design and trial
execution environment if only one real-life study is performed. Thus, clinical trial
simulation is an excellent tool to optimize study designs, especially in pediatric
populations where appropriate study populations are oftentimes scarce and study
performance is limited by ethical and logistical constraints. For this reason, the U.S.
Food and Drug Administration recommends to perform clinical trial simulation as a
routine approach to assess the appropriateness of trial designs in pediatric drug
development (Gobburu 2010).
convert into sinus rhythm for a sotalol plasma concentration of 0.4 mg/ml, and a
more than 95% probability for 1.0 mg/ml, with no indication of an age-dependent
difference in antiarrhythmic efficacy.
All three analysis components were subsequently combined to derive dosing
recommendations via Monte Carlo simulations for five age groups, neonates,
infants under 6 months, infants 6 months to 2 years, children 2–6 years, and children
6–12 years. For start and target dose simulations the treatment goal was defined to
achieve a 50% probability (start dose) and more than 95% probability (target dose)
to respond to sotalol therapy. An 8-h dosing interval was chosen to ensure a similar
Fig. 5 Simulation results for sotalol dosing recommendation development: (a) Simulated sotalol
trough concentrations (125 patients per group and dose level) for pediatric patients with supraven-
tricular tachycardia. Lines indicate 50% and more than 95% efficacy. (b) Patient fraction with 50%
and more than 95% probability of arrhythmia suppression. Black box plots and hatched bars
indicate recommended dosing range. Arrows indicate start and target doses. From Laer et al.
(2005)
Study Design and Simulation Approach 141
Fig. 6 Predicted and observed arithmetic mean (SD) plasma concentration time curves of
alfentanil in healthy controls and patients with liver cirrhoses according to Edginton and Willmann
(2008)
Fig. 7 Predicted pharmacokinetic parameters for volume of distribution, clearance, and terminal
half-life of theophylline as function of age, together with literature data according to Bj€
orkman (2004)
Another example was presented in Edginton et al. (2006). The goal of this study
was to extend an existing adult PBPK model in order to reflect the age-related
physiological changes in children from birth to 18 years old. Information about age
dependencies of the relevant physiological parameters in children were gathered
from the literature and the simulations were carried out using PK-Sim® in conjuga-
tion with a previously developed age-specific clearance model. To evaluate the
accuracy of plasma profiles prediction in children by the developed pediatric
model, a group of five drugs (paracetamol, alfentanil, morphine, theophylline,
and levofloxacin) was used. These drugs were selected based on the availability
of concentration-time data in the literature for both adults and children. At the
beginning, the pharmacokinetic profile of these drugs was simulated in adults and
was then compared with observed data for evaluation. When the simulated curves
in adults matched the observed data with sufficient accuracy, a predicted pediatric
clearance value for each drug was generated using the clearance model mentioned
144 S. L€aer and B. Meibohm
previously and pediatric simulations were done. The simulated plasma concentra-
tions–time curves and pharmacokinetic parameters were then compared with the
corresponding observed values and the pediatric simulations were evaluated for
appropriateness. The overlap between predicted and observed data was satisfying.
As already illustrated in Fig. 4, predicted clearance values can be used to calculate
drug exposure and dosing regimens, for example, in specific age groups of children.
Unfortunately, many pediatric efficacy trials are still performed with devastating
limitations and design flaws, resulting in a high frequency of trial failures. Benjamin
and co-workers (2008) analyzed these failures in a recent publication on antihyper-
tensive trials. The authors examined six antihypertensive dose-ranging trials with
enalapril, liniopril, losartan, amlodipine, fosinopril, and irbesartan. They could
show that trial failures were largely related to poor dose selection, with widely
overlapping responses for different dose levels. In contrast, successful studies used
wider dose ranges resulting in less overlap in responses. In addition, these studies
used diastolic blood pressure rather than systolic blood pressure, which is more
reflective of systolic hypertension which is more common in elderly, but not in
pediatric populations.
Modeling and simulation approaches, including clinical trial simulation, can
contribute to overcome some of these trial limitations by allowing to explore in
silico different dose levels, dosing regimens, and efficacy biomarkers if the respec-
tive drug- as well as system-specific parameters are available. For antihypertensive
drugs, some of these system-specific parameters may be derived from already
published trials in this indication and population, for example, the typical variability
in systolic and diastolic blood pressure assessment in pediatric populations.
The pharmacometrics team at the US Food and Drug administration recently
published a related example where prior knowledge from an investigational antihy-
pertensive drug together with pediatric data from a drug with similar mechanism of
action and approved indication in pediatric patients were used to perform clinical
trial simulations to explore the optimal choice of dose range, sample size endpoints,
and other design elements (Jadhav et al. 2009).
In another example, Mouksassi et al. (2009) applied clinical trial simulation to
develop a clinical trial design for a pediatric multiple-dose phase I study to
determine the safety, efficacy, and pharmacokinetics of teduglutide, a glucagon-
like peptide-2 analogue indicated for the treatment of short-bowel syndrome and
Crohn’s disease. In this analysis, specific emphasis was put on a realistic simulation
of demographic covariates to obtain an accurate assessment of the variability in the
expected response. This was accomplished with a generalized additive modeling
Study Design and Simulation Approach 145
for location, scale and shape, and qualified with an external age-weight data set.
The analysis allowed to optimize the phase I dosing strategy and the likelihood of
achieving target exposure and therapeutic effect.
5 Conclusion
Modeling and simulation techniques used either as “top down” or “bottom up”
approaches are deeply interwoven with pediatric drug development. Within the
three pillars mentioned earlier (see Fig. 1), the modeling and simulation pillar is a
tool that fastens knowledge gaining and helps to understand the pharmacological
properties of the drug in the pediatric population. The idea that modeling and
146 S. L€aer and B. Meibohm
Plasma
concentration
(log)
Recommended
sampling times
LOQ
Time
Acknowledgement The authors want to thank Feras Khalil from the Department of Clinical
Pharmacy and Pharmacotherapy at the Heinrich-Heine University of D€
usseldorf for some literature
review and comments about the physiologically based pharmacokinetics (see also Khalil and
Laer 2011).
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basis of developmental physiology and pharmacokinetic considerations. Clin Pharmacokinet
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Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
2 Setting the Scene for Evaluation of Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
3 Aspects on Determining Endpoints in Paediatric Clinical Trials . . . . . . . . . . . . . . . . . . . . . . . . . 153
3.1 Endpoints Affected by Development and Performance Capacity . . . . . . . . . . . . . . . . . . 154
3.2 Endpoints Influenced by Differences in the Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
3.3 Endpoints Depending on Different Symptoms in Adult
and Paediatric Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
4 Relationship Between Efficacy Measures and Diagnostic Tools . . . . . . . . . . . . . . . . . . . . . . . . . 161
5 Standardisation of Outcome Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
6 Conclusions and Future Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Abstract Even though the regulatory authorities to some extent accept the extra-
polation of efficacy data from adults to paediatric patients, it is often the case that
differences in the disease process and the developmental stage of the children
prevent the extrapolation of efficacy in these populations. Where efficacy studies
are needed, the development, validation, and employment of different endpoints for
specific age and developmental subgroups become necessary. Children are in
continuous development and any measure to assess the efficacy of an intervention
should take carefully into account how this development affects the endpoints,
including the performance capacity of the child and differences in the condition and
symptoms presented. Clinical endpoints that are used in the adult trials to evaluate
S. Wang (*)
Norwegian Medicines Agency, Tønsberg Hospital Pharmacy, Sven Oftedalsvei 6, N-0950 Oslo,
Norway
e-mail: siri.wang@noma.no
P. Laitinen-Parkkonen
Health Care and Social Services, City of Hyvink€a€a, Suutarinkatu 2 C, 05801 Hyvink€a€a, Finland
e-mail: pirjo.laitinen-parkkonen@hyvinkaa.fi
1 Introduction
The regulatory authorities accept to some extent the extrapolation of efficacy data
from adult data to paediatric patients in the case the disease process and the
expected outcome of the therapy are comparable to that of the adults (ICH E 11
2001). However, it is often the case that differences in the disease process and the
developmental stage of the children prevent the extrapolation of efficacy in these
populations. Especially, extrapolation of the efficacy data from older children and
adults to neonate population is rare. Where efficacy studies are needed, it may be
necessary to develop, validate, and employ different endpoints for specific age and
developmental subgroups.
The progress in the legislation regarding the development of medicinal products
based on adequate and well-controlled studies also in paediatric population in the
USA and in EU, such as the Best Pharmaceuticals for Children Act in 2002,
Paediatric Research Equity Act in 2003, and Paediatric Regulation in 2006, has
encouraged the stakeholders to find alternative ways to measure the magnitude of
the treatment response in paediatric population (Regulation EC 2006). Therefore,
the interest on assessing development-appropriate endpoints and developing
biomarkers and surrogate endpoints suitable to paediatric studies has increased.
The increasing interest on biomarkers has led the working group of National
Institute of Health to provide discussion and definitions for clinical endpoints,
biomarkers, and surrogate endpoints.
A clinical endpoint is defined as a variable reflecting how the patient feels,
functions, or survives. Biomarkers are defined as biological characteristics that can
be objectively measured and evaluated as an indicator of normal biological process,
pathogenic process, or pharmacological response to a therapeutic evaluation
(Biomarkers Definitions Working Group 2001). Biomarkers can be further classi-
fied into Type 0 biomarkers, which are markers of the natural history of a disease
Efficacy Assessment in Paediatric Studies 151
that correlates longitudinally with known clinical indices, and Type I biomarkers,
which capture the effects of a therapeutic intervention in accordance with its
mechanism of action (Puntman 2009). A surrogate endpoint, defined as a biomarker
intended to substitute a clinical endpoint, is not directly measuring clinical impact,
but is believed to adequately reflect the clinical benefit or harm based on epidemio-
logic, pathophysiologic, other scientific evidence, or on therapeutic effect
(Biomarkers Definitions Working Group 2001).
The most robust way to define the clinical impact of the therapeutic intervention
is to use well-defined clinical endpoints in the randomised controlled trials. The
clinical endpoints selected for the trial should provide the clinically relevant and
scientifically sound evidence to support the primary objectives of the study (FDA
1998). The clinical endpoints can be further categorised into intermediate
endpoints, which is not the ultimate outcome, but of clinical benefit such as exercise
tolerance, and into ultimate outcome, such as survival or symptomatic response that
captures the benefits and risks of an intervention (Lesko and Atkinson 2001).
Clinical endpoints that are conventionally used in the adult trials to evaluate
treatment effect may not be suitable in paediatric trials. The experience
accumulated from earlier adult studies for a certain indication may not be applica-
ble in the paediatric population (Della Pasqua et al. 2007). Additionally, in a recent
systematic review, very few paediatric studies even address the choice of outcomes
for clinical research in children (Sinha et al. 2008).
Outcome variables should ideally be measured without bias in a reliable manner
using validated instruments with adequate sensitivity to detect real change in
patient’s health status. The validation process generally assesses this link between
changes in the instrument’s score and the actual clinical benefit and should be
sensitive to treatment effects as well as be clinically relevant (Redmond and Colton
2001). The instrument’s validity might be tested through larger clinical trials, or
through meta-analysis. For children, the challenge will be the feasibility of large
clinical trials and the lack of standardised clinical trial methodology in many
paediatric areas, leaving the validation process potentially even more challenging
than for adults.
Biomarkers and surrogate endpoints frequently used are physiological and
laboratory measurements. The classical examples are the effect of lipid-lowering
drugs on LDL-cholesterol levels as surrogate of the cardiovascular health and the
effect of antihypertensive drugs on blood pressure as surrogate of the stroke.
Biomarkers such as these have traditionally been identified through pathophysio-
logical and epidemiological studies, and some confirmed with clinical trails.
Despite the current acceptance of cholesterol lowering as a surrogate endpoint,
not all treatment effects can be captured by a single biomarker (Lesko and Atkinson
2001). New developments in molecular science and sophisticated imaging
technologies have increasingly facilitated the industrialised process of biomarker
discovery, supported by standardised paradigms of biomarker validation (Puntman
2009; Dancey et al. 2010; EMEA 2009a). There is an ongoing discussion between
the European regulatory authorities, academia and pharmaceutical industry, on the
152 S. Wang and P. Laitinen-Parkkonen
Children are in continuous development and any measure to assess the efficacy of
an intervention should take carefully into account how this development affects the
endpoints. For example, in patients with chronic diseases, the response to a medici-
nal product may vary among patients not only because of the duration of the disease
and its chronic effects but also because of the developmental stage of the patient.
Measurement of subjective symptoms such as pain requires different assessment
instruments for patients of different ages, as children may not be able to comply
with the endpoints used in adult trials (ICH 2001).
In neonates, either preterm or full term, symptoms, diseases, and management
might differ significantly from that seen in older children. Thus, when evaluating
medicinal products in neonates, the endpoints should be carefully chosen, linked to
the condition and the degree of prematurity. There is a need for establishing
appropriate surrogate endpoints in this age group. The known complications and
sequelae of prematurity (e.g. intracerebral/intraventricular haemorrhage,
necrotising enterocolitis, retinopathy of prematurity, and bronchopulmonary dys-
plasia) as well as survival should be evaluated at least as secondary endpoints in
trials that include the neonatal population (EMEA 2008a).
When patient reporting-based endpoints are used for defining the magnitude of
treatment benefits, pre-defined age-appropriate instruments are needed (EMEA
2004; Rothman and Kleinman 2009). The current guidance provided by the FDA
on the use of patient reporting-based instruments in children highlights the impor-
tance of age-related vocabulary, language comprehension, comprehension of the
health concept measured, and duration of recall when developing and using such
tools. Instrument development within fairly narrow age groupings is important to
account for developmental differences and to determine the lower age limit at
which children can understand the questions and provide reliable and valid
responses that can be compared across age categories. The proxy-reported outcome
measures for this population are not recommended. For patients who cannot
respond for themselves (e.g. infants), observer reports that include only those
events or behaviours that can be observed are encouraged (FDA 2009c).
This section illustrates some paediatric-specific issues on assessing efficacy in
clinical studies. Examples given are not intended to cover all aspects or areas, nor
154 S. Wang and P. Laitinen-Parkkonen
could be significant in the first years. Currently, the primary goal of cystic fibrosis
therapy is supportive and includes slowing the decline in lung function by clearing
airways of mucus and controlling respiratory infections and inflammation to
improve or maintain respiratory function. As in asthma, FEV1 is the recommended
primary endpoint, but similarly sub-optimal or potentially inappropriate in children
beyond 5–6 years. As stated in the recently updated EMA guideline (EMEA
2009b), respiratory function tests in young children can be performed in specialised
centres able to promote standardised methods. Tests currently used include
plethysmography and RVRTC (compression technique) (Davis et al. 2010;
Rosenfeld 2007), but these procedures most often require sedation, partly
depending on age group (Davis et al. 2007). Measuring lung clearance index
(LCI) by multiple breath washouts might show to be a useful method for appropri-
ate lung function testing in younger children. However, these alternative measures
still need to be further validated.
Although paediatric pulmonary arterial hypertension (PAH) differs in physiology,
progression rate, and treatment response compared to the adult type, the definition
of PAH is basically the same (EMA 2010) and the symptoms are similar although
with potential different severity (Haworth and Beghetti 2010). However, the tradi-
tional endpoint used in adult studies of pulmonary hypertension, the 6-min walking
test (6MWT), is of questionable value in younger children (<6 years), obviously
inappropriate in the very youngest infants, but considered valid at least in
adolescents. In the age group 7–11 years, this test needs further validation (Li
et al. 2005). Additionally, its predictive value on the long-term improvement of the
disease is not established in the adult population, questioning its usefulness in the
paediatric population >6 years (EMEA 2009c).
Time to clinical worsening (TTCW) is probably a more appropriate endpoint to
assess disease progression, and is also used in adults. Of note, the definition of the
composite endpoint of clinical worsening in children will have to be done carefully.
In particular, there is a need for paediatric-specific endpoints that could be used in
intervention studies in the early phase of the disease to prevent the fast deterioration
seen in many children. TTCW could be such an endpoint (Haworth and Beghetti
2010).
Data on vascular resistance, obtained by invasive haemodynamic measurements
or by non-invasive techniques such as echocardiography, could potentially serve as
a surrogate endpoint and should be studied as additional endpoint to assess the
correlation to final clinical outcome in paediatric studies.
Even more limited data are available regarding relevant endpoints in the field of
persistent pulmonary hypertension of the neonate (PPHN), having different
aetiology and management and being considered a different clinical entity. At
present, several potential endpoints might be useful; however, all-cause mortality
and the need for membrane oxygenation (ECMO) are considered the less disputable
ones (EMA 2010).
Another example of challenges in assessing efficacy in children is the evaluation
of pain. According to the International Association of study of pain (IASP), pain
includes an unpleasant sensory and emotional experience associated with actual or
156 S. Wang and P. Laitinen-Parkkonen
As disease course as well as consequences might not necessarily be the same for
different paediatric variants of a condition, the aims of the treatment might vary and
this could also affect the endpoints. For example, for incontinence in children,
while the goal for all children would be continence, in neurogenic detrusor
158 S. Wang and P. Laitinen-Parkkonen
drugs. A variety of instruments are available for measuring disease activity; how-
ever, no single measure would be considered optimal for all patients. Therefore,
a core set of parameters has been established by the American College of Rheuma-
tology (ACR) that includes physician scoring, parent assessment, affected joint
counts, functional assessment, and laboratory measures, particularly tailored for the
paediatric condition (ACR Pedi 30, Pedi 50 and Pedi 70). These tools focus on
individual changes in disease activity over time and as such are useful for assessing
the effect of an intervention. However, comparison of absolute disease activity
between individuals and group comparison is not optimal with this scoring system.
Thus, a composite disease activity score for JIA has been developed, called the
Juvenile Arthritis Disease Activity Score (JADAS), enabling a single continuous
measure of disease activity (Consolaro et al. 2009). The score has been developed
and validated by the Paediatric Rheumatology International Trials Organisation
(PRINTO) and could be of significant value both in standard clinical care and
particularly in clinical trials, potentially minimising inter-centre variations and
thereby reducing the sample size required in clinical trials.
The establishment of international networks within the area of paediatric rheu-
matic diseases has significantly contributed to the standardisation of the evaluation
of response to therapy in juvenile idiopathic arthritis (JIA), juvenile systemic lupus
erythematosus (JSLE), and juvenile dermatomyositis (Ruperto et al. 2006).
It should be noted that even if a disease differ between adults and children
this may not necessarily have impact on the choice of endpoint, as for some
conditions the same endpoints might be appropriate, although the disease is not to
be considered entirely the same. In these cases, separate studies could be needed or
at least provide more meaningful data, since the effect of the intervention could
differ for the separate subtypes of the diseases and significantly influence the
outcome of the trials.
Headache Society (IHS) standards, the definition of the attack differs in pre- and
post-pubertal children (IHS 2004).
Several investigators have observed the high and variable placebo response
observed in many migraine trials in paediatric population, which makes it difficult
to assess efficacy (Winner et al. 2007; H€am€al€ainen et al. 1997; Ahonen et al. 2004,
2006; Rothner et al. 2006). The reasons for the high placebo response in children
are not fully understood. The proposed underlying reasons include differences in
presentation of the disease, such as the shorter attacks in children, especially in
adolescents, compared to adults, and the different baseline severity of attacks. The
trial design-related issues (such as cross-over versus parallel group) and site
selection may also affect the placebo response as well as communication and
expectancy of the caregivers (Evers et al. 2008; Rothner et al. 2006). Additionally,
the sensitivity of the pain rating scales to distinguish the differences in the pain
intensity in children should be confirmed (Lewis et al. 2005).
The European regulatory guidelines recommend the percent of patients being
pain-free at 2 h after administration of the study agent as primary endpoints in acute
paediatric migraine treatment trials similarly as in adults. Recommended secondary
endpoints are, for example, the percent of patients pain-free at 2 h after administra-
tion of the study product with no use of rescue medication and no relapse within
48 h after administration of the study agent, percentage of subjects with partial
relief (including children asleep in 2 h), use of rescue medication, global evaluation
by patient and/or parents, and functional disability at 2 h and other time points (e.g.
using behavioural scales). In prophylaxis studies, the frequency of the attacks and
the speed of effect should be monitored (EMEA 2007b).
It has been suggested to explore other primary endpoints as well, such as the
migraine-free primary endpoint (pain-free and symptom-free composite endpoint),
1-h headache response, coupled with the 2-h sustained response and the 24-
h sustained headache, and pain-free response to handle the outcome challenge
(Lewis et al. 2005; Lewis 2007; Winner et al. 2007). New approaches in the
study design are warranted to meet the challenges of efficacy assessment in
developmental age migraine.
Studies on antihypertensive treatment with ACE inhibitors and ARBs for
paediatric hypertension have revealed diverging results. Attempts to analyse the
different factors influencing success or failure of these trials have shown that in
addition to trial design, dose ranges tested, and dosing accuracy, the choice of
primary endpoint might also be relevant (Benjamin et al. 2008). Using change in
diastolic blood pressure (DBP) instead of sitting systolic blood pressure (sSBP) as
the primary endpoint seemed to give a closer relationship between dosage and
blood pressure reduction, probably related to the less variability seen for DBP
measures compared to SBP, underlining the potential importance of the inherent
characteristics of the endpoint of choice. Another aspect would be that these two
endpoints, when used as tools for inclusion, could select different population
subsets and thereby affect outcome of the trials. Which endpoint that best correlate
to hard cardiac endpoints in children is a vital question. Discussion is ongoing
on which endpoint to be considered optimal, also taking into account the
Efficacy Assessment in Paediatric Studies 161
As briefly mentioned in the examples of lung function tests in asthma, the possibil-
ity to make an appropriate diagnosis in children is often hampered by the lack of
relevant measures to properly define the condition. Consequently, further research
on diagnosis-related pathophysiological measures and severity classification of
162 S. Wang and P. Laitinen-Parkkonen
diseases would also be relevant for further measures of drug efficacy, as the same
methods might be valid for both appropriate diagnoses and appropriate endpoints
for measuring any effect of intervention.
The development of biomarkers may also facilitate the understanding of disease
mechanisms and natural history, expedite the development of new diagnostic tools,
and assist the clinical practice (Lesko and Atkinson 2001).
clinical trials in children. Collaboration and sharing the advances between acade-
mia, pharmaceutical industry, and regulatory authorities are of paramount
importance.
Disclaimer. The views expressed here are the personal views of the authors and
may not be understood or quoted as being made on behalf of the Paediatric
Committee or reflecting the position of the Paediatric Committee.
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Safety Assessment in Pediatric Studies
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
2 Pharmacoepidemiological Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
3 Pemoline-Index Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
3.1 Pediatric ALF Cases Receiving Pemoline and Reported to the FDA . . . . . . . . . . . . . . 173
3.2 Calculating Relative Risk of Pemoline Associated with ALF . . . . . . . . . . . . . . . . . . . . . . 173
4 Laboratory-Based Methods of Predicting Serious Adverse Reactions in Children . . . . . . 174
4.1 The Lymphocyte Transformation Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
4.2 The Lymphocyte Toxicity Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
4.3 The LTA in the Diagnosis of AHS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Abstract It typically takes many years before an association of a drug with a rare,
serious adverse reaction is established. As related to pediatric drug use, evidence is
even more erratic, as most drugs are used off labels. To enhance child safety, there
is an urgent need to develop robust and rapid methods to identify such associations
in as timely a manner as possible. In this chapter, several novel methods, both
clinically based pharmacoepidemiological approaches and laboratory-based methods,
are described.
G. Koren (*)
The Motherisk Program, Division of Clinical Pharmacology and Toxicology, Hospital for Sick
Children, University Avenue 555, Toronto M5G 1X8, ON, Canada
e-mail: gidiup_2000@yahoo.com
A. Elzagallaai • F. Etwel
Division of Clinical Pharmacology and Toxicology, Hospital for Sick Children,
University Avenue 555, Toronto M5G 1X8, ON, Canada
1 Introduction
Each year prescription drugs cause fatal adverse drug reactions (ADR) to 100,000
individuals in the USA, making prescription drugs between the fourth and sixth
leading cause of death, after heart disease, cancer, stroke, pulmonary disease, and
accidents (Lazarou et al. 1998).
Before a pharmaceutical product is marketed, the manufacturer must prove that it is
both effective and safe by performing extensive studies in animals and in human
clinical trials. However, premarketing studies cannot guarantee product safety as they
are limited by the small numbers of patients (between 1,000 and 3,000 subjects).
Importantly, serious ADRs (e.g., agranulocytosis) occur at a rate of between 1:1,000
and 1:10,000 patients. Additionally, clinical trials typically exclude vulnerable
populations such as pregnant women, children, elderly people, those with complicated
diseases, or those taking other medications. Hence, uncommon adverse effects,
delayed effects, or consequences of long-term drug administration often are not
observed before the drug has been marketed (Stricker and Psaty 2004). While the
more common type A ADRs (reactions that are an augmentation of the normal
pharmacological actions of the drug) may already have been identified by the time
of licensing (Pirmohamed et al. 1998), type B ADRs (idiosyncratic or bizarre reactions
that cannot be predicted from the known pharmacology of the drug) will only be
detected after licensing through postmarketing surveillance (Meyboom et al. 1997).
Postmarketing studies are based on collecting spontaneous case reports of
ADRs. There are two systems where clinical observers can use to address their
voluntary reporting of ADRs. The first is the published medical literature, which is
a highly efficient warning system for new adverse reactions, and often recognizes
rare events and people at high risk (Begaud et al. 1994). The second consists of
national and international adverse drug reaction monitoring centers, such as the
Food and Drug Administration (FDA). In the USA, the FDA started a voluntary
reporting system in the late 1960s, receiving reports from health care providers,
consumers, and pharmaceutical companies. Unlike health care providers and
consumers, the manufacturers have a regulated duty to report to the FDA on any
ADR. The system had been criticized in the 1970s for its delay in sending reports of
the newly identified ADRs to the Physicians Desk Reference (Zielinskin 2005). The
FDA system is probably overwhelmed by ADR reports from all interested parties,
as the experts at the Agency have insufficient time to analyze all incoming reports
in depth. Moreover, the FDA does not have the regulated authority to mandate drug
manufacturers to conduct directed postmarketing surveillance studies (Millichap
1976), which could help in detecting uncommon serious ADRs.
2 Pharmacoepidemiological Approaches
Over the last few years, we have developed a novel detection method to allow
regulatory agencies and manufacturers to create a rapid signal for an association
between the drug and the corresponding ADRs, in the postmarketing period. This
Safety Assessment in Pediatric Studies 171
method can allow early identification of rise in the incidence rate of severe organ
failure associated with the medication. This method can help to protecting the
public from unexpected harmful effects of new drugs. Herein, we will use the
pemoline-associated acute liver failure (ALF) as a model for the development of
this novel system.
3 Pemoline-Index Case
the study consisted of children in the USA and Canada. For each calendar year after
1975 when pemoline was approved to be marketed as a treatment for ADHD, the
number of children who were on pemoline was estimated as was the number of
reported cases of ALF associated with pemoline.
After obtaining the yearly number of children on pemoline and the yearly
number of children who developed ALF while on pemoline, a comparison was
made between these data and the background incidence rate of idiopathic ALF in
children in the general population. This comparison was made year by year to
define the earliest year when the rate of serious ALF due to pemoline was signifi-
cantly higher than predicted in the general population.
Data were synthesized from systematic review of the published literature. Only
studies calculating the rate of ALF in children and their etiologies, including
idiopathic liver failure, were included.
Information regarding the number of children on pemoline in Canada per year
was obtained from IMS (International Medical Statistics, Montreal Quebec). The
IMS is a holder of statistical medical information that can be accessed by
researchers, academics, and government. For US data, we gathered the information
by synthesizing available published data, by systematic review of Medline
EMBASE and Scopus, and by obtaining all articles that reported on the number
of children prescribed pemoline.
The annual number of children on pemoline in the USA and Canada who
developed ALF was obtained from the FDA under the Freedom of Information
Act. All pemoline cases reported to the FDA between 1975 and 1999 were
analyzed. The criteria for selection of liver injury cases were age between 0 and
18 years, any report of irreversible damage to the liver, and children who received
the dose schedule recommended for its primary indication. We excluded cases
reporting increased liver enzyme levels that returned to normal once pemoline was
discontinued. Some of these cases have also been published in the literature and
articles were obtained. We used the same criteria for selection of the literature cases
as was used in the FDA cases. All the published cases were subjected to causality
assessment using the Naranjo ADR probability Scale (Naranjo et al. 1981). The
Naranjo ADR probability scale is a tool widely used to determine the likelihood
that an ADR is caused by the implicated medication. Ten questions are answered
and assigned a weighted score of +2 to 2. Where there were insufficient data
available, the particular question receives a score of 0. Based on the Naranjo criteria
15, each case is scored between (<1 and >9) and assigned a likelihood of causing
an ADR from doubtful, possible, probable, to highly probable.
Based on a recent large comprehensive study of fulminant hepatic failure,
approximately 230 children are estimated to be afflicted each year in the USA
(Liu et al. 2001). The number of children who lived in the USA has been estimated
at 73,043,506 (Children Defense fund), and hence the overall rate of ALF in
children is estimated at 1:300,000.
Based on all available studies, 16% of the cases of ALF were due to unknown
reasons (idiopathic). Hence, we estimated that the rate of idiopathic liver failure in
North American children is 1:2,000,000.
Safety Assessment in Pediatric Studies 173
We identified all papers that surveyed the prevalence of medication use to treat
children with ADHD in the USA and they were used to calculate the yearly number
of American school children on ADHD medication from 1975 through 1993. For
any missing year for which no publication was available, we calculated the mean
value from the closest years before and after. The percentage of children receiving
treatment with stimulant medication for ADHD ranged between 2.1 and 6%. The
percentage of reported pemoline use among ADHD children was 1% in 1975 and
increased gradually to 6% in 1987. Between 1987 and 1993, there was no data
available on the percentage of pemoline use among ADHD children, so we assumed
that the percentage was not changed since 1987. The overall number of school
children in the USA was obtained from international statistics. Based on the above
number, we estimated the number of children taking pemoline in the USA.
We estimated that a total of 45,404 Canadian children years were treated with
pemoline from 1978 to 2004. In Canada, the marketing of pemoline started only in
the 1980s. The Canadian Drug Identification Codes are drug product database
books published annually. The first time pemoline was included in these databases
was in 1981 (the first time pemoline was included in the Compendium of
Pharmaceuticals and Specialties was in 1986) (Canadian Pharmaceutical Associa-
tion and Canadian Pharmacists Association 1986).
Thirty cases of children who were on pemoline therapy and who developed
irreversible ALF were reported to the FDA. The first case was in 1977.
Using the FDA reports, each year after introducing pemoline the relative risk of
children on pemoline developing ALF was high, ranging between 9.12 and 24.08.
The highest RR was detected in 1978. All these RR were statistically significant
(Etwel et al. 2008).
Using pemoline as a model, we were able to show that employing existing data
at the time one could estimate the incidence rate of serious ADRs early in the
marketing cycle.
Hence, as early as 1978, a significant signal existed indicating that pemoline is
associated with ALF, 16 years before the first published suggestion by Berkovitch
and colleagues (1995), 22 years before removal of the medication from the
Canadian market, and 28 years before removal from US market. While we present
analysis related to ALF, similar population-based statistics are available for all
other adverse events, from agranulocytosis to pulmonary fibrosis. This method
174 G. Koren et al.
The concept of developing laboratory tests that can predict rare, but potentially
fatal, adverse drug reactions is ideally exemplified in the case of the anticonvulsant
hypersensitivity syndrome (AHS).
We will review critically the usefulness of available in vitro tests in the diagnosis
of AHS.
Anticonvulsant hypersensitivity syndrome (AHS), also known as drug hyper-
sensitivity syndrome or drug rash with eosinophilia and systemic symptoms
(DRESS), is a type B (“bizarre”) adverse drug reaction (ADR) that develops in
susceptible patients following exposure to certain drugs, including aromatic
anticonvulsants (Shear and Spielberg 1988; Zaccara et al. 2007) Although lacking
a defined clinical picture, AHS is typically associated with the development of skin
rash, fever, and internal organ dysfunction that may include blood dyscrasias,
hepatitis, nephritis, myocarditis, thyroiditis, and interstitial pneumonitis and
encephalitis (Peyriere et al. 2006). The pathophysiological mechanisms underlying
AHS are not well understood; however, it is believed to be immune mediated in
general and involve generation of electrophilic reactive metabolites that react
covalently with macromolecules to form immunogenic adducts able to activate
the immune system (Shapiro and Shear 1996; Spielberg et al. 1981a, b). The
accurate incidence of AHS is unknown due to underreporting, but it has been
estimated to range from 1 in 1,000 to 1 in 10,000 in patients newly exposed to
aromatic anticonvulsants (Tennis and Stern 1997). While the disorder is rare, it is
potentially fatal and represents a clinical dilemma to treating doctors. Diagnosis of
AHS is challenging, as a reliable and safe diagnostic test is not available to confirm
causality or identify the culprit drug. A number of in vivo and in vitro tests have
been devised and used to aid the diagnosis of AHS. These include skin tests (patch
test, prick test, and intradermal test), the lymphocyte transformation test (LTT), and
the lymphocyte toxicity assay (LTA) (Pourpak et al. 2008).
In vitro diagnostic tests have the advantage over in vivo tests (patch test and
rechallenge) of bearing no potential harm to patients. A number of in vitro diagnos-
tic tests have been used to aid the diagnosis of delayed-type drug hypersensitivity
reactions (Naranjo et al. 1992; Beeler and Pichler 2007; Lan et al. 2006); however,
their true value is yet to be defined. Among these tests are those that utilize
peripheral blood mononuclear cells (PBMCs) as target cells, including the LTT
and the LTA. Unfortunately, these techniques require expensive equipment and
sophisticated laboratories as well as specialized experience with biochemical and
Safety Assessment in Pediatric Studies 175
molecular methods, so only a few centers are sufficiently equipped to perform them.
Hence, these methods, although successfully employed as research tools, have not
been successfully translated into diagnostic tests (Wu et al. 2006; Beeler et al. 2006).
Leukocytes are present in peripheral blood at densities of 5–7 103 cells/mm3;
20–50% of these cells are lymphocytes, whereas 2–10% are monocytes.
Lymphocytes are favored as a model for investigation of immune-mediated
diseases because of their unique characteristics, which include that (1) they are
easily obtained at adequate density; (2) they play a key role in the immune system
by orchestrating different elements of the immune response and thus represent the
state of the immune system in the specific patient; (3) they are metabolically active
and express most of the enzymes required for drug detoxication; and (4) individual
genetically based defects in the expression or activity of these detoxication
enzymes are phenotypically expressed in lymphocytes.
The in vitro lymphocyte transformation phenomenon was first described during the
late 1950s. In short, human peripheral blood leukocytes (PBLs) differentiate in
short-term primary cultures, forming plasts. This effect was later attributed to the
presence of a constituent [phytohemagglutinin (PHA)] of a plant extract from red
kidney beans (Phaseolus vulgaris) that is used to isolate blood peripheral leukocytes
(Rigas and Osgood 1955). PHA causes erythrocytes to aggregate and sediment,
allowing leukocytes to separate from whole blood preparations. In a later report,
Nowell (1960) demonstrated that PHA also initiates mitotic activity (transforma-
tion) in cultured human leukocytes. To show that lymphocyte behavior in vitro has
an immunological basis, Pearmain et al. (1963) exposed PBLs isolated from both
tuberculin-sensitive and tuberculin-nonsensitive patients to tuberculin in vitro. Only
PBLs from tuberculin-sensitive patients showed mitotic activity, whereas cells from
patients not previously exposed to the antigen showed no mitosis.
One of the first reports of using the LTT for diagnosis of drug allergy was by
Holland and Mauer (1964) who evaluated the effect of phenytoin on cultured
lymphocytes isolated from patients sensitive to the drug and nonsensitive (control)
subjects. In these experiments, PHA used as a positive control showed nonspecific
stimulation of all cells sampled, whereas phenytoin stimulated only the cells from
phenytoin-sensitive patients. When tested with peripheral lymphocytes isolated
from a sulfadiazine-sensitive patient and incubated with the culprit drug in vitro,
this effect was found to be concentration-dependent.
The procedure includes incubation of PBMCs isolated from drug-hypersensitive
patients with the incriminated agent at nontoxic concentrations and observation
of any increase in the rate of cell proliferation measured by [3H]thymidine
incorporation. The increase in cell proliferation is expressed as a ratio between
proliferation of cells incubated with and without the drug (vehicle alone; control).
This ratio is defined as the stimulation index (SI) and it is calculated as follows (1):
176 G. Koren et al.
Introduced by Spielberg and colleagues (1980), the LTA is an in vitro test that
utilizes isolated PBMCs to investigate the mechanistic pathogenesis of idiosyn-
cratic drug reactions. The test is based on the hypothesis that drug hypersensitivity
develops as a result of imbalance between generation of toxic reactive metabolites
(metabolic activation or toxication) and detoxication capacity that leads to accu-
mulation of toxic metabolites (the “reactive metabolite” hypothesis). In this test,
lymphocytes are used not as immunogenic cells but rather as easy-to-obtain surro-
gate target cells. The procedure of the test entails incubation of PBMCs isolated
from the patient with the culprit drug in the presence of Phenobarbital-induced
mouse, rat, or rabbit liver microsomal 19,000 g supernatant fraction (S9), as a
source of cytochrome P450 (CYP) mono-oxygenase activity.
CYP activity in the rodent (or sometimes human) liver preparation is
hypothesized to oxidize drug to its active (cytotoxic) metabolite(s). Lymphocytes
contain enzymes that are required for drug detoxication, including epoxide
hydrolases and glutathione S-transferases, and any genetic defect in the function
of these enzymes is phenotypically expressed in these cells. The percentage of cell
death is then determined using different methods for assessing cell death [e.g.,
trypan blue exclusion or with a tetrazolium dye; for example, by the MTT (3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method]. Cell death is
assumed to reflect the vulnerability of the cells to the toxic effects of the drug,
which is hypothesized to indicate the susceptibility of the patient to develop
hypersensitivity reactions to the parent drug and its reactive metabolite(s), presum-
ably via differences in detoxication capacity and immune processing.
Aromatic anticonvulsants are excellent examples of metabolically activated
cytotoxicants, metabolized primarily by hepatic CYP isozymes into reactive
Safety Assessment in Pediatric Studies 177
electrophilic arene oxide metabolites (Begaud et al. 1994). These unstable and
highly reactive intermediate metabolites are readily detoxified by epoxide hydro-
lase and/or glutathione S-transferase enzymes, usually to non-electrophilic products
(dihydrodiols and S-glutathione conjugates, respectively).
Although the same cell model (isolated PBMCs) is used in both types of assay,
LTT and LTA are completely different approaches to the diagnosis of AHS.
Whereas the former detects the in vivo immunological generation of drug-specific
T lymphocytes used as a sign of hypersensitivity, the latter detects genetic defects
that lead to accumulation of toxic metabolites, which are assumed to be a major
factor in the etiology of drug hypersensitivity in addition to possible differences in
cell death. Because the two tests use the same cell model and have similar
nomenclature, it is not uncommon for individuals to confuse the LTT for the
LTA or vice versa, or to use different nomenclature to describe these tests.
Retrieved publications were manually reviewed and the following selection
criteria were applied: (1) original article written in English; (2) study performed
in human subjects; (3) LTA or LTT used to diagnose AHS due to one or more
aromatic anticonvulsant drug(s); and (4) sufficient technical data for scientific
evaluation.
Thirty-one articles from PubMed, 22 articles from MED-LINE, and 28 from
EMBASE were found that met our selection criteria. The search results from the
three databases were then combined and duplicates were removed. The final
number of included articles from the three databases was 48. Thirty-six articles
used the LTT and 12 used the LTA for the diagnosis of AHS (Figure 4). Although
single case reports were included in the review, none of these reports were used to
calculate any of the tests’ epidemiological characteristics.
In the systematic review we have conducted recently its use was almost always
confined to experienced technicians in well-equipped research centers, primarily
for the purpose of investigating the mechanism of T-cell-mediated reactions rather
than diagnosis of drug allergy (Elzagallaai et al. 2009). In addition, because of its
low laboratory-to-laboratory reproducibility and difficulty in evaluating results, this
test cannot be described as user friendly and requires a great deal of experience for
interpretation of results. For this reason, the test has not been translated into
widespread clinical use. In fact, only a few research groups worldwide use this
technique routinely.
In an attempt to determine the sensitivity and specificity of the LTT in the
diagnosis of allergy to different drugs, the files of 923 patients with possible
hypersensitivity reactions to drugs were studied. These patients were classified
based on their medical history, follow-up, and provocation tests into four groups
where drug allergies were “definite,” “probable,” “less probably,” or “negative.”
One hundred cases were considered to have a very high probability of drug allergy,
of which 78 had a positive LTT. Only three of these 100 cases were attributed to
anticonvulsants (2 to carbamazepine and 1 to phenytoin). The two carbamazepine
cases exhibited positive LTTs, whereas for the phenytoin case, the LTT was
negative. Although the chemistry of the drug in question appears to play a major
role in determining the usefulness of the LTT, the overall specificity and sensitivity
178 G. Koren et al.
of this test in this study were found to be in the range of 85 and 76%, respectively. It
is not known whether or not these numbers can be applied to anticonvulsant drugs.
However, because many different factors are involved in determining the final
result of the LTT as discussed below, one cannot generalize these figures to include
all types of drugs taken under various conditions.
Numerous factors have been found to affect the predictive value of the LTT
in the diagnosis of drug hypersensitivity reactions. These factors include the
timing of the test in relation to the beginning of the reaction, the type of clinical
manifestations cause by the drug, the nature of the suspected drug, and the test
procedure itself.
The use of the LTA in diagnosing AHS dates back to the early 1980s. However, the
lack of large-scale application is quite obvious. Shear and Spielberg (1988) studied
53 patients with a medical history suggesting AHS due to phenytoin, carbamaze-
pine, or phenobarbital, as well as 49 unexposed healthy controls and 10 phenytoin-
exposed healthy controls. Symptoms include fever, skin rash (varying in severity
from generalized exanthema to TEN), eosinophilia, atypical lymphocytosis, and
internal organ involvement (liver, kidney, thyroid, or lung). The performance of the
LTA as a diagnostic test in this cohort of patients was excellent, with only two false
positives and one false negative result in patients with hypersensitivity reactions to
phenobarbital.
AHS is a rare but potentially lethal disorder. One of the most challenging aspects
of this disease is the difficulty of establishing a solid diagnosis in a timely manner.
Lack of a diagnosis or misdiagnosis may result in increased morbidity, increased
mortality, and extended hospitalization. Between 10 and 27% of patients with
epilepsy discontinue their first antiepileptic drug because of the development of
adverse reactions (Kwan and Brodie 2001). Aromatic anticonvulsant drugs such as
phenytoin, carbamazepine, phenobarbital, and lamotrigine are linked to a relatively
high risk of development of hypersensitivity reactions. Carbamazepine was found
to be the most common cause of severe forms of AHS (i.e., SJS and TEN).
The diagnosis of AHS entails two main processes: first, establishing the diagno-
sis of the hypersensitivity reaction, usually from a series of clinically similar
differential diagnoses; and second, identifying the culprit drug, potentially among
a number of other concomitantly prescribed, innocent drugs. Numerous diagnostic
tests are available and have been attempted for the diagnosis of drug hypersensitiv-
ity reactions; however, their epidemiological qualities are dependent on the type of
reaction (immediate vs. delayed reactions) and type of drug, and choosing the best
test for a specific drug or drug class can be challenging.
The sensitivity and specificity of the LTT in the diagnosis of drug allergy have
been estimated to range from 56 to 78% and from 85 to 93%, respectively, although
these estimates are generally based on cases of allergy to b-lactam antibacterials
Safety Assessment in Pediatric Studies 179
and cannot be extended to other types of drugs. In the diagnosis of AHS due to
aromatic anticonvulsants, the LTT has frequently shown a sensitivity between 71
and 100%, but this also ranges as low as 19–40%.
Combined use of pharmacoepidemiological approaches and biological markers
is needed to improve the ability to predict adverse drug reactions in children and
prevent severe morbidity and mortality.
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Contents
1 Part 1: Design of Pharmacokinetic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
1.1 Pharmacokinetics Trials, the Classical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
1.2 Population Pharmacokinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
2 Part 2: Phase III Clinical Trials: Classic and Novel Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
2.1 When Is a Phase III Clinical Trial Necessary? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
2.2 Classical Sample Size Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
2.3 Inadequate Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
2.4 Classical Strategies to Minimize Sample Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
2.5 Group Sequential Design, Boundaries Design,
and Adaptive Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
3 Part 3: Conduct of Trials and Working with DMCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Abstract In this chapter, the design of pharmacokinetic studies and phase III trials
in children is discussed. Classical approaches and relatively novel approaches,
which may be more useful in the context of drug research in children, are discussed.
The burden of repeated blood sampling in pediatric pharmacokinetic studies may be
overcome by the population pharmacokinetics approach using nonlinear mixed
effect modeling as the statistical solution to sparse data. Indications and contrain-
dications for phase III trials are discussed: only when there is true “equipoise” in the
medical scientific community, it is ethical to conduct a randomized clinical trial.
The many reasons why a pediatric trial may fail are illustrated with examples.
Inadequate sample sizes lead to inconclusive results. Twelve classical strategies to
minimize sample sizes are discussed followed by an introduction to group
sequential design, boundaries design, and adaptive design. The evidence that these
designs reduce sample sized between 35 and 70% is reviewed. The advantages and
disadvantages of the different approaches are highlighted to give the reader a broad
idea of the design types that can be considered. Finally, working with DMCs during
the conduct of trials is introduced. The evidence regarding DMC activities, interim
analysis results, and early termination of pediatric trials is presented. So far
reporting is incomplete and heterogeneous, and users of trial reports may be misled
by the results. A proposal for a checklist for the reporting of DMC issues, interim
analyses, and early stopping is presented.
be acknowledged that many factors have to be taken into account (Ogungbenro and
Aarons 2008).
In the Christmas issue of the British Medical Journal of 2003, a paper was published
entitled “Parachute use to prevent death and major trauma related to gravitational
challenge: systematic review of randomised controlled trials” (Smith and Pell
2003). It is not surprising that the literature search preformed to detect any such
RCTs yielded no results. When the natural course of a disease is known, and case
reports show clearly and unambiguously that a particular intervention changes the
natural course in the preferred direction, it would be unethical to include patients in
a randomized clinical trial (Glasziou et al. 2007; Peto and Baigent 1998). Examples
of this principle are PGE1 infusion for ductus patency in newborns with obstructive
right heart malformation and indomethacin treatment of newborns with
life-threatening polyuric salt-losing tubulopathies (SLTs). The therapeutic advan-
tage of these treatments is beyond any doubt. Only when there is true “equipoise” in
the medical scientific community, it is ethical to conduct an RCT (Edwards et al.
1998). In the development of new drugs, RCTs usually cannot be avoided. How-
ever, it is not always necessary or ethical to perform these trials in children
(Sammons 2011).
Imagine a pediatrician who wants to investigate whether a new drug leads to more
improvement in a specified outcome than the old drug. How many patients does he
or she need to include in the study? The consulted statistician will explain that the
required sample size is defined by the power of the study, the significance level,
whether a one- or two-sided test is required, the variance of the outcome in the study
population, and the expected or clinically relevant difference in the outcome
between the two intervention groups to be detected.
hypothesis testing. When the threshold a for the level of statistical significance is set
at 0.05, this means that we accept a false-positive rate of 5%.
The null hypothesis H0 to be tested states that there is no difference in outcome
between the groups and the alternative hypothesis states that there is a difference. In
case of a two-sided test, which is usually applied, the difference can either mean
superiority or inferiority of the experimental intervention compared to the control
intervention.
A one-sided test is applied if inferiority of the experimental intervention is
considered very improbable (Knottnerus and Bouter 2001). The result of a one-
sided test can either be non-inferiority, i.e., not worse, possibly better than the
control intervention, or superiority, i.e., definitely better than the control interven-
tion. When a one-sided test is applied, the null hypothesis states that the effect of the
experimental intervention is either worse, in case of a non-inferiority trial, or worse
than or equal to the control intervention, in case of a superiority trial. If the data that
are obtained in the study are very unlikely under the null hypothesis, so unlikely
that the probability to obtain these or more extreme data is smaller than a, we reject
the null hypothesis. This leaves a probability of a for a false-positive result or type I
error.
If the alternative hypothesis is true, there is a risk, called b, of obtaining data that
are not unlikely under the null hypothesis, which leads to a false-negative result or
type II error. Usually, the risk of a type II error (false-negative result) is considered
to be less undesirable than a type I error. Therefore, b is usually set at 10 or 20%.
The power of a study is the probability of rejecting the null hypothesis if
the alternative hypothesis is true, i.e., 1 b. As an example, the general formula
for a continuous outcome measure to calculate the required sample size for a T-test
is as follows:
s2
N ¼ ðZa=2 þ Zð1bÞ Þ2 (1)
ðm1 m2 Þ2
In which N is the number of subjects per group, Za/2 is the value of the standard
Normal distribution corresponding with the chosen value of a (two-sided), Z(1b) is
its equivalent for the chosen value of b, s2 is the variance of the outcome variable in
the study population, which is the sum of the variances in the two groups minus two
times the product of the standard deviations in the two groups multiplied by the
correlation between the observations (r ¼ 0: unpaired t-test, r > 0 paired t-test),
and m1 and m2 are the estimated means of the outcome variable in the two groups to
be compared.
From this formula, it becomes clear that the required sample size increases if we
choose a smaller risk of type I (a) or type II errors (b), if the variability s2 is larger,
or if the difference that we want to be able to detect (m1 m2) is smaller.
These days regulatory authorities and many journal editors request that the
results of a study are expressed as point estimates and 95% Confidence Intervals
(CIs). The advantage of this presentation, estimation instead of hypothesis testing,
is that the size of the effect can be appreciated as well as its statistical significance.
Thus, a small effect with a narrow CI may be statistically significant, i.e., the neutral
value lies outside the CI, but because of its small size the effect may be considered
to be clinically irrelevant, whereas a large effect that is not statistically significant –
i.e., p > 0.05; neutral value inside CI – may be considered to be important for
clinical practice. However, if the CI is wide, more information is needed to get a
precise estimate. It is quite possible that the effect found in one small study turns
out to be negligible when the study is replicated in a larger sample.
When designing a clinical trial, the probability of finding an effect if there is one in
reality, i.e., a true-positive result, should be maximized, irrespective of whether the
result will be expressed as estimation or as a hypothesis test. As we have seen, this
can be achieved by maximizing the number of subjects included in the study.
However, there are practical and ethical restraints to the inclusion of large numbers
of subjects, especially in the pediatric population. Usually, the number of children
eligible for the study is limited because many conditions are uncommon.
Furthermore, the financial and time resources are always limited. Apart from
that, clinicians have an ethical obligation to give the best treatment to their patients.
As long as there is equipoise, i.e., the medical scientific community is uncertain
which treatment is best, it is justified to include patients in a clinical trial. However,
suppose there were no practical limitations to including patients in a trial, and a
researcher would continue including patients, at a certain moment the results could
be expressed in a very narrow CI. At what moment would equipoise be abandoned?
That would be the moment to stop including patients in the trial and to start treating
consecutive patients with the optimal intervention mode. Therefore, for each trial it
has to be stated in advance when to stop including patients. Usually, this is done by
calculating the number of patients needed to get 80 or 90% certainty that if there is
an effect of a predefined size, it will be found statistically significant at a ¼ 0.05.
However, this calculation often leads to required sample sizes that are very hard, or
impossible to attain.
Small Sample Approach, and Statistical and Epidemiological Aspects 187
underpowered trial for a later meta-analysis, and (12) the prospective meta-analysis
approach. Table 3 gives an overview of these approaches, their drawbacks, and
their applicability in pediatric drug development trials.
Ad (1) One-sided instead of two-sided testing has been suggested for ethical and
efficiency reasons when inferiority of the experimental intervention is
considered very improbable (Knottnerus and Bouter 2001). However,
other authors are convinced that each randomized trial should also be
able to detect harm in terms of a worse outcome due to the experimental
intervention (Moye and Tita 2002). Usually, one-sided testing is limited to
the non-inferiority design.
Ad (2) The assumptions to be made in advance in the design phase of the study are
often arbitrary. Sometimes negotiations take place between the researcher
and the statistician. “If we want to detect a 10% difference, we need 132
patients but if we expect the difference to be 15%, we need 52 patients.”
Since there are no criteria to be used in defining the minimal clinically
relevant difference, this is often used as a “closing entry.” The number of
patients that can be recruited is usually the limiting factor, a and b are
more or less predetermined, and the variance in the study population
cannot be altered. This leaves the minimal clinically relevant difference
as the only input in the power formula that can be adjusted. This procedure
has been referred to as a “sample size samba” (Schulz and Grimes 2005).
Ad (3) In the field of AIDS research, the “simple” outcome mortality became less
frequent due to advances in treatment. The use of mortality as an outcome
variable would have led to an increase in the required sample size.
Therefore, composite outcomes were formulated, consisting of a number
of possible adverse events, e.g., first symptoms of disease progression
expressed as neurological symptoms or growth retardation (McKinney
et al. 1998).
Ad (4) Another way of increasing power is to use surrogate outcomes, which
allow a smaller size of the study population, for instance, glomerular
filtration rate instead of patient or graft survival in renal transplant trials
(Filler et al. 2003). An important prerequisite for a surrogate outcome is
that its predictive validity or association with the “true clinical outcome”
should be established (CHMP 2006a).
Ad (5) If the outcome measure is a continuous variable, it may be possible to
improve its reproducibility and in this way reduce the Standard Deviation.
Improving the reproducibility typically starts with a clinimetric study,
sometimes called a Generalizability study, in which the influence of
several possible sources of variability, called “facets,” is quantified. Sub-
sequently, approaches are proposed and investigated to improve the
reproducibility of the measurement. Depending on the type of measure-
ment, these approaches may consist of better standardization of the mea-
surement process or of the use of a mean value of repeated measurements
instead of one single measurement value. The effect of such a mean value,
Small Sample Approach, and Statistical and Epidemiological Aspects 189
The principles of randomized clinical trials were originally derived from agricultural
research, in which the statistical methods of analysis of variance and regression
analysis were developed (Whitehead 1997). An essential difference between agricul-
tural and clinical trials is the time period during which data are gathered. In an
agricultural field trial, all crops are harvested simultaneously at the end of the growth
season, whereas in clinical trials it usually takes weeks or months, sometimes even
years before all subjects are included, and consequently the gathering of the outcome
data is extended over a similarly long time period. Thus, it is possible that before the
end of the inclusion phase of a clinical trial enough information has already been
assembled, though usually not analyzed, to decide which intervention is superior.
Because subjects will be included and randomized until the sample size that was
determined in advance has been reached, this may lead to inefficiency, that is,
inappropriate inclusion of subjects, unnecessarily prolonging the trial duration, and,
more importantly, to allocation of trial subjects to the “inferior” intervention at a
time when the evidence of its inferiority might be available. Some authors have
referred to such practices as substandard or unethical (van der Lee et al. 2010;
Whitehead 1997). Sequential designs were developed to overcome these problems.
Various sequential procedures exist, and they can be (roughly) divided into two
types, namely those derived from the repeated significance test approach, also
called group sequential designs, and those derived from the boundaries approach.
Because there is no uniform terminology, we make a distinction between “design”
and “analysis” (Sebille and Bellissant 2003). Thus, within the boundaries design a
distinction can be made between “continuous sequential analysis” and “group
sequential analysis.” Recently, a modification of the group sequential design has
192 M. Offringa and H. van der Lee
been proposed, called the adaptive design. We will discuss the group sequential
design, the boundaries design, and adaptive design in more detail below.
60 60
a b
40 40
Z 20 Z 20
0 0
-20 -20
0 100 200 300 0 100 200 300
V V
60 60
c d
40
40
20
Z 20 Z 0
-20
0
-40
-20 -60
0 100 200 300 0 100 200 300
V
Fig. 1 Boundaries design in four hypothetical cases – see text for details (reprinted with
permission from van der Lee et al. 2008)
194 M. Offringa and H. van der Lee
At each analysis, which can be done after each patient (continuous sequential
analysis) or after a fixed or variable number of patients (group sequential analysis),
the two statistics Z and V are calculated based on the data accumulated thus far, and
plotted, creating a so-called sample path. This is illustrated in Fig. 2.
Inclusion and randomization of subjects are continued as long as the sample path
remains between the boundaries (continuation region). A conclusion is reached
when a boundary is crossed. In case of a one-sided test, that is, investigating only
whether the experimental treatment leads to a better outcome than the control
treatment, a single pair of boundaries is plotted (Fig. 1a–c). Crossing of the upper
boundary leads to rejection of the null hypothesis; crossing of the lower boundary
leads to non-rejection of the null hypothesis.
Two pairs of boundaries are plotted symmetrically around the horizontal axis in
case of a two-sided test, in which both possibilities of better and worse outcomes of
the experimental compared to the control treatment are investigated (Fig. 1d).
Crossing of the upper or lower boundary leads to the conclusion that the experi-
mental treatment is superior or inferior, respectively; crossing of the boundaries
between both pairs of boundaries leads to non-rejection of the null hypothesis.
Alternatives that are useful in clinical trials are the truncated SPRT (Fig. 1b) and
the triangular test (TT) (Fig. 1c) (Anderson 1960; Whitehead 1997). In the
truncated SPRT, a maximum value (L) of V is determined after which the trial
stops, irrespective of the result. This truncation point L is chosen more or less
arbitrarily, but it has to be beyond the amount of information VFIXED required for
the equivalent fixed sample design to correct for multiple hypothesis testing. The
space between the parallel boundaries is influenced by the choice of L. In other
words, the choice of L has consequences for the sample size. For a given a, b, and
effect size, the boundaries are closer to each other with increasing L. In case of the
TT (Fig. 1c, d), the boundaries are convergent, resulting in a finite “continuation
region.” Therefore, the optimal properties of the SPRT and TT differ: the average
sample size reduction is larger with the SPRT when the actual effect size is (much)
larger than expected and smaller when the actual effect size is smaller than
expected (Fig. 1a vs. c) (Sebille and Bellissant 2000). When the actual and expected
effect sizes are similar, the expected sample size reductions are about equal.
Obviously, it is impossible to predict whether the actual effect size will be smaller
or larger than the expected effect size. In practice, in most trials, the actual effect
size turns out to be smaller than expected. In those cases, the TT is more efficient
(Sebille and Bellissant 2000). In contrast to the classical fixed sample size design,
the eventual amount of information, that is, number of patients, needed to complete
a trial is unknown at the start of a sequential trial. The choice of design usually
depends on the statistician’s expertise and the availability of the software.
Although correction for multiple testing results in a larger maximal possible
sample size (the amount of information which is represented by the apex of the
triangle in Fig. 1c, d), the average sample size needed to complete a trial using a
sequential method in simulations was always smaller than that of the corresponding
fixed design, irrespective of the effect size or power (Sebille and Bellissant 2000).
The 90th percentiles of the sample size distributions of the sequential designs were
Small Sample Approach, and Statistical and Epidemiological Aspects 195
in the same order of magnitude as the corresponding fixed designs, when the actual
effect was close to the expected effect, but larger when the actual effect was smaller
than expected, especially for the SPRT. In principle, Z and V can be calculated after
each individual patient, but generally Z and V are calculated after the data of a
number of patients have become available, that is, group sequential analysis.
Given the possibility that intermediate points, if plotted, could have lain outside
the triangular region during long gaps between inspections, and thus opportunities
for stopping might have been missed, an adjustment of the stopping boundaries is
made, resulting in a so-called Christmas tree shape (Fig. 2). After a boundary has
been crossed, an adjusted point estimate and CI of the effect can be calculated with
the computer program PEST or EaSt (2004; Cytel Software Corporation 1992). Due
to the sequential nature of the analysis, the CIs are wider than those obtained with
conventional fixed sample size methods of analysis.
In summary, the advantage of a sequential design is that the inclusion and
randomization can be stopped when enough information is available to draw a
definite conclusion, of either futility or efficacy, based on statistical significance.
For a sequential trial to be feasible, the time from randomization to outcome should
be limited relative to the recruitment rate. On average, the number of subjects
needed is smaller than in a classical fixed sample size design. However, in a
particular trial it may be larger than that. Drawbacks are that the eventual sample
size is not exactly known at the start, which hampers logistic and financial planning,
and that the 95% Confidence Intervals around the point estimate of the effect size
are somewhat wider than when there is only one analysis at the end of the trial.
Fig. 2 One-sided superiority triangular test and sample path of a trial (reprinted with permission
from van der Lee et al. 2008)
196 M. Offringa and H. van der Lee
Table 4 Relative benefits and drawbacks of fixed sample size and triangular test
Fixed sample size Triangular test
Risk of biased end Small if conducted according to Data analysis should be
result well-known standards; if no independent from trial
interim analyses have been performance and masked;
planned, analysis can be done important that confidentiality of
by investigators after all trial results is ensured until the end
data have been assembled of the trial
Feasibility in a Logistics are known in advance; Number of patients to be included
multicenter trial planning for a specific number unknown at study onset;
of trial patients; outcome planning may be hampered by
information may be assembled uncertainties; block-
per center and sent to randomization necessary to
coordinating center later avoid discrepancies in numbers
per arm; outcome information
has to be sent to coordinating
center immediately when it
occurs or is measured
Familiarity, Very well known, generally Less familiar design; despite unjust
acceptance by accepted as the most valid suspicion for increased risk of
funders, editors, design to answer questions of type I errors, final analysis is
peers, and readers effects of interventions valid, maintaining type I error
and power
In Table 4, the relative benefits and drawbacks of the fixed sample size and
triangular test are presented (van der Lee et al. 2009).
Bellissant et al. described a TT to assess the efficacy of metoclopramide on
gastroesophageal reflux in infants (Bellissant et al. 1997). The trial was designed to
detect a mean benefit on a continuous outcome scale of 0.5 with an expected
standard deviation of 0.5 with 95% power and a one-sided a of 0.05. In a fixed
design, 23 patients per treatment arm would have to be included. The authors
anticipated that recruitment would be difficult and wanted to stop the study as
soon as sufficient information was collected and decided, therefore, to use the TT.
After 3 years and 9 months and inclusion of 39 children, the trial ended in futility,
because the lower boundary was crossed (Fig. 2). The observed benefit of
metoclopramide over placebo was approximately 0.2 instead of 0.5.
Adaptive designs share a number of features with sequential designs, in which the
null hypothesis is tested at a sequence of interim analyses (Wassmer 2000).
However, in contrast, the design of an adaptive trial can be changed based on full
knowledge gained from the interim analyses. When modifications are made, a new
phase of trial starts, and data accumulated in (an) earlier phase(s) are no longer
combined with data from the new phase. All phases are analyzed separately, and the
P-values of the different phases are then combined using a predefined rule.
Small Sample Approach, and Statistical and Epidemiological Aspects 197
Examples of combination rules are the product criterion of Fisher (Bauer and
Kohne 1994) and the inverse normal method by Lehmacher (Lehmacher and
Wassmer 1999). The emphasis in these designs is more on flexibility of the design
than on minimization of the average sample size.
Different adaptations are possible including reassessment of sample size (see critical
reflection by Jennison and Turnbull 2003), selection of treatments (e.g., Hommel 2001;
Kelly et al. 2005), adaptation of end points (e.g., Bauer and Kieser 1999; Kieser
et al. 1999), or inserting or deleting interim analyses. See for a more extensive
description of this design the tutorial by Bretz et al. (2009). However, many features,
for example, definition of stopping rules (van Houwelingen 1999) or interpretation
of the results when primary end points have been changed, for instance, are still
subject for debate (CHMP 2006b).
The term “adaptive design” is a comprehensive term comprising many possible
design adaptations (CHMP 2006b). It should not be confused with the more specific
term “response-adaptive design,” discussed in section “Inadequate Sample Size”,
where the allocation ratio can be adapted based on preliminary results from the trial
(Coad and Ivanova 2005). To our knowledge, no pediatric trials with an adaptive
design have been published so far. Because it maximizes the efficiency of data
gathering from individual patients, this approach deserves more attention (Hirtz
et al. 2006).
Table 5 Proposed minimal set of parameters to be reported about DMC activities, interim
analysis and early stoppinga, b
Data Monitoring Committees and interim analysisb
Terminology
Use of the standard nomenclature “Data Monitoring Committee”
Composition of the DMC
Members’ name, affiliation, and training
Independence status from research team and sponsor
Tasks of the DMC
Whether the DMC reviewed and accepted the protocol before the start of the trial
Main roles (e.g., monitoring of safety and/or efficacy), and explicit definition of which outcomes
were analyzedc
Any additional roles (e.g., monitoring recruitment and quality assurance)
To which outcome(s) was the DMC blinded or unblinded
Interim analysis and statistical monitoring methods
Whether the protocol included a predefined statistical monitoring plan
Number of planned interim analyses
Timing of planned interim analyses and parameter defining timing (i.e., participants or person-
time recruitment, number of end points, and ad hoc time interval)
Type of analysis planned (i.e., efficacy, harm, futility, and/or sample size adjustment), specific
statistical methods used (with references and uniform terminology), description of boundaries
(i.e., their symmetry, p-value/confidence interval, and adjustment, if applicable), and outcome
(s) to which they were applied (i.e., primary/secondary, any subgroup analysis)
Any formal predefined stopping rules, to which outcome(s) did they apply, and whether they
included statistical boundaries and/or other considerations
Whether the statistical monitoring plan was completed as planned; if not, which changes were
performed, and their rationale
Adjustment for multiple analysis in final results (i.e., reported p-values and/or confidence
intervals)
Recommendations to the sponsor/steering committee
DMC recommendation regarding continuation or termination of the trial (with or without
adjustments in protocol)
Rationale (i.e., statistical boundaries and/or other considerations)
Whether the sponsor followed the DMC’s recommendations
Early terminated trials
Motive(s) for termination (e.g., efficacy, harm, futility, and recruitment)
All previously stated items, particularly rationale for early termination (including predefined
statistical monitoring plan, type of analysis, predefined stopping rules, and DMC
recommendation), and adjustment for multiple analysis and early termination in final results
Timing of early termination, i.e., which of the interim analyses led to trial termination, and on
which parameter the timing of this interim analysis was based (e.g., number of participants
enrolled and predefined number of end points)
Planned and final sample size
Total number of events after which the trial was terminated, including definition of these events
Discussion of implications of early termination (i.e., concerning type I ands II errors)
Report early termination in the abstract of the paper
a
These recommendations are for main reports; further details could be available using other modes
of publication (e.g., online appendices, trial design/protocol papers, and web-based repositories),
to which the report should refer to; planned items of this minimal set of parameters should be
included in prospective trial registries
b
Based on the book by Ellenberg et al. and the report of the DAMOCLES group (Ellenberg et al.
2002; Grant et al. 2005)
c
Particularly regarding safety – whether it included adverse events and/or main efficacy outcomes
Small Sample Approach, and Statistical and Epidemiological Aspects 199
4 Conclusion
The goal of trialists in pediatric drug development is to design and conduct trials
that are valid, efficient, and safe. Various techniques are available to enhance the
efficiency of trials, without compromising their validity and safety. Few of these
techniques have been used on a large scale in pediatric drug development. We
suggest that experience and knowledge are shared on (internet) forums, such as
StaR Child Health (http://www.starchildhealth.org), to improve the standards of
pediatric trials and make sure that all children participating in drug trials benefit
from these standards (Klassen et al. 2009).
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Sample Collection, Biobanking, and Analysis
Maurice J. Ahsman, Dick Tibboel, Ron A.A. Mathot, and Saskia N. de Wildt
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
2 Sample Types and Collection Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
2.1 Blood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
2.2 Urine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
2.3 Saliva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
2.4 Breath Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
2.5 Meconium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
2.6 Hair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
3 Leftover Material and Biobanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
4 Storage and Shipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
5 Drug Assays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
5.1 Assay Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
5.2 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
5.3 Multiple Drug Assays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
5.4 Alternative Drug Matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
1 Introduction
The ICH guidelines on pediatric drug studies (Anonymous 2000, 2001a) emphasize
patient safety, which has consequences for the volume of, and methods for,
sampling of biofluids. This has consequences for pharmacokinetic studies in chil-
dren by imposing challenges upon sample collection and drug analysis. The main
questions are as follows:
• Which biological specimen can be used and how can this specimen be collected
in the intended study population?
• What are the maximum allowed sample volumes per occasion and per study
period?
• By what methods can we store samples and acquire reliable drug concentrations?
In this chapter, we discuss these questions and aim to provide practical solutions
and examples to help those planning pharmacokinetic studies in children. The
details of designing population PK studies are outside the scope of this chapter
and are discussed elsewhere.
2.1 Blood
with invasive blood sampling and by using methods aimed to reduce the blood
volume needed for drug analysis. In children, blood for pharmacokinetic analysis is
preferably sampled from indwelling central venous or arterial catheters, already in
place for clinical care. Sampling from these catheters is easy, causes only minimal
or no discomfort, and allows for sufficient sample volume collections. Risks
associated with the use of these catheters are bloodstream-related infections and
unintended blood loss. If these catheters are not already in place for clinical
purposes, placement of these catheters solely for research purposes is usually not
considered acceptable by research ethics committees and/or patients and their
family. Alternatively, blood can be sampled from peripherally inserted catheters.
Insertion of these catheters solely for research purposes is sometimes acceptable,
more specifically in the context of therapeutic drug trials. The main limitation,
especially in neonates, is that blood draws are difficult if not impossible from small
bore catheters as used in this population. To overcome this problem, blood can be
taken from heel prick or venepuncture, the latter being much less painful, prefera-
bly when done together with regular blood work. When combining research blood
sampling with regular blood work, the burden for the child may be considered
acceptable both by children and their parents as well as by research ethics
committees. Disadvantages of heel prick samples are the limitation in the volume,
timing of blood samples, and painfulness. In general, blood volumes sampled per
heel prick are limited to 0.5–0.6 ml, including blood collected for regular clinical
blood work. Hence, blood volumes needed for pharmacokinetic analysis should
preferably not exceed 0.2–0.3 ml per sample. In addition, timing of sampling is
restricted if it needs to coincide with clinical blood sampling. Consequently,
extensive and timed sampling for a full pharmacokinetic washout curve is not
possible using this method.
A more detailed and practical guide for different blood sampling methods in
children and neonates has been published by the UK Medicine for Children
Research Network (Hawcutt et al. 2008).
2.2 Urine
For renally cleared drugs, urine sampling may provide an alternative to blood for the
estimation of pharmacokinetics. Also, urinary excretion of the drug and its metabolites
may provide valuable insight into developmental changes in drug metabolism and
excretion (Streetman et al. 2001; Allegaert et al. 2006; Tucker et al. 1998). From a
pharmacokinetic standpoint, the preferred method to collect urine is by urinary
catheter or by direct collection in older children. Using a catheter facilitates complete
urine collection over predefined time periods. A major limitation of the use of urinary
catheters in children is the burden and risks associated with insertion of the catheter,
such as pain, infection, urethral restriction (mainly in boys), and displacement. Hence,
in general, if a catheter is not already in place for clinical purposes, most research
ethics boards will not approve its use for research purposes only in children. Adhesive
206 M.J. Ahsman et al.
collection bags are also frequently used to collect urine, especially in infants and
neonates (Allegaert et al. 2006). In these younger infants, the repeated use of adhesive
urinary bags may result in skin abrasion. Skin abrasion is not only painful and causes
discomfort; it may also increase the risk of invasive infections in a vulnerable
population. The “gauze/cotton ball method” can be used alternatively. A small
gauze with cling film (the latter facing the diaper material to prevent urine absorption
in the diaper) is put in the diaper and urine is collected by expressing the urine from the
gauze (Fell et al. 1997). In a similar fashion, nonabsorbent diapers can be used (Burke
1995). An important limitation of both the bag and gauze/diaper collection methods is
that complete urine collection is most often not possible. Urine may leak along the bag
into the diaper and not all urine can be expressed from the gauze/diaper. This
limitation can be overcome by weighing the diapers to estimate total urine volume
and to multiply volume with urine drug concentrations to be able to estimate total
urinary drug and/or metabolite excretion.
2.3 Saliva
Breath tests using stable or radioactive isotopes are used in the context of drug
metabolism studies (Paine et al. 2002; de Wildt et al. 2007). Breath sampling of
exhaled labeled CO2 is easiest when children can follow instructions to breathe in a
Sample Collection, Biobanking, and Analysis 207
balloon, from which breath samples can be taken. In younger or critically ill
children, this approach is obviously not feasible. The original collection method
of respiratory CO2 used in children, including neonates, occurs via trapping of CO2
in sodium hydroxide. This method involves a tight-fitting face mask and passing of
the expired air through a condenser containing sodium hydroxide (Pons et al. 1988).
This is impractical and difficult in neonates. Alternatively, a direct nasopharyngeal
sampling technique can be used (van der Schoor et al. 2004). This technique allows
for direct sampling from the nasopharynx using a gastric tube attached to a syringe
or direct attachment of a syringe to a side-port of the endotracheal tube. During
observed expiration, the researcher collects air by pulling the syringe. The collected
air is then transferred to a vacuum tube for laboratory analysis.
2.5 Meconium
By accumulating from the 12th gestational week until birth, meconium acts as a
reservoir for exogenous compounds, such as drugs and metabolites. Drugs are
incorporated into meconium through swallowing drug-contaminated amniotic
fluid or via biliary excretion. Meconium analysis is thought to detect maternal
drug use during the second and third trimesters. Meconium passage occurs in the
first 1–3 days after birth, but may be prolonged in preterm infants. Collection of
meconium from diapers is easy, by scraping meconium from the diaper. 0.5–1 g of
meconium is usually enough for toxicological, quantitative analysis. Contamination
of meconium with urine may occur, which obscures the results. After collection,
meconium can be stored at low temperatures ( 20 C). Storage at room temperature
may reduce the concentrations of drug by degradation. Due to its complex compo-
sition, consisting of epithelial cells, swallowed amniotic fluid, bile salts, lipids,
other endogenous compounds, and xenobiotics until birth, extraction of drugs is
difficult (Gray et al. 2009).
2.6 Hair
Drugs can be incorporated in hair through blood supply of the hair, by external
exposure (through, e.g., smoke) or through secretion from sweat and sebum adja-
cent to the hair follicle.
Hair samples are mainly used for toxicological screening in prenatal alcohol and
drug exposure.
These samples are best collected from the back of the head. The proximal zone
(i.e., the zone which is closer to the root) should be clearly indicated if segmental
analysis is to be performed. The sample can then be stored and transported light and
moisture protected at room temperature. Since hair grows about 1 cm per month,
208 M.J. Ahsman et al.
segmental analysis can be done to estimate the time window of drug exposure
(Gallardo and Queiroz 2008).
for instance, be used to study the effect of age and other covariates in the pediatric
population (Ince et al. 2009; de Wildt and Knibbe 2009).
5 Drug Assays
different analytes of interest in the same sample, e.g., drugs and their metabolites or
combinations of coadministered drugs.
The required sensitivity can be reached using mass spectrometric techniques such
as liquid (LC-MS) or gas (GC-MS) chromatography–mass spectrometry. These
techniques rely on chromatographic separation of analytes from each other and
from matrix components, followed by ionization and counting of analytes of a
selected molecular mass. Compounds of similar mass can be distinguished via mass
filters that allow a single analyte to be selected in the presence of other drugs,
metabolites, or endogenous compounds. To enhance selectivity even further, the
selected compounds can be subsequently fragmented by collision with an inert gas.
This leads to molecular fragments that are highly specific for the original drug or
metabolite. After selection of one of these fragments via another mass filter, the
compound of interest can be quantified. This is called tandem mass spectrometry or
MS/MS (Fig. 1). The mass spectrometric techniques carry a distinct advantage over
other sensitive assays such as enzyme-linked assay, fluorometric assay, and
radioassay. Whereas the latter often suffer from cross-reactivity between structur-
ally related compounds such as drugs and their metabolites or endogenous
substrates (Tribut et al. 2005; Moyer et al. 1986; de Paula et al. 1998; Premaud
et al. 2006; Tate and Ward 2004), the mass spectrometric methods allow
Sample
Sample preparation
Chromatography /
Electrophoresis
Mass spectrometer
Inert gas
F1, F2, F3
M1 F1
Mass filter Mass filter Detector
Fig. 1 Principle of liquid or gas chromatography with tandem mass spectrometry detection. The
sample is cleaned up for chromatographic separation of drugs and metabolites from matrix
components. After chromatography or electrophoresis, the effluent enters the mass spectrometer.
After selection of molecules of a specific molecular weight (M1) by the first mass filter, the
molecules are fragmented with an inert gas. The resulting fragments (F1, F2, and F3) are
sent through the second filter in which one individual fragment is selected to be quantified at
the detector
Sample Collection, Biobanking, and Analysis 211
Exogenous and endogenous components in the biological matrix can interfere with
sample preparation or quantification, which compromises accuracy and precision.
The mechanisms of these so-called matrix effects are not fully understood, but have
been linked to coelution of different compounds (including inorganic ions and
plasma phospholipids) that can interfere with analyte ionization (Taylor 2005;
Careri and Mangia 2006). The degree of signal enhancement or suppression
could therefore vary from individual to individual, but also within individuals
upon changes in physiological constitution, either due to disease progression or
growth and maturation. This implies that validation of the assays should include an
evaluation of matrix effects in biological specimens (“blank matrix”) from the
intended patient population. The US Food and Drug Administration has issued
guidelines on the validation requirements for bioanalytical chromatographic
methods (Anonymous 2001b) without mentioning a specific method to assess
matrix effects; current reports on new LC-MS and GC-MS assays often contain a
212 M.J. Ahsman et al.
For studies on fetal drug or pollutant exposure, compounds are assayed in unusual
biological matrices such as meconium, hair, or cord blood. For these biofluids, it
may be even more difficult to find suitable blank material. For meconium in
particular, special sample preparation methods may be necessary to prepare
solutions that are suitable for LC-MS or GC-MS analysis. See Gray et al. (2009),
Rigourd et al. (2008), Frison et al. (2008), Kacinko et al. (2008), and Yeh et al.
(2009) for examples of analytical methods that were developed specifically for
these matrices.
Sample Collection, Biobanking, and Analysis 213
6 Conclusion
Table 1 Items to be considered before engaging in a pediatric study involving sample collection
and drug quantification
Sample collection
What are the maximum allowed sample volumes per occasion and per study period?
Which sampling times are informative (based on population PK study design) and practical?
Is blood the preferred biological specimen or can alternatives be used?
How much sample is required, taking into account the intended assay requirements and potential
future studies into different analytes with leftover material?
Which sampling methods are suitable?
Can these methods be implemented as part of routine clinical procedures and/or do involved staff
need extra training?
Biobanking and leftover samples
Have patients or their guardians given permission for biobanking and use of leftover samples?
Is there a separate long-term storage facility with temperature control, compliant with GCP
guidelines available?
How are patient data being recorded; is the database suitable for (anonymized) long-term storage
and extraction?
Who decides whether to grant individual researchers access to samples and data, and is there a
system that allows tracking of individual samples and researchers that use them?
Which departments or individuals are responsible for maintenance, logging access rights to
samples, etc?
Shipping and storage
How stable are the biofluid specimens and analytes at standard storage conditions: ambient
temperature (20–25 C), refrigerated (4–7 C), frozen ( 20 C), and deep-frozen ( 80 C)?
What are the average and worst-case shipping conditions and time?
Is privacy of study participants guaranteed during storage and shipping?
What arrangements have been made to allow sampling, storage, and processing outside standard
working hours, in weekends, and on holidays?
Have roles and responsibilities been agreed upon by the clinical department, logistical services,
and the laboratory?
Have standard operating procedures (SOP) containing contact details, storage conditions, etc.,
been agreed upon by and made available to the involved staff?
Assay
How much sample is required for the assay, taking into account reassay in case of instrument
failure?
Are the expected concentrations within the assay’s calibration range?
Has the assay been validated for this specific type of sample and analyte?
Have matrix effects been evaluated in appropriate batches of blank matrix? (preferably from
patients of the intended age, comedication, and disease state)
214 M.J. Ahsman et al.
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Contents
1 Children as Research Subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
2 The Principle of Scientific Necessity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
3 Appropriate Balance of Risk and Potential Benefit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
3.1 Component Analysis and Additional Safeguards for Children . . . . . . . . . . . . . . . . . . . . . 224
3.2 Interventions or Procedures that Do Not Offer the PDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
3.3 Interventions or Procedures that Offer the PDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
4 Selected Ethical Issues in the Design and Conduct of Pediatric Research . . . . . . . . . . . . . . . 231
4.1 Clinical Equipoise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
4.2 Choice of Control Group and Placebo Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
4.3 Alternatives to Placebo Controlled Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
4.4 Special Concerns in FIH Pediatric Clinical Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
4.5 Data and Safety Monitoring in Pediatric Clinical Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
4.6 Compensation for Pediatric Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
5 Child Assent and Parental Permission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
5.1 The Assent Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
5.2 Parental Permission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
5.3 The Definition of a Child . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Abstract The critical need for pediatric research on drugs and biological products
underscores the responsibility to ensure that children are enrolled in clinical
research that is both scientifically necessary and ethically sound. In this chapter,
we review key ethical considerations concerning the participation of children in
clinical research. We propose a basic ethical framework to guide pediatric research,
and suggest how this framework might be operationalized in linking science and
and Drug Administration (FDA) proposed establishing regulations for the pro-
tection of human subjects in 1979, including protections pertaining to clinical
investigations involving children (Department of Health Education and Welfare
1979). In 1981, FDA regulations were promulgated regarding informed consent
(21 CFR Part 50, 2011) and institutional review board (IRB) review of research
(21 CFR Part 56, 2011). Based on recommendations made by the National Com-
mission, regulations were promulgated in 1983 that governed research on children
conducted or funded by the Department of Health and Human Services (Depart-
ment of Health Education and Welfare 1983). In 2001, similar protections were
extended to research regulated by FDA (2001).
Specific guidelines on pediatric research within the European Union were
promulgated in 2001. Directive 2001/20/EC required Member States to develop
laws, regulations, and administrative provisions for the implementation of good
clinical practice in the conduct of clinical trials (European Parliament and the
Council 2001). Specific protections were to be implemented to ensure adequate
protections for minors, including parental permission and assent of able children,
assurance of direct benefit for the child or for the group of patients with the
particular condition, minimization of risk, and scientific necessity of the research.
An ad hoc group responsible for guideline development made further recom-
mendations for implementation of this Directive (2008).
The additional protections for children to be enrolled in a clinical investigation
can be divided into four “nested” domains with each protection building on an
adequate response to the prior protection. The enrollment of children in a clinical
investigation must be considered scientifically necessary before the evaluation of
whether the research interventions or procedures present an appropriate balance
of risk and potential benefit. A clinical investigation must be found to have an
appropriate balance of risk and potential benefit before considering the role of
parental permission and child assent. This chapter will address these four nested
protections.
(21 CFR 56.111(a)(1) 2011), and that the selection of subjects must be equitable
(21 CFR 56.111(b) 2011).
Consistent with the recommendations of the National Commission, equitable
selection requires that subjects who are capable of informed consent (i.e., compe-
tent adults) should be enrolled prior to subjects who cannot consent (e.g., children)
(Department of Health Education and Welfare 1978b). There is broad international
agreement on this approach, assuming there are no significant scientific reasons
to enroll younger children preferentially to older children and/or adults. EMA
regulations (2001), International Conference on Harmonisation (ICH) guide-
lines E6 (1996) and E11 (2000), and the Declaration of Helsinki (World Medical
2008) all state explicitly that vulnerable populations such as children should not be
enrolled in a clinical investigation unless their involvement is essential to answer a
scientific objective relevant to the health and welfare of that vulnerable population.
The ethical principle of “scientific necessity” has been operationalized in the
scientific principle of “extrapolation.” As described in the Pediatric Research
Equity Act of 2007 “if the course of the disease and the effects of the drug are
sufficiently similar in adults and pediatric patients, the Secretary may conclude that
pediatric effectiveness can be extrapolated from adequate and well-controlled
studies in adults, usually supplemented with other information obtained in pediatric
patients, such as pharmacokinetic studies” (Food and Drug Administration Amend-
ments Act of 2007). The principle of extrapolation also can be found in the
International Conference on Harmonization guidance on pediatric research (ICH
2000). The need for pediatric studies is assessed by asking a series of questions
about the similarity of the adult and pediatric disease, response to treatment, drug-
exposure response, and pharmacokinetic and pharmacodynamic measurements that
could be used to predict efficacy (see Fig. 1).
The additional safeguards for children enrolled in research are based on two ethical
principles. First, the risks to which children would be exposed must be low if there
is no prospect of direct therapeutic benefit (PDB) to the enrolled children. Second,
children should not be placed at a disadvantage by being enrolled in a clinical trial,
either through exposure to excessive risks or by failing to get necessary health care.
Consequently, the data necessary to initiate a pediatric investigation must demon-
strate either an acceptably low risk of the experimental intervention or a sufficient
PDB to justify the risks of the intervention. A major challenge facing the develop-
ment of a new product for the treatment of a pediatric disorder or condition
is bridging this “risk gap” between (a) research involving procedures and/or
interventions that present only a low risk given the absence of sufficient data to
establish the PDB, and (b) the conduct of either “proof of concept” or pivotal trials
for dosing, safety and/or efficacy that offer a sufficient PDB to the enrolled children
to justify exposure to interventions that present greater than low risk.
Ethical Considerations in Conducting Pediatric Research 223
Fig. 1 FDA algorithm for determining need for pediatric studies using the principle of scientific
necessity/extrapolation
For adult subjects, the risks of research participation can be justified either by the
anticipated direct benefits to the subjects or by the importance of the anticipated
knowledge. Investigations involving children that pose more than low risk cannot
be justified by the importance of anticipated knowledge. In pediatric studies, the
allowable risk exposure for an intervention or procedure not offering a PDB must be
restricted to low risk. Thus, the individual research interventions and procedures
that are contained in an investigational protocol must be categorized and assessed
according to whether they do or do not offer PDB – an approach referred to as
“component analysis.”
Component analysis has come under recent criticism for using the norm of
clinical equipoise as the standard for determining the ethical acceptability of
therapeutic interventions or procedures (Miller et al. 2003; Miller and Brody
2007). The concept of clinical equipoise will be discussed more fully below. A
related (albeit unconvincing) criticism of component analysis is directed toward the
manner in which the distinction between therapeutic and non-therapeutic
procedures is made (Wendler and Miller 2007). Wendler and Miller (2007) argue
that the consequences of the intervention are what matters to the determination of
the PDB, rather than the intent of the investigator or the design of the individual
intervention. All parties to the debate agree on the need to avoid the term “thera-
peutic research” which may justify (or offset) the risks of non-beneficial procedures
through the inclusion of unrelated beneficial procedures in the same protocol
(i.e., the fallacy of the “package deal”) (Department of Health Education and
Welfare 1978b; Institute of Medicine 2004; Medical Research Council 2004).
Otherwise a non-beneficial research intervention that presents considerable risk
could be justified by adding unrelated therapeutic components to the protocol, such
as free health care.
The analysis of a proposed clinical investigation can be approached either (1) by
assessing whether or not each intervention or procedure does or does not offer the
PDB, followed by an assessment of the risks of each component, or (2) by assessing
the risks of each intervention and procedure, followed by an assessment of the PDB
Ethical Considerations in Conducting Pediatric Research 225
for those components that present greater than minimal risk. An intervention or
procedure that presents no more than minimal risk may or may not offer a PDB. We
will discuss the “minimal risk” category under the heading of interventions or
procedures that do not offer the PDB.
For research on non-consenting subjects that does not offer direct therapeutic
benefit, the ICH (1996) E6 Guidelines specify that “the foreseeable risks to the
subjects are low” and that “the negative impact on the subjects’ well-being is
minimized and low.” FDA regulations use the term “minimal risk” (21 CFR
50.51, 2011) and define it as “the probability and magnitude of harm or discomfort
anticipated in the research are not greater in and of themselves than those ordinarily
encountered in daily life or during the performance of routine physical or psycho-
logical examinations or tests” (21 CFR 50.3(k) 2011). This definition appears to
allow for a “relativistic interpretation” indexed to the research participants’ own
experiences as well as provides two comparators for assessing minimal risk (a)
ordinary daily life, and (b) routine physical or psychological examinations or tests
(Institute of Medicine 2004). There is well-documented variability in the interpre-
tation and application of “minimal risk” (Shah et al. 2004; Institute of Medicine
2004; Kopelman 2000).
Three US-based advisory panels – the Institute of Medicine (IOM), The
Secretary’s Advisory Committee on Human Research Protections (SACHRP),
and The National Human Research Protections Advisory Committee – recommend
the international use of a uniform standard for minimal risk (Fisher et al. 2007).
Grounded in the ethical principle of justice as fairness (Institute of Medicine 2004),
this approach indexes minimal risk to the normal experiences of average, healthy
children rather than to risk levels routinely experienced by the research participants.
According to this standard, research interventions and procedures should not
involve potential harm or discomfort beyond that which average, healthy, normal
226 M. Roth-Cline et al.
FDA regulations also include a classification of “minor increase over minimal risk”
(21 CFR 50.53, 2011). An intervention or procedure approved under this category
must also involve “experiences to subjects that are reasonably commensurate with
those inherent in their actual or expected. . . situations” and be “likely to yield
generalizable knowledge about the subjects’ disorder or condition that is of vital
importance for the understanding or amelioration of the subjects’ disorder or
condition.” This category has been the most controversial, garnering two dissenting
votes from members of the US National Commission (Department of Health
Education and Welfare 1978b). The justification for this classification has included
that the increased risk is warranted due to scientific necessity (CIOMS 2002;
Institute of Medicine 2004), scrupulous parents can be entrusted with the authority
to evaluate such non-beneficial risk exposures (Nelson and Ross 2005), and that
the absolute difference in risk exposure is meant to be “slight” (Department of
Health Education and Welfare 1978a). The regulations do not, however, define
“disorder or condition,” “vital importance,” “reasonably commensurate,” and
“minor increase over minimal risk.” These concepts are explored below.
The IOM defined “disorder or condition” as a set of “specific physical, psy-
chological, neurodevelopmental, or social characteristics” that scientific evidence
or clinical knowledge has shown to compromise the child’s health or “to increase
risk of developing a health problem in the future” (Institute of Medicine 2004).
Therefore, a child could be healthy, but “at risk” for the condition that is the object
of the research based on scientific and/or clinical evidence. Consistent with
international guidelines, this definition excludes the use of healthy not-at-risk
children from greater than minimal risk research without a PDB (CIOMS 2002;
European Parliament and the Council 2001; ICH 1996). The IOM also understood
the requirement for “vital importance” to be consistent with the principle of
scientific necessity and thus closely tied to the child’s “disorder or condition”
(Institute of Medicine 2004). The overall plan for pediatric product development
should be taken into consideration since information gained from the specific
protocol under consideration may be an important yet intermediate step leading to
further investigations.
The National Commission uses “commensurate” to describe research activities
that are reasonably similar (but need not be identical) to procedures that prospective
research participants may ordinarily experience. The IOM elaborated on this
approach, noting that “although a child might not have experienced a particular
research procedure. . .the procedure could still be described to the child as poten-
tially presenting levels of pain, immobility, anxiety, time away from home, or other
effects that would be similar to those produced by procedures that they have
experienced” (Institute of Medicine 2004). The goal is to make the research
procedures tangible for the child and parents, thereby improving child assent and
parental permission (CIOMS 2002; Department of Health Education and Welfare
1978b).
228 M. Roth-Cline et al.
individual exposed to risk; the severity of the disease (e.g., degree of disability, life-
threatening); and the availability of alternative treatments.
The concept of equipoise combines two separate principles (Miller and Brody
2007). The first principle is the scientific principle of “uncertainty” (i.e., the null
hypothesis between the investigational product and the comparator or control
group). However, this principle is a requirement of all ethical research, and the
specification and application of this principle of “uncertainty” is complex (Veatch
2007). The uncertainty of the individual clinician is not decisive, but rather the
uncertainty of the relevant community. The morally problematic area is where
sufficient data have been developed such that clinical equipoise is disturbed, but
insufficient data exist to justify a scientific (or policy) conclusion (Veatch 2007;
Gifford 2007).
The second principle contained within the concept of equipoise is the ethical
norm that no one enrolled in a trial should receive an inferior treatment (i.e., known
effective treatment should be provided). Here clinical equipoise is seen as a
specification of the “duty of care” (Miller and Brody 2007). From this perspective,
the dispute about the role of equipoise is primarily about whether the “duty of care”
(carried over from the clinical setting based on the fiduciary duty of a physician to
act in a patient’s best interest) should be the ethical framework for clinical research
(Institute of Medicine 2004). Proponents of equipoise may argue in favor of
actively-controlled comparator trials, as such trials may provide more useful clini-
cal information. However, this approach does not solve the tension between having
enough information to make an “individual patient decision” and enough to “war-
rant making a policy decision” (Gifford 2007).
All parties to the debate over equipoise as a guiding principle of clinical research
accept the need for a demarcation between interventions or procedures that either
offer or do not offer a PDB. The regulations of many countries are grounded on this
distinction. The view that no child should be disadvantaged by participation in a
clinical trial bears some resemblance to clinical equipoise. However, an affirmation
of the child-patient’s right to competent medical care and to protection from undue
risk of harm when participating in a clinical investigation does not require nor entail
the principle of clinical equipoise. The patient-subject’s right to competent medical
care should be operationalized in the structure of the investigational protocol
(London 2007). The nature of the scientific uncertainty to be resolved by the
study design should be specified, and the comparability of alternatives – namely,
the ethical and scientific argument in favor of the chosen control group – should be
justified.
treatment from children enrolled in the placebo arm of a study, for example, must
be limited to no more than a minor increase over minimal risk because the placebo
arm of a study does not offer a PDB.
A variant of the discussion about placebo (or no treatment) controls concerns
the use of “local” versus “universal” standards to determine the appropriate
control group. In other words, should “proven effective therapy” only refer to
treatments that are actually available in the location where the clinical investi-
gation is being conducted? Some argue that the purpose of a clinical investiga-
tion is to alter clinical practice. Thus, “it is crucial. . . to take the study context
into account when designing and conducting such studies.” Simply, the appro-
priate control group (or comparator) should be drawn from actual clinical
practice in that setting (Weijer and Miller 2004). However, others argue that
the withholding of known effective treatment based on the underlying inequities
in the distribution of medical care is unjust and exploits those less fortunate
(Shaddy and Denne 2010). A middle ground in this debate requires that the
proposed study provide valuable and timely information about a health care need
important to the local population, such that there is a reasonable likelihood that
the local population could benefit from the research (World Medical Association
2008).
Non-inferiority trials are intended to show that the effect of a new treatment is
not worse than that of an active control by more than a specified margin (Snapinn
2000). The design and interpretation of NI trials is not straightforward. For the NI
trial to be valid, one must have historical studies that provide reliable and precise
estimates of the effect of the active control regimen relative to placebo (ICH 2001).
Further, NI trials do not assure that the experimental agent is “at least as effective”
as the active regimen unless superiority of the experimental agent is demonstrated.
An experimental intervention may be inferior to the active control and still demon-
strate non-inferiority.
Therefore, the primary ethical question is whether it is appropriate to use an NI
design for pediatric trials where the inferior performance of the experimental
intervention may be associated with serious morbidity or mortality in children.
For example, suppose a new antibiotic were tested for life-threatening infections.
Even if the experimental drug were shown to be non-inferior, more children may
still be at risk of dying due to inferiority of the experimental drug. The ethical
acceptability of this design depends on a variety of factors. There may be times
when the new treatment offers a potential benefit in lower toxicity or improved
usability that may justify using the new treatment in a given population even if it
were shown to be slightly inferior to standard care. However, the burden of proof
should be on the advocates of the NI study to present convincing evidence that the
benefits of the new product outweigh the potential inferiority such that the trial
should be allowed to proceed.
Data Monitoring Committees (DMC) are advisory to the sponsor, and charged with
conducting periodic reviews of accumulated data from ongoing clinical trials to
assess for substantial evidence of benefit, harm, or futility of collecting additional
data (U.S. Department of Health and Human Services FDA 2006). While all
pediatric clinical trials require careful safety monitoring, they do not uniformly
require a formal DMC. The only mandatory use of a DMC in US regulations is for
research studies in emergency settings in which the informed consent requirement
has been waived [21 CFR 50.24(a)(7)(iv) 2011].
However, a DMC is recommended in additional circumstances: large, multi-
center studies of long duration; strong a priori safety concerns, potential serious
toxicity related to study product use; and populations at elevated risk of death/
serious morbidity or in populations deemed potentially fragile (U.S. Department of
Health and Human Services FDA 2006). Current guidance from the American
Academy of Pediatrics recommends DMCs for all pediatric trials (Shaddy and
Denne 2010). In practice, however, DMCs may not be warranted in trials with
few or well-characterized risks or at early stages of product development when
studies have few participants and are not blinded.
Ethical Considerations in Conducting Pediatric Research 237
The requirement for child assent emerged in a 1978 report by The National
Commission (1978b). William Bartholome defined four fundamental elements of
238 M. Roth-Cline et al.
Since children are unable to provide informed consent, pediatric research relies on
parental permission to authorize the enrollment of children in research. There is
wide international agreement on this requirement of surrogate (usually parental)
consent. A parent is generally defined as a child’s biological or adoptive parent, and
a guardian is defined as an individual who is authorized under applicable state or
local law to consent on behalf of a child to general medical care. The parental
permission requirement is intended to protect the child from assuming unreasonable
risks (Rossi et al. 2003).
However, the feasibility of obtaining parental permission may be a problem in
certain circumstances. For example, great distances, lack of communication infra-
structure, social dislocation, or high parental mortality (e.g., HIV affected
populations) may serve to make parents unreachable. US regulations governing
Health and Human Services-funded research at (45 CFR 46.408(c) 2011) allow for
a waiver of the requirement for parental or guardian permission if a research ethics
committee determines that the requirement is unreasonable. However, FDA
regulations for the protection of children (21 CFR 50, Subpart D 2011) do not
include this waiver. Thus, for the majority of FDA-regulated research, parental
permission is required for the enrollment of children. The exception from informed
consent allowed under (21 CFR 50.24, 2011) for research conducted in emergency
settings applies to children as well as adults.
Children are defined in FDA regulations as “persons who have not attained the legal
age for consent to treatments or procedures involved in clinical investigations,
under the applicable law of the jurisdiction in which the clinical investigation
will be conducted” (21 CFR 50.3(o) 2011). In effect, whether or not an individual
subject is considered a child for the purposes of the application of Subpart D
depends on how the age of majority is defined by state law. State law also defines
certain conditions under which a child who is younger than the age of majority may
be considered emancipated (i.e. not under the control of a parent or guardian) and
thus effectively an adult. These conditions generally include marriage, military
service, or a court order, but vary considerably from state to state. FDA regulations
would allow a minor who meets one of these conditions to be considered an adult
for the purposes of research. In addition, state law may allow a minor to consent for
certain interventions and procedures such as treatment for sexually transmitted
diseases and drug abuse. If the clinical investigation involves one of these con-
ditions, a minor may be considered an adult for the purposes of obtaining informed
consent (absent parental permission). Such a determination would be made by the
local research ethics committee in consultation with legal counsel.
240 M. Roth-Cline et al.
6 Summary
In recognition of the benefits of pediatric research, research ethics has evolved from
a position of excluding children to one of cautious advocacy – acknowledging the
critical role of pediatric research, but accompanied by careful consideration of the
scientific context, evaluation of risks and benefits, and protection to participants.
Many countries have adopted regulations or guidelines to protect children in
research. Typically, this requires a careful analysis of the risk associated with
each intervention and/or procedure, an evaluation of potential benefits, provisions
for child assent, and ensuring adequate parent/guardian permission. The regulatory
agencies overseeing pediatric research need to make a careful ethical assessment
weighing sometimes complex trade-offs so as to protect children’s welfare and
prevent undue risk of harm while generating scientifically valuable information to
answer important questions concerning the health and welfare of children.
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Contents
1 Regulatory Part 1: United States Federal Pediatric Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
1.2 Brief Regulatory History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
1.3 Early Efforts to Address Pediatric Therapeutics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
1.4 First Generation of Coordinated Federal Pediatric Initiatives . . . . . . . . . . . . . . . . . . . . . 249
1.5 Second Generation of Pediatric Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
1.6 Use of Extrapolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
1.7 Comparison and Interaction of the Pediatric Regulatory Initiatives . . . . . . . . . . . . . . . 254
1.8 Extension of Human Research Subject Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
1.9 Interim Results of the Pediatric Regulatory Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
1.10 Third Generation of Pediatric Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
1.11 International Harmonization and Other Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
2 Regulatory Part 2: The European Regulation and Pediatric Medicines . . . . . . . . . . . . . . . . . . . 258
2.1 European Legislation and Pharmaceutical Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
2.2 The European Pediatric Regulation: A Concise History . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
2.3 Major Aspects of the Pediatric Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
2.4 The Paediatric Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
2.5 The Paediatric Investigation Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
2.6 Waivers and Deferrals of the Pediatric Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
2.7 Characteristics of the European Pediatric Initiative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
2.8 Further Research on Pediatric Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
2.9 International Collaboration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
2.10 Rewards and Incentives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
2.11 Transparency Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
2.12 Pharmacovigilance and Long-Term Safety Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
S. Hirschfeld (*)
National Children’s Study Eunice Kennedy Shriver, National Institute of Child Health and Human
Development, 31 Center Drive, Room 2A03, MSC 2425, Bethesda, MD 20892, USA
e-mail: hirschfs@mail.nih.gov
A. Saint-Raymond
Scientific Advice, Paediatrics, and Orphan Drug Sector, European Medicines Agency, 7 Westferry
Circus, Canary Wharf, London E14 4HB, United Kingdom
Abstract A series of government actions have evolved since the 1990s to facilitate
the development of medicinal products for pediatric use using a combination of
incentives and mandates. The initiatives have been successful in stimulating activity
and interest in products developed for pediatric use. The initiatives continue to evolve
as experience accumulates and regulatory agencies develop robust cooperative
programs. A multidimensional program is necessary to achieve the necessary goal
of aligning pediatric therapeutics with adult therapeutics and providing children the
most favorable opportunity to benefit and minimize risk to vulnerable populations.
1.1 Introduction
the Congress and signed by the President, it becomes effective. The term “Law” is
synonymous with the term “Act.” Once a law is in effect it becomes part of the
United States Code. The Executive Branch has the authority to issue Regulations
(or Rules) to further clarify the law. Regulations are not voted on but are vetted for
public comment before they become finalized. A Final Rule or Regulation is
published in the Code of Federal Regulations. Regulations are enforceable, but
can be challenged in a Federal court.
The general regulation of biologics and medicines in the United States began in the
early twentieth century with a series of laws triggered by several widely publicized
events involving the administration of tainted products causing the deaths of
children. The establishment of laws to regulate the medicinal products began in
1902 when the use of an equine tetanus antitoxin that was not properly purified and
resulted in fatalities among those who received it was widely circulated as a news
story. The United States Congress passed the Biologics Control Act in 1902 to
regulate the purity and safety of serums, vaccines, and other biologics. In 1906,
deaths among infants given a colic syrup containing morphine contributed to the
passage of the Food and Drug Act that required the ingredients of products to be
listed. The authority of the federal government to regulate interstate commerce for
medicinal products was challenged in the courts and upheld in 1912. A subsequent
amendment to the Food and Drug Act known as the Sherley Amendment confirmed
the federal government’s authority.
Over 100 deaths due to a preparation of the antibiotic sulfanilamide containing
diethylene glycol in 1937 triggered debate that led to the Food Drug and Cosmetic
Act of 1938, establishing a legal requirement to demonstrate safety of regulated
medicinal products prior to marketing. The law was amended in 1962 following
deaths and malformations associated with the use of thalidomide to include a
requirement for establishing effectiveness through investigations. Subsequent
regulations clarified the intent to state that the investigations must be adequate
and controlled studies with descriptions of the characteristics of such studies.
The last major principle to be enacted into law was the authority of the federal
government to grant incentives for certain classes of products through the Orphan
Drug Act of 1983. Support for the law came from reports of children with rare
diseases unable to find any available therapy in the United States and traveling to
other countries to seek treatment.
Due to different legal definitions for different types of products, the Food and
Drug Administration (FDA) operates under the authority of many laws and
regulations. Administratively the FDA is organized into different centers based
on the type of product. For example, the Center for Biologics Evaluation and
Research, the Center for Devices and Radiological Health, and the Center for
Drug Evaluation and Research each operate under and apply different sets of
laws and regulations, and other FDA Centers each have their own specific legal
248 S. Hirschfeld and A. Saint-Raymond
The term “therapeutic orphan” was invented in 1968 to describe the status of sick
children who lacked appropriate medications. The American Academy of Pediat-
rics published a White Paper in 1974 outlining expectations for research enrolling
infants and children. Concurrently awareness of the need for adequate information
to treat children with medicinal products led to several analyses of product package
inserts of FDA-approved products that showed 78% had no information pertaining
to pediatric use other than, in some cases, a disclaimer that the product is not for use
in children.
The FDA began to specifically address the needs of children with a regulation
establishing a Pediatric Use section for the product package insert, also known as
the product label, in 1979. The FDA subsequently encouraged voluntary develop-
ment of products for pediatric use through the potential use of extrapolation of
adult efficacy under certain conditions in a regulation known as the Pediatric Rule
of 1994. The result of the initiative, despite a new regulation and FDA staff
writing hundreds of letters to companies and promoting the opportunity, was
that the most common response was a statement that a product is not intended
for use in children.
Pediatric Regulatory Initiatives 249
The enactment of the Prescription Drug User’s Fee Act of 1992 provided the FDA
with additional resources and the Food and Drug Administration Modernization
Act of 1997 (FDAMA) followed with FDA review performance standards and a
section (Section 111) that introduced an incentive for pediatric use of medicinal
products. The principle of providing an incentive that first appeared in the Orphan
Drug Act was now extended not just to products intended to treat diseases or
conditions that met the definition of a rare disease, but to most medicinal products
classified as drugs, with a few exceptions, independent of intended use. Biologics
and some antibiotics were not included in the program. The intent was to enhance a
voluntary program with a financial incentive.
The specific incentive was a 6-month extension of patent life or marketing
exclusivity for all indications, doses, and dosage forms of a product from a sponsor
that use the same chemical moiety as its active ingredient. A patent in the United
States is issued by the Patent and Trademark Office of the Department of Commerce
to protect intellectual property. Marketing exclusivity is a license granted by the FDA
in the form of an NDA to provide product innovators with a period of time without
competition in the market place to sell a product for its claimed use. The initial
standard exclusivity period is 5 years and exclusivity for Supplements (known in
other regions of the world as Variations) is for 3 years. A product approved for an
orphan indication receives 7 years of exclusivity. The result of receiving a 6-month
exclusivity extension for a product was 5½ years of exclusivity for a new product,
3½ years for a Supplement, and 7½ years for a product with orphan designation.
When marketing exclusivity expires, other manufacturers may sell a similar
product if they either have intellectual property rights under license from an active
patent holder or the patent has expired, in which case no license is required. The
new manufacturer must make the product within legal specifications as determined
by federal regulations and register the product through an Abbreviated New Drug
Applications (ANDA) with the FDA in order to market it. A 6-month extension
blocks other manufacturers from entering the market place until the extension
expires. The general expectation is that when marketing exclusivity expires, the
price of a product will decrease due to competition from other manufacturers. The
potential economic impact of a delay caused by an exclusivity extension on the US
health care system costs as well as the potential economic benefit to a product
innovator was considered in the selection of the 6-month time frame.
The incentive process is initiated by a formal pediatric Written Request from the
FDA. The rationale for requiring a pediatric Written Request from the FDA to
perform studies that could qualify for an incentive was to ensure that the studies
were of sufficient quality, design and public health need to justify the potential risks
to children, and avoid the perception of exploitation of a vulnerable population for
financial gain.
The specific model was that the FDA would issue a Written Request to the
product sponsor stating a general framework for the type of pediatric information
250 S. Hirschfeld and A. Saint-Raymond
expected and an outline of the types of studies, both nonclinical and clinical, to be
performed and a due date. The types of studies could include dose finding studies in
various pediatric populations, safety studies, pharmacokinetic, or pharmacody-
namic studies in various pediatric populations, or a demonstration of clinical
benefit. The specific diseases or conditions and the relevant pediatric populations
were independent of whatever use the product may have for adults and determined
by the public health needs. The due date was determined by a reasonable estimate of
the time and resources needed to generate the requested information and was not
influenced by expiration dates for a marketing license or patent.
The deliverable from a pediatric Written Request was a report describing how
the sponsor responded to the terms of the Written Request by the due date.
A sponsor or a third party could send to the FDA a Proposed Pediatric Study
Request outlining a proposal. The FDA then had the option to utilize or modify the
proposal in developing a formal Written Request. The FDA also had the option to
issue a Written Request without an external proposal.
Proposed Pediatric Study Requests and the study reports in response to a
pediatric Written Request were reviewed in the various review divisions within
the Center for Drug Evaluation and Research to provide the most specific subject
matter expertise. The review divisions would then submit the draft Written
Requests to a centralized multidisciplinary Pediatric Implementation Team to
provide consistency and additional expertise. Following secondary review and
discussion by the Pediatric Implementation Team, the Written Request would be
issued by the appropriate FDA Office Director.
The study reports in response to a Written Request were submitted to the issuing
FDA review division for initial review. Subsequently, the review division would
present a summary and recommendations as to the adequacy of the response to a
multidisciplinary Pediatric Exclusivity Board. The adequacy of the response was
evaluated on the basis of the data quality, information content, and adequacy to
inform pediatric use. It was not based on whether the requested studies
demonstrated efficacy or suggested effectiveness in children. The major principle
was to obtain high-quality information to guide pediatric use, regardless of the
potential for clinical benefit. The knowledge that a product is not effective in a
particular population has value in avoiding risk and unnecessary exposure. The
Pediatric Exclusivity Board then made a determination that was subsequently
communicated to the sponsor. The establishment of the Pediatric Implementation
Team and the Pediatric Review Board provided a uniform framework for pediatric
needs and product assessment.
The entire pediatric incentive program was developed on a time-limited basis of
5 years after inception and scheduled to expire in the year 2002. The rationale was
that if the program were successful, it could be renewed and even improved, and if
it were not successful, other approaches would have to be developed.
In 1998, the FDA published a regulation known as the Pediatric Rule of 1998
that was intended to be a mandate to complement the incentive program in the
FDAMA. The Pediatric Rule targeted products where the disease or condition that
the product was intended to be used for in adults also existed in a pediatric
Pediatric Regulatory Initiatives 251
population. All products with a new active ingredient, new indication, new dosage
form, new dosing regimen, or new route of administration that were likely to be
used in children either due to their potential meaningful therapeutic benefit that
would be considered an advance over currently existing therapy in a limited
population or the product had the potential for widespread use in the pediatric
population were included. Widespread use was calculated use by greater than
50,000 children using the assumption that the threshold for an orphan indication
was a prevalence of less than 200,000 in the United States and that children are
about one quarter of the population; therefore, an adjusted threshold could be used.
In contrast to the incentive program that only applied to medicinal drugs, the
mandate program applied to both drugs and biologics. It did not, however, apply
to products with orphan designation for the orphan indication. The contemplated
penalty for noncompliance was that a product could be considered to be
misbranded, meaning that the product had a use that was intended but not included
in the language of the product package insert or label. A product that is misbranded
can be subject to injunction (legal blockage of production or distribution) and
product seizure.
The 1998 Pediatric Rule had provisions for waivers of the requirement for some
or all pediatric subpopulations on the basis that the disease or condition did not exist
in children or that pediatric studies would not be practical. In addition, sponsors
could request a deferral for compliance so that licensing and marketing a product
for adult use would not be compromised if the pediatric data were not yet available.
Waivers and deferrals had to be requested from the FDA, and deferrals would be
granted with a due date for when the pediatric data would be submitted for review to
the FDA. A full waiver referred to all children and a partial waiver would refer to
only a pediatric subpopulation, usually defined on the basis of age.
The incentive program and the mandate were intended as complementary
regulatory tools in a comprehensive program to advance the need for adequate
information to manage the risks and provide the benefits that medicinal products
can provide to children. As early as 1998, discussions on the pediatric initiatives
between the FDA and other regulatory authorities began, built partially on the
successful experience of developing orphan drug programs in other regions based
on the experience of the US Orphan Product program. In December 2000 under the
French presidency of the European Union, with the FDA consulting on the prepa-
ration of documents, the European Council of Health Ministers adopted a resolution
requesting the European Commission to develop a program for pediatric therapeu-
tics. Further details and elaboration are given in the next section on the European
Regulation.
The initial experience with the FDAMA incentive program was favorable, so in
January 2002, the pediatric incentive program was renewed for another 5 years
252 S. Hirschfeld and A. Saint-Raymond
when the Best Pharmaceuticals for Children Act (BPCA) became law and included
some new provisions including the study of off-patent medications in partnership
with the National Institutes of Health (NIH), establishment of pediatric specific
FDA advisory committees, enhanced safety reviews, and publication of FDA
clinical and pharmacology reviews on the FDA Web site.
The 1998 Pediatric Rule was challenged in court under the premise that if a
sponsor did not intend to market a product for a particular use, the federal govern-
ment lacked authority to force a sponsor to develop a product for an unintended use.
In October 2002, a federal court in Washington, DC, heard the case and ruled
against the 1998 Pediatric Rule partially on the basis that the US Congress did not
intend to give the FDA the authority to compel a manufacturer to study medicinal
products in children. The court opinion was based in part on the recent renewal
of the pediatric incentive program in BPCA using the argument that Congress
had an opportunity to contemplate pediatric therapeutics and chose an incentive
mechanism.
Rather than challenge the court decision, the Department of Health and Human
Services waited until 2003 when the Pediatric Research Equity Act (PREA) became
law and gave the FDA the authority to enforce the development of therapeutic
products for children under the same conditions as in the 1998 Pediatric Rule –
when the disease or condition was similar in adults and children and when the
product was either a meaningful therapeutic advance or would be widely used. As
in the original 1998 Rule, options to request waivers and deferrals were included
and orphan products were excluded.
The PREA required that products develop a Pediatric Assessment and Plan. The
specific language is that all applications (or supplements to an application) submit-
ted under section 505 of the Act (21 U.S.C. 355) or section 351 of the Public Health
Service Act (PHSA) (42 U.S.C. 262) for a new active ingredient, new indication,
new dosage form, new dosing regimen, or new route of administration to contain
a pediatric assessment unless the applicant has obtained a waiver or deferral
(section 505B(a) of the Act). It also authorizes FDA to require holders of approved
NDAs and Biologic Licensing Applications for marketed drugs and biological
products to conduct pediatric studies under certain circumstances (section 505B
(b) of the Act). The PREA applied to all products that received marketing authori-
zation since April 1, 1999, because that was the date the 1998 Pediatric Rule
became effective.
If a product did not meet the criteria for compliance with the need for
pediatric studies, then the Pediatric Assessment and Plan would be to request a
waiver. Nonetheless, the potential use of a product in children must be
contemplated by every sponsor wishing to file a product use claim for marketing
authorization.
Waivers are considered for three general circumstances:
• Studies are not practical due, for example, to the rarity of the disease or condition
in children.
• The product is likely to be unsafe or ineffective in children.
Pediatric Regulatory Initiatives 253
The US regulations in the Code of Federal Regulations Title 45 Part 46 that pertain
to human research protection developed during the 1970s and 1980s and revised in
the 1990s apply to research that is funded by the federal government. Research not
funded by the federal government but regulated by the FDA is covered under
regulations in Title 21 Part 50. In 1996, the FDA published the International
Conference on Harmonization of Technical Requirements for Registration of
Pharmaceuticals for Human Use (ICH) E6 Guidelines, also known as the Good
Clinical Practice Guidelines as a Guidance Document. In 2000, the FDA published
ICH E11 on Clinical Investigation of Medicinal Products in the Pediatric Popula-
tion as a Guidance Document. Guidance documents, however, are not legally
binding, so in order to provide the same level of protection to children who
participate in nonfederal government funded research as provided to children who
participate in federally funded research, the FDA adapted the provisions in Title 45
Part 46 Subpart D that pertain to children to Title 21 Part 50 in 2003.
The BPCA and the PREA were scheduled to expire in 2007. By the end of March
2007, under the incentive programs in FDAMA and BPCA, the FDA had issued
about 340 Written Requests, granted the incentive for 136 products representing
256 S. Hirschfeld and A. Saint-Raymond
129 active chemical moieties, and revised 118 product package inserts with new
pediatric information. The total number of submissions for an incentive was 149, so
the favorable determination rate was about 91%. Under the mandate program for
PREA, the FDA revised 55 product package inserts with new pediatric information.
The total for both programs was 173 products with new pediatric information.
Of products that received the incentive, 73 had FDA medical or pharmacology
reviews or both posted on the FDA Web site by March 2007.
An analysis of these reviews showed that there were 195 individual pediatric
studies across 33 drug classes in 12 disease categories. The average number of
studies per product was about 3 with a range from 1 to 9 and the average number of
patients per product was about 360 with a range from 11 to 1,550. The total number
of pediatric patients enrolled for all products was about 25,000.
Studies could be classified into four types – pharmacokinetic only (19%),
pharmacokinetic and pharmacodynamic (17%), pharmacodynamic only (conven-
tionally referred to as proof of concept or Phase 2 studies) (32%), and efficacy
studies (32%). An efficacy study was defined as a study with a clinically relevant
outcome measure and with adequate statistical power to formally establish efficacy.
All studies were considered to varying degrees to be safety studies. About one third
of all studies had a formal pharmacokinetic component, underlying the importance
of dose determination in different pediatric subpopulations. A common theme in
many of the studies was the need for dose adjustments in 3- to 5-year-old children.
The Food and Drug Administration Amendments Act of 2007 (FDAAA) renewed
the BPCA as Title V of FDAAA with some modifications and the PREA for an
additional 5 years. The major modifications in the BPCA are as follows:
• Listing of off-patent drug prioritization process.
• Prioritization of off-patent products to be studied framed by public health needs
based on diseases and conditions rather, as in the prior version of the BPCA,
based on specific products.
• Flexibility in funding mechanisms that the NIH may use for pediatric studies
related to either off-patent drugs or on-patent drugs in the case of the sponsor
declining a Written Request.
• Enhanced program for training in pediatric pharmacology.
• Description of the role and responsibilities of the Pediatric Committee (PeRCO)
at the FDA to review Written Requests, review pediatric study reports, and track
and make public pediatric activity.
The PREA was renewed as Title IV of FDAAA and a new law, Title III – The
Pediatric Medical Device Safety and Improvement Act, was added. The Pediatric
Medical Device Safety and Improvement Act has provisions for:
Pediatric Regulatory Initiatives 257
The near term future of the US pediatric initiatives includes the harmonization and
coordination of a fragmented and diverse clinical research infrastructure. The NIH
are supporting several programs designed to augment current clinical research
efforts and transform the culture of research to one of stability, cooperation, and
collaboration. The most comprehensive is the Clinical and Translational Science
Awards Consortium administered by the National Center for Research Resources to
build a national infrastructure for translational and clinical research with a man-
dated pediatric component. Additional programs from other institutes and centers
are coordinating with the Clinical and Translational Science Awards program as
they evolve their own programs.
A major operational principle of all the efforts is the concept of interoperability –
the capacity to integrate technical and scientific functions on multiple levels.
Examples include standards for data acquisition, data transmission and data archiv-
ing, agreement on terminology and harmonization of definitions, and assessments
of outcome measures. The technical and scientific alignment in several domains has
been a priority for the pharmaceutical and biotech industries for over a decade and
is actively supported by and has participation of the FDA.
In the United States, most pediatric patients enrolled in clinical research studies
are referred and evaluated by academic investigators. A series of workshops and
meetings over the last decade have addressed the expectations of commercial
258 S. Hirschfeld and A. Saint-Raymond
The adoption of legislation took more time in Europe than in the USA. Despite
European publications and active lobbying by pediatricians as early as the 1980s,
the first initiative was in 1997 with the organization of a roundtable by the European
Commission; the need for legislation was identified, but more time elapsed before
the legislative initiative.
In the meantime, Europe with the USA and Japan adopted a guideline on the
development of pediatric medicines through the ICH process. This guideline was a
follower to the 1997 European guideline. This new guideline, named Clinical
Investigations of Medicinal Products in the Pediatric Population, ICH E11, became
effective in 2000 in the European Union (EU).
Made of six countries in 1957, the European Union includes an expanding number
of countries. These Member States have over the years signed various successive
Treaties creating a specific supranational environment of free circulation of
citizens, goods, and capital. The Union has progressively accumulated laws to
harmonize the internal market. To date, the EU includes 27 Member States: Austria,
Belgium, Bulgaria, Cyprus, Czech Republic, Estonia, Finland, Denmark, France,
Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, The Netherlands,
and the UK. Several countries are candidate to accession (Croatia, Former
Yugoslavian Republic of Macedonia, Turkey, and Iceland). Three more countries
from the European Economic Area/European Free Trade Area are associated with
the work of the European Union without having formally joined: Norway,
Liechtenstein, and Iceland (which has now requested accession). They apply the
same regulation of medicinal products and participate in the work of the European
Agency. The EU has currently 23 official languages (not including Norwegian and
Icelandic) among 60 regional or minority languages. All approval decisions
concerning medicines are issued in all official languages.
The European Parliament, representing the people of Europe, in consultation
with the European Council of Ministers, representing governments, usually adopt
European legislation through a co-decision procedure, but a legislative initiative is
under the sole responsibility of the European Commission. Two sets of laws can be
adopted in the European Union: Regulations and Directives. A Regulation is a law
directly applicable to Member States; a Directive is a more flexible framework,
which requires to be transposed into national law in a given timeframe. A Regula-
tion has clearly a different meaning in the USA and in the EU.
Since 1965, the EU issued various Directives regulating the authorization and
pharmacovigilance of medicines (i.e., medicinal products encompassing
biologicals, vaccines, and chemicals), medical devices, and clinical trials. In
1993, a Regulation created a European Medicines Evaluation Agency (EMEA),
since 2004 the European Medicines Agency (EMA), and established a Community
260 S. Hirschfeld and A. Saint-Raymond
1
Please note that American English spelling is used except where specific terms are referred to, as
British English spelling is generally used in Europe.
Pediatric Regulatory Initiatives 261
(Committee for Medicinal Products for Human Use, CHMP), the Committee for
Orphan Medicinal Products (COMP), the Committee on Advanced Therapies
(CAT), the Committee on Herbal Medicinal Products (HMPC), and the Paediatric
Committee PDCO. The sixth one is a Committee on veterinary medicines (CVMP).
Most Committees have set up and delegated preparatory work (e.g., guidelines) to
expert groups, the Working Parties. One is of particular relevance for the pediatric
development of medicines, the Scientific Advice Working Party, which advises
companies on their proposed development. For orphan and pediatric medicines, the
Agency staff has a direct complementary role in the evaluation. For other proce-
dures, the Agency has only a coordination role, as the evaluation is performed by
experts and regulators working in the Member States and finalized by the relevant
Committee.
Following the receipt of an Agency opinion, the European Commission takes all
administrative decisions (e.g., orphan designation) except on Paediatric Investiga-
tion Plans (PIP), which are signed into Decisions by the Executive Director of the
Agency.
The Pediatric Regulation is extremely complex and affects many other regulatory
procedures. It creates not only rewards or incentives, but also obligations for
262 S. Hirschfeld and A. Saint-Raymond
The PDCO consists of one expert member per Member State, including five
holding simultaneous membership of the approval Committee (CHMP). In addi-
tion, there are three patients’ representatives and three health professionals;
Norway and Iceland are represented (Liechtenstein has no representative). Each
member has an alternate, so currently the full Committee includes 33 members,
plus the 2 Norwegian and Icelandic members, and 35 alternates. The scope of
expertise of the Committee members is defined by the Regulation. The Committee
was established in July 2007 with a Chair elected for 3 years (renewable once). The
Committee meets once a month for 4 days and its main activity is to issue scientific
opinions on PIP and compliance; it can also provide pediatric expertise to the other
Committees of the Agency, or to the Member States.
A PIP or a request for a Waiver must be proposed at an early stage by any company
intending to apply for marketing authorization, i.e., around the end of phase 1 in
adults, and must be agreed by the PDCO. The development must aim at a full
pediatric indication including an age-appropriate formulation and timelines, and
cover all pediatric age groups, i.e., from birth to 17 years inclusive. The least
studied subset of the pediatric population, the neonate, should always be included
in the development where relevant. The scope relates to the potential pediatric use
generally close to the condition developed for adults, or the proposed pediatric
indication when adults are not affected. This is mandatory for new medicines
(biologicals, vaccines, and chemicals are all regulated by the same laws in the
EU), and when the company applies for a new indication, new route of administra-
tion, and/or a new pharmaceutical form for an active substance covered by a SPC or
by a patent, which qualifies for an SPC. The SPC is a European extension of the
patent to compensate for the unusually long development phase of medicinal
Pediatric Regulatory Initiatives 263
Similar to the USA, waivers can be obtained where pediatric development is not
necessary, but the legal basis is not identical. In the EU, the pediatric development
can be waived if the disease does not occur in children, if the product is likely to be
unsafe or ineffective in children, and/or if the product does not bring significant
therapeutic benefit, which means that the medicine would not meet an unmet
pediatric need. Development in rare conditions is not waived (unless a study
would not be feasible). In addition, systematic waivers can be issued by the
PDCO to avoid repeated administrative procedures; these are published on the
Agency pediatric webpage and can be referred to without applying to the PDCO
(Class waivers).
Although the PIP must be agreed early, the performance of studies and trials in
children can be deferred until it is safe to do so, consistent with the ICH E11
guideline.
264 S. Hirschfeld and A. Saint-Raymond
As of December 2009, after less than 2.5 years of operation more than 620
applications for PIP or a Waiver covering more than 960 conditions have been
received by the Agency. The Committee has finalized more than 200 PIP opinions
and the pediatric development has been completed for 14 medicines. The product
information for these medicines is being updated after assessment, and the first
companies can now claim the patent extension.
In the EU, an extension by 6 months of the SPC (patent extension) can be granted to
a marketing authorization holder who has not only completed the pediatric devel-
opment in conformity with the agreed PIP, but also included all results in the
Product information and obtained a marketing authorization in all Member States
of the EU. The reward can be obtained even when the results show that the product
is unsafe or ineffective in children. It can be obtained only once despite the fact that
several PIPs might still be required.
Provided the same requirements for information and authorization are met,
pediatric development of orphan medicines is rewarded by two supplemental
years of market exclusivity, in addition to the 10 years granted for medicines
intended for rare diseases in the EU.
The voluntary procedure of PUMA attracts incentives of reduced application
fees and 10-year data protection for the pediatric indication and formulation.
266 S. Hirschfeld and A. Saint-Raymond
As requested by the Regulation and based on data provided by each Member State
on all pediatric uses of medicines, the Agency is preparing a report on pediatric use
of medicines to the European Commission, who will make it available to the public.
This report will contribute to the identification of pediatric needs that the PDCO has
to consider when assessing a PIP.
In addition to the impact reports due after 6 and 10 years of operation of the
Pediatric Regulation prepared by the European Commission, the European
Medicines Agency should report every year on companies and products, which
268 S. Hirschfeld and A. Saint-Raymond
have benefited from incentives and rewards, and on those which fail to comply with
the Regulation. This information will be made public and can be considered as part
of a “naming and praising” or “naming and shaming” process to encourage com-
pliance. Additionally, financial penalties could be imposed by the Commission on
companies failing to comply, but to date the legislation on penalties has not been
updated to take account of pediatric obligations; thus, this possibility remains quite
theoretical.
2.17 Conclusions
Several years after the USA, the European Union adopted a complex law aimed at
improving the available information on medicines for pediatric use through ethical
high-quality research and increasing the overall number of medicines specifically
authorized for children. Through a stringent system of obligations compensated by
economic rewards, a dramatic change in the way medicines are developed is taking
place. This effort is placed under the sign of international collaboration with the
USA and with other regions including developing countries. These new measures
are implemented within an ethical framework to obtain evidence-based information
while protecting the children involved in research.
References
Magnus Westgren
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
2 Basic Principles for Placental transfer of Drugs and Fetal Pharmacokinetics . . . . . . . . . . . . 272
3 Different Fetal Treatment Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
3.1 Fetal Transfusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
3.2 Fetal Stem Cell Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
3.3 Fetal Analgesia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
3.4 Fetal Medical Treatment Due to Fetal Heart Arrhythmias . . . . . . . . . . . . . . . . . . . . . . . . . . 278
3.5 Corticosteroids for Accelerated Fetal Lung Maturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
3.6 Medical Treatment for Intrauterine Fetal Virus Infections . . . . . . . . . . . . . . . . . . . . . . . . . 279
3.7 Medical Treatment for Fetal Goiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
M. Westgren
Division of Obstetrics and Gynecology, Department of Clinical Science, Intervention and
Technology, Centre for Fetal Medicine, Karolinska University Hospital, Karolinska Institutet,
S-141 86 Stockholm, Sweden
e-mail: magnus.westgren@ki.se
1 Introduction
During the last decades fetal medicine has evolved from traditional obstetrics.
Cornerstones in this process have been the development of effective fetal diagnostic
means such as advanced ultrasound techniques, cytogenetics, and more recently
molecular genetics. Improved knowledge about fetal conditions has formed the
diagnostic foundation for different fetal treatment strategies.
The pioneering work within this new field was made by physicians and scientists
from New Zealand. Liley, frustrated by severely hydropic fetuses in rhesus
immunized mothers and a devastating high stillborn rate among these patients,
introduced intrauterine transfusions in 1959 (Liley 1963). He showed that it was
possible to rescue severely ill fetuses, and his contribution is not only that he
developed effective treatment but also that the human fetuses could be regarded
as a patient accessible for diagnosis and therapy.
Effective non-invasive fetal therapy was introduced by his countryman Liggins
(Liggins 1969; Liggins and Howie 1972). He reported on the effectiveness of
transplacental steroid treatment to the mother in preventing respiratory stress syn-
drome. Intrauterine transfusion and corticosteroids are still by far the most common
modalities for fetal therapy. There are continuous attempts to introduce new treat-
ment strategies, and the present chapter will give a brief review on this topic.
Most drugs move across the placenta by simple diffusion and the degree of
diffusion depends on the chemical properties and concentration of the unbound
drug (Boreus 1967; Yaffe 1980). Drugs with a molecular weight less than 1,000 are
Fetal Medicine and Treatment 273
lipid soluble and these drugs penetrate the trophoblast barrier easily and can reach
the fetal circulation readily (Juchau and Dyer 1972). With advancing gestational
age, drug transfer is increasing. Any drug in maternal blood will cross the placenta,
especially if maternal effective drug concentrations have been maintained under
extended periods (Leeder 2009). Different pathological conditions affecting the
placenta such as preeclampsia, preterm premature rupture of membranes, etc. can
affect the placental blood flow and thus placental transfer. Some drugs will be
metabolized and biotransformed in the placenta as occurs in liver. Drugs may also
induce or inhibit placental enzymes necessary for metabolic conversion of exoge-
nous substances.
For most drugs that cross the placenta fetal concentration will be 50–100% of the
mother concentration. When steady state is reached, the fetal concentration can
be higher than in the mother. The complete exposure of the drug and its metabolites
are more important than the rate of placental transportation. In the human fetus
proportionally more blood is directed to the brain, and the blood–brain permeability
is greater in the fetus than in the adult (Myllynen et al. 2009). Consequently, the
developing brain is more vulnerable to circulating drug levels. Despite preferential
circulation to the brain, the distribution eventually becomes diffuse. Plasma protein
concentration and protein binding capacity is lower in the fetus than in the mother
leading to higher unbound drug concentration. Thus, conclusions about drug dispo-
sition in the fetus based on maternal and fetal serum concentrations may not
accurately reflect true fetal pharmacokinetics.
Receptor and the strength of the receptor response for different drugs
may differ with advancing gestational age. Several fetal organs are capable of
substantial metabolic activity, but drug metabolism does preferentially take
place in the liver. Human fetal liver microsomes have significant P-450 levels
and NADPH cytochrome c reductase (Yaffe 1980). Oxidation and reduction
reaction have been observed already from the first trimester but are probably less
than in the adult. Therefore direct effects of drugs can be more prolonged in the
fetus than in the mother. The excretion in the fetus is slower than in the mother.
Primary routes for excretion are placenta and amniotic fluid. The placental
transfer of the drugs from the fetus to the mother is the primary route in early
pregnancy while drug elimination in late pregnancy depends on the immature
fetal kidneys.
The transplacental route is the standard means of administrating drugs to the
fetus. Exceptions are if the drug crosses the placenta poorly, or if the disease of
the fetus affects the placental transfer, the fetus is moribund requiring fast interven-
tion, or if severe maternal side effect can be anticipated. Direct administration to the
fetus can be performed in several ways; intraamniotically, intravascularly, intra-
muscularly, and finally intraperitoneally (Table 1). There is limited information on
how the route for direct administration affects the pharmacokinetics of different
drugs.
274 M. Westgren
Fetal transfusions were introduced in the 1960s. From the beginning, blood was
transfused into the intraperitoneal cavity, but later intravascular transfusions were
introduced. In 1984, Rodeck published a report on fetoscopically guided intravas-
cular transfusions (Rodeck et al. 1981). Later Bang introduced ultrasound-guided
fetal transfusions, and this technique is considered common practice fetal medicine
today (Bang et al. 1982). The most common sites for intravascular transfusions are
the umbilical vein close to the placental insertion, umbilical vein in a free lope, and
the intrahepatic part of the umbilical vein. The free lope approach is associated with
a higher rate of complications; i.e., bleedings into the amniotic cavity. Puncturing
of the umbilical vein is associated with certain risks, and the procedure-related
complication rate is about 3%. The most common reason for fetal transfusions is
severe erythrocyte immunization. Another well-known indication is fetal anemia
due to parvovirus infection.
Patients at risk of fetal anemia are monitored non-invasively with Doppler flow
recordings of the cerebral arteries. In case of signs of anemia (increased velocities),
the patient will undergo cordocentesis with direct measurement of fetal hemoglobin
concentration. If the fetus is anemic, a blood transfusion will be carried out. Mostly
O negative blood with high hematocrit will be used and the amount of blood
required will be calculated from the initial hemoglobin value and the size of the
fetus. Usually, repeated transfusions are required and typically a patient will
undergo treatment every second week. Most centers for fetal medicine today prefer
to perform transfusions until the 33rd–34th week. Intravascular transfusions can be
commenced as early in the 18th–19th week of gestation, and such a patient will
require 7–8 transfusions until she can be safely delivered. Depending on the degree
of anemia and if the fetus has developed hydrops survival rate differ, but most units
report survival rates in the range of 80–95% (Westgren et al. 1988; Weiner et al
Fetal Medicine and Treatment 275
1991). Long-term outcome of children treated in utero for fetal anemia is favorable,
and it is amazing how the human fetus can withstand very severe anemia.
Other blood products have been transfused for other fetal disorders. Platelets
have been administrated in cases of fetal alloimmune thrombocytopenia. The risk
for bleedings in increased in such cases, and today most fetal medicine units avoid
cordocentesis in this condition. In cases of non-immune hydrops of unknown
origin, plasma and albumin have been given to the fetus. However, this is highly
experimental and is practiced in very few centers.
The fetus and its environment are unique in many ways. This has led to the
assumption that the fetus is a potential suitable candidate for stem cell
transplantations (Touraine et al 1989; Flake and Zanjani 1999). The arguments
for fetal transplantations are the following: In some disorders the fetus is severely
affected already during fetal life. An example of such a condition is homozygous
alpha-thalassemia, almost always lethal before birth. Furthermore, from experience
with bone marrow transplantation in cases of metabolic disorders or hemoglobi-
nopathies, it is quite clear that the earlier in life a transplantation is carried out the
better the prognosis. Thus, there are many arguments favoring early stem cell
transplantation. The immunological naivety in the early gestation fetus has given
rise to the concept of fetal tolerance, i.e., the inability to raise an immunological
response against foreign antigens. During fetal life, the developing immune system
is educated to distinguish between autologous and foreign antigens. However, if
introduced early enough, foreign antigens can be recognized as self and not
rejected. Consequently, in theory it should be possible to carry out fetal stem cell
transplantations without chemotherapy and myoablation and across HLA barriers.
Furthermore, during normal fetal life, naturally occurring stem cells expand and
migrate and seed different anatomical compartments. An example of this relation-
ship is the development of hematopoietic stem cells that originally are located in
the dorsal aorta, from the 5th week in the liver and from week 12 in the bone
marrow. These different compartments provide a potential and specialized support-
ive environment for engraftment, proliferation, and differentiation of stem cells.
Exogenous administrated stem cells could possibly take advantage of these favor-
able conditions. Other arguments are that the intrauterine environment is sterile and
very protective and the small size of the fetus ensures a much larger cell dose on a
per kilogram basis than can be achieved after birth.
In-utero stem cell transplantation has been studied in several different animal
models, most extensively in mouse, sheep, canine, and primates (Zanjani et al. 1992;
Harrison et al. 1989; Blakemore et al. 2004). With few exceptions mixed chimerism
of different percentage (0.5–30%) is achieved in these models. Thus it seems
possible to perform intrauterine transplantation if it is done early during fetal life.
276 M. Westgren
In humans the experience with fetal stem cell transplantation is limited, and we
know about 50 cases reported so far. Most of these cases have been reported
adequately in previous reviews on this topic (Tiblad and Westgren 2008; Westgren
2009). The most successful group of patients transplanted in utero are those with
immunodeficiencies. Engraftment has been reported in 8 of 12 cases, and several of
these children have had a benign clinical course. In comparison with postnatal
transplantation, in-utero transplantation is associated with several advantages. It is
less expensive and the recipient does not need any chemotherapy or radiation.
Furthermore, it might reduce the risk for graft-versus-host disease, a problem
associated with SCID, and it has an obvious psychological advantage before
postnatal transplantations (Flake et al. 1996; Westgren et al. 2002).
In quite a number of cases with hemoglobinopathies and storage disorders,
intrauterine transplantation has convincingly failed (Westgren et al. 1996). In a
few of these cases engraftment has occurred but the phenotype has not been
changed. The reason why intrauterine transplantation has failed in these cases is
unclear but it seems that the human fetal immunological system is more mature than
has been anticipated and failure of transplant could also be considered. In recent
years, there are some reports on successful transplantation of mesenchymal stem
cells (MSC) for osteogenesis imperfecta (Le Blanc et al. 2005). Interestingly, some
of these transplantations have been performed across HLA barriers and rather late
during gestation. It seems that MSC have unique immunological properties and if
these results will be confirmed in larger studies MSC could be used for transplanta-
tion between mismatched individuals.
In conclusion, intrauterine transplantation is a highly experimental type of
fetal treatment. Widespread clinical application is premature based on the limited
success that has been achieved so far.
Invasive therapeutic options have drawn attention to the need of fetal analgesia.
Currently no defined evidence-based fetal anesthesia or analgesia protocol exists
for these procedures. Whether the fetus can respond to noxious stimulus with
pain is based on our current knowledge on neurodevelopment of anatomical
pathways as well as observational studies on fetal behavior at pain exposition
in utero.
It has been claimed that an intact spinothalamic connection exists as early as in
the seventh week of gestation (Lagercrantz and Changeux 2009; Derbyshire
2006). At this stage, no laminal structure is present connecting thalamus to cortex,
and without thalamic projection to the cortex the neuronal cells cannot process
noxious information from the periphery. The first projections from thalamus
to cortex appear at 12th–16th week. However, not until the 23rd–25th week
afferent neurons penetrate and form synapses to the cortex. Theoretically, the
Fetal Medicine and Treatment 277
spinothalamic projections into the cortex may provide the necessary anatomical
foundation for pain experience in the human fetus. That the human fetus is
capable to experience pain from late second trimester is also supported by several
observational studies.
Withdraw reflexes at needling procedures as a sign of nociceptial reaction can be
observed from the 19th week. Fisk et al. showed from their experience on punctur-
ing the human fetus with a needle an increase in cortisol, beta-endorphin, and
noradrenalin in cord blood from the 20th week (Giannakoulopoulos et al. 1994;
Fisk et al. 2001; Teixeira et al. 1999). In preterm children, face reactions similar to
that seen in adults experiencing pain can be observed from the 28th week (Van de
Velde et al. 2006).
Thus, there is evidence suggesting that analgesia to blunt nociceptive responses
in utero should be used from the 20th–23rd week of gestation. However, although
most centers performing invasive fetal procedures are using analgesia, there is a
general lack of information on how it may be safely and effectively administrated.
Opioid agonists have been widely used and have been given directly intravenously
to fetuses before open surgery. Direct administration into the intravascular space of
the fetus is known to be associated with certain risks. Direct intravenous adminis-
tration has later in most centers been replaced by intramuscular administration, but
due to slower absorption this will prolong the procedure and might require multiple
injections of the fetus (Van de Velde et al. 2006). In our center, we have since more
than a decade used intraperitoneal administration for administration of different
pharmacological agents at invasive procedures (cisatracurare 0.30 mg/kg, alfentanil
0.015 mg/kg) after the 20th week of gestation. The intraperitoneal cavity is easy
to puncture and rapid absorption enables us to perform fetal procedures within
5 min after administration without any sign of fetal distress. Other routes to
consider is intra amniotic where it was recently shown that intra-amniotic sufentanil
is easily absorbed by the sheep fetus and it was suggested that this route might
provide a simple and fast method for fetal analgesia (Van de Velde et al. 2005;
Strumper et al. 2003).
Different fetal procedures may require a different type of analgesia. In open fetal
surgery, inhalation agents to the mother provide effective maternal and fetal
analgesia and anesthesia. In addition, uterine relaxation is often obtained by these
agents. Most endoscopic procedures are performed under regional or local maternal
analgesia. If analgesia and paralysis of the fetus are required, this is usually
obtained by injection of opioids and/or muscle relaxants. If only immobilization
of the fetus is wanted during the procedure, maternally administrated remifentanil
resulted in effective maternal sedation and fetal immobilization.
The potential benefit of the fetus with analgesia and anesthesia needs to be
balanced against the risk for the mother. In such equation it is important to consider
the old obstetric dictum that the mother’s life should always be at highest priority.
Finally, we are lacking information on long-term outcome of fetuses exposed for in-
utero procedures. In this context pain experience during fetal life is an area of
concern that requires much more attention in the future.
278 M. Westgren
The most common reason for medical treatment is fetal tachycardias. It is defined as
a tachycardia of non-sinus origin with a heart frequency exceeding 180–200 beats
per minute. There are several variants with different electrophysiological back-
ground and prognosis. The most common is an atrioventricular re-entry tachycardia
caused by the presence of an accessory pathway between the atrium and the
ventricle. Another type is the one with atrium flatter with re-entry in the atrium
wall. Altogether these two types represent approximately 95% of all cases of fetal
tachycardias (Simpson and Sharland 1998; Carvalho et al. 2007; Krapp et al. 2003).
Usually the mother will not experience any symptoms and the high fetal heart
rate is picked up at a routine antenatal check-up in weeks 28–34. In some cases, the
fetus has developed signs of heart failure with polyhydramniosis and/or reduced
fetal movements. Ultrasound examination will in a third of these cases reveal
increased amount of fluid in the fetus or in more severe cases full blown hydrops.
The reason for the heart failure is an impaired diastolic filling of the ventricules
when the heart rate increases. Consequently, cardiac output decreases and the
intraatrial and central vein pressure increases. The increased pressure in the atria
predisposes for atrial flatter.
Management of fetal tachycardia requires knowledge about the electrophysiologi-
cal background and the hemodynamic situation of the fetus. The degree of heart
failure or hydrops will be in most cases an important denominator for prediction of
the prognosis. Other issues to consider are if the tachycardia is continuous or
intermittent, frequency of the ventricles, relationship between atrial and ventricular
systolic phase, heart malformations, and finally the gestational age. If the fetus has no
hemodynamic signs of heart failure, different options can be considered. Maternal
medication and treatment across the placenta, direct therapy to the fetus, delivery and
treatment of the newborn, or if tachycardia is intermittent just to observe. To deliver a
fetus with heart failure is usually a worse alternative than treating the fetus in utero.
In absence of hydrops, first line drug is digoxin. In many cases digoxin needs to
be combined with sotalol or flecainide (Oudijk et al. 2000; Jaeggi et al. 2004).
Approximately 85% of the cases will convert to normal heart rate on this treatment,
and these children will do well. In fetuses with hydrops there is poor transplacental
passage of digoxin, and in these cases sotalol is to be recommended. Another option
is to treat the fetus with direct dixoxin administration.
Fetal bradycardia is defined as a heart rate less than 100 bpm. Short episodes of
bradycardia is a common phenomenon and of no significance. In cases of continued
ventricular arrhythmia, treatment with beta blockers could be considered. A severe
form of bradycardia is due to a complete A–V block. In approximately 50% of these
cases, it is combined with heart malformations. In cases with no malformations,
the condition is usually caused by anti-Ro and Anti-L antibodies (Bergman et al.
2009; Strandberg et al. 2008). Transplacental treatment with digoxin for improve-
ment of ventricular contractions, beta stimulator for increasing the heart rate and
dexamethasone for anti-inflammation could be considered in these cases.
Fetal Medicine and Treatment 279
Fetal goiter may be associated with hypo- or hyperthyroidism. With high resolu-
tion ultrasound the thyroid gland can easily be visualized and consequently most
cases of fetal goiter are diagnosed in utero (Ballabio et al. 1989). Congenital
hypothyroidism is rare and is mostly caused by thyroid dysgenesis. Transient fetal
hypothyroidism is usually caused by maternal antithyroid drug intake, commonly
carbimazole or propylthiouracil due to Grave’s disease. Fetal hyperthyroidism
is usually caused by maternal Grave’s disease. Some of these mothers have
thyroid-stimulating immunoglobulins, and sometimes these stimulating immuno-
globulins cross the placenta and may activate fetal TSH receptors (Mitsuda et al.
1992).
Timely diagnosis and treatment are important in cases of fetal thyroid
disturbances. The diagnosis of fetal goiter is usually quite straightforward. It
warrants a thorough evaluation of other thyroid-associated manifestations such as
tachycardia, polyhydramniosis, and growth restriction.
Fetal thyroid status can be assessed by cordiocentesis and direct blood sampling.
If the fetal goiter is found in an euthyroid mother, it is usually possible to treat the
mother with antithyroid drugs and get a good response in the fetus. However, the
mother usually needs T4 supplementation during the treatment. If the fetal goiter
is diagnosed in a mother with Grave’s disease it is necessary to evaluate if the
goiter is a result from transplacental passage of thyroid-stimulating antibodies. At
concomitant fetal hyperthyroidism, the mother usually requires higher doses
of antithyroid drugs. In cases of need for T4 supplementation to the fetus,
direct administration of thyroid hormones can be carried out by intra-amniotic,
intravascular or intramuscular routes. Since the fetus in this situation often requires
repeated injections the intra-amniotic route is preferable. Adequate fetal thyroid
replacement therapy can be achieved by intra-amniotic administration of
250–500 mg T4 at 7–10 days intervals.
Fetal Medicine and Treatment 281
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Gideon Koren
Contents
1 Principles of Teratology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
2 Confounding Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
2.1 Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
2.2 Bias by Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
2.3 Time of Enrollment as a Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
2.4 Bias in Retrospective Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
2.5 Recall Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
2.6 Bias in Not Including Elective Abortion Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
2.7 Bias in Retrospective Ascertainment of Maternal Lifestyle . . . . . . . . . . . . . . . . . . . . . . . . . 291
2.8 Bias Against the Null Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
G. Koren (*)
The Motherisk Program, Division of Clinical Pharmacology and Toxicology, Hospital for Sick
Children, University Avenue 555, Toronto M5G 1X8, ON, Canada
e-mail: gidiup_2000@yahoo.com
1 Principles of Teratology
Congenital defects occur in 1–3% of the general population. Of the major defects,
about 25% are of genetic origin (genetically inherited diseases, new mutations and
chromosomal abnormalities) and 65% are of unknown etiology (multifactorial,
polygenic, spontaneous errors of development and synergistic interactions of
teratogens). Only 2–3% of malformations are thought to be associated with drug
treatment (Table 1). The remaining defects are related to other environmental
exposures including infectious agents, maternal disease states, mechanical
problems, and irradiation (Koren et al. 1998).
The importance of timing of drug exposure is critical; the effect produced by
a teratogenic agent depends upon the developmental stage in which the conceptus is
exposed. The following phases in human development must be recognized:
• The “all or none” period, the time from conception until somite formation.
Insults to the embryo in this phase are likely to result in death and miscarriage
or intact survival. The embryo is undifferentiated, and repair and recovery are
possible through multiplication of the still totipotential cells. Exposure to
teratogens during the presomitic stage usually does not cause congenital
malformations unless the agent persists in the body beyond this period.
• The embryonic period, from 18 to 60 days after conception when organogenesis
occurs. This is the period of maximum sensitivity to teratogenicity since tissues
are differentiating rapidly and damage becomes irreparable. Exposure to terato-
genic agents during this period has the greatest likelihood of causing a structural
anomaly. Critically because half of all pregnancies are unplanned, many women
taking drugs at that stage are not aware of their risks.
• The fetal phase, from the end of the embryonic stage to term, when growth and
functional maturation of formed organs and systems occurs. The only organ that
continues to differentiate until birth is the brain and hence ethanol and drugs of
abuse may adversely affect the fetal brain at any stage. Teratogen exposure in
this period will affect fetal growth (e.g., intrauterine growth restriction) and the
size or function of an organ, rather than cause gross structural anomalies.
Many organ systems continue structural and functional maturation long after
birth. Most of the adenocarcinomas associated with first trimester exposure to
diethylstilbestrol occurred many years later.
Teratogens must reach the developing fetus in sufficient amounts to cause their
effects. Large molecules with a molecular weight greater than 1,000 (e.g., heparin)
do not easily cross the placenta into the embryonic–fetal bloodstream. Other factors
influencing the rate and extent of placental transfer of drugs include polarity, lipid
solubility, and the existence of a specific protein carrier (e.g., P-glycoprotein).
Every year scores of new pharmaceuticals enter the market, almost never with
human fetal safety data. Such data typically accumulate during the first years of
clinical use, in the form of case reports, case series, prospective and retrospective
cohorts, and case control studies. All of these methods suffer from serious sources
Fetal Risks of Maternal Pharmacotherapy: Identifying Signals 287
Table 1 (continued)
Drug Adverse effects
Hydantoins (phenytoin) Fetal hydantoin syndrome: craniofacial dysmorphology, anomalies and
hypoplasia of distal phalanges and nails, growth restriction, mental
deficiency, and cardiac defects
Lithium Small increase in risk for cardiac teratogenesis in early gestation (1%).
The risk of Ebstein’s anomaly exceeds spontaneous rate of
occurrence. Fetal echocardiography if exposed in first trimester
Misoprostol First trimester exposure: limb defects and Moebius sequence. Absolute
teratogenic risk: probably low. Uterine contraction inducing activity
Retinoids (acitretin, Systemic exposure: potent human general and behavioral teratogen.
isotretinoin) and Retinoic acid embryopathy: craniofacial anomalies cardiac defects,
megadoses of abnormalities in thymic development and alterations in CNS
vitamin A development. Risk for associated miscarriage: 40%
Tetracyclines Discoloration of the teeth after 17-week gestation when deciduous teeth
begin to calcify. Close to term: crowns of permanent teeth may be
stained. Oxytetracycline and doxycycline associated with a lower
incidence of enamel staining
Thalidomide Malformations limited to tissues of mesodermal origin, primarily limbs
(reduction and defects), ears, cardiovascular system and gut
musculature. Critical period: 34th–50th day after the beginning of
the last menstrual period. A single dose of <1 mg/kg has produced
the syndrome. Embryopathy found in about 20% of pregnancies
exposed in the critical period
Valproic acid First trimester exposure: neural tube defects with 1–2% risk of
meningomyelocele, primarily lumbar or lumbosacral,
cardiovascular malformations and hypospadias. Fetal valproate
syndrome: craniofacial dysmorphology, cardiovascular defects,
long fingers and toes, hyperconvex fingernails and cleft lip, has been
delineated by some investigations. Neurobehavioral teratogen
2 Confounding Effects
Major birth defects are relatively rare, accounting on average to 1–3% of all births.
Hence large numbers are needed to show excess risk at alpha of 5% and beta of
80%. For example, 800 women are needed in a two arm study to show a doubling
of major malformations. The situation is much more complex in trying to quantify
major malformation (rather than all of them lumped together). For example, neural
tube defects occur in 1:1,000 births. Valproic acid increases that risk to 20:1,000.
Hence, hundreds of cases of maternal exposure to valproic acid during the first
28 days post conception may be needed to be able to document a difference from
baseline risk.
The vast majority of cohort studies published to date are underpowered to
show significant differences, a problem acknowledged by many of their authors.
A common way to overcome this issue is synthesizing similar studies into meta-
analysis, thus gaining a large sample size. As would be expected, lumping studies
together into meta-analysis introduces its own set of issues, some of which will be
addressed herein, including heterogeneity among studies, not being able to control
for confounders, and under-reporting of negative studies [i.e., those showing no
excess in adverse effects (Einarson et al. 1988)].
Women taking medications during and after conception often suffer from con-
ditions which, per se, may affect pregnancy outcome. For example, chronic hyper-
tension in pregnancy is associated with high risk of prematurity, unrelated to which
drug is used to treat the hypertension. We have recently shown that hypertensive
women have above 20% rates of prematurity in their offspring, whether treated with
labetolol or methyldopa, as compared to only 4% among healthy controls (Nulman
et al. 2010).
This source of bias can often be corrected by having, in addition to the drug
exposed group and healthy control groups, an additional group with the same
condition, treated with another pharmaceutical.
290 G. Koren
Many administrative database studies do not have data on findings among women
who had elected to have an abortion. Rather, they report of “liveborn infants.” Levy
and colleagues hypothesized that a significant number of elective abortions are
performed to date due to a major malformation diagnosed in utero. By not having
such data, one takes the risk of missing a signal. Using the example of antifolates in
pregnancy, known to increase the risk of neural tube defects, Levy et al. have
showed that in their cohort such an association was apparent only when elective
abortion data were considered too, but not when only live births were counted
(Levy et al. 2009).
Alcohol, maternal smoking and other drugs of abuse may increase fetal risks, both
in terms of birth defects, as well as in terms of prematurity, intrauterine growth
retardation, miscarriage, still birth, and developmental teratogenicity.
292 G. Koren
Due to shame, guilt, and fear of losing custody of a child, it is conceivable that
women experiencing adverse effects in their offspring may underreport on drugs
and alcohol abuse. This hypothesis was proven by Wong et al., studying a cohort of
women who were counseled by a teratology information service during the first
trimester of pregnancy. In particular, their reports on cigarette smoking were
probed. When re-interviewed after the birth of the child, women who had healthy
babies reported again very similar patterns of smoking as they had done originally.
In contrast, women giving birth to offspring experiencing adverse outcome tended
to minimize the numbers of cigarettes consumed when compared to their original
reports (Wong and Koren 2001). This type of bias may seriously impair studies on
the effect of alcohol, cigarettes, and drugs of abuse by introducing misclassification,
i.e., women who smoked are erroneously classified as non smokers.
Bias against the null hypothesis occurs when “positive” studies (e.g., showing
a drug to be teratogenic) are more likely to be submitted for scientific meetings
and journals, to be presented, published, and publicized than “negative” studies
(e.g., those suggesting the pharmaceutical is safe). The seriousness and pervasive-
ness of this bias has been shown at each step of the act of reporting results.
Investigating the fate of studies submitted to the Oxford University ethics
committee, Easterbrook and colleagues have shown that “negative” studies were
significantly less likely to be submitted or published in peer reviewed journals. Of
interest, this was not only due to the journals rejecting them more (Easterbrook
et al. 1991), but also due to the perception of the investigators that their studies are
less likely to be accepted. More related to adverse pregnancy outcome, we have
shown that abstracts failing to identify reproductive risks of cocaine were less likely
to be accepted by the Society for Pediatric Research than “positive” studies, despite
the negative studies being overall of better quality (Koren et al. 1989).
The bias against the null is further augmented by the lay media, which tends to
publicize significantly more “positive” studies than “negative” ones. This grim
reality was documented unequivocally in the case of two studies published back
to back by the Journal of the American Medical Association. In 1992, JAMA
published two studies dealing with the risk of radioactive exposure (Koren and
Klein 1991). A study on the fate of several thousand workers in Oakridge develop-
ing the American Atomic bomb in the 1940s has shown increased risk of leukemia.
In contrast, a study investigating whether residing near nuclear energy plants failed
to show excess of cases of cancer. Despite similar exposure in the journal, the
“positive” study was cited by the lay media significantly more often (Koren and
Klein 1991).
It is now evident that the bias against the null hypothesis is pervasive and
encompasses every step of the production of new knowledge, starting with the
Fetal Risks of Maternal Pharmacotherapy: Identifying Signals 293
3 Conclusions
Due to the inability to collect safety fetal data of sufficiently high quality, assess-
ment of pharmaceutical molecules is one of the most challenging areas of
pharmacoepidemiology.
It will be important to continue and refine the methodology involved in this quest
for critical data, to avoid misinformation, which may lead to both unwarranted
anxiety, as well as unjustified sense of safety.
It is critical to remember that physicians and patients, alarmed by an impression
or perception of teratogenic risk may take extreme measures of either terminating
an otherwise wanted pregnancy (Koren and Pastuszak 1990), or avoiding treatment
even in life-threatening situations (Cohen et al. 2006). We must facilitate a new
climate, where this practice is evidence based.
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Torbj€
orn Tomson and Dina Battino
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
2 Teratogenic Effects of AEDs: Methodological Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
3 Growth Retardation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
4 Minor Anomalies and Dysmorphisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
5 Major Congenital Malformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
5.1 Overall Malformation Rates with AEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
5.2 Specific Malformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
5.3 Comparative Malformation Rates with Different AEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
6 Postnatal Cognitive Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
7 Dose-Dependency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
8 Mechanisms of Teratogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
T. Tomson (*)
Department of Clinical Neuroscience, Karolinska Institutet, S-171 76 Stockholm, Sweden
e-mail: torbjorn.tomson@karolinska.se
D. Battino
Department of Neurophysiopathology and Epilepsy Centre, IRCCS Foundation Carlo Besta,
Neurological Institute, Milan, Italy
1 Introduction
The first report on possible human teratogenic effects of antiepileptic drugs (AEDs)
was published more than 40 years ago (Meadows 1968). Meadows reported six
children with orofacial clefts, some with additional abnormalities of the heart and
face, all of whom had been exposed to AEDs in utero. Treatment was mainly
different combinations of phenobarbital, phenytoin and primidone. In a subsequent
retrospective survey of more than 400 pregnancies with epilepsy Speidel and
Meadow (Speidel and Meadow 1972) found a twofold increase in malformation
rate among children of mothers with epilepsy exposed to AEDs. A specific associ-
ation between trimethadione and a very high prevalence of malformations was also
reported early (German et al. 1970). Since then numerous studies with different
methodologies have reported increased rates of teratogenic outcomes in mothers
with epilepsy (Harden et al. 2009; Meador et al. 2008; Tomson and Battino 2005;
Tomson and Hiilesmaa 2007). These adverse outcomes include major congenital
malformations, minor anomalies and dysmorphism, growth retardation, and
impaired cognitive development. In addition to trimethadione, all of the major
old generation AEDs such as phenobarbital, phenytoin, valproate and carbamaze-
pine, have been reported to be associated with increased risks for major congenital
malformations, while less is known about the teratogenic potential of the newer
generation AEDs that have been introduced to the market during the last 20 years.
Epilepsy is a condition characterised by the occurrence of recurrent epileptic
seizures, with potentially serious consequences. Uncontrolled seizures significantly
affect the quality of life of the patient with epilepsy, and major convulsive seizures
could be harmful and occasionally even fatal (Tomson et al. 2004a). In addition to
these harmful effects on the person with epilepsy, maternal seizures during preg-
nancy may also adversely affect the foetus (Tomson and Hiilesmaa 2007). Hence,
the potential adverse outcomes in the offspring due to maternal use of AEDs need to
be weighed and balanced against the risks associated with the underlying disease
itself. In epilepsy, the maternal and foetal risks with uncontrolled major convulsive
seizures are generally considered to outweigh the teratogenic risks with AEDs.
Treatment is therefore maintained also during pregnancy in women with active
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 297
Many different methods have been used to assess the foetal risks associated with
exposure to AEDs. The first years after the initial report on possible teratogenic
effects of AEDs saw many publications of case-series of adverse pregnancy
outcomes collected in individual centres or regions. A slightly more systematic
method is spontaneous reporting of pregnancy outcome to the manufacturers,
to drug agencies or surveillance programmes. Such methods can be useful in
providing signals. However, reporting is selective, and since information on the
denominator (total number of pregnancies exposed to the drug) is missing, these
methods cannot be used for a proper risk assessment.
Case–control designs are generally considered useful for assessment of uncom-
mon outcomes, such as birth defects. Cases with malformations are compared to
controls regarding exposure to AEDs in foetal life. The method has been used
to study the association between some specific malformations and exposure to
individual AEDs, e.g. neural tube defects and exposure to valproate and oral clefts
and lamotrigine. Case–control studies have also been utilised to analyse exposure
to different AEDs and congenital abnormalities in general (Kjaer et al. 2007).
A drawback of case–control studies is the risk of recall bias. Mothers of children
with malformations are more likely to report drug intake during pregnancy.
Other studies have utilised existing general registries. Information on exposure
could be obtained from a national drug prescription database (Artama et al. 2005) or
from other registries that systematically and prospectively obtain information on
drug intake in early pregnancy. The Swedish and Norwegian Medical Birth
Registries are examples of the latter. These can be crosslink with registries of
birth defects to assess the association between use of AEDs in early pregnancy
and adverse outcome (Veiby et al. 2009; Wide et al. 2004). Such registries can have
the advantage of recording exposure before pregnancy outcome is known and in
addition being population-based, nationwide and thus representative. Contrarily,
they often lack details on important information such as drug dosage, indication for
treatment and classification of epilepsy, seizure control during pregnancy and on
other factors that could contribute to the outcome. Furthermore, the teratogenic
298 T. Tomson and D. Battino
outcome might not be classified according to uniform criteria and the assessor of the
child might be influenced by information on drug intake during pregnancy.
Another common approach is cohort studies of pregnancies in women with
epilepsy. Retrospective cohort studies (where women are included at a time when
pregnancy outcome might be known) are associated with a risk of selection bias.
This is avoided in prospective studies where women ideally are identified and
enrolled in early pregnancy before any information on pregnancy outcome is
known. Such studies have traditionally often been hospital based and many studies
based on cohorts from single hospitals or epilepsy centres or from several
collaborating clinics were published in the 1980s and 1990s (Tomson et al.
2004b). Additional advantages with such prospective cohort studies is that they
usually have a reliable classification and details on the mothers’ epilepsy, the course
of the epilepsy during pregnancy and on other potential risk factors. The major
disadvantage is that they represent selected epilepsy populations, probably more
severe cases under specialist care. A further major limitation has been in the
number of included pregnancies, often a few hundred and at best a thousand
pregnancies (Tomson and Battino 2005).
Special types of cohort studies, antiepileptic drugs and pregnancy registries,
were established in the late 1990s and have thus now been operational for more than
a decade (Tomson et al. 2010). These registries are prospective observational
studies enrolling women with epilepsy early in pregnancy collecting information
on drug exposure and other potential risk factors before outcome of the pregnancy
is known. Women are followed throughout pregnancy and the outcome in terms of
occurrence of birth defects in the offspring is recorded. The advantage of such
studies is that they may collect high numbers of pregnancies, the type of drug
exposure is recorded in an unbiased way without prior knowledge of teratogenic
outcome, and detailed data on other relevant patient characteristics could be
obtained. They share the limitations of many previous cohort studies in being
based on selected patients, which hampers the possibilities to generalize from the
results and although they share many methodological features, there are also
significant differences between them (Tomson et al. 2010).
The aforementioned studies are designed primarily to evaluate the risk of major
congenital malformations. Assessment of postnatal cognitive development poses
further difficulties and challenges. An extended follow-up is necessary. By this,
however, environmental factors such as psycho-social factors, including maternal
education, cognitive status and epilepsy may all affect the child’s performance. The
assessor needs to be blinded and appropriate controls included.
Even results of prospective studies of teratogenic effects of AEDs may be
difficult to interpret. For obvious reasons, women considering pregnancy have not
been randomised to different types of treatment. The selection of a particular
treatment depends on individual environmental and genetic factors that could be
linked to the risk of adverse pregnancy outcome. An association between exposure
to a certain AED and occurrence of adverse pregnancy outcome in an observational
study is thus not evidence of a causal relationship. The impact of possible
confounders, such as type of epilepsy, seizure frequency, family history of birth
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 299
defects and exposure to additional risk factors needs to be assessed, which requires
large sample sizes. It is thus important to pay attention to methodological issues
such as statistical power, reliability of collected data, and attempts to control for
appropriate confounding factors in the analyses, rather than to just compare rates
of adverse pregnancy outcome in published studies.
3 Growth Retardation
Reduced birth weight, body length and head circumference in the offspring of
women treated with phenytoin was reported already in the 1970s (Hanson et al.
1976). Such reductions in body dimensions were confirmed in subsequent studies of
larger cohorts (Battino et al. 1992, 1999; Dessens et al. 2001; Hiilesmaa et al. 1981;
Wide et al. 2000). In general, more pronounced effects were found in infants
exposed to polytherapy, whereas the association between reduced body dimensions
and specific AEDs in monotherapy varies. Phenobarbital and primidone have been
implicated, whereas others have reported carbamazepine to be most strongly
associated with small head circumference. A population-based Swedish study
spanning 25 years, found a clear trend towards normalization of the head circum-
ference in parallel with a shift from polytherapy towards monotherapy despite an
increasing use of carbamazepine (Wide et al. 2000). Other more recent studies also
suggest that, with present treatment strategies, microcephaly may no longer be
more common among infants of mothers treated for epilepsy during pregnancy
(Choulika et al. 1999). A very recent populations-based nationwide Norwegian
study found low birth weight, small for gestational age, and small head circumfer-
ence to be significantly more common in infants of mothers with epilepsy compared
to the general population (Veiby et al. 2009). However, small for gestational age
was more common in the offspring of mothers with epilepsy whether the mothers
were taking AEDs or not.
A committee of the American Academy of Neurology and the American Epi-
lepsy Society recently reassessed the evidence related to the care of women with
epilepsy during pregnancy (Harden et al. 2009). The committee concluded that
neonates of women with epilepsy taking AEDs probably have an increased risk of
small for gestational age about twice the expected rate.
(Puho et al. 2007). Recent data from the North American AED Pregnancy Registry
suggested a tenfold increase in risk of oral clefts among lamotrigine exposed infants
(Holmes et al. 2008a), but this specific association has not been confirmed in other
registries (Dolk et al. 2008; Holmes et al. 2008a). Exposure to phenobarbital has
been suggested to increase the risk of cardiac malformations (Canger et al. 1999).
For reasons discussed above, women with active epilepsy will need continued
treatment throughout pregnancy. The relative safety during pregnancy is therefore
a major criterion for selection of an AED for a woman with epilepsy who is of child-
bearing potential. Large studies are needed to draw conclusions on the relative
teratogenic potential of different AEDs as the prevalence of birth defects with
AEDs fortunately is no more than 4–10%. However, surprisingly few studies in
the past have comprised more than 500 pregnancies in total. Clearly much larger
cohorts are needed to permit a meaningful assessment of individual AEDs. During
the last decade, some different strategies have been applied to achieve this.
One method, which has been used in the Nordic countries, is to utilise different
existing national registries and databases for the purpose of assessing the safety of
AED use in pregnancy. One example is the Swedish Medical Birth Registry, a
nationwide population-based health registry compiled from antenatal maternal health
clinic records, and those of the delivery and maternity wards. Drug exposure is
recorded at the first visit to the maternity health clinics (typically gestational week
9). Pregnancy outcome is assessed based on registries of birth defects. A report from
this registry was based on 1,398 pregnancies with exposure to AEDs (Wide et al.
2004). The odds ratio (OR) for having a malformation in the AED-exposed offspring,
compared with the expected estimate from all infants born, was 1.86 (1.42–2.44)
overall. OR in monotherapy exposed was 1.61 (1.18–2.19), and in polytherapy 4.20
(2.42–7.49). The OR was higher after exposure to valproate monotherapy compared
with carbamazepine monotherapy 2.59 (1.43–4.68).
Another nationwide population-based study utilized the Finnish drug prescrip-
tion database and the National Medical Birth Registry to identify all women who
were prescribed AEDs during pregnancy (Artama et al. 2005), including 1,411
pregnancies with AED exposure. Congenital malformations were more common
among offspring of these women (4.6%) than among offspring of untreated patients
with epilepsy (2.8%). Compared with untreated patients, the risk of malformations
was higher in foetuses exposed to valproate monotherapy (malformation rate
10.7%; OR ¼ 4.18; 2.31–7.57) or valproate as part of polytherapy (malformation
rate 9.2%; OR ¼ 3.54; 1.42–8.11). In contrast, the risk of malformations was not
elevated in association with exposure to carbamazepine, oxcarbazepine, or phenyt-
oin monotherapy.
A third example is a recent study from Norway. The nationwide compulsory
Medical Birth Registry of Norway was surveyed from 1999 to 2005 (Veiby et al.
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 303
2009). A total of 961 pregnancies with AED exposure were identified. An increased
risk for major congenital malformations compared to unexposed could be
demonstrated only for valproate monotherapy (5.6 vs. 2.5% in the general popula-
tion) and AED polytherapy (6.1%).
The advantage of these studies is that they are population based and the results
are likely to be representative. However, they lack detail concerning other potential
risk factors, e.g. the indication for treatment and type of epilepsy, seizure control
during pregnancy, AED dosage and other. Pregnancies ending in elective abortions
are also not included even if the indication was foetal abnormalities. Most impor-
tantly, although nationwide, the number of included pregnancies on different
specific AEDs is too small to permit a more precise comparison of their teratogenic
potential.
In order to facilitate enrolment of greater numbers of pregnancies with AED
exposure, and thus more meaningful comparisons, different groups established
specific Epilepsy and Pregnancy Registries in the late 1990s (Tomson et al.
2010). Some were set up by pharmaceutical companies and collect data on the
manufacturers’ own product (e.g. GlaxoSmithKline’s International Lamotrigine
Registry) (Cunnington et al. 2007). Others have been established by independent
research groups and include information on all AED exposures. These are national,
regional (e.g. Australia, UK, North America, Kerala, India) or broadly international
(European and International Registry of Antiepileptic Drugs in Pregnancy,
EURAP). Many of the registries have now been operational for more than
10 years and are beginning to release results.
Malformation rates reported from pregnancy registries and from some other
larger and contemporary studies are presented for the five most frequently used
AEDs (valproate, carbamazepine, lamotrigine, phenobarbital and phenytoin) in
Table 1.
In the absence of a comparator, the results from the company-sponsored
registries are difficult to interpret. However, GlaxoSmithKline’s International
Lamotrigine Pregnancy Registry reported a malformation rate of 2.9% based on
802 monotherapy exposures (Cunnington et al. 2007).
The largest independent AED and pregnancy registries are The North American
Antiepileptic Drugs and Pregnancy Registry (NAAPR), the United Kingdom Epi-
lepsy and Pregnancy Register, and EURAP, an international registry enrolling
pregnancies from more than 40 countries, in Europe, Australia, Asia, Oceania and
South America (Tomson et al. 2010). These registries have enrolled 6,000–14,000
pregnancies and two of them, NAAPR and the UK register, have published results
on teratogenic outcome. These three registries are slightly different in their scope
and differ significantly in their methodologies, which should be kept in mind when
malformation rates are compared across the registries.
NAAPR has reported increased malformation rates in comparison with the
general population with phenobarbital monotherapy (6.5%), relative risk (RR) 4.2
(1.5–9.4) (Holmes et al. 2004), and valproate (10.7%) RR 7.3 (4.4–12.2)
(Wyszynski et al. 2005). The malformation rate was 2.8% with lamotrigine
monotherapy (Holmes et al. 2008a), 2.5% (n ¼ 873) with carbamazepine and
304 T. Tomson and D. Battino
with rates ranging from 2.2 to 7.9%, lamotrigine from 1.4 to 4.9%, phenytoin from
0.7 to 9.1%, and valproate from 5.7 to 13.3% (Table 1). The wide ranges in
malformation rates reflect differences in study populations, criteria and methodol-
ogy. Prevalences of malformations with different AEDs should therefore not be
compared across studies. However, there appears to be a consistent pattern within
studies with higher rates with valproate and lower rates with carbamazepine and
lamotrigine (Table 1). Even within-study comparisons should be made with caution
considering the possible effects of confounding factors.
There is very limited published data on pregnancy outcome with other new
generation AEDs than lamotrigine. Malformation rates in reports based on prospec-
tive pregnancies with monotherapy exposure to newer generation AEDs other than
lamotrigine, such as gabapentin, topiramate, levetiracetam, oxcarbazepine and
zonisamide, are shown in Table 2. Even when pregnancies from all available
studies are added up, the total number of monotherapy exposures for each of
gabapentin, topiramate, levetiracetam, oxcarbazepine is limited to approximately
250–300 pregnancies, and much less for zonisamide. Clearly these numbers are too
small for a reliable assessment of the risks.
In their recent evidence-based review, the American Academy of Neurology and
the American Epilepsy Society Committee concluded that it is highly probable that
valproate exposure during the first trimester is associated with higher risk of major
congenital malformations compared to taking carbamazepine, and possibly
During the past 3 decades, several studies with different designs have aimed at
assessing whether exposure to AEDs in utero could also adversely affect the cogni-
tive development of the child after birth. Such studies are complicated to perform,
requiring long-term follow-up. But they are also difficult to interpret because of
confounding (e.g. parental cognitive function, socio-economic circumstances, mater-
nal epilepsy) and in particular since environmental factors become more important
with increasing age of the child. Few studies have been published, and mostly based
on small cohorts. Studies from the 1980s and 1990s have aimed at assessing
phenobarbital and more often phenytoin and carbamazepine, the most frequently
used AEDs at that time. A prospective population-based study from Helsinki, Finland
found no influence of AED (mainly phenytoin and carbamazepine) exposure on
global IQ (Gaily et al. 1990). Observed cognitive dysfunction was attributed to
maternal seizures and educational level of the parents rather than to the treatment.
A Swedish population-based prospective study found no difference in psychomotor
development in children exposed to carbamazepine compared with control children
of healthy mothers, but a trend for phenytoin exposed children to do slightly worse in
some tests of motor coordination (Wide et al. 2002). Scolnik et al. (1994) reported
lower global IQ in children exposed to phenytoin but not in those exposed to
carbamazepine.
A Cochrane Review from 2004 concluded that at that time there was little
evidence about which drugs carry more risks than others to the development of
children exposed (Adab et al. 2004b). Some subsequent studies, however, have
suggested that exposure to valproate might carry a particular risk of adverse
developmental effects (Adab et al. 2001; Meador et al. 2009; Vinten et al. 2005).
A retrospective survey from the UK found additional educational needs to be more
common among children that had been exposed to valproate than in those exposed
to carbamazepine or unexposed control children (Adab et al. 2001). A more detailed
investigation revealed lower verbal IQ in those exposed to valproate than in
unexposed children and children exposed to carbamazepine or phenytoin (Adab
et al. 2004a; Vinten et al. 2005). Multiple regression analysis identified exposure to
valproate, frequent tonic-clonic seizures in pregnancy and low maternal IQ to be
associated with lower verbal IQ also after adjustment for confounding factors.
Given the retrospective design, small numbers and poor participation rate, the
results need to be interpreted with some caution. However, some subsequent
prospective studies report similar observations concerning valproate. Hence, a
small population-based prospective study from Finland found a lower verbal
IQ in children exposed in utero to valproate monotherapy (n ¼ 13) and to
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 307
7 Dose-Dependency
A dose–effect relationship has so far been shown most consistently for teratogenic-
ity in association with valproate. Dosages above 800–1,000 mg/day have thus been
associated with significantly greater risks than lower dosages (Artama et al. 2005;
Kaneko et al. 1999; Morrow et al. 2006; Samrén et al. 1997, 1999; Vajda et al.
2007). Data on cognitive outcome reveal a similar pattern. The retrospective study
from Liverpool found that verbal IQ was no different from unexposed controls
among children exposed to valproate doses <800 mg/day (Vinten et al. 2005).
Likewise, the prospective NEAD study found IQ of children whose mothers took
valproate in doses <1,000 mg/day to be similar to IQs in those exposed to other
AEDs (Meador et al. 2009).
The UK Epilepsy and Pregnancy Register reported a positive dose response for
major congenital malformations also for lamotrigine. Doses above 200 mg/day
were associated with higher risks (Morrow et al. 2006). This pattern was, however,
not found in the International Lamotrigine Registry of GlaxoSmithKline, nor did
the North American pregnancy registry find lamotrigine doses to be significantly
higher in mothers to children with malformations than in mothers to healthy
children (Cunnington et al. 2007).
The American Academy of Neurology and the American Epilepsy Society
Committee concluded that there is probably a relationship between the dose of
valproate and lamotrigine and the risk of major congenital malformations (Harden
et al. 2009).
8 Mechanisms of Teratogenesis
The mechanisms for the developmental toxicity of AEDs are likely to be multiple
and also to partly vary with different AEDs. There is clearly an individual suscep-
tibility as only a fraction of those exposed to the same treatment show signs of
teratogenic effects. This is further supported by clinical observations of greater
risks of AED-related embryopathy among siblings exposed to the same drug (Malm
et al. 2002). A similar variability in the frequency and pattern of adverse pregnancy
outcomes has been related to strain differences in experimental studies in mice
(Buehler et al. 1990; Dean et al. 1999; Finnell 1991; Lindhout and Omtzigt 1992;
Raymond et al. 1995; Strickler et al. 1985; Volcik et al. 2003). The outcome likely
depends on gene–environment interactions and susceptible embryos probably carry
genetic factors determining their susceptibility to AED-induced adverse foetal
effects (Zhu et al. 2009).
A favoured hypothesis for many years suggests that the developmental toxicity of
AEDs is related to their interference with folate metabolism. Folates are co-factors
involved in the biosynthesis of nucleic acids and in the re-methylation of homocys-
teine to methionine. Many AEDs, including phenobarbital, phenytoin, primidone
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 309
and carbamazepine, are known to reduce folate levels. Some clinical studies have
reported an association between low maternal serum folate levels and risk of
malformations (Dansky et al. 1987; Ogawa et al. 1991), although this has not been
a consistent finding. In humans, extra periconceptional supplementation with folate
has been demonstrated to reduce the risk of neural tube defects and at higher doses
also the risk of recurrence in high-risk groups (MRC 1991). It is, however, important
to understand that women with epilepsy were excluded from these studies. Obser-
vational data from epilepsy and pregnancy registries have unfortunately not
demonstrated any protective effect against adverse pregnancy outcomes of peri-
conceptional folate supplementation to women with epilepsy (Morrow et al. 2009).
The 5,10 methylene tetrahydrofolate reductase (MTHFR) gene has been
suggested as one candidate to explain genetic susceptibility to folate sensitive
malformations (Dean et al. 1999). MTHFR is involved in the biotransformation
of folate and is highly polymorphic. Some mutations have been associated with
increased risks of malformations such as neural tube defects, cleft palate and
congenital heart disease that are often seen in relation to exposure to AEDs.
Bioactivation of AEDs to toxic reactive intermediate metabolites has been
another suggested mechanism for the teratogenic effects (Amore et al. 1997;
Bennett et al. 1996; Buehler et al. 1994; Finnell et al. 1995; Finnell and Dansky
1991; Lillibridge et al. 1996; Lindhout et al. 1984; Martz et al. 1977; Pantarotto
et al. 1982; Rane and Peng 1985; Roy and Snodgrass 1990; Strickler et al. 1985).
Reactive epoxides could be the result of CYP450 mediated oxidation of phenytoin,
carbamazepine or phenobarbital. Individual differences in rates of their formation
and in their elimination could contribute to the individual susceptibility to adverse
outcomes. This could be genetically determined as well as affected by interactions
between different AEDs. However, some of the most potent teratogenic AEDs such
as trimethadione lack the premises to form epoxides. Additionally, the CYP450
activity in the embryo during the sensitive periods is very low.
Another postulated bio-activating pathway is co-oxidation of AEDs to free
radical intermediates. These could release reactive oxygen species (ROS), which
may cause oxidative stress and thus teratogenicity. Deficiency of free radical
scavenging enzymes, responsible for eliminating ROS, has been associated with
malformations in the offspring of epileptic mothers exposed to AEDs (Parman et al.
1998; Wells et al. 1997; Wells and Winn 1996).
A more recent hypothesis suggests that many AEDs, such as phenytoin,
trimethadione, carbamazepine, phenobarbital, and possibly lamotrigine may exert
their teratogenic effects by inducing embryonic cardiac arrhythmia during specific
sensitive restricted periods (Danielsson et al. 2000). These effects on the embryonic
heart have been linked to the drugs’ ability to block the rapid component of the
delayed rectifying K ion current, Ikr (Azarbayjani and Danielsson 2002). It is
postulated that the embryonic arrhythmia will cause temporary hypoxia followed
by re-oxygenation and generation of ROS, which will cause tissue damage. Oro-
facial clefts, heart defects, distal digital defects and growth retardation could be
hypoxia related and thus explained by such mechanisms.
310 T. Tomson and D. Battino
9 Conclusions
It has been known for more than 40 years that children of mothers with epilepsy
have an increased risk of adverse pregnancy outcomes. Although multifactorial, the
greater risk is mainly due to teratogenic effects of the AEDs. However, due to the
significant maternal and foetal risks associated with uncontrolled epileptic seizures,
AED treatment is generally maintained during pregnancy in the majority of women
with active epilepsy.
Adverse pregnancy outcomes that have been associated with AED exposure
include foetal growth retardation, major congenital malformations and impaired
postnatal cognitive development. In earlier publications, the prevalence of major
malformations in children exposed to AEDs has been 2–4 times higher than in the
general population. More recent studies suggest a smaller increase in malformation
rates. This seemingly more favourable outcome may be relating new treatment
strategies with less polytherapy, lower AED dosages and different AED selection.
Recent data from large prospective pregnancy registries have revealed differences
between AEDs in their teratogenic potential. Malformation rates have consistently
been higher in association with exposure to valproate than with carbamazepine and
lamotrigine. Other, albeit more limited, prospective cohort studies also indicate
reduced cognitive outcome in children exposed to valproate compared to carba-
mazepine and possibly lamotrigine. Information on pregnancy outcomes with
newer generation AEDs other than lamotrigine are still insufficient.
References
Adab N, Jacoby A, Smith D et al (2001) Additional educational needs in children born to mothers
with epilepsy. J Neurol Neurosurg Psychiatry 70:15–21
Adab N, Kini U, Vinten J et al (2004a) The longer term outcome of children born to mothers with
epilepsy. J Neurol Neurosurg Psychiatry 75:1575–1583
Adab N, Tudur SC, Vinten J et al (2004b) Common antiepileptic drugs in pregnancy in women
with epilepsy (Cochrane Review) The Cochrane Library. Wiley, Chichester
Antiepileptic Treatment in Pregnant Women: Morphological and Behavioural Effects 311
Wells PG, Kim PM, Laposa RR et al (1997) Oxidative damage in chemical teratogenesis. Mutat
Res 396:65–78
Wide K, Winbladh B, Tomson T et al (2000) Body dimensions of infants exposed to antiepileptic
drugs in utero: observations spanning 25 years. Epilepsia 41:854–861
Wide K, Henning E, Tomson T et al (2002) Psychomotor development in preschool children
exposed to antiepileptic drugs in utero. Acta Paediatr 91:409–414
Wide K, Winbladh B, Kallen B (2004) Major malformations in infants exposed to antiepileptic
drugs in utero, with emphasis on carbamazepine and valproic acid: a nation-wide, population-
based register study. Acta Paediatr 93:174–176
Wyszynski DF, Nambisan M, Surve T et al (2005) Increased rate of major malformations in
offspring exposed to valproate during pregnancy. Neurology 64:961–965
Zhu H, Kartiko S, Finnell RH (2009) Importance of gene-environment interactions in the etiology
of selected birth defects. Clin Genet 75:409–423
Preventive Medicines
Vaccination, Prophylaxis of Infectious Diseases,
Disinfectants
Ulrich Heininger
Contents
1 Vaccination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
1.1 Development of Vaccines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
1.2 Preclinical Vaccine Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
1.3 Clinical Vaccine Trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
1.4 Specific Pediatric Aspects in Pre-licensure Vaccine Trials . . . . . . . . . . . . . . . . . . . . . . . . . 327
1.5 Licensure of Vaccines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
1.6 Vaccine Safety Assessment in Post-marketing Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
2 Prophylaxis of Infectious Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
2.1 Avoidance of Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
2.2 Pre- or Post-exposure Passive Immunization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
3 Disinfectants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
3.1 Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
3.2 Aldehydes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
3.3 Phenolics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
3.4 Quaternary Ammonium Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
3.5 Oxidizing Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
3.6 Iodine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
U. Heininger (*)
Universit€ats-Kinderspital beider Basel (UKBB), Postfach, CH-4005 Basel, Switzerland
e-mail: Ulrich.Heininger@ukbb.ch
candidate vaccine is very critical in making the licensure decision for regulatory
authorities, supported by their scientific committees. It includes analyses of immu-
nogenicity, efficacy, reactogenicity or tolerability, and safety of the vaccine. Public
trust in vaccines is a key to the success of immunization programs worldwide.
Maintaining this trust requires knowledge of the benefits and scientific understand-
ing of real or perceived risks of immunizations.
Under certain circumstances, pre- or post-exposure passive immunization can be
achieved by administration of immunoglobulines. In terms of prevention of infec-
tious diseases, disinfection can be applied to reduce the risk of transmission of
pathogens from patient to patient, health-care workers to patients, patients to
health-care workers, and objects or medical devices to patients.
1 Vaccination
Table 1 (continued)
Yeara Live-attenuated Inactivated Component vaccines Gene technology
vaccines whole organism (inactivated)
vaccines
2006 Meningococcal groups A,
C,W135,Y (protein
conjugated)
2006/2007 Human HPV-6, -11, -16, -18
papilloma (quadrivalent),
virus (HPV) HPV-16, -18
(bivalent)
2007 Herpes zoster
2009 Pneumococcal (protein
conjugated, 10-valent
and 13-valent)
a
First used routinely in humans
shift towards true and alleged “side effects” of vaccines. This can lead to the
dilemma of waning public confidence in the necessity, tolerability, and safety of
vaccinations (Guillaume and Bath 2008). It is therefore important to continuously
evaluate risks and benefits of vaccines and results of these evaluations need to be
openly communicated to health professionals and the public in order to strengthen
the confidence in existing and new immunization programs.
There are several prerequisites for successful and meaningful vaccine development
which include the following:
• The microorganism (or its specific mediators of disease, such as toxins and other
major virulence factors) that causes an infectious disease needs to be identified
• Characteristics of the causative agent that leads to disease in the human host
should be explored in order to determine the optimal composition of the vaccine
to be designed against it
• Protective immune responses against the targeted microorganism in the human
host need to be explored in order to identify the optimal route of delivery
(mucosal, systemic) of the vaccine antigen(s)
• The disease is severe enough, i.e. life threatening or even potentially fatal,
leading to significant complications and/or the disease is frequent enough to
cause a significant health or economic burden in the population. This requires
precise description of the overall (or regional) distribution and frequency of the
disease by age groups and characterization of complications caused by the
targeted disease. Frequently this is required on a national basis, if possible, as
immunization recommendations will usually also be formulated nationally
• Lack of successful and rational alternatives to prevent and/or treat the targeted
disease
• Incentives for investment in the development of a new vaccine by research
groups and/or manufacturers should be secured
Preventive Medicines 321
Preclinical vaccine trials are being performed under the principles of “Good
Manufacturing Practices”, as established by major regulatory and scientific
authorities such as the US Food and Drug Administration (FDA) and the European
Medicines Agency (EMA, formerly called EMEA). Specifically, EMA has devel-
oped guidelines for the development of medicines for paediatric use, including
vaccines (http://www.ema.europa.eu/pdfs/human/qwp/13893108en.pdf) which
specify the particular needs for such products in infants and children, including
pre-term infants.
For preclinical testing of a candidate vaccine, adequate preparations are first
tested in cell culture or tissue culture systems. If results are promising, the candidate
will then enter the phase of testing in animals such as mice, rats, guinea pigs or
sometimes even primates (usually monkeys). More recently, three-dimensional
visualization of vaccine compounds by use of sophisticated computer technology
has entered preclinical testing. This technology can assist researchers to predict
how a candidate vaccine will interact with the host’s immune system.
Further, preclinical tests comprise
• Proof of non-toxicity:
Local and systemic toxicity is first assessed in appropriate animal models and
in vitro settings before clinical testing in humans can be initiated. Further,
mutagenicity needs to be assessed as some chemical compounds included in
322 U. Heininger
vaccines may potentially act as base analogs and get inserted into the DNA strand
during replication instead of the natural substrates. Other compounds may react
with DNA and cause structural changes that can lead to miscopying of the
template strand when the DNA is replicated. Similarly, carcinogenicity of vac-
cine compounds may be of concern, especially when the microorganism against
which the vaccine is directed can lead to cancer, for example, human papilloma
virus. Carcinogens alter the cellular metabolism or directly damage DNA in cells
by inducing uncontrolled cell division, inhibiting the programmed cell death,
leading to malignant cell expansion and finally the development of tumours.
• Pharmacodynamic and pharmacokinetic vaccine trials:
The main purpose of these early steps in preclinical testing in animal models is to
estimate the appropriate content of vaccine antigens (dose) and schedule of
administration (number of doses, intervals). This is followed by secondary
vaccine trials on the dose effect, tolerability, and distribution of vaccine antigens
in different organs of the immunized host (¼primary safety assessment).
• Product characteristics:
After a candidate vaccine has successfully passed non-toxicity and pharmaco-
dynamic and pharmacokinetic vaccine trials, the next step before entering
clinical vaccine trials is demonstration of a reliable production process. This
requires demonstration of genetic stability of the seed microorganism (which is
repeatedly used to produce consecutive batches of vaccine), stability and purity
(i.e., absence of substances introduced during the manufacturing process which
are neither needed nor accepted to be present in the final product) of the vaccine
formulation, and characterization of its shelf life under defined storing
conditions (e.g. cold temperature, room temperature conditions etc.).
If the vaccine candidate performs to the researchers’ satisfaction during these
preclinical evaluations, it will be called “investigational vaccine” and can finally be
used in human volunteers in Clinical Vaccine Trials.
Traditionally, most inactivated vaccines have been supplemented by chemicals
called adjuvants which support the host’s immune response to vaccine antigens.
This is frequently necessary to allow a sufficient immune response without increas-
ing the antigen content to a magnitude which would cause significant intolerability
due to side effects (e.g. large local injection site swelling or febrile reactions). In the
past, most adjuvants have been chemical formulations based on aluminium, mainly
in the form of aluminium hydroxide (AlOH) and phosphate (AlPO4). More
recently, new (modern) adjuvants have entered clinical testing and proven success-
ful by means of better immunogenicity and similar tolerability in terms of local and
systemic reactions in the immunized human host including young children, immu-
nocompromised individuals, and elderly people (Pichichero 2008).
An overview of selected promising or proven to be successful new adjuvants is
shown in Table 2.
• The adjuvant system 02 (AS02) is included in the currently most advanced anti-
malaria vaccine, undergoing clinical testing in Phase III vaccine trials in children
and adults in several African countries (Sacarlal et al. 2009; Abdulla et al 2008).
Table 2 New adjuvants in vaccines for use in humans
Preventive Medicines
It induces strong immune-specific responses and the vaccine has proven suc-
cessful in Phase II vaccine trials.
• The adjuvant system 04 (AS04) combines the TLR4 agonist MPL (3-O-desacyl-
40 -monophosphoryl lipid A) and aluminium salt. It has first been used in hepatitis
B conventional vaccine non-responders and immunocompromised hosts (Boland
et al. 2004). Its further inclusion in novel anti-human papilloma virus vaccines,
aimed at precancerous lesions and cancer primarily in the female genital
tract (cervical cancer and others), has led to the development of successful and
licensed vaccines for women 9–26 years of age (Giannini et al. 2006;
Didierlaurent et al 2009).
• CpG 7907 is an adjuvant that directly activates B-lymphocytes and
plasmacytoid dendritic cells and indirectly activates macrophages and other
monocytes by inducing the secretion of Th1-like cytokines and chemokines. It
also facilitates a Th1-type immune response via cytotoxic T-lymphocytes and
has been successfully tested in hepatitis B vaccines and malaria caused by
Plasmodium falciparum (Cooper et al. 2004, Sagara et al 2009) in Phase II
and III trials.
• Finally, oil-in-water adjuvants such as MF59 and adjuvant system 03 (AS03)
have recently been used to develop antigen sparing influenza vaccines against
the novel H1N1 subtype, also called “swine-flu” (www.emea.europa.eu/
humandocs/PDFs/. . ./pandemrix/H-832-de1.pdf; Ellebedy and Webby 2009;
Keitel et al. 2010). With the help of these adjuvants, vaccine antigen content
could be reduced by as much as sixfold compared to conventional, non-
adjuvanted influenza vaccines. Further, these adjuvanted vaccines induced
very potent immune responses after even a single dose administration. They
have been licensed and used worldwide during the winter in 2009/2010. More-
over, an MF59 adjuvanted seasonal influenza vaccine has been licensed and
made available for use in elderly individuals in Europe for several years and was
recently also shown to be of use in children (Vesikari et al 2009).
Specific pediatric needs and requirements in the context of clinical vaccine trials on
drugs, including vaccines, have received special attention recently (http://www.
ema.europa.eu/htms/human/paediatrics/pips_procedural.htm).
328 U. Heininger
immunization, AEFI (i.e., events which occur in temporal but not necessarily causal
relationship after immunization) are categorized by frequency of occurrence fol-
lowing the terminology as proposed by WHO (http://www.who.int/vaccines-
documents/DocsPDF05/815.pdf):
Causality assessment is also an integral part of vaccine safety evaluation. Assess-
ment of local reactions after injected vaccines (e.g. swelling, induration, injection site
pain) is straight forward: the time interval between immunization and occurrence of
the reaction is usually short (several hours to few days) and a causal association with
immunization therefore is obvious. Systemic reactions, however, such as fever or
malaise may or may not be causally related to previous immunization. Here, the kind
of vaccine (inactivated versus live-attenuated) determines the temporal relationship
between vaccination and occurrence of causally related side effects. The attributable
risk of a systemic event after vaccination has to be determined by comparing the
observed rate after vaccination with the background rate to see if and by which
magnitude it is increased. Again, this is straightforward in controlled vaccine trials.
For example, in a clinical study with an oral rotavirus vaccine, fever, and irritability
occurred in more than 50% of study subjects and loss of appetite, diarrhea, vomiting,
and cough in 20–60% (Ruiz-Palacios et al. 2007), irrespective of administration of
placebo or the vaccine. This example illustrates the difficulty to attribute systemic
adverse events after immunization to the vaccine in an individual. Of note, side
effects after vaccination are therefore a diagnosis of exclusion.
Admittedly, there are many examples of real side effects after vaccination. For
example, a nasal influenza vaccine that was available in Switzerland for a short
period of time clearly was temporally associated with an increased risk for periph-
eral facial palsy. The initial hypothesis of a causal relation was based on several
reports of facial palsy to the Swiss regulatory authority which had occurred shortly
after nasal influenza vaccine administration. In a well-organized post-marketing
surveillance system, these observations prompted a prospective controlled study
which finally proved that the relation to immunization was causal and not only
temporal (Mutsch et al. 2004).
Potential uncertainty about the safety of vaccines – particularly in countries
where some vaccine preventable diseases have disappeared from the public aware-
ness due to efficacious vaccines and high immunization rates in well structured
immunization programs – is currently aggravated by a large volume of unstructured
information of varying quality available to health care professionals and parents,
frequently via the worldwide web and other mass media. However, in the obvious
absence of perfectly safe health interventions, patients have the right to be objec-
tively advised about benefits and possible risks.
As mentioned, providing evidence of the safety of a given vaccine is of para-
mount importance. From a health professional’s perspective, this can be achieved
by individual search of the literature (which is time-consuming and can be cumber-
some especially when personal resources are limited) or reliance on informa-
tion provided by experts specialized in pharmacovigilance, public health, and
vaccinology. For these specialists, published information on characteristics of a
vaccine and study results is usually more easily accessible. However, scrutinizing
and evaluating the information again is cumbersome.
330 U. Heininger
In the past, a major obstacle to compare results of vaccine tolerability and safety
as published in scientific journals, has been the lack of standardized case definitions
for AEFI (Ioannidis and Lau 2001; Bonhoeffer et al. 2002). In the meantime, a
considerable number of standardized adverse event case definitions and guidelines
on how to use them has been developed by “The Brighton Collaboration” (http://
brightoncollaboration.org), an independent international organization, dedicated to
standardizing vaccine safety assessment (Kohl et al. 2007).These case definitions
have undergone (Tapiainen et al 2006) or are currently undergoing validation and
are increasingly recommended by national and international authorities including
WHO, EMA, FDA, and the US Centers for Disease Control (CDC).
The availability and use of standardized case definitions for certain AEFI will
improve vaccine safety assessment in the future for the following reasons:
• Clinical vaccine trials can be designed in a way that allows obtaining relevant
clinical information depending on the requirements of a given case definition.
• Metaanalyses of vaccine safety issues can be performed over different clinical
trials if the same standardized case definitions have been used in the individual
trials.
• Also clinical reports of AEFI in surveillance settings (post-marketing) can be
verified by use of standardized case definitions.
• Frequencies and incidences of AEFI as obtained from different surveillance
systems can be compared in a meaningful way if standardized case definitions
have been used.
The importance of alleged vaccine side effects, because of their influence on the
public perception of vaccine safety, needs to be stressed, too. After many carefully
conducted vaccine trials and plausibility assessments, the great majority of
suspected, mostly serious suspected “side effects” of specific vaccinations receiv-
ing public attention in the recent past have turned out to be coincidental
observations. These events include diabetes mellitus in young children after
Haemophilus influenzae type b vaccination (Black et al. 2002), autism and inflam-
matory bowel disease after measles–mumps–rubella (MMR) vaccine (De Stefano
et al. 2004), demyelinating diseases in adolescents after hepatitis B immunization
(Hocine et al. 2007), asthma after various childhood immunizations (Gr€uber et al.
2003), and sudden infant death syndrome (SIDS) after pertussis component
containing combination vaccines for infants (Stratton et al. 1994).
Differentiation between coincidence and causality therefore is of high impor-
tance to maintain public trust in immunization programs.
3 Disinfectants
Disinfectants are antimicrobial agents that are frequently used in medical settings
with the goal to reduce the load of pathogenic or facultative pathogenic
microorganisms (pathogens) on body surfaces (mainly hands) and objects in the
environment of patients or medical devices (Dettenkofer and Daschner 1997). The
ultimate goal of disinfection is to reduce the risk of transmission of pathogens from
patient to patient, health-care workers to patients, patients to health-care workers,
and objects or medical devices to patients. Usually, a reduction of 3–5 log of the
pathogens at the site of application (i.e., by 99.9–99.999%) is achieved by disinfec-
tion. In contrast to disinfection, sterilization describes the process of complete
elimination of pathogenic microorganisms.
Disinfection can be achieved by means of
• Heat
• Physical treatment
334 U. Heininger
• Chemical treatment
Heat is frequently used to disinfect heat-resistant objects. Before disinfection,
thorough cleaning is required to eliminate biologic (blood, phlegm, other
excretions) and non-biologic material. Afterwards, decontamination by residing
pathogens is achieved by exposing the objects to 75 C for at least 10 min. This
procedure can be standardized and programmed by use of disinfection machines.
Heat acts by disrupting membranes and denaturing proteins and nucleic acids.
Physical disinfection can be attempted by ultraviolet light at 260 nm. Applica-
tion of UV light leads to the formation of pyrimidine dimers in DNA which then
lead to genetic damage to cells. Theoretically, ultraviolet irradiation is an effective
method of reducing the amount of pathogens on surfaces and in the air, but it does
not penetrate glass. Its effect, however, is questionable among hygiene experts and
it is not frequently used.
Use of chemicals is the preferred method of disinfection in medical settings. The
properties, modes of action, advantages, disadvantages, and indications of
chemicals most widely used now or in the past are discussed here.
3.1 Alcohol
3.2 Aldehydes
3.3 Phenolics
Phenolics are active ingredients in some disinfectant soaps, e.g. used for
handwashing in medical settings. They are active against bacteria and fungi, but
not against bacterial spores and enveloped and non-enveloped viruses. Therefore,
they should only be used in combination with other disinfectants.
Due to their potential toxicity to sensitive individuals and also for reasons of
environment protection (toxicity to newborns, accumulation in water and food,
slow natural degradation) phenolics are less frequently used today than previously.
3.6 Iodine
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and guidelines for adverse events following immunization. Vaccine 25:5671–5674
Kombo LA, Gerber MA, Pickering LK et al (2001) Intussusception, infection, and immunization:
summary of a workshop on rotavirus. Pediatrics 108(2):E37
Mutsch M, Zhou W, Rhodes P et al (2004) Use of the inactivated intranasal influenza vaccine and
the risk of Bell’s palsy in Switzerland. N Engl J Med 350:896–903
Pichichero ME (2008) Improving vaccine delivery using novel adjuvant systems. Hum Vaccin
4:262–270
Ruiz-Palacios GM, Guerrero ML, Bautista-Márquez A et al (2007) Dose response and efficacy of a
live, attenuated human rotavirus vaccine in Mexican infants. Pediatrics 120:e253–e261
Sacarlal J, Aide P, Aponte JJ et al (2009) Long-term safety and efficacy of the RTS, S/AS02A
malaria vaccine in Mozambican children. J Infect Dis 200:329–336
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immunogenicity of the AMA1-C1/Alhydrogel + CPG 7909 vaccine for Plasmodium
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who received either the Lederle/Takeda acellular pertussis component DTP (DTaP) vaccine,
the Lederle whole-cell component DTP vaccine or DT vaccine. Pediatrics 101:1–11
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other than pertussis and rubella. Summary of a report from the Institute of Medicine. JAMA
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vaccination. Vaccine 27:6291–6295
Postmarketing Surveillance
Contents
1 General background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
1.1 The Importance of Postmarketing Surveillance in Paediatric Practice . . . . . . . . . . . . . 340
1.2 Off-Label and Unlicensed Drug Use in Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
1.3 Orphan Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
2 Pharmacovigilance for Paediatric Medicines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
2.1 Pharmacovigillance for Off-Label and Unlicensed Drug
Use and Orphan Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
2.2 Paediatric Formulation and Dosing Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
2.3 Enhanced Spontaneous Reporting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
2.4 Signal Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
3 Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
4 The Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
V. Vlahović-Palčevski (*)
Department for Clinical Pharmacology, University of Rijeka Medical School, University Hospital
Center Rijeka, Krešimirova 42, 51000 Rijeka, Croatia
e-mail: vvlahovic@inet.hr
D. Mentzer
Paul-Ehrlich-Institut, Referate Arzneimittelsicherheit, Paul-Ehrlich-Str. 51-59, 63225 Langen,
Germany
1 General background
Postmarketing drug surveillance refers to the monitoring of drugs once they reach
the market after three phases of clinical trials that are designed to test safety and
efficacy of drugs. Postmarketing drug surveillance using interventional or non-
interventional clinical trial aims to evaluate drugs taken by individuals under a wide
range of circumstances in real-world conditions over an extended period of time.
Such surveillance is much more likely to detect any undiscovered positive or
negative effects, which may be associated with a drug. Postmarketing drug surveil-
lance is critical to ensuring that a medication is safe for use by a wide variety
of people (i.e. varying ages, genders, races, lifestyles, etc.) under different
circumstances (i.e., people with comorbidities or on multiple drugs, with varying
nutritional status, taking over-the-counter supplements, etc.). The majority of
postmarketing surveillance encompasses adverse drug reaction (ADRs) monitoring
and evaluation.
Postmarketing surveillance in paediatric population denotes surveillance of
approved drugs used by persons aged 0–18. Many medicines are prescribed to
paediatric patients on an unlicensed or “off-label” basis because they have not been
adequately tested and/or formulated and authorized for use in appropriate paediatric
age group. Thus, additional important postmarketing surveillance components
involve unapproved or off-label drug use, problems with orphan drugs and lack
of paediatric formulations, the issues of conduction international clinical trials.
Postmarketing Surveillance 341
The term off-label relates to the use of a medicine in a manner different from that
recommended by the manufacturers in their product license i.e., on a trial and error
basis. It may result either in benefit, no therapeutic effect, or adverse reaction.
The assumption that children with diseases or conditions similar to that of adults
respond similarly has perpetuated the use of medications approved in adults to treat
children, frequently without the appropriate studies in paediatric population. Only
one third of drugs used to treat children have been studied adequately in the
population in which they are being used and have appropriate use information on
the product label. For the other two thirds of drugs, information regarding safety
and efficacy for paediatric patients is insufficient or absent. The younger the
patient’s age group, the more likely the lack of information. It is estimated that
80–97% of infants in neonatal wards receive at least one off-label or unlicensed
drug (Pandolfini and Binati 2005; Grégoire and Finley 2007). Typically, labels for
new medications provide physicians with no guidance regarding a product’s effec-
tiveness, dosing or safety among paediatric patients. For most drug classes, there
exists almost no information on use in patients less than 2 years of age (Roberts
et al. 2003; Clark et al. 2006). The problem of off-label use is international and
affects hospitalized or non-hospitalized children. Those who administer drugs to
children are forced to deviate from the established labeling indications, for exam-
ple, by manipulating a drug’s formulation to obtain a “paediatric” dose (e.g.
splitting tablets into pieces), or by changing the indicated route of administration
(e.g. to avoid intramuscular injections in young patients) (Pandolfini and Binati
2005). Paediatric patients may also be deprived of potentially effective medication
because of the prescriber’s reluctance to use a medication for an off-label use.
Not all off-label drug use is inappropriate. A distinction should be made between
“well-founded” and “ill-founded” (disputable) off-label prescriptions. In contrast to
“ill-founded”, “well-founded” off-label prescriptions are recommended in clinical
practice guidelines or pharmcotherapeutic handbooks. These recommendations are
based on systematic examination of the published literature. The efficacy of “ill-
founded” off-label prescription is often questionable and adverse drug reactions and
unjustified healthcare costs may result (Gijsen et al. 2009).
Unlicensed is the use of drugs that do not have a product license, most often
those whose formulation is modified, that are prepared as extemporaneous
preparations, are imported or used before a license is granted, or that are chemicals
used for therapeutic purposes (Kimland et al. 2007). The reasons for a drug being
unlicensed in children are many. It occurs often because a drug has not been tested
in children, and this may be due to financial constraints or because of the apparent
difficulties with trial design and ethics of testing drugs in children.
The extent to which drugs are prescribed to children in an off-label manner vary
among different countries and settings. Data from UK suggest that in primary care
about 11% of drugs prescribed for children are used off-label (McIntyre et al. 2000).
In a retrospective cohort study analysing 1.74 million prescriptions in primary care
342 V. Vlahović-Palčevski and D. Mentzer
Orphan drugs are usually defined as drugs that have been abandoned or “orphaned”
by major drug companies. However, this definition can be extended to medications
that could be useful to a minority of population (i.e. orphan group), such as children,
physically or cognitively disabled patients, or the elderly if the medications were
available and approved for those groups.
According to European Medicines Agency (EMA), a medicinal product is
designated as an orphan medicinal product if: it is intended for the diagnosis,
prevention or treatment of a life-threatening or chronically debilitating condition
affecting no more than five in 10,000 persons in the European Union at the time of
submission of the designation application (prevalence criterion), or it is intended for
the diagnosis, prevention, or treatment of a life-threatening, seriously debilitating or
serious and chronic condition and without incentives it is unlikely that expected
sales of the medicinal product would cover the investment in its development, and
no satisfactory method of diagnosis, prevention, or treatment of the condition
concerned is authorized, or, if such method exists, the medicinal product will be
of significant benefit to those affected by the condition (EMA 2010, http://www.
ema.europa.eu, accessed 27 Jan 2010).
associated with drug use in children is limited due to few paediatric drug safety
studies. At registration, little information on adverse drug reactions in children is
available since many drugs have not been tested in children. Risk–benefit analyses
of drugs for children are dependent on observations of adverse drug reactions and
effects from clinical use. The limited available information regarding adverse drug
events in paediatric population is based on medication errors such as overdosing or
accidental exposure (Fortescue et al. 2003; Kaushal et al. 2001). The potential for
adverse drug reactions among children is greater than that in adults. Young children
have immature metabolizing mechanisms, which decreases their ability to process
drugs and metabolites. In addition, drug doses must be adjusted individually for a
significantly broader range of body sizes and weights.
Paediatric pharmacovigilance is therefore the process of evaluating and improv-
ing the safety of medicines used in paediatric patients of all ages (Choonara 2006).
Most investigations concerning ADRs in children have focused on hospitalized
patients. In a meta-analysis of nine prospective studies among hospitalized children,
Impicciatore and colleagues calculated an overall incidence of ADRs of 9.5%, of
which 12.3% was regarded as severe. ADRs in hospitalized children require atten-
tion because they often involve serious illnesses, advanced drugs, and complicating
factors such as concomitant medication and comorbidity (Impicciatore et al. 2001).
However, ADRs outside the hospital should not be overlooked. Not only do many
children in primary care continue drug therapy that has been initiated in the hospital,
but also the number of drug-using children in primary care is much larger than the
number of hospitalized patients. Based on the few prospective studies, it has been
estimated that 1–1.5% of the drugs used by children outside the hospital result in an
ADR (Impicciatore et al. 2001; Sanz and Boada 1987; Cirko-Begovic et al. 1989). In
reported suspected paediatric adverse drug reactions (ADRs) in Sweden using data
from a nation-wide ADR reporting system during a period of 15 years, it was found
that the proportion of children suffering from a serious ADR was 13.0% and that for
drug related deaths was 0.14% (Kimland et al. 2005). In a report from the US, 6% of
the total ADR reports in a 5-year period concerned individuals aged less than 18
years (Johann-Liang et al. 2009).
Off-label and unlicensed drug use in children has resulted in questions to drug
information centers and has been reported to be extensive, and, as reported, has
resulted in an increased risk of adverse drug reactions. A French study that involved
more than 1,400 children has shown that 42% of outpatients were exposed to at
least one off-label prescription, and the incidence of adverse drug reactions was 1.4
in the whole population and 2.0% in patients exposed to at least one off-label
prescription (Horen et al. 2002). An observational analysis of spontaneous adverse
344 V. Vlahović-Palčevski and D. Mentzer
regimen, the dosage interval may need to be increased and the total dose decreased
depending on hepatic and renal function. For medicines that are cleared by liver,
they may have a longer plasma half-life and thus a longer time to reach steady state.
Similarly, for medicines that are entirely eliminated through kidneys, the greater the
prematurity, the less are the kidneys able to excrete the substance and consequently
the longer will be the half-life.
The lack of reliable pharmacokinetic and pharmacodynamic data in paediatric
populations deriving from systematic drug development and clinical trials are
claimed to be responsible for some complications and difficulties following treat-
ment in paediatric population. In most cases it has been related to missing informa-
tion on the right dose and appropriate formulation. These deficiencies need to be
reflected according to each of the different age subpopulations in paediatrics in
order to strive toward safer medicines for children (Hartford et al. 2006; Interna-
tional Conference on Harmonisation 2000).
Where unlicensed and off-label paediatric use is common, it is important for
both the marketing authorization holder and the regulatory authorities to monitor
for any consequential safety concerns and to take appropriate measures to address
them and include in the Summary of Product Characteristics as a standard risk
minimisation measure. The reasons for a relative or absolute contraindication
should also be presented in the product information leaflet to appropriately com-
municate the risk of off-label use (WHO 2007).
The major concern with ADRs is for serious adverse reactions, which are often rare,
and will generally not be observed in paediatric clinical trial programme, particu-
larly if there is a latent period before the onset or a trigger such as change in growth
or development (Impicciatore et al. 2001). Some serious ADRs may only be
diagnosed in a distinct age subgroup of paediatric population (e.g. febrile convul-
sion, growth retardation). Taking this into account, collection and extrapolation of
safety data in paediatric population from data in adults is not always possible due to
physiological facts such as metabolism, growth, and mental development.
Therefore, routine pharmacovigilance measures for detecting new safety signals
with extensively used drugs in adults may be much less effective in paediatric
population. A different, more proactive, approach is needed to conduct pharmacov-
igilance for these types of low usage products.
Clinical trial protocols should set out actions to be taken and their timing, by
category of ADR, if it occurs. For example, if a serious ADR is suspected, a blood,
saliva or urine sample (as appropriate) should be taken as soon as possible after the
suspected event. Preferably the samples should be frozen for drug and metabolite
measurement. For postauthorization safety studies, similar provisions might be
appropriate, but then it needs to be understood that including such a provision in
a trial protocol would disqualify it from having non-interventional status.
346 V. Vlahović-Palčevski and D. Mentzer
By definition a drug safety signal may arise from a previously unrecognized safety
issue, a change in the frequency or severity of a known safety issue or identification
of a new at risk group. These aspects are all relevant in paediatric population and
both Marketing Authorisation Holder and regulatory authorities are responsible for
identifying these kinds of signals.
Signal detection and data mining in paediatric population are dependent on
detection methods used which needs to be effective for small populations and low
numbers of possible cases. Enhanced data capture techniques can increase the
completeness and quality of the information obtained (Bate et al. 1998; Evans
et al. 2001).
Signal detection should include appropriate stratification for the data collected
based on specific needs (for example by age group or specific medicines like
vaccines), as this can be helpful to increase the ability to detect signals from
spontaneous databases. However, signal detection is an evolving field and the
most up-to-date and suitable statistical methods should be considered based on
the content of the data and the size of database used (Evans 2008).
348 V. Vlahović-Palčevski and D. Mentzer
The review and interpretation of results coming from signal detection analyses
should be at a high and cautious level of suspicion and should have an emphasis on
follow-up to obtain essential information before coming to a final conclusion. Even
one case report may be enough to trigger further investigation or risk minimisation
measures.
In paediatric drug development, the age-related physiological aspects should not
only be considered when conducting clinical trials in children and adolescence as it
is routine for efficacy-related objectives, but they are also very important for signal
detection methods and monitoring of the safety aspect of the product once used in
children.
Given these limitations every opportunity should be taken to maximise the
information obtained following the occurrence of an ADR during the paediatric
development programme.
3 Legislation
to amend the Federal Food, Drug, and Cosmetic Act to improve the safety and
efficacy of pharmaceuticals for children (Best Pharmaceuticals for Children Act.
Pub L No. 107–109). A fund was created for research and studies on older products
devoid of commercial interest. This fund is managed by the National Institutes of
Health (NIH) and the Food and Drug Administration (FDA). On 17 October 2002,
the Pediatric Rule was enjoined. As a consequence, the Pediatric Research Equity
Act of 2003 became a law on 3 December 2003. This Act gave the FDA the
authority to require certain research into drugs used in paediatric patients. On
September 27, the Food and Drug Administration Amendments Act of 2007, was
signed. Among the many components of the law, the Best Pharmaceuticals for
Children Act (BPCA) and the Pediatric Research Equity Act (PREA) were
reauthorized. Both of these are designed to encourage more research into, and
more development of, treatments for children. They cover many issues including
the need to strengthen surveillance of adverse events and to define the role of the
Paediatric Advisory Committee which now bears the requirement to review all
paediatric safety data at least 1 year post approval.
In a meeting on June 14–15, 2007, the US Food and Drug Administration
(FDA), the European Commission (EC), and the European Medicines Agency
(EMEA) have agreed to expand their current cooperative activities in several
important areas, in particular paediatrics (http://www.ema.europa.eu/htms/human/
paediatrics/).
4 The Future
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Global Aspects of Drug Development
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
2 Meeting the Health Needs of Children Around the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
3 The Concept of Essential Medicines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
4 WHO Essential Medicines List for Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
5 Developing Appropriate Paediatric Formulations for the Different Environments . . . . . 359
6 Accounting for Sociocultural Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
7 Paediatric Fixed-Dose Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
8 The New Paradigm for Global Paediatric Formulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
9 Simplified Dosage Regimens Needed: Without Compromising Safety and Efficacy . . 363
10 Paediatric Clinical Trials in the Developing World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
10.1 Ethical Aspects of Clinical Trials in the developing world . . . . . . . . . . . . . . . . . . . . . . 365
10.2 Scientific Aspects of Paediatric Clinical Trials in Developing World . . . . . . . . . . . 366
11 Price, Quality, and Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
11.1 Providing Access to Essential Medicines for Children at Country Level . . . . . . . 367
11.2 Quality: A Major Challenge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
11.3 Medicines Have to Be Affordable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
12 Rational Use of Medicines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
13 National Medicine Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
14 Public Health Approach to Innovation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
K. Hoppu (*)
Poison Information Centre, Helsinki University Central Hospital and Hospital for Children and
Adolescents, Institute for Clinical Sciences, University of Helsinki, P.O. Box 790 (Tukholmankatu
17), 00029 HUS (Helsinki), Finland
e-mail: kalle.hoppu@hus.fi
H.V. Hogerzeil
Essential Medicines and Pharmaceutical Policies, World Health Organization, 1211 Geneva 27,
Switzerland
Abstract About nine million children die every year before they reach the age of
5 years, of conditions largely amendable with existing medicines. Lack of medicines
is not the single most important health problem of children, but work to provide
children with better access to appropriate medicines is essential for achievement
of the child health goals set. Taking into consideration the global aspect in
the development of paediatric medicines the benefits of the regional paediatric
initiatives can be spread worldwide. This chapter provides insights in the challenges
and opportunities of developing paediatric medicines for health needs of children in
the developing world. The Essential Medicines List for children first made available
in 2008 serves as an example of the many tools available from WHO to improve
children’s access to the medicines they need.
1 Introduction
About 28% of the 2008 world population of 6.7 billion is of less than 15 years of
age. In less developed countries children and adolescents less than 15 years of age
make out about a third, and in the sub-Saharan Africa about 43% of the population.
The trend in childhood mortality has been favourable on the global level and
contributes to the increase in life expectancy. However, many countries still have
high child mortality, particularly in sub-Saharan Africa and South Asia, and in
recent years made little or no progress in reducing the number of child deaths.
While lack of medicines is not the single most important health problem of
children, it is clear that work to provide children with better access to appropriate
medicines is essential for achievement of the child health goals set, like the
Millennium Development Goals (MDG) – MDG 4 (Reduce child mortality by
two thirds) and MDG 6 (combat HIV/AIDS, malaria, and other major diseases).
The paediatric medicines initiatives launched in the US and the EU, in essence
public health interventions to improve child health, have successfully increased
interest in study and development of paediatric medicines and already led to
positive results. However, the increased research and development of paediatric
medicines initiated by these regional initiatives are unlikely to benefit children of
the less developed world unless their special needs and requirements are considered
in the process. The aim of this chapter is to discuss factors to be considered,
challenges but also opportunities of developing paediatric medicines that meet
the needs of children in less developed world.
It is estimated that about nine million children die every year before they reach the
age of 5 years, 70% of them from treatable conditions. More than three million die
in the neonatal period. The main causes of death in the first month are preterm birth,
Global Aspects of Drug Development 355
birth asphyxia, and infections. After the age of one month and up until the age of
five, the main causes of death are pneumonia (approximately two million/year),
diarrhoeal diseases (approximately 1.9 million/year, comprising 18% of all
under-five deaths), malaria (estimated one million/year), measles, and HIV/AIDS.
Malnutrition contributes to more than one third of under-five deaths.
Effective interventions in the form of medicines exist for many of these
conditions, but a significant proportion of the children do not have access to
these medicines. Like even in the richest countries of the world, the medicines
available for children are often not appropriate for their needs. Many of the
medicines that do exist do not exist in appropriate formulations for children. A
recent study on the inclusion of key medicines for children in national essential
medicines lists (EMLs) and standard treatment guidelines, and to assess the avail-
ability and cost of these medicines in 14 countries in central Africa found that
the availability of key essential medicines for children was poor (Robertson
et al. 2009).
Making medicines available, medicines supply, is part of a functioning health
care system. Most health programmes depend on access to affordable medicines;
without quality medicines success is not possible. Recognizing that better access to
medicines is a prerequisite for improving health outcomes in children, in May 2007
the World Health Assembly passed Resolution WHA60.20 “Better Medicines for
Children”, which identified key steps for ensuring better medicines for children
(World Health Assembly 2007). Key points of the Resolution are summarized in
Table 1.
The WHA60.20 resolution set goals and called for action by Member States and
WHO to address the global need for children’s medicines. One important target for
action was the WHO Model List of Essential Medicines (EML), a global standard
for 30 years, used by many countries as a model for national lists to guide drug
procurement and supply. Although this list has included some paediatric medicines,
a children’s list had not been systematically developed.
Essential medicines are those that satisfy the priority health care needs of the
population. They are selected on the basis of disease prevalence, evidence on
efficacy, safety and comparative cost-effectiveness. The selection of essential
medicines is one of the core principles of a national medicine policy because it
helps to set priorities for all aspects of the pharmaceutical system. This is a global
concept, which can be applied in any country, in private and public sectors and at
different levels of the health care system.
There is good evidence that clinical guidelines and essential medicines lists,
when properly developed, introduced and supported, improve prescribing quality
and lead to better health outcomes (Grimshaw and Russell 1993; Kafuko and
Bagenda 1994; Woolf et al. 1999; Laing et al. 2001). But there is also an economic
356 K. Hoppu and H.V. Hogerzeil
Table 1 Key points of the World Health Assembly resolutionWHA60.20 on Better medicines for
children
WHA60.20 urges member states:
To take steps to identify appropriate dosage forms and strengths of medicines for children, and
to encourage their manufacture and licensing
To encourage research and development of appropriate medicines for diseases that affect
children, and to ensure that high-quality clinical trials for these medicines are conducted in an
ethical manner
To facilitate timely licensing of appropriate, high-quality and affordable medicines for children
and innovative methods for monitoring the safety of such medicines
To encourage the marketing of adequate paediatric formulations together with newly developed
medicines
To promote access to essential medicines for children through inclusion, as appropriate, of those
medicines in national medicine lists, procurement and reimbursement schemes, and to devise
measures to monitor prices
To collaborate in order to facilitate innovative research and development on, formulation of,
regulatory approval of, provision of adequate prompt information on, and rational use of,
paediatric medicines and medicines authorized for adults but not approved for use in children
WHA60.20 requests the WHO director-general
To promote the development, harmonization, and use of standards for clinical trials of
medicines for children
To revise and regularly update the Model List of Essential Medicines in order to include missing
essential medicines for children
To ensure that all relevant WHO programmes, including but not limited to that on essential
medicines, contribute to making safe and effective medicines as widely available for children
as for adults
To promote the development of international norms and standards for quality and safety of
formulations for children, and of the regulatory capacity to apply them
To make available evidence-based treatment guidelines and independent information on dosage
and safety aspects of medicines for children, and to work with Member States in order to
implement such guidelines
situations where the availability of medicines in the public sector is often erratic.
Under such circumstances measures to ensure a regular supply of essential
medicines will result in real health gains and in increased confidence in the health
services.
The concept of essential medicines was launched in 1977 with the publication of
the first WHO Model List of Essential Medicines. Since then the List was revised
every 2 years. Both its content and the process by which it is updated are intended as
a model for developing countries. In 2002, WHO completed a rigorous overhaul of
the process to update the list. An important change was that affordability changed
from a precondition into a consequence of the selection. For example, before 2002
effective but expensive medicines, such as single-dose azithromycin for trachoma,
were not listed because of their price. The new definition of essential medicines is:
Essential medicines are those that satisfy the priority health care needs of the population.
They are selected with due regard to disease prevalence, evidence on efficacy and safety,
and comparative cost-effectiveness. Essential medicines are intended to be available within
the context of functioning health systems at all times, in adequate amounts, in the appro-
priate dosage forms, with assured quality, and at a price the individual and the community
can afford. The implementation of the concept of essential medicines is intended to be
flexible and adaptable to many different situations; exactly which medicines are regarded as
essential remains a national responsibility (WHO 2003)
Under the new definition, twelve antiretroviral medicines for HIV/AIDS were
listed, irrespective of their high cost at that time. Their listing implied that these
medicines should become affordable to all patients who need them; and seven years
later we can conclude that prices have indeed come down dramatically.
Within a country, market approval of a pharmaceutical product is usually
granted on the basis of efficacy, safety and quality, and rarely on the basis of a
comparison with other products already on the market, or cost. This regulatory
decision defines the availability of a medicine in the country. In addition, most
public drug procurement and insurance schemes have mechanisms to limit procure-
ment or reimbursements of drug costs. For these decisions, an evaluation process is
necessary, based on a comparison between various drug products and on
considerations of value for money. This second step leads to a national list of
essential drugs.
A list of essential drugs is best developed for different levels of care, and on the
basis of standard treatment guidelines for common diseases and complaints that can
and should be diagnosed and treated at that level. National lists of essential
medicines are used to guide the procurement and supply of medicines in the public
sector, reimbursement schemes, medicine donations and local medicine production;
they also help define the training of health workers. In short, essential medicines
lists provide the scientific and public health basis for focus and expenditure in the
pharmaceutical sector.
In many countries it has taken several years and several editions of treatment
guidelines and lists of essential medicines before a more or less stable product was
developed which was accepted by most prescribers and actually used for training,
procurement and supply. Although time-consuming, the wide involvement of a
358 K. Hoppu and H.V. Hogerzeil
Effective treatments exist for many of the priority diseases and conditions of
children, however many of these essential medicines do not exist in formulations
for children. There are many gaps in evidence and knowledge about the use of
existing medicines in children and in identifying what medicines do not exist. The
development of the first WHO Essential Medicines List for children (EMLc) in
2007 was a first step in addressing this knowledge gap.
The first EMLc (WHO 2008a), which was adopted on the day of the 30th
Anniversary of the EML, was developed using the same procedures that are used
to update the main list. Selection of medicines as essential is based on public health
need and evidence of their efficacy and safety. In selecting essential medicines for
children, one of the first difficulties encountered was the relative lack of evidence
about medicines used to treat children with “neglected” diseases such as leishmani-
asis. The first EMLc included about 200 medicines in about 450 dosage forms.
Many were marked as needing further review, or had age restrictions on use
because of lack of data. The meeting report also lists many medicines for which
further evidence is required to confidently assess the benefits and harms of their use
in children. Some of the questions might be answered by systematic reviews of
existing information, but others require more research and drug development. The
published report of the WHO Expert Committee (WHO 2008a) also includes a
listing of Research Priorities for Children’s Medicines developed by a group of
experts convened by the WHO in October 2007.
A second EMLc was adopted in March 2009, and included for the first time a
listing of essential medicines that can be used in neonates (WHO 2009b). A
temporary Subcommittee of the WHO Expert Committee on the Selection and
Use of Essential Medicines prepared these first two Essential Medicines Lists for
children. The subcommittee meetings were held from 9 to 12 July 2007 and 29
September to 3 October 2008. In its last meeting, the Subcommittee recommended
that for the foreseeable future, it is essential that the EMLc remain separate from the
Global Aspects of Drug Development 359
Many of the essential medicines do not exist in formulations for children, and many
of the existing dosage forms of medicines for children are associated with significant
problems. Practical experience from the children, their caregivers, and health care
professionals from all over the world is that the existing paediatric formulations are
not optimal when it comes to dosing, dispensing, and administering the medicines
to children. This problem of lack of age-appropriate paediatric formulations has
been widely recognized, including by the US and EU paediatric initiatives, which
include measures designed to try to alleviate the problem.
The problems of paediatric formulations are even more difficult in resource poor
settings, and especially in areas of the world where high temperature and humidity
combined with problems of transport make logistics and storage a real challenge.
These problems exist at the country level for logistics needed for medicines supply,
at the level of local health care delivery and for the end users, the children and their
caregivers.
High humidity, present often in combination with high temperature, is detrimen-
tal to the quality of medicines and may render them inactive quite rapidly. Access to
electricity is not given in areas where temperatures are highest, therefore facilities
for cold storage of medicines – common requirement for liquid formulations such
as anti-infective agents once reconstituted – may not be reliably available in all
health care facilities, and even less so in households. Bulky formulations – liquids
are much more bulky than solid dosage forms – pose significant logistical
challenges, require more warehouse space, pharmacy space and compel parents to
carry home a heavier load of medicines. The transport problems for the end users
become even more significant in case of multi-drug treatments, long distances and
lack of means of transportation.
Paediatric formulations are most often in a liquid form but at the time of
dispensing or before administration may have to be dissolved in water. Water
360 K. Hoppu and H.V. Hogerzeil
In a global world sociocultural differences still play a major role, also when it
comes to paediatric medicines. Colour, form and taste of a medicine may not only
affect the success of administration to children but also the assessment people make
on the strength and effect of medicines. The preferences and interpretations can
have a significant cultural variability. These differences have been noted and for
example taste preferences routinely influence development of paediatric medicines
for the developed world. When the cultural variability of the less developed world is
added to that, the issue becomes even more complicated. A large pill may be
interpreted as “stronger” than a small one, and a bitter tasting medicine more
powerful than a sweet one. “Western” medicines may be considered too “strong”
and with too many “side effects” and traditional (homeopathic or herbal) medicines
may be preferred, a phenomenon not unfamiliar in the “western” world either. Pill
burden is a pragmatic problem, in any culture. Multiple concomitant diseases
increase the pill burden irrespective of geography, but are more common in areas
of high disease burden.
Traditional beliefs, misconceptions, irrational use of medicines are not unfamil-
iar anywhere in the world, but their variability and effect may be more pronounced
in resource poor setting where education and other services are available only to a
limited extent. The global coverage of data on sociocultural differences is limited,
and we do not even know the real relevance of the existing information. While there
Global Aspects of Drug Development 361
The possible benefit of the potentially greater dose accuracy of liquid vs. solid
formulations is not always necessary, when the active substance has a broad
therapeutic range (e.g. common antimicrobials) or is lost when inaccurate measur-
ing devices (e.g. a tablespoon) are used. Liquids are expensive, less stable than solid
forms, difficult to ship and store. As indicated earlier, liquid formulations are
particularly problematic in many areas of the developing world.
In the current growing interest and need to develop new paediatric formulations
of old and new medicines to benefit from the incentives and fulfil the requirements
of the US and EU paediatric legislations, great global benefit could be achieved if
one of the development specifications would be appropriateness for global use. An
expert meeting was convened by the WHO in December 2008 to identify the dosage
forms of medicines most suitable for children with particular attention to conditions
prevailing in the developing countries, and to flag future research required in this
area (WHO 2008c). The most important proposal was a shift from the traditional
paradigm of liquid paediatric formulations to flexible solid dosage forms. Many
stakeholders have subsequently endorsed this recommendation.
Flexible solid oral dosage forms such as tablets that are oro‐dispersible and/or
that can be used for preparation of oral liquids (for example, suspension or solution)
could potentially be used in very young children (0–6 months) provided the product
can be dispersed in breast milk from the mother. This type of product is feasible to
manufacture in facilities that have conventional tableting facilities, but requires
excipients that ensure stability and palatability. Examples of existing dispersible
tablet products suggest that they can be more affordable than standard liquid dosage
forms. These dosage forms could be used for many of the medicines necessary to
treat the diseases that are the major causes of mortality and morbidity in under five-
year-olds (lower respiratory tract infection, malaria, diarrheal diseases).
Some medicines require precise dose measurement or titration. For such oral
medicines, the most suitable dosage form should be based on use of a solid platform
technology (multi particulate solid, including those that could be dispersed to form
a liquid dose), rather than oral liquids. This makes possible production of tailored
doses and strengths as well as preparation as a range of dosage forms such as tablets
or capsules. Examples of currently existing forms are mini‐tablets and spherical
granules (pellets). These dosage forms are feasible to manufacture and can be
produced from standard excipients including those that are pre‐mixed and suitable
for a range of actives, and they have potential flexibility for constructing appropri-
ate FDCs.
Some chemical substances are “difficult molecules”, with problems of perme-
ability and/or solubility (defined using BCS classes). Techniques for these difficult
molecules need to be developed/or evaluated, including manipulation (e.g. spray
drying, micronization) prior to use with some platform technology that may pro-
duce suitable dosage forms for children.
Global Aspects of Drug Development 363
patients and may drive the development of drug resistance in the population.
Overdosing may lead to serious adverse effects in individuals and may negatively
affect the reputation of an efficacious medicine in communities, thereby affecting
use and compliance.
Population pharmacokinetic modelling (POPPK) and simulations have been
undertaken to evaluate some of the recommended ARV and TB treatment regimens
(WHO 2009a). The advantages of using POPPK modelling is that a broad spectrum
of subjects can be included, and covariates for size, age, genotype, binding proteins,
diet, and interacting drugs are incorporated into the model. For many important
medicines in use today, paediatric-specific PK data from large, well-conducted
clinical trials spanning the continuum of the paediatric age spectrum do not
generally exist. Paediatric PK data may be available from only a few published
studies, with small subject cohorts that restrict the ability to accurately determine
the true variability associated with specific PK parameters for each of the drugs.
However, modelling and simulation based on limited PK data in children can be
supplemented to a certain extent with information from adult studies and provide
valuable information, which ideally should be validated by exposure data collected
from subjects of different age ranges. The information from the modelling exercises
can also be used to design future studies of these drugs to better eliminate the
knowledge gaps.
Many essential medicines have not been properly tested in children for efficacy and
safety. Without adequate clinical trials, regulatory authorities cannot approve use of
medicines in children. Approval of paediatric medicines by regulatory authorities,
even the stringent ones, in earlier times were often based on efficacy and safety
data-sets, which would be today considered insufficient. Clinical experience from
years of use may strongly indicate that there are no major paediatric safety concerns
with the dosage used. However, paediatric dosages tend to be biased towards
underdosing as a consequence of conscious or unconscious fear of dose related
toxicity and lack of appropriate PK and dose-ranging studies. These problems
affecting paediatric drug therapy, well illustrated by the TB medicines, are global
and call for additional clinical trials of many medicines having already approval for
use in children.
The need for paediatric clinical trials is global. The general ethical and scientific
principles for clinical trials are the same all over the world, and are discussed in
Section “The Concept of Essential Medicines”. However, differences between high
and lower income countries lead to problems and challenges, which require some
comments.
Global Aspects of Drug Development 365
Clinical trials must be done in the developing world for diseases that do not exist
elsewhere, and to account for variables, which may affect dosing, safety, or efficacy.
These variables include differences in genetic and environmental factors, and
health-care provision. Such trials are necessary and provide a direct benefit for the
paediatric population from which the trial subjects come. It would be unethical not
do the trials, and treat the children without proper knowledge or not treat them at all.
Less developed countries have some characteristics, which make them increas-
ingly attractive for clinical trials not, or at least not primarily, intended to benefit the
local paediatric population. These characteristics include high prevalence of
diseases, commonly in treatment-naı̈ve form, and lower trial costs. Such trials
are usually intended to provide data for regulatory approval of a medicine in the
developed countries, and in the case of paediatric medicines especially in the areas
providing lucrative incentives for development of medicines for children. These
trials are not necessarily inherently unethical, but run the risk of leading to
exploitation, if the paediatric population from which the trial subjects come will
not have access to the medicine once it is approved.
For an individual child participating in a clinical trial in a developing country, the
ethical framework for recruitment and protection of the study subjects is provided
by international agreements (Chapter Ethical Considerations in Conducting Pediat-
ric Research). However, also at the individual level the real situation in a resource-
poor country may often be significantly different from that of a high-income country
child. In the environment the child is living, participation in a clinical trial may be
the only real chance to get a treatment that may be life saving, a maximum benefit on
individual level. In relation to this, the risk–benefit ratio would be positive even
when the risks could be long-term adverse effects not treatable in the local health-
care system or risk of relapse when the child has no longer access to the study
treatment after the trial ends. Children in resource-poor settings have an increased
risk of being exploited. In poor settings almost any form of reimbursement of
expenses may run the risk of being an undue inducement for the family to provide
consent for the participation of the child. Problematic may also be, if the study offers
a big benefit for the local community in the form of an improvement in health-care
infrastructure (facility, equipment etc.) that will remain after the study, but the risks
are borne by the child. However, a clinical trial may also bring risks to the local
community and health-care provision, if it focuses too much of the local resources
and captures the best health-care workers for a single disease, and leads to deterio-
ration of care for other health needs.
Principally the ethical framework of the international agreements makes provi-
sion to take care of these special challenges of the resource poor settings by the
local ethical committees and/or national authorities. In practice, it is not uncommon
that even when a system of ethical assessment and approval is in place paediatric
expertise may be lacking, or at least expertise on paediatric clinical trials of
medicines. A somewhat functional system of ethical assessment lacking appropri-
ate paediatric trials expertise, but recognizing vulnerability and rights of children,
366 K. Hoppu and H.V. Hogerzeil
tends not to approve applications for paediatric trials, often by not at all or belatedly
responding to the applications. While this may protect the children from exploita-
tion, it also denies them the opportunity to have better treatments through research.
The scientific criteria for planning and performance of a valid paediatric clinical
trial are similar all over the world. In the developing world, it may be easier to
recruit enough patients to find a significant difference, and to find treatment-naı̈ve
patients. On the other hand, normal values or validated scales used to measure end-
points may not be available for the population to be studied. Confounding variables
may be completely different or have a different scale. For example the capacity to
offer concomitant non-medical treatment for a psychiatric condition may not be
comparable to other settings and render the results difficult to generalize.
Practical problems in performing trials in developing world settings are numer-
ous, ranging from illiteracy of parents who should give consent, lack of electricity,
and problems of logistics to corruption and unforeseeable changes in regulations,
which may delay or make it impossible to export collected samples for the planned
analysis.
Within the scope of this book it is possible only to give some ideas about the wide
variety of ethical, scientific, and practical challenges of paediatric clinical trials in
developing world settings. It is clear that the international agreements and
conventions on ethics do not go to the level of interpretation needed to handle the
increasing redistribution of paediatric clinical trials to the developing world. Sup-
port to build competency and capacity for paediatric clinical trials is also needed. It
remains to be hoped that the WHO within the tasks set by the WHA 60.20 resolution,
and the main profiteers of the trial redistribution, the US and EU, take initiative to fill
the gaps in the international ethical framework and provide other support needed.
lists and treatment guidelines. Drug regulatory review of medicine for children in
these countries is also highly variable.
After new medicines for children have been developed and appropriate
formulations and data on dosing, safety, and efficacy have become available, the
question comes up how to improve access to these new and better medicines at
country level.
Any discussion on access to medicines for children has to start with the question:
access to which medicines? In practice, this implies that every national essential
medicines programme must first agree on the clinical guidelines for children, and
draw up a list of essential medicines for children. The most sustainable solution is
that the clinical guidelines for children be included in the national clinical
guidelines used for training and supervision, and that the list of essential medicines
for children be included in the national list of essential medicines for supply and
reimbursement (Fig. 1). When the national list of essential medicines for children
has been defined, focused efforts can start to increase funding for these medicines
through government supply, bilateral support, donations, Global Fund grants,
World Bank loans, etc.
This explains also why the selection of essential medicines for children was also
the first and most important step to guide future drug development. In 2006, an
analysis of the then current WHO Model List of Essential Medicines showed that
over hundred medicines listed by WHO did not include a formulation for children,
Treatment choice
Prevention
and care
Fig. 1 Link between selection of essential medicines, clinical guidelines and the supply system
368 K. Hoppu and H.V. Hogerzeil
either because they were simply forgotten, or because they did not exist in the
market. The resulting list of “missing essential medicines for children” added a new
dimension to WHO’s concept of essential medicines.
When new children’s formulations have become available and added to WHO’s
global Model List of Essential Medicines, it is equally important that national
clinicians include the new medicine in their updated national clinical guidelines;
and that the national formulary committee includes the new medicine in their new
national list. In this regard it may help to prepare and present short clinical update-
sheets to make clinicians and formulary committee members aware of the new
evidence.
With regard to quality, there is always a tendency to buy the cheapest medicines
irrespective of quality. This is a dangerous approach, which needs to be resisted.
The product with the lowest price can only be chosen when at least minimum
quality standards are guaranteed. Within the UN system (but also used by the
Global Fund, World Bank, UNITAID and international NGOs), WHO operates a
programme of “prequalification” of suppliers and products for the treatment of
HIV/AIDS, tuberculosis, malaria (including the paediatric formulations for these
diseases) and a few other essential medicines for children (e.g. zinc tablets). This
system is based on rigorous international assessments of the product dossiers and
manufacturing site inspections (www.who.int/medicines; look under “prequali-
fication”). By the end of 2009, 239 products had been prequalified for UN procure-
ment, of which 34 are children’s formulations.
This prequalification programme is of great practical relevance for all national
and international procurement agencies, as it gives clear guidance in which
paediatric products available in international commerce have been approved for
UN procurement. This also removes the need for each and every national regulatory
agency to invest heavily in their own dossier assessments and expensive site
inspections in countries such as India, where most of the cheapest generic
medicines are produced. But the programme also has a special function in
paediatric drug development, by offering a mechanisms by which the quality of
newly developed medicines can be assessed and endorsed at the global level,
facilitating their regulatory uptake and procurement in developing countries.
Prices of children’s medicines are often significantly higher than the cost of adult
dosages making procurement and supply a challenge. There are many ways
to improve affordability of essential medicines, including those for children.
Global Aspects of Drug Development 369
About half of the medicines used are not prescribed in the most cost-effective
manner: overprescription, unnecessary prescription, wrong doses, overuse of
antibiotics, overuse of injections and prescriptions not in line with clinical
guidelines are very common. After that, about half the patients do not adhere to
the treatment; many never collect the medicines of the prescription; do not follow
the instructions or interrupt the treatment before it is completed. All this leads to
enormous medical and economic waste. The situation is not any better in the
treatment of children.
There are many proven effective ways to promote rational and cost-effective
prescribing (WHO 2002), such as the use of clinical guidelines and essential
medicines lists, drugs and therapeutic committees in districts and major hospitals,
and problem-based undergraduate training in pharmacotherapy. In general a com-
bination of interventions is more effective than isolated measures. In the case of
treatment of children, the use of clinical guidelines and standard protocols for use
by doctors and other health workers is the best option; especially for the treatment
and follow-up in rural clinics. This is also the way to promote the introduction and
use of newly developed essential medicines for children.
commitment to a common goal and a framework for action. For example, the 1996
national medicine policy of South Africa (Ministry of Health 1996) strongly
focuses on equity. By the turn of the century, 109 developing countries had
developed a national medicines policy.
With regard to children, in many developing countries the needs are so great
that drastic nation-wide measures are needed. In addition, several aspects of the
problem touch upon other departments, such as the medicine regulatory agency
(for speedy registration of medicines, quality assurance, licensing of national
production), supply and distribution (for inclusion of medicines for children in
the regular medicine supply system) and human resources (for clinical guidelines
and prescriber training programmes); or other ministries, such as the Ministry of
Finance (for additional funding for essential medicines for children, tax reductions,
inclusion of paediatric formulations in health insurance and reimbursement
schemes), the Ministry of Trade (for international trade agreements, patent legisla-
tion, compulsory licenses) and the Ministry of Education (for undergraduate and in-
service training).
WHO gives public health-based guidance to innovation in many ways (Table 2).
First, the list of “missing essential medicines for children” describes exactly which
medicines or formulations are missing. This can help interested companies to
choose a certain niche in the market for drug development. Secondly, the published
criteria for the Model List of Essential Medicines describe exactly which clinical
and safety data will be needed for considering the new medicine for inclusion on
WHO’s Model List of Essential Medicines. This helps companies in designing the
necessary studies and also further strengthens the public health approach to
innovation. These clinical and safety data, which are public, can later also
assist decision-making by national formulary committees. Thirdly, the WHO/UN
prequalification programme describes exactly the quality requirements for the
product application file, again guiding the innovation process and subsequent
national regulatory review.
The advantages for the manufacturers are not only that the clinical, safety, and
quality requirements of the missing paediatric formulations are clearly described
and that the assessment process is predictable. In addition, if the product is indeed
prequalified by WHO, most international and national medicine procurement
agencies are likely to procure the new product, and an increasing number of
national regulatory agencies will fast-track regulatory approval for their private
markets. The advantages for public health authorities are that separate in-depth
regulatory assessments are no longer needed, and that a fair competition is pro-
moted between “prequalified” products of assured quality, leading to lower prices.
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Index
Data Monitoring Committee (DMC), 198, DPI See Dry powder inhalers
199, 236 Dried blood spot (DBS), 82–83, 211
DBS See Dried blood spot Drugs, 170, 171, 173–179 See also
Decision study, 188, 190 Medicinesabsorption, 53–55, 65, 66
Deductive, 129, 130, 137 The Gastrointestinal Tract, 53–55, 70
DeMets, D.L., 192 skin, 53, 55
Depression(s), 21–22, 35–38 abuse, 34, 37
Designs addiction, 34
adaptive, 187–198 assays, 209–212
crossover, 187, 189, 190 clearance(s), 25
response-adaptive, 187–190, 197 disposition, 9, 19–21, 24, 37
sequential, 191–198 distribution, 56–57
Deterministic simulation, 127–129 body composition, 53
Development extracellular water, 53
brain, 19, 22, 23 drug-metabolizing enzymes, 21, 36
changes, 6–9, 13, 18–19, 24–25, 39 elimination, 9, 24
period(s), 6–39 enteral absorption, 19–20
pubertal, 33, 34, 36, 37 excretion, 64–65
window(s), 16–17, 22–23, 27–28, renal function, 64, 65
31–32, 37–39 serum creatinine, 64
Developmental exposure, 129, 138, 144
pharmacokinetics, 51–70 illicit drug use, 37
stage, 150, 153, 154 metabolism
Dexamethasone, 187 cytochromes P450 (CYP450), 57
Diabetes, 18, 28, 31, 34, 37 metabolizing enzymes, 55, 57–60, 62,
Diapers, 206, 207 66, 68–69
Diethylstilbestrol, 286, 287 rash with eosinophilia and systemic
Difference, 182, 184–189, 191, 192 symptoms (DRESS), 174
clinically important, 189 targets, 10–16, 21–23, 25–27, 29–31, 37
clinically relevant, 184, 187, 188 Dry powder inhalers (DPI), 101
relevant, 182, 184, 187, 188, 192 Ductus arteriosus
statistically significant, 187 ductal closure, 13, 14
Direct benefit, 221, 224–230, 233, 237, 238 ductal constriction, 14
Directive 2001/83/EC, 260 ductal tone, 13–14
Disease, 150–162 patent ductus arteriosus (PDA), 8
Disinfectants perinatal switch, 12
alcohols, 334 Dysmenorrhea
aldehydes, 334 therapy, 34
chemicals treatment, 334 Dysmorphisms, 296, 299–300
description, 334
heat, 334–335
iodine, 335 E
oxidizing agents, 335 EaSt, 195
phenolics, 334–335 Eating disorders, 36
physical treatment, 334 Effect
quaternary ammonium compound, 335 actual, 194–195
Diuretics carry-over, 189, 190
furosemide, 14–15 expected, 194–195
thiazide, 14–15 size, 190, 192–195, 197
DMC See Data Monitoring Committee Effervescent dosage forms, 95
Dosages, 182, 183, 189 Efficacy, 183, 187, 195, 196, 198
Dose assessment, 149–162
loading, 7, 9 Elective abortion, 291, 303
maintenance, 9 EMA See European Medicines Agency
376 Index
Suppositories, 97 U
Surrogate endpoints, 150–153, 155, 162 Uncertainty, 128, 129
Surrogate markers, 37, 39 United States Code, 246–247
Symptoms, 151, 153–156, 159–161 United States Congress, 247, 248
neurological, 188 Unlicensed, 340–345
drug, 341–344
Unmet medical needs, 115–118
T Urinary catheters, 205
Tablets Urine, 205–207, 211
dispersible, 95
enteric-coated, 95
orally disintegrating, 97 V
orodispersible, 96, 97, 104, 105 V(d) See Volume of distribution
splitting, 95, 96 Vaccination
sustained-release, 95 AEFI, 318
Taste clinical vaccine trials
electronic tongues, 104 endpoints, proof of efficacy, 326
taste-masking, 97, 104, 105 international databases, 325
taste perception, 104, 105 oral rotavirus vaccine, 327
Teratogenic risk, 287, 288, 290, 293, 296, 301 phase I, II and III, 325–326
Termination phase IV, 327
early, 198, 199 phases, post-marketing
Tests, 182, 184–189, 191–196 assessment, 324, 325
non-inferiority, 185, 188 pre-licensure vaccine, 324–325
one-sided, 185, 188, 194 developments
superiority, 195 academic/private research
triangular, 194–196 laboratories, 321
two-sided, 184, 185, 188, 189, 194 good laboratory practice, 321
Tetracyclines, 288 live-attenuated, 321
Thalidomide, 247, 288 prerequisites, 320–321
Theophylline, 141–143 immunizations, 318
apnea, 10 licensure, 328
therapeutic drug level post-marketing settings, safety assessment
monitoring (TDM), 10 alleged vaccine side effects, 330
Thin film strips, 96–97, 105 “The Brighton Collaboration”, 330
Top down, 127, 129–130, 137–141, 145 causality, 329
Transdermal products, 98 health professionals, 329
Transplant trials immunization programs, 329
renal, 188 nasal influenza vaccine, 329
Transporters, 55–57, 66–68, 70 public trust, 328
developing brain, 19, 22 reactogenicity, 328–329
protein P-gp, 20 risk-benefit, 328
the skin, 37, 38, 57 standardized case definitions, 329–330
transepithelial electrolyte transport, 14–15 preclinical vaccine trials
Trials, 182–199 adjuvants, 322–324
agricultural, 191 FDA and EMEA, 321
clinical, 184–198 non-toxicity proof, 321–322
N-of-1, 190 pharmacodynamic and
non-inferiority, 185 pharmacokinetic, 322
randomized, 188 product characteristics, 322
randomized clinical, 184, 191, 192 three-dimensional visualization, 321
superiority, 185 pre-licensure vaccine trials, 327–328
underpowered, 187–188, 191 EudraCT, PIP, 328
Triangular Test (TT), 194–196 EU Paediatric Regulation, 327–328
Tubular secretion, 134, 139 programs, immunization, 318, 320
Index 383