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SELF EMULSIFYING DRUG DELIVERY SYSTEM (SEDDS): A Review

PALLAVI M. NIGADE*, SWAPNIL L. PATIL, SHRADHA S. TIWARI
Padm. Dr. D Y Patil College Of Pharmacy,
Akurdi, Pune, Maharashtra, India, 411018.
*Corresponding Author Email: swapnilpatil.mun@gmail.com

PHARMACEUTICAL SCIENCES REVIEW ARTICLE

ABSTRACT
Self-emulsifying drug delivery systems (SEDDS), which are isotropic mixtures of oils, surfactants, solvents and co-
solvents/surfactants, can be used for the design of formulations in order to improve the oral absorption of highly
lipophilic drug compounds. It can be orally administered in soft or hard gelatin capsules. These systems form fine
emulsions (or micro-emulsions) in gastro-intestinal tract (GIT) with mild agitation provided by gastric mobility.
Many parameters like surfactant concentration, oil/surfactant ratio, polarity of the emulsion, droplet size and charge
plays a critical role in oral absorption of drug from SEEDS. This formulation enhanced bioavailability due to increase
the solubility of drug and minimizes the gastric irritation. The fact that almost 40% of the new drug compounds are
hydrophobic in nature implies that studies with SEDDS will continue, and more drug compounds formulated as SEDDS
will reach the pharmaceutical market in the future.

KEYWORDS: Self-emulsifying drug delivery systems, isotropic, emulsions, bioavailability

INTRODUCTION 1 ADVANTAGES OF SEEDS:10,11

SEDDS formulations can be simple binary  Quick Onset of Action
systems: lipophilic phase and drug, or lipophilic  Reduction in the Drug Dose
phase, surfactant and drug. The formation of a  Ease of Manufacture & Scale-up
SEDDS requires the use of a co‐surfactant to  Improvement in oral bioavailability
generate a micro emulsion. SEDDS  Inter-subject and Intra-subject variability
formulations are characterized by in vitro lipid and food effects
droplet sizes of 200 nm–5 mm and the  Ability to deliver peptides that are prone
dispersion has a turbid appearance. to enzymatic hydrolysis in GIT
Self-emulsifying drug delivery systems  No influence of lipid digestion process
(SEDDS) are mixtures of oils and surfactants,  Increased drug loading capacity
ideally isotropic, and sometimes containing co- DISADVANTAGES OF SEDDS 11
solvents, which emulsify spontaneously to  Traditional dissolution methods do not
produce fine oil-in-water emulsions when work, because these formulations
introduced into aqueous phase under gentle potentially are dependent on digestion
agitation4-8,. Recently, SEDDS have been prior to release of the drug.
formulated using medium chain tri-glyceride  This in vitro model needs further
oils and non-ionic surfactants, the latter being development and validation before its
less toxic. Upon per oral administration, these strength can be evaluated.
systems form fine emulsions (or micro-  Further development will be based on in
emulsions) in gastro-intestinal tract (GIT) with vitro - in vivo correlations and therefore
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mild agitation provided by gastric mobility2,4,9. different prototype lipid based

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formulations needs to be developed and a surfactant mixture into which the drug is
tested in vivo in a suitable animal model. incorporated. They emulsify when mixed with
 The drawbacks of this system include aqueous environment. The self-emulsification
chemical instabilities of drugs and high process is specific to the particular pair of oil
surfactant concentrations in formulations and surfactant, surfactant concentration,
(approximately 30-60%) which GIT. oil/surfactant ratio, and the temperature at
which self-emulsification occurs. After self-
FORMULATION OF SEDDS: dispersion, the drug is rapidly distributed
The following points should be considered in throughout the gastrointestinal tract as fine
the formulation of a SEDDS: droplets. The SDLFs are of two kinds namely,
Selection of oils, surfactant and co-solvent Self-Emulsifying Drug Delivery Systems (SEDDS)
based on the solubility of the drug .The formed using surfactants of HLB < 12 and Self-
preparation of SEDDS formulation by dissolving Micro Emulsifying Drug Delivery Systems
the drug in mixture of oil, surfactant, co- (SMEDDS) formed surfactants of HLB > 12.
solvents .The addition of drug to SEDDS is Both SEDDS and SMEDDS are stable
critical because the drug interferes with the preparations and improve the dissolution of
self emulsifying process to certain extent, the drug due to increased surface area on
which leads to a change in optimal oil- dispersion. Many researchers have reported
surfactant ratio so design of optimal SEDDS applications of SEDDS for delivering and
require pre-formulation solubility and phase targeting lipophilic drugs,
diagram study. Recently synthesized drug that e.g.: Coenzyme Q1014, Vitamin E15,
are being discovered are lipophilic in nature Halofantrine16 and Cyclosporine A17.
and have poor aqueous solubility, thereby
posing problems in their formulation into THE EMULSIFICATION PROCESS:
delivery systems. Because of their low aqueous Self-emulsification is a phenomenon which has
solubility and low permeability, dissolution been widely exploited commercially in
and/or release rate from the delivery system formulations of emulsifiable concentrates of
forms the rate limiting step in their absorption herbicides and pesticides18. Concentrates of
and systemic availability. crop sprays are to be diluted by the user, such
More than 60% of potential drug products as farmers or house-hold gardeners, allowing
suffer from poor water solubility. For the very hydrophobic compounds to be
therapeutic delivery of lipophilic active transported efficiently. In contrast, SMEDDS,
moieties (BCS class II drugs), lipid based using excipients acceptable for oral
formulations are inviting increasing attention12, administration to humans, have not been
13
. Currently a number of technologies are widely exploited and knowledge about their
available to deal with the poor solubility, physicochemical principles is therefore limited.
dissolution rate and bioavailability of insoluble (a) Mechanism of Self Emulsification 19:
drugs. The Self-Dispersing Lipid Formulations In emulsification process the free energy (ΔG)
(SDLFs) is one of the promising approaches to associated is given by the equation:
overcome the formulation difficulties of ΔG = ΣNiπri ------------------------------ (1)
various hydrophobic/lipophilic drugs and to In which ‘N’ is Number of droplets with radius
43

improve the oral bioavailability of poorly ‘r’ and ‘σ’ is interfacial energy. It is apparent
absorbed drugs11, 33. The SDLFs contain oil and from equation that the spontaneous formation
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of the interface between the oil and water • The rate of digestion (for formulations
phases is energetically not favored. The system susceptible to digestion) and possibly
commonly classified as SEDDS have not yet • The solubilization capacity of the digested
been shown to emulsify spontaneously in the Formulation.
thermodynamic sense. EXCIPIENTS:
The emulsification process may be associated A) OILS 11, 26, 27:-
with the ease with which water penetrates the The oil represents one of the most important
oil-water interface with the formation of liquid excipients in the SEDDS formulation not only
crystalline phases resulting in swelling at the because it can solubilize the required dose of
interface thereby resulting in greater ease of the lipophilic drug or facilitate self
emulsification20-22. However, for system emulsification but also and mainly because it
containing co- surfactant, significant can increase the fraction of lipophilic drug
partitioning of components between the oil transported via the intestinal lymphatic
and aqueous phases may take place leading to system, thereby increasing absorption from
a mechanism described as “diffusion and the GI tract depending on the molecular
stranding”, where by the oil is solubilized, nature of the triglyceride 28-30. Both long and
leading to migration in to the aqueous phase. medium chain triglyceride (LCT and MCT) oils
b) Dilution phases: with different degrees of saturation have been
Upon dilution of a SMEDDS formulation, the used for the design of self-emulsifying
spontaneous curvature of the surfactant layer formulations.
changes via a number of possible liquid B) SURFACTANTS 31, 32:
crystalline phases. The droplet structure can Several compounds exhibiting surfactant
pass from a reversed spherical droplet to a properties may be employed for the design of
reversed rod-shaped droplet, hexagonal phase, self-emulsifying systems, but the choice is
lamellar phase, cubic phase and various other limited as very few surfactants are orally
structures until, after appropriate dilution, a acceptable. The most widely recommended
spherical droplet will be formed again dilution. ones being the non-ionic surfactants with a
EXCIPIENTS USED IN SEDDS23-25: relatively high hydrophilic-lipophilic balance
Pharmaceutical acceptability of excipients and (HLB) 34. Safety is a major determining factor in
the toxicity issues of the components used choosing a surfactant
makes the selection of excipients really critical. The four main groups of surfactants are
There is a great restriction as which excipients defined as following-
to be used. Early studies revealed that the self A) Anionic surfactants
emulsification process is specific to the nature B) Cationic surfactant
of the oil/surfactant pair, the surfactant C) Ampholytic surfactants
concentration and oil/surfactant ratio, the D) Nonionic surfactants
concentration and nature of co-surfactant and A) Anionic Surfactants:- where the hydrophilic
surfactant/co-surfactant ratio and the group carries a negative charge such as
temperature at which self emulsification carboxyl (RCOO-), sulphonate (RSO3 -) or
occurs. sulphate (ROSO3 -).
Important parameter for excipient-to sedds: Examples: Potassium laurate, sodium lauryl
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• The solubility of drug in the formulation as sulphate.

such and upon dispersion (for SEDDS),
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B) Cationic surfactants: - where the B) Polarity of the lipophilic phase:

hydrophilic group carries a positive charge. The polarity of the lipid phase is one of the
Example: quaternary ammonium halide. factors that govern the drug release from the
C) Ampholytic surfactants: - (also called micro emulsions. The polarity of the droplet is
zwitterionic surfactants) contain both a governed by the HLB, the chain length and
negative and a positive charge. Example: degree of unsaturation of the fatty acid, the
sulfobetaines. molecular weight of micronized for their
D) Nonionic surfactants: - where the propensity to inhibit crystallization and,
hydrophilic group carries no charge but derives thereby, generate and maintain the
its water solubility from highly polar groups supersaturated state for prolonged time
such as hydroxyl or polyoxyethylene. period.
Examples: Sorbitan esters (Spans), poly - CRITERIA OF DRUG PROPERTIES: 12-13
sorbates (Tweens). BCS (Bio-pharmaceutical classification system)
C) CO-SOLVENTS35:- classifies the drug based on solubility and
The production of an optimum SEDDS requires permeability of a drug. Mainly Class 2 (Low
relatively high concentrations (generally more Solubility, High Permeability) is used for
than 30% w/w) of surfactants, thus the SEDDS.
concentration of surfactant can be reduced by Ex. Azithromycin Carbamazepine Carvedilol
incorporation of co surfactant.Role of the co- Chlorpromazine Cisapride Ciprofloxacin.
surfactant together with the surfactant is to DOSAGE FORM OF SEDDS:
lower the interfacial tension to a very small (1) Oral delivery:
even transient negative value36. (A) Self emulsifying capsule 39-42:
.At this value the interface would expand to After administration of capsules containing
form fine dispersed droplets, and subsequently conventional liquids SE formulations,
adsorb more surfactant and surfactant/co- microemulsion droplets form and
surfactant until their bulk condition is depleted subsequently disperse in the GIT to reach site
enough to make interfacial tension positive of absorption. If irreversible phase separation
again. However, the use of co-surfactant in self of microemulsion occurs an improvement of
emulsifying systems is not mandatory for many drugs absorption can’t be expected. For
non-ionic surfactants. The selection of handling this problem, sodium dodecyl sulfate
surfactant and co-surfactant is crucial not only was added into the SE formulation43.
to the formation of SEDDS, but also to (B) Self--Emulsifying sustained / controlled
solubilization of the drug in the SEDDS. release:
FACTOR AFFECTING OF SEDDS: Combination of lipids and surfactant has
A) Nature and dose of the drug: presented great potential preparing SE tablets.
Drugs which are administered at very high SE tablets are of great utility in obviating
dose are not suitable for unless they exhibit adverse effect. Inclusion of indomethacin (or
extremely good solubility in at least one of the other hydrophobic NSAID) for example, into SE
components of SMEDDS, preferably lipophilic tablets may increase its penetration efficacy
phase. The drugs which exhibit limited through GI mucosal membrane, potentially
solubility in water and lipids (typically with log reducing GI bleeding37, 38.
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P values of approximately are most difficult to (C) Self emulsifying sustained / controlled
deliver by SMEDD. release pellets:
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Pellets, as a multiple unit dosage form, possess e) Changes in the physical barrier function of
many advantages over conventional solid the GI tract.
dosage form, such as flexiability of f) The polarity of lipid phase is one of the
manufacture, reducing intra subject and inter factors that govern the release from the micro-
subject variability of plasma profile and emulsion.
minimizing GI irritation without lowering drug
bioavailability. METHOD OF PREPARATION:
(D) Self emulsifying solid dispersions: A) Solidification techniques for transforming
Solid dispersions could increase the dissolution liquid/semisolid44:
rate and bioavailability of poorly water soluble Various solidification techniques are as listed
drugs but still some manufacturing difficulties below;
and stability problems existed. Serajuddin 1) Capsule filling with liquid and semisolid
pointed out that these difficulties could be self-emulsifying formulations:
surmounted by the use of se excipients31. Capsule filling is the simplest and the most
(2) Topical Delivery: common technology for the encapsulation of
Topical administration of drugs can have liquid or semisolid SE formulations for the oral
advantages over other methods for several route. For semisolid formulations, it is a four-
reasons, one of which is the avoidance of step process:
hepatic first pass metabolism of the drugs and A) Heating of the semisolid excipient to at least
related toxicity effects. 20˚C above its melting point.
(3) Oculars and Pulmonary delivery: B) Incorporation of the active substances (with
For the treatment of eye disease, drugs are stirring).
essentially delivered topically o/w C) Capsule filling with the molt cooling to room
microemulsion have been investigated for temperature. For liquid formulations, it
ocular administration, to dissolve poorly involves a two-step process.
soluble drugs, to increase absorption and to D) Filling of the formulation into the capsules
attain prolong release profile. followed by sealing of the body and cap of the
(4) Parenteral delivery: capsule, either by banding or by micro spray
Parenteral administration of drugs with limited sealing.
solubility is a major problem in B) Spray drying:
industrybecause of the extremely low amount Essentially, this technique involves the
of drug actually delivered as target site. preparation of a formulation by mixing lipids,
BIOPHARMACEUTICAL ASPECTS: surfactants, drug, solid carriers, and
The ability of lipids and/or food to enhance the solubilization of the mixture before spray
bioavailability of poorly watersoluble drugs is drying. The solubilized liquid formulation is
well known. Although incompletely then atomized into a spray of droplets.
understood, the currently accepted view is The droplets are introduced into a drying
that lipids may enhance bioavailability via a chamber, where the volatile phase (e.g. the
number of potential mechanisms, including. water contained in an emulsion)
a) Alterations (reduction) in gastric transit. evaporprepared into tablet pattern and the
b) Increases in effective luminal drug solubility. drying chamber design are selected according
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c) Stimulation of intestinal lymphatic transport to the drying characteristic the product and
d) Changes in the biochemical barrier function powder specification.
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Fig 1 -Spray Drying.

C) Adsorption to solid carriers: stability can lead to phase separation of the
Free flowing powders may be obtained from excipient, affecting not only formulation
liquid SE formulations by adsorption to solid performance, but visual appearance as well. In
carriers. The adsorption process is simple and addition, incompatibilities between the
just involves addition of the liquid On to formulation and the gelatin capsules shell can
carriers by mixing in a blender. lead to brittleness or deformation, delayed
D) Melt granulation: disintegration, or incomplete release of drug.
Melt granulation is a process in which powder a) Heating cooling cycle: Six cycles between
agglomeration is obtained through the refrigerator temperature (40ºC) and 45ºC
addition of a binder that melts or softens at with storage at each temperature of not
relatively low temperatures. less than 48 hr is studied. Those
E) Melt extrusion/extrusion spheronization: formulations, which are stable at these
Melt extrusion is a solvent-free process that temperatures, are subjected to
allows high drug loading (60%), as well as centrifugation test.
45
content uniformity . Extrusion is a procedure b) Centrifugation: Passed formulations are
of product of uniform shape and density, by centrifuged thaw cycles between 21 ºC and
forcing it through a die under controlled +25 ºC with storage at temperature for not less
temperature, product flow, and pressure than 48 hr is done at 3500 rpm for 30 min.
46
conditions . Those formulations that does not show any
phase separation are taken for the freeze thaw
47-49
EVALUATION :- stress test.
A) Thermodynamic stability studies: c) Freeze thaw cycle: Three freeze for the
The physical stability of a lipid –based formulations. Those formulations passed this
formulation is also crucial to its performance, test showed good stability with no phase
which can be adversely affected by separation, creaming, or cracking.
47

precipitation of the drug in the excipient B) Dispersibility test:-

matrix. In addition, poor formulation physical
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The efficiency of self-emulsification of oral be easily pourable into capsules and such
nano or micro emulsion is assessed using a system should not too thick to create a
standard USP XXII dissolution apparatus 2. One problem. The rheological properties of the
milliliter of each formulation was added to 500 micro emulsion are evaluated by Brookfield
mL of water at 37 ± 0.5 0C. A standard stainless viscometer.
steel dissolution paddle rotating at 50 rpm This viscosities determination conform
provided gentle agitation. The in vitro whether the system is w/o or o/w. If system
performance of the formulations is visually has low viscosity then it is o/w type of the
assessed using the following system and if high viscosities then it are w/o
Grading system: type of the system.
Grade A: Rapidly forming (within 1 min) E) Droplet Size Analysis Particle Size
nanoemulsion, having a clear or bluish Measurements:
appearance. The droplet size of the emulsions is
Grade B: Rapidly forming, slightly less clear determined by photon correlation
emulsion, having a bluish white appearance. spectroscopy (which analyses the fluctuations
Grade C: Fine milky emulsion that formed in light scattering due to Brownian motion of
within 2 min. the particles) using a Zetasizer able to measure
Grade D: Dull, grayish white emulsion having sizes between 10 and 5000 nm.
slightly oily appearance that is slow to emulsify APPLICATIONS:
(longer than 2 min).  Improvement in Solubility and
Grade E: Formulation, exhibiting either poor or bioavailability:
minimal emulsification with large oil globules If drug is incorporated in SEDDS, it increases
present on the surface. the solubility because it circumvents the
Grade A and Grade B formulation will remain dissolution step in of Class-П drug (Low
as nanoemulsion when dispersed in GIT. While solubility/high permeability). Ketoprofen, a
formulation falling in Grade C could be moderately hydrophobic (log P 0.979)
recommend for SEDDS formulation. nonsteroidal anti-inflammatory drug (NSAID),
C) Turbidimetric Evaluation: is a drug of choice for sustained release
Nepheloturbidimetric evaluation is done to formulation has high potential for gastric
monitor the growth of emulsification. Fixed irritation during chronic therapy. Also because
quantity of Selfemulsifying system is added to of its low solubility, ketoprofen shows
fixed quantity of suitable medium (0.1N incomplete release from sustained release
hydrochloric acid) under continuous stirring formulations.
(50 rpm) on magnetic plate at ambient This formulation enhanced bioavailability due
temperature, and the increase in turbidity is to increase the solubility of drug and minimizes
measured using a turbidimeter. However, the gastric irritation. Also incorporation of
since the time required for complete gelling agent in SEDDS sustained the release of
emulsification is too short, it is not possible to Ketoprofen. In SEDDS, the lipid matrix
monitor the rate of change of turbidity (rate of interacts readily with water, forming a fine
emulsification), particulate Oil in-water (o/w) emulsion. The
D) Viscosity Determination: emulsion droplets will deliver the drug to the
48

The SEDDS system is generally administered in gastrointestinal mucosa in the dissolved state
soft gelatin or hard gelatin capsules. So, it can readily accessible for absorption. Therefore,
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increase in AUC i.e. bioavailability and Cmax is This problem can be successfully overcome
observed with many drugs when presented in when Ketoprofen is presented in SEDDS
SEDDS. formulation. This formulation enhanced
 Protection against Biodegradation: bioavilability due to increase the solubility of
The ability of self emulsifying drug delivery drug and minimizes the gastric irritation. Also
system to reduce degradation as well as incorporation of gelling agent in SEDDS
improve absorption may be especially useful sustained the release of Ketoprofen.
for drugs, for which both low solubility and FUTURE TREND:
degradation in the GI tract contribute to a low In relation to formulation development of
oral bioavailability. Many drugs are degraded poorly soluble drugs in the future, there are
in physiological system, may be because of now techniques being used to convert
acidic PH in stomach, enzymatic degradation liquid/semi-solid SEDDS and SMEDDS
or hydrolyte Such drugs when presented in the formulations into powders and granules, which
form of SEDDS can be well protected against can then be further processed into
these degradation processes as liquid conventional 'powder-fill' capsules or even
crystalline phase in SEDDS might be an act as compressed into tablets.
ebarrier between degradating environment
and the drug. Hot melt granulation is a technique for
Ex: - Acetylsalicylic acid (Log P = 1.2, Mw=180), producing granules or pellets, and by using a
a drug that degrades in the GI tract because it waxy solubilising agent as a binding agent, up
is readily hydrolyzed to salicylic acid in an acid to 25% solubilising agent can be incorporated
environment. The oral bioavailability of in a formulation. There is also increasing
undegraded acetylsalicylic acid is improved by interest in using inert adsorbents, such as the
73% by the Galacticles Oral Lipid Matrix Neusilin products for converting liquids into
 Controlling the release of drug: powders – which can then be processed into
Different formulation approaches that have powder fill capsules or tablet.
been sought to achieve sustained release, Oral delivery of poorly water-soluble
increase thebioavailability, and decrease the compounds is to pre-dissolve the compound in
gastric irritation of ketoprofen include a suitable solvent and fill the formulation into
preparation of matrix pellets of nano- capsules.
crystalline ketoprofen, sustained release The main benefit of this approach is that pre-
ketoprofen microparticles and floating oral dissolving the compound overcomes the initial
ketoprofen systems and transdermal systems rate limiting step of particulate dissolution in
of ketoprofen. Preparation and stabilization of the aqueous environment within the GI tract.
nano-crystalline or improved solubility forms However, a potential problem is that the drug
of drug may pose processing, stability, and may precipitate out of solution when the
economic problems. formulation disperses in the GI tract.
49
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Table 1: MARKETED SEDDS FORMULATION 40, 49-52:

Brand name Drug used Dosage form Company
Neoral Cyclosporine SGC Novartis
Norvir Ritonavir SGC Abott laboraties
Fortovase Saquinavir SGC Hoffmann roche
Agenerase Amprenavir SGC GSK
Convulex Volporic acid SGC Pharmacia

CONCLUSION 6. Craig DQM, Lievens HSR, Pitt KG, Storey DE. (1993).
An investigation into the physic-chemical properties
SMEDDS formulation can be optimized for the
of self-emulsifying systems using low frequency
delivery of hydrophobic compounds with drug dielectric spectroscopy surface tensions
loading; minimum surfactant concentration measurements and particle size analysis. Int J
and proper infinite dilution can be achieved Pharm, 96, 147-155.
7. Charman SA, Charman WN, Rogge MC, Wilson TD,
without drug precipitation.
Dutko FJ, Pouton CW. (1992).Self-emulsifying drug
Self-emulsifying drug delivery system can be delivery systems: formulation and
use for the formulations of drugs compounds biopharmaceutical evaluation of an investigational
with poor aqueous stability. Development of lipophilic compound. Pharm. Res. 9, 87–93.
this technology SEDDS will continue to enable 8. Constantinides PP. Lipid microemulsion for
improving drug dissolution and oral absorption
novel applications in drug delivery system.
Physical and biopharmaceutical aspects. J Pharm
SEDDS have been shown to be reasonably Res, 12,1561-1572
successful in improving the oral bioavailability 9. Pouton CW. (1985). Self emulsifying drug delivery
of poorly water-soluble and Traditional system assessment of the efficiency of
emulsification. Int J Pharm, 27,335-348.
preparation of SEDDS involves dissolution of
10. Patel PA, Chaulang GM. Self Emulsifying Drug
drugs in oils and their blending with suitable Delivery System: A Review. Research J Pharm and
solubilizing agents. Tech 2008; 1(4): 313‐323.
11. Hauss DJ, Fogal SE. (1998). Lipid-based delivery
systems for improving the bioavailability and
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*Corresponding Author:
SWAPNIL L. PATIL*
Padm. Dr. D Y Patil College Of Pharmacy,
Akurdi, Pune, Maharashtra, India, 411018.
52
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