Indo American Journal of Pharmaceutical Research, 2014
ISSN NO: 2231-6876
REVIEW ON: SOLUBILITY ENHANCEMENT OF POORLY WATER SOLUBLE DRUG
Sachin S. Gaikwad*, Rahul S. Mhalaskar, Yogesh D. Mahale, Nitin P. Jain
SND College of Pharmacy, Babhulgaon, Yeola, Dist-Nashik 423401 Maharashtra (INDIA).
ARTICLE INFO
Article history
Received 10/11/2014
Available online
30/11/2014
Keywords
Solubility,
Solid Dispersion,
BCS Classification.
ABSTRACT
Solubility is one of the important parameter to attain desired concentration of drug in
systemic circulation for pharmacological response to be shown. It is vital to improve the
solubility and dissolution rate for poorly soluble drugs since these drugs possess low
absorption and bioavailability. About 40% of all new chemical entity has poor bioavailability.
Increasing the bioavailability of poorly soluble drugs will be one of the biggest challenges for
formulation scientists in the future. This review is intended to discuss thoroughly the various
traditional novel techniques like sono crystallization, spray freezing in to liquid, pearl milling,
solid dispersion, salt formation and pH adjustment etc. for solubility enhancement of
hydrophobic drugs for oral pharmaceutical formulation and also tried to focus on the
polymers used for to achieve solubility enhancement, process of Solubilization and factor
affects on it. In this article we focused on, solubility of the drug is the most significant factor
and prime requirement for to achieve good bioavaibility after the absorption of drug so it is
most critical factor in the formulation development.
Copy right © 2014 This is an Open Access article distributed under the terms of the Indo American journal of Pharmaceutical
Research, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
www.iajpr.com
Page
Please cite this article in press as Sachin S. Gaikwad et al. Review on: Solubility Enhancement of Poorly Water Soluble Drug.
Indo American Journal of Pharm Research.2014:4(11).
5530
Corresponding author
Sachin S. Gaikwad
Department of Pharmaceutics,
SND College of Pharmacy, Babhulgaon,
Yeola, Dist-Nashik 423401 Maharashtra (INDIA),
sachingaikwad619@gmail.com,
+91-9860070924
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
INTRODUCTION
Therapeutic efficiency of a drug is not only depends upon the bioavailability but also the solubility of drug molecules. Drug
solubility is the greatest concentration of the drug dissolved in the solvent under specific condition of temperature, pH and pressure.
As solubility is an important determinant in drug liberation hence it plays a key function in its bioavailability. For absorption of any
drug it must be present in the form of an aqueous solution at the site of absorption. About 40% of all new chemical entities have poor
bioavailability. The bioavailability can be increased by changes in disintegration and dissolution. Aqueous solubility smaller than 1
μg/ml will definitely create a bioavailability problem and will affects the efficacy of the drug. There are number of methods through
which aqueous solubility of the drug can be increased. Especially for class II substances according to the Bio pharmaceutics
Classification System (BCS), the bioavailability may be improved by raising the solubility and dissolution rate of the drug in the
gastro-intestinal fluids [1].
There are many approaches accessible and reported in literature to enhance the solubility of poorly water soluble drug. The
techniques are selected on the basis of certain aspects such as property of drug under consideration, nature of excipients to be selected
and nature of intended dosage form [2].
The difficulty is even more intense for drug such as intraconazole and carbamazepine as they are poorly soluble in both
aqueous and organic media, and for drugs having a log p (The logarithm of the ratio of the concentrations of the un-ionized solute in
the solvents is called log P) value of 2 Such drugs often have an erratic absorption profile and highly variable bioavailability because
their performance is dissolution rate limited and is affected by the fed / fasted state of the patient.
There are successive two processes can be identified to describe the oral absorption of drugs from solid dosage forms:
• Dissolution of the drug in vivo to produce a solution and
• Transport of the dissolved drug across the gastrointestinal membrane.
Each process can be characterized by a rate constant. If the rate of dissolution of the drug is significantly slower than the rate
of absorption, the dissolution of the drug becomes the rate-limiting step in the absorption process. Consequently, numerous attempts
have been made to modify the dissolution characteristics of certain drugs in an effort to attain more rapid and more complete
absorption. The particle size of the drug is having great importance in the transport from the gastrointestinal (GI) tract to the site of
action by increasing the dissolution rate in the GI tract [3].
The techniques generally employed for solubilization of drug includes micronization, chemical modification, pH adjustment,
solid dispersion, complexation, co‐solvency, micellar solubilization and hydrotropy etc. Solubilization of poorly soluble drugs is a
often encountered dispute in screening studies of new chemical entities as well as in formulation design and development. The
solubility of a drug is represented through various concentration expressions such as parts, percentage, molarity, molality volume
fraction mole fraction [4].
The Indian Pharmacopeia classified the solubility of drugs [5] in seven classes as listed in Table 1.
Table 1: IP Solubility criteria.
Descriptive term
Very soluble
Freely soluble
Soluble
Sparingly soluble
Slightly soluble
Very slightly soluble
Practically insoluble
Part of solvent required per part of solute
Less than 1
From 1 to 10
From 10 to 30
From 30 to 100
From 100 to 1000
From 1000 to 10,000
10,000 and over
Page
Class II ‐Low Solubility, High Permeability
Class II drugs have a high absorption number but a low dissolution number. In vivo drug dissolution is then a rate limiting
step for absorption apart from at a very high dose number. The bioavailability of these products is likely to be dissolution‐rate limited,
for this reason, a correlation between in vivo bioavailability and in vitro dissolution rate may be observed.
e.g. Phenytoin, Danazol, Ketoconazole, Mefenamic acid, Nifedinpine
5531
BCS Classification: [6]
Class I-High Solubility, High Permeability
Class I drugs show a high absorption number and a high dissolution number. For those Class I compounds formulated as
immediate release products, dissolution rate generally exceeds gastric emptying so, nearly 100% absorption can be predictable if at
least 85% of a product dissolves inside 30 min of in vitro dissolution testing across a range of pH values accordingly, in vivo
bioequivalence data are not necessary to assure product comparability.
E.g. metoprolol, diltiazem, verapamil, propranolol
www.iajpr.com
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
Class III – High Solubility, Low Permeability
In this class for drug absorption permeability is rate limiting step. These drugs show a high variation in the rate and amount
of drug absorption. Dissolution will most likely occur very rapidly but absorption is permeability‐rate limited so there has been some
proposal that as extended as the test and reference formulations do not contain agents that can modify drug permeability or GI transit
time, waiver criteria similar to those associated with Class I compounds may be appropriate.
e.g. Cimetidine, Acyclovir, Neomycin B, Captopril
Class IV- Low Solubility, Low Permeability
Those compounds have a poor bioavailability usually they are not well absorbed over the intestinal mucosa and a high
variability is expected with very poor oral bioavailability. These compounds are not only difficult to dissolve but once dissolved, often
show incomplete permeability across the GI mucosa. These drugs tend to be extremely tricky to formulate and can exhibit very large
inter subject and intra subject variability.
Class boundaries:
Highly Soluble:
When the highest dose strength is soluble in < 250 ml water over a pH range of 1 to 7.5 then drug substance is considered
highly soluble
Highly Permeable:
When the extent of absorption in humans is determined to be > 90% of an administered dose then drug substance is
considered highly permeable.
Rapidly Dissolving:
A drug product is considered to be rapidly dissolving when > 85% of the labeled amount of drug substance dissolves within
30 minutes using USP apparatus I or II in a volume of < 900 ml buffer solutions.
Process of solubilization
The process of Solubilization involves the breaking of inter-ionic or intermolecular bonds in the solute, the separation of the
molecules of the solvent to provide space in the solvent for the solute, interaction between the solvent and the solute molecule or ion
shown in figure 1. [7].
www.iajpr.com
Page
Factor affecting solubilization:
Molecular size:
Increasing the particle size or its molecular weight of substance will decrease its solubility. Larger molecules are not
easy to encircle with solvent molecules in order to solvate the substance. In the case of organic compounds the quantity of carbon
branching will increase the solubility since more branching will reduce the size (or volume) of the molecule and make it easier to
solvate the molecules with solvent.
5532
Figure 1: Steps of Solubilization.
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
Temperature:
If the solution process absorbs energy then the temperature is increased as the solubility will be increased. If the solution
process releases energy then the solubility will decrease with increasing temperature. Generally, an increase in the temperature of the
solution increases the solubility of a solid solute. For all gases, solubility decreases as the temperature of the solution increases.
Pressure:
For gaseous solutes, solubility is increases with the application of presser. For solids and liquid solutes, changes in
pressure have nearly no effect on solubility.
Particle size:
The dimension of the solid element influences the solubility because particle size inversely proportional to the surface area.
The larger surface area allows a greater interaction with the solvent. The effect of particle size on solubility can be describe by Eq.1
log S/S0 = 2γ V/2.303 RTr
………………Eq. 1
Where, S is the solubility of infinitely large particles.
S0 is the solubility of fine particles.
V is molar volume.
r is the radius of the fine particle.
Polymorphs:
The shape or habit of a crystal of a given substance may differ but the angles between the faces are forever constant. The
ability for a substance to crystallize in more than one crystalline form is polymorphism. It is possible that all crystals can crystallize in
different forms or polymorphs. If the change from one polymorph to another is reversible, the process is called enantiotropy. If the
system is monotropic, there is a transition point above the melting points of both polymorphs. The two polymorphs cannot be
transformed from one another without undergoing a phase transition. Polymorphs can differ in melting point. Since the melting point
of the solid is related to solubility, so polymorphs will have different solubilities. Usually the range of solubility differences between
different polymorphs is only 2-3 folds due to comparatively small differences in free energy [8].
Rate of solution:
The rate of solution is determination of how fast substances dissolve in solvents. A various factors affecting rate of solution likeSize of the particles:
Breaking a solute into smaller pieces increases its surface area, when the total surface area of the solute particles is increased;
the solute dissolves more rapidly because the action takes place only at the surface of each particle and hence increases its rate of
solution.
Temperature:
For liquids and solid solutes, rising the temperature not only increases the amount of solute that will dissolve but also
increases the rate at which the solute will dissolve. For the gases reverse is true.
Amount of solute already dissolved:
When there is little solute previously in solution, dissolution takes place relatively rapidly. As the solution approaches the
point where no solute can be dissolved, dissolution takes place more slowly.
Stirring:
With liquid and solid solutes, stirring brings fresh portions of the solvent in contact with the solute, thereby increasing the
rate of solution [7].
www.iajpr.com
Page
Surfactants:
Conservative approach to solubilize a poorly soluble substance is to reduce the interfacial tension between the surface of
solute and solvent for better wetting and salvation interaction. A wide variety of surfactants like polyglycolized glyceride, tweens,
spans, polyoxyethylene stearates and synthetic block copolymers like poly (propylene oxide)-poly (ethylene oxide)- poly (propylene
oxide) like poloxamers based micelles, Poly (beta-benzyl-L-aspartate)-b-poly (ethylene oxide), Poly (caprolactone)-b-poly (ethylene
oxide) etc are very successful as excipient and carrier for dissolution enhancement. Improvement of drug solubility by using the
amphiphilic surfactants is due to lowering surface tension between drug and solvent, improvement of wetting characteristics and
micellar solubilization [9].
5533
Methods of solubility enhancement:
There are various techniques available to improve the solubility of poorly soluble drugs.
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
pH adjustment:
It is well documented that the influence of the changes in pH inside the gastrointestinal tract upon the bioavailability of
pharmaceuticals. The absorption of drug is largely dependent upon diffusion, which vary with pH of the individual regions within the
gastrointestinal tract, the pKa of the drug and permeability, which are not only moderated by the surface area of the region in which it
is released, but also the regional pH effects upon drug ionization. By applying a pH change, poorly water soluble drugs with parts of
the molecule that can be protonated (base) or deprotonated (acid) may potentially be dissolved in water. While the significance of
critical parameters like salt selection and pH adjustment has been stressed on pre-formulation, the use of pH altering excipients within
drug delivery systems is also of significant utility. pH adjustment can in principle be used for both oral and parenteral administration.
Because blood is a strong buffer, upon intravenous administration the poorly soluble drug may be precipitate with pH between 7.2 –
7.4. To assess the suitability of the approach, the buffer capacity and tolerability of the selected pH are important to consider. In the
stomach the pH is around 1 to 2 and in the duodenum the pH is between 5-7.5, so upon oral administration the degree of solubility is
also likely be influenced as the drug passes through the intestines. Solubilized excipients that boost environmental pH within a dosage
form (tablet or capsule), to a range higher than pKa of weakly-acidic drugs increases the solubility of that drug, those excipients which
act as alkalizing agents may increase the solubility of weakly basic drugs [9].
Salt formation:
Salt formation of poorly soluble drug candidates (weak acids and bases) has been a strategy for several decades to enhance
solubility. It is an successful method in parenteral and other liquid formulations, as well as in solid dosage forms of approximately 300
new chemical entities approved by the FDA during the 12 years from 1995 to 2006 for marketing, 120 were in salt forms. In count,
out of the 101 approved salts of basic drugs, 54 salts were prepared with hydrochloric acid, representing the hydrochloride was the
predominant salt form the aqueous solubility of an acidic or basic drug as a function of pH dictates whether the compound will form
suitable salts. The pH-solubility interrelationships also dictate what counter ions would be necessary to form salts, how easily the salts
may dissociate into their free acid or base forms, what their dissolution behavior would be under different GI pH conditions, and
whether solubility and dissolution rate of salts would be influenced by common ion. Several reviews have outlined general strategies
and considerations for salt selection. For the salt formation drug should have ionizable groups that will assist salt formation. The
criteria used to select counter ion is as follows:
a) There should be least difference of 2-3 pKa units between the drug and the counter ion.
b) Counter ion should decrease crystal lattice forces.
c) It must be FDA approved or should have sufficient toxicological data to support the selection of the counter ion.
d) This technique has tremendous capability to enhance dissolution rate but it is grasped with disadvantages like approval of salts is a
tedious task and also not useful for neutral molecules [9].
www.iajpr.com
Page
Co-grinding/Co-micronization:
Co-grinding of a poorly water-soluble drug with water-soluble polymers like hydroxyl propyl methyl cellulose (HPMC), poly
vinyl alcohol (PVA) etc in the presence of small amount of water is extremely effective to improve its apparent solubility with
preservation of drug crystallinity to some level. However, energy added to decrease particle size results in increased Van der Waal’s
interactions and electrostatic magnetism between particles leading to reduce effective surface area due to agglomeration thus
decreasing dissolution rate.
Co-micronization of drugs by using excipients like microcrystalline cellulose can be used as an option to reduce or remove
cohesive and electrostatic forces. This approach increases apparent surface area available for drug dissolution by creating an ordered
mixture, thereby causing a decrease in particle-particle agglomeration or by reducing Van der Waal’s interactions. Increase in true
surface area of the ordered powdered mixture is expected due to the inherent surface roughness and porosity of microcrystalline
cellulose-Drug mixture
Following methods can be used for achieving Micronization:
Jet milling
Solid solution & eutectic mixtures
Micro precipitation.
Controlled crystallization
Supercritical fluid technology
Spray freezing into liquid
Spray freeze dry (SFD)
5534
Particle Size Reduction:
Micronization or nanonization is one of the most probable approaches to improve the bioavailability of lipophilic drugs by an
increase in surface area and saturation solubility by means of reduction of the particle size to sub-micron level.
It is not possible to reduce particle size submicron level by the conventional milling techniques. Patented engineering
processes have come up based on the principles of pearl milling high-pressure homogenization, solution enhanced dispersion by
supercritical fluids (SEDS), rapid expansion from supercritical to aqueous solution (RESAS), spray freezing into liquid (SFL) and
evaporative precipitation into aqueous solution (EPAS) [9].
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
Pearl Milling:
Based on pearl milling the drug micro particles are ground to nanoparticles (< 400 nm) in stuck between the moving milling
pearls. The milling effectiveness is dependent on the properties of the drug, the medium and the stabilizer. rapamune, an immune
suppressant agent, is the first FDA approved nanoparticle drug using Nano-Crystals technology developed by Elan Drug Delivery.
Emend is another product containing 80 or 125 mg aprepitant formulated by this technique. In general the limitation of the pearl
milling process is the introduction of contamination to the product from the grinding material, batch-to-batch variations and the danger
of microbiological harms after milling in an aqueous environment.
High- Pressure Homogenization:
Disso Cubes development involves dispersing a drug powder in an aqueous surfactant solution and passing through a highpressure homogenizer, afterward nano suspensions are obtained. The cavitation force experienced is enough to break up drug from
micro particles to nanoparticle. The particle size is dependent on the rigidity of the drug substance, the processing pressure and the
number of cycles applied. The possible interesting features of Nano suspensions are:
Increase in saturation solubility and dissolution rate of drug
Increase in adhesive nature, thus resulting in enhanced bioavailability
Increase the amorphous fraction in the particles, leading to a potential change in the crystalline structure and higher
solubility
Possibility of surface modification of nano-suspensions for site-specific delivery
Though, only fragile drug candidates might be broken up into nanoparticle by this method. A few points has to be careful, such as
chemical instability of fragile drugs under the harsh production conditions, Ostwald ripening in long-term storage, toxicity of
surfactants, redispersibility of the dried powder, batch-to-batch variation in crystallinity level and finally the difficulty of quality
control and the stability of the partially amorphous nanosuspensions.
Solution Enhanced Dispersion by the Supercritical Fluids (SEDS):
The SEDS process was developed and patented by the University of Bradford. The use of a coaxial nozzle provide a means
whereby the drug in the organic solvent solution mixes with the compressed fluid CO 2 (antisolvent) in the mixing chamber of the
nozzle prior to dispersion, and flows into a particle-formation vessel via a restricted orifice. Such nozzle achieves solution breakup
through the impaction of the solution by a higher velocity fluid. The high velocity fluid creates high frictional surface forces, causing
the solution to disintegrate into droplets. A wide range of materials has been prepared as carriers of micro particles and nanoparticles
using the SEDS process. A key step in the formation of nanoparticles is to enhance the mass transfer rate between the droplets and the
antisolvent before the droplets coalesce to form bigger droplets. In another study, a significant decrease in the particle size is achieved
by using the ultrasonic nozzle-based supercritical antisolvent process.
Sono crystallization:
Sono crystallization is a novel particle engineering technique to improve solubility and dissolution of hydrophobic drugs and
to study its effect on crystal properties of drug. Recrystallization of poorly soluble materials using liquid solvents and antisolvents has
also been employed productively to reduce particle size by using ultrasound. Sono crystallization utilizes ultrasound power
www.iajpr.com
Page
Ultra-Rapid Freezing:
Ultra-rapid freezing is a novel, cryogenic technology that creates nano-structured drug particles with greatly enhanced
surface area. The technology has the flexibility to produce particles of varying particle morphologies, based on control of the solvent
system and process conditions. This process involves freezing a dissolved drug in a aqueous of anhydrous polymer water solution onto
the surface of a cryogenic substrate with a thermal conductivity (k) between 10 and 20 W/(m K), collecting the frozen particles and
removing the solvent, resulting in highly porous, agglomerated particles.
The polymer acts as a stabilizer acting as a crystal growth inhibitor. Because of rapid conductive heat transfer, resulting in
high super-saturation and nucleation rates, the URF technology has the potential to create powders with superior physicochemical
properties, similar to those produced by other rapid freezing technologies. As in other freezing technologies, the rapid freezing of the
drug/polymer composition is decisive in preventing phase separation during freezing, allowing for the active to be molecularly
dispersed with the polymer. As with controlled precipitation; this process uses pharmaceutically acceptable solvents, excipients and
conventional process equipment making it fast and scalable.
Recrystallization of the drug is avoided by the inclusion of high glass-transition temperature (Tg) polymers such as PVP or
HPMC. This technique is widely applicable to enhance in vivo absorption for the BCS class-II compounds.
5535
Rapid expansion from Supercritical to Aqueous Solution (RESAS):
This procedure induces fast nucleation of the supercritical fluid dissolve drugs and surfactants resulting in particle formation
with a desirable size distribution in a extremely short time. The surfactants in the supercritical fluid stabilize the newly formed small
particles and suppress any tendency of particle agglomeration or particle growth when spraying this solution (drug + surfactant +
CO2) into an aqueous solution containing a second surface modifier. The low solubility of poorly water soluble drugs and surfactants
in supercritical CO2 and the high pressure required for these processes restrict the utility of this technology in pharmaceutical
industry.
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
characterized by a frequency range of 20–100 kHz for inducing crystallization. Most applications use ultrasound in the range 20 kHz-5
MHz [10].
Solvent Deposition/Evaporation:
In this method drug is dissolve in a solvent like methylene chloride to create a clear solution. The carrier is then discrete in
the solution by stirring and the solvent is removed by evaporation under temperature and pressure. The resultant mass is then
dehydrated, pulverized, and passed through a sieve. The Increase in the dissolution rate is ascribed to the reduced particle size of the
drug deposited on the carrier and enhanced wettability of the particles brought about by the carrier [9].
Solid solutions/dispersions:
Solid dispersion is defined as a dispersion of one or more active ingredients in an inert carrier or matrix at solid state. It was
initially introduced to overcome the low bioavailability of lipophilic drugs by forming of eutectic mixtures of drugs with water-soluble
carriers. It was defined as the dispersion of one or more active ingredients in an inert carrier matrix in solid-state prepared by melting
(fusion), solvent or melting-solvent method. The solubility of celecoxib, halofantrine, ritonavir can be improved by solid dispersion
using suitable hydrophilic carriers [9, 11].
Method of solid dispersions:
Hot melt method (fusion method):
In this method, the physical mixture of a drug and a water-soluble carrier was heated directly until it melted. The melted
mixture was then cooled and solidified rapidly in an ice bath under rigorous stirring. The final solid mass was crushed, pulverized, and
sieved, which can be compressed into tablets with the help of tabletting agents. The melting point of a binary system is dependent
upon its composition, i.e., the selection of the carrier and the weight fraction of the drug in the system.
An important requisite for the formation of solid dispersion by the hot melt method is the miscibility of the drug and the
carrier in the molten form. Another important requisite is the thermo stability of the drug and carrier.
Solvent Evaporation Method:
Tachibana and Nakumara were the first to dissolve both the drug and the carrier in a common solvent and then evaporate the
solvent under vacuum to produce a solid solution. This enabled them to produce a solid solution of the highly lipophilic -carotene in
the highly water soluble carrier polyvinyl pyrrolidone.
The main advantage of the solvent method is that thermal decomposition of drugs or carriers can be prevented because of the
low temperature required for the evaporation of organic solvents. However, some disadvantages associated with this method are the
higher cost of preparation, the difficulty in completely removing liquid solvent, the possible adverse effect of the supposedly
negligible amount of the solvent on the chemical stability of the drug, the selection of a common volatile solvent, and the difficulty of
reproducing crystal forms [7].
Hot melt extrusion:
Hot melt extrusion is essentially the same as the fusion method except that intense mixing of the components is induced by
the extruder. Just like in the traditional fusion process, miscibility of drug and matrix can be a problem. High shear forces resulting in
high local temperature in the extruder is a problem for heat sensitive materials. However, compared to the traditional fusion method,
this technique offers the possibility of continuous production, which makes it suitable for large-scale production. Furthermore, the
product is easier to handle because at the outlet of the extruder the shape can adapted to the next processing step without grinding [7].
Characterization of solid dispersion:
Solid dispersion can be characterized with several analytical methods. FT-IR Spectroscopy, scanning electron microscopy
(SEM), X-ray diffraction, dissolution rate determination and thermal analysis methods like thermo-microscopic method, differential
thermal analysis (DTA), and differential scanning colorimetry (DSC) can be employed for solid dispersion evaluation [11].
www.iajpr.com
Page
Inclusion Complexes:
Cyclodextrins are a group of cyclic oligosaccharides obtained from enzymatic degradation of starch. The three major
cyclodextrins α, ß, and -CD are composed of six, seven, and eight D-(+) -glucopyranose units. These agents have a torus structure
with primary and secondary hydroxyl groups orientated outwards. Consequently, cyclodextrins have a hydrophilic exterior and a
hydrophobic internal cavity. CD and their derivatives have been employed as complexing agents to increase water solubility,
dissolution rate and bioavailability of lipophilic drugs for oral or parenteral delivery [9].
5536
Co-evaporate System / Co-precipitation:
Weak basic drugs like prochlor perazine maleate contain good solubility in acidic pH but in alkaline pH solubility is
significantly reduced and when a conventional formulation containing weak base is given orally precipitation of poorly soluble free
base occurs within formulation in intestinal fluid. Precipitated drug is no longer capable of release from formulation leading to
decrease in bioavailability of drug. This problem can be solved by use of co-evaporate system which incorporates a carrier with
solubilizing effect in alkaline intestinal fluid which may operate in the microenvironment, immediately surrounding the drug particle
and polymers for controlling the dissolution rate to formulate dosage forms ensuring maximum bioavailability with controlled release
of weak base [9].
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
Supercritical fluid method:
A supercritical fluid (SCF) procedure allows the micronization of drug particles inside sub-micron levels. Supercritical fluids
are fluids whose temperature and pressure are superior than critical temperature (Tc) and critical pressure (Tp). At near-critical
temperature, SCFs are highly compressible, allowing reasonable changes in pressure to greatly alter the density and mass transport
characteristics of a fluid that largely decide its solvent power. Once the drug particles are solubilised within SCF, they may be
recrystallised at greatly reduced particle size. Carbon dioxide and water are the most usually used supercritical fluids. The SCF
process can create nanoparticulate suspensions of particles 5–2,000 nm in diameter. e.g. enhancing water solubility of etraconazole
with water soluble polymer HPMC by using supercritical fluid processing [10, 12].
Drug dispersion in carriers:
The term “solid dispersions” refers to the dispersion of one or more active ingredients in an inert carrier in a solid state, often
prepared by the melting method, solvent method, or fusion solvent-method. Novel additional preparation techniques have included
rapid precipitation by freeze drying and by means of supercritical fluids and spray drying, often in the presence of amorphous
hydrophilic polymers and also using methods such as melt extrusion. The most commonly used hydrophilic carriers for solid
dispersions include polyvinyl pyrrolidone, polyethylene glycols, and plasdone-S630. Many times surfactants may also use in the
formation of solid dispersion. Surfactants like Tween-80, docusate sodium, Myrj-52, Pluronic-F68 poloxamer and sodium lauryl
Sulphate used.
Table 2: List of solubility enhanced drug [13-41]
Celecoxib
Indomethacin
Raloxifene
Flutamide
Tinidazole
Clonazepam
Ketoprofen
Glipizide
Steviol Glycosides rebaudioside
Fluconazole
Ibuprofen
Meloxicam
Prednisolone
Aceclofenac
Theophylline
Cefixime
Etoricoxib
Telmisartan
Nimesulide
Irbesartan
Cyclodextrins
Bicalutamide
Escitalopram Oxalate
www.iajpr.com
Investigation
Mahajan A. et al.
Hasan A. et al.
Kumar S. et al.
Khan MA. et al.
Lingam M. et al.
Yadav VB. et al.
Rai VK. et al.
Dixit M. et al.
Chhaprel P. et al.
Minhaz A. et al.
Nagar G. et al.
Rote H. et al.
Mani U. et al.
Shivhare UD. et al.
Hasnain MS. et al.
Jafar M. et al.
Milani P. et al.
Kumar T. et al.
Jayakumar.C.et al
Reddy SA. et al.
Kulthe VV. et al.
Lakshmi K. et al.
Gunturu S. et al.
ChawlaG. et al.
Kumar SK. et al.
shrikant MV. et al.
Nirav SP. et al.
5537
Mefenamic Acid,
Diclofenac Sodium
Polymers Used
Polyethylene glycol 6000 (PEG 6000)
Poly ethylene glycol 4000 (PEG 4000), HPMC K4,
HPMC K100, Poloxamer-407.
HPMC
PEG4000, PEG6000,and co-solvents PEG200,
PEG400
PEG 400, Ethanol
Hydroxy propyl methylcellulose (HPMC), Kollicoatir,
chitosan,
Polyvinyl pyrrolidone.
Polyvinyl pyrrolidone, Hydroxy propyl methyl
Cellulose (HPMC) Hydroxy propyl cellulose.
Prostatic carcinoma
Polyethylene glycols (PEG 4000,Hydroxypropyl
Methyl cellulose (HPMC 5cps),
And cyclodextrin.
Polyethylene glycol 6000 (PEG- 6000),Kollicoat IR,
Kollidon VA 64, and Poloxomer
Ketoprofen Gelucire 44/14, PVP K30
Polyvinyl Pyrrolidone (PVP K30), Polyethylene
glycol (PEG 6000). Kneading, Skimmed Milk
cyclodextrin
Oleic acid, Dimethyl sulfoxide
PEG 6000, PVP K 30.
Polyvinyl pyrrolidone (pvp)
Poly ethylene glycol (peg6000).
PEG 6000
Polyethylene glycol (PEG 6000). Polyvinyl
Pyrrolidone (PVP K30),
HPMC
wherein natural
poloxamer-407
PVP K30 aerosil 200
PVP K-40, PEG 4000, PEG-6000
(polyvinyl pyrrolidone,
PVP, and hydroxypropyl methylcellulose,
HPMC)
PEG 4000
Povidone K 30, Poloxamer 407
Polyvinyl alcohol and Urea
Page
Name of Drug
Atenelol
Olmesartan medoxomil
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
Alprazolam
polyethylene
glycol-6000
(PEG-6000)
and
polyvinylpyrrolidone-K30 (PVP-K30)
Dimyristoyl phosphatidyl glycerol (DMPG)
Poloxamer 188 and Poloxamer 407
-cyclodextrin, microcrystalline
cellulose, croscarmellose sodium, sodium starch
glycolate,
Piroxicam
Glimepiride
Amisulpride
ISSN NO: 2231-6876
Roul LK. et al.
Mirza S. et al.
Wagh VT. et al.
Murli KT. et al.
Carriers for Solubility Enhancement:
Carriers, which are soluble and dissolve in water at a fast rate, are widely used in pharmaceutical formulations to enhance
solubility and dissolution of drugs. Various carriers are used for solubility enhancement listed mentioned in the table 3 [42].
Table 3: List of carriers used for solubility enhancement.
Category
Polymeric materials
Acid
Miscellaneous
Hydrotrops
Sugars
Surfactants
Insoluble or enteric polymer
Examples of carrier
Povidone (PVP), polyethylene glycol (PEG), cyclodextrin,
hydroxypropyl methyl cellulose, methyl cellulose, hydroxy ethyl cellulose, hydroxy
propyl cellulose.
Citric acid, succinic acid.
Microcrystalline cellulose, dicalcium phosphate, silica gel, sodium chloride.
Urea, sodium acetate, nicotinamide, sodium benzoate, sodium salicylate, sodium-ohydroxy benzoate.
Dextrose, sucrose, galactose, sorbitol, maltose, mannitol, lactose.
Deoxycholic acid, tweens, spans, polyoxyethylene stearate, renex, poloxamer 188.
Eudragit L100, Eudragit S100, Eudragit RL,
Eudragit RS, Hydroxy propyl methyl cellulose phthalate.
Advantages & disadvantages [12, 43]:
Advantages:
Complexation:
Complexing agent such as hydroxyl propyl beta cyclodextrin and sulfobutyl beta cyclodextrin are less toxic
compared to other solubilizing agent such as surfactants and co-solvents.
Melt extrusion:
The pre-concentrates are relatively easy to manufacture.
Well-developed micro-emulsion pre-concentrates are not normally dependent upon digestion for drug release. Therefore,
optimal bioavailability and reproducibility can be also being expected without co-administration of food (i.e. the fasted
state).
Particle size reduction:
Liquid forms can be rapidly developed for early stage testing (pre-clinical) that can development.
Typically, low excipients to drug ratios are required.
Formulations are generally well tolerated provided that strong surfactants are not required for stabilisation.
Solid Dispersions:
Particles with reduced particle size: Dispersions, as solid dispersion, represent the last state on particle size reduction, and
after inert carrier or matrix dissolution the drug is molecularly dispersed in the dissolution medium. A high surface area is
formed which results an increased dissolution rate and further improved the bioavailability of the poorly water-soluble drug.
Particles with improved wetability: The solubility enhancement of the drug is related to the drug wetability improvement
verified in solid dispersion.
www.iajpr.com
Page
pH adjustment:
Simple to formulate and analyze.
Simple to produce and fast track.
5538
Hydrotropy:
Hydrotropy is suggested to be superior to other solubilization method, such as miscibility, micellar solubilization, cosolvency and salting in, because the solvent character is independent of pH, has high selectivity and does not require
emulsification
It does not require chemical modification of hydrophobic drugs, use of organic solvents, or preparation of emulsion system.
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
Particles with higher porosity: Particles in solid dispersions have been found to have a higher degree of porosity and the
increase in porosity also depends on the properties of the carrier. More porous nature of the particle results higher dissolution
rate.
Drugs in amorphous state: Water-soluble crystalline drugs, when in the amorphous state tend to have higher degree of
solubility. Drug in its amorphous state shows higher drug release because no energy is required to break up the crystal lattice
during the dissolution process.
Disadvantages:
Particle size reduction
Due to the high surface charge on discrete small particles, there is a strong tendency
for particle agglomeration.
Developing a solid dosage form with a high pay load without encouraging agglomeration may be technically challenging.
Technically, development of sterile intravenous formulations is even more challenging.
pH adjustment
Hazard for precipitation upon dilution with aqueous media having a pH at which the compound is less soluble. Intravenously
this may lead to emboli, orally it may cause unpredictability.
As with all solubilized and dissolved systems, a dissolved drug in an aqueous environment is often less steady chemically
compared to formulations crystalline solid. The chosen pH may accelerate hydrolysis or catalyze
Solid Dispersions
The major disadvantages of SDs are related to their instability. Several systems have shown changes in crystallinity and a
decrease in dissolution rate on ageing. By absorbing moisture, phase separation, crystal growth or a change from metastable
crystalline form to stable form can take place which leads to the reduction of drug solubility. Moisture and temperature have more of
deteriorating effect on solid dispersions than on physical mixtures. Sometimes it is tricky to handle because of tackiness.
Summary and conclusion:
In this article we concluded that, solubility of the drug is the most significant factor and prime requirement for to achieve
good bioavaibility after the absorption of drug so it is most critical factor in the formulation development.
There are number of methods and techniques available to improve the solubility and enhance bio availability we had tried to
discuss all these methods in this script. But Solid dispersion systems have been realized as extremely useful tool in improving the
dissolution properties of poorly water-soluble drugs. In recent years, a great deal of knowledge has been accumulated about solid
dispersion technology, but other methods like micronization, complexation, and pro-drugs concepts also useful in pharmaceutical
operations. The deep study is required to prevent the limitation of any method. We gather the list of drug (Table 2.)Whose solubility
was enhanced by using one of above methods, also tried to focus on the polymers used and carrier for (Table 3.) to achieve solubility
enhancement.
ACKNOWLEDGEMENT
The authors are grateful to SND College of Pharmacy, Yeola, Nashik, India, for providing necessary library facilities to carry
out this work. The authors like to thank to Dr. Vikas Patil for their help in improving the quality of this article.
www.iajpr.com
Page
REFERENCES
1) Ahmad Z., Maurya N., Mishra K., Khan I., Solubility enhancement of poorly water soluble drugs: a review, International Journal
of Pharmacy and Technology 2011; 2:1:807-23.
2) Kumar A., Sahoo K., Padhee K., Singh P., Satapathy A., Pathak N., Review on solubility enhancement techniques for
hydrophobic drugs, International journal of comprehensive pharmacy 2011; 3:3:1-7.
3) Kumar P., Singh C., Study on solubility enhancement methods for poorly water soluble drugs, American Journal of
Pharmacological Sciences 2013; 1:4: 67-73.
4) Vemula V., Lagishetty V., Lingala S., Solubility enhancement techniques, International Journal of Pharmaceutical Sciences
Review and Research 2010; 5:1: 41-51.
5) Indian Pharmacopoeia, Controller of Publication, Govt. of India, Ministry of Health and Family Welfare, New Delhi, 2007.p. 143.
6) Reddy B., Karunakar A., Biopharmaceutics classification system: a regulatory approach, Dissolution Technologies 2011; 31-37.
7) Chaudhary A., Nagaich U., Gulati N., Sharma V., Khosa R., Enhancement of solubilization and bioavailability of poorly soluble
drugs by physical and chemical modifications: A recent review, Journal of Advanced Pharmacy Education and Research 2012;
2:1: 32-67.
8) Reddy N., Reddy A., Kavitha K., Kumar R., et al. Review on: better solubility enhancement of poorly water soluble drugs,
International Journal of Inventions in Pharmaceutical Sciences 2013; 1:4: 267-73.
5539
Authors’ Statements
Competing Interests
The authors declare no conflict of interest
ISSN NO: 2231-6876
9) Thorat Y., Gonjari D., Hosmani A., Solubility enhancement techniques: a review on conventional and novel approaches,
International journal pharmaceutical science and research 2011; 2;10: 2501-13.
10) Zaheer A., Naveen M., Mishra K., Khan I., Solubility enhancement of poorly water soluble drugs: a review, International Journal
of Pharmacy and Technology 2011; 3:1: 807-23.
11) Wairkar S., Gaud R., Solid dispersions: solubility enhancement technique for poorly soluble drugs, International Journal of
Research in Pharmaceutical and Biomedical Sciences 2013; 4:3: 847-54.
12) Kumar M., Manjula B., A Review and enhancement on solubility techniques, Universal journal of pharmacy 2013;2:2: 27-36.
13) Mahajan A, Singh S, Kaur S, Aggrwal A., Studies on solubility enhancement and In-vitro dissolution profile of poorly water
soluble drug atenolol using solid dispersion technique, International journal of research in pharmaceutical science, 2013; 4:3:
344-49.
14) Hasan A., Jayalakshmi J., Enhancement of solubility and dissolution rate of olmesartan medoxomilby solid dispersion technique.
Journal of current chemical and pharmaceutical scinces 2013; 3:2: 123-34.
15) Kumar S., Parkash C., Kumar P., Singh S., Application of some novel techniques for solubility enhancement of mefenamic acid a
poorly water soluble drug, International Journal of Pharmaceutical Sciences and Drug Research 2009;1:3:164-71.
16) Khan M., Enhancement of solubility of poorly water soluble drugs diclofenac sodium by mixed solvency approach, International
Journal of Research and Development in Pharmacy and Life Sciences 2013; 2:5: 580-82.
17) Lingam M., Venkateswarlu V., Enhancement of solubility and dissolution rate of poorly water soluble drug using cosolvancy and
solid dispersion techniques, International journal pharmaceutical sciences and nanotechnology 2012; 1:4: 349-56.
18) Rai V., Singh R., Sharma M., Agarwal A., Gupta A., Solubility enhancement of poorly water-soluble drug (Raloxifene
Hydrochloride) by using different hydrophilic binders in solid dosage form, International journal of comprehensive pharmacy
2010; 3:5:1-5.
19) Dixit M., Kini A., Parthasarthi K., Shivakumar G., A novel technique to enhancing the solubility and dissolution of flutamide
using freeze drying, Turk journal pharmacy science 2012; 9:2: 139-50.
20) Chhaprel P.,Talesara A., Jain A., Solubility enhancement of poorly water soluble drug using spray drying technique, International
Journal of Pharmaceutical Studies and Research 2012; 3:2: 1-5.
21) Minhaz A., Rahman M., Ahsan Q. Chowdhury M., Dissolution enhancement of poorly soluble drug by solvent evaporation
method using hydrophilic polymer: a solid dispersion technique, International Journal of Pharmaceutical and Life Sciences 2012;
1:2: 1-18.
22) Nagar G., Luhadiya A., Agrawal S., Dubey P., Solubility enhancement of a poorly aqueous soluble drug ketoprofen using solid
dispersion technique, Pelagia Research Library 2011:2:4: 67-73.
23) Rote H., Thakare V., Tekade B., Zope R., Chaudhari R., Patil V., Solubility enhancement of glipizide using solid dispersion
technique, World Journal of Pharmaceutical research 2011; 1:4: 1096-115.
24) Upreti M., Strassburger K., Wu S., Prakash I., Solubility enhancement of steviol glycosides and characterization of their inclusion
complexes with gamma-cyclodextrin, International Journal of Molecular Sciences 2011; 12:2: 7529-53.
25) Shivhare U., Mathur V., Nanhe S., permeation enhancement of poorly water soluble drug flucanozole, Journal of drug delivery
research 2013;2:2: 1-6.
26) Jafar M., Dehghan M., Shareef A., Enhancement of dissolution andanti-inflammatory effect of meloxicam using solid dispersions,
International Journal of Applied Pharmaceutics 2010; 2:1: 22-27.
27) Milani P, Nezhadi S., Jalali M., Studies on dissolution enhancement of prednisolone, a poorly water-soluble drug by solid
dispersion technique, Advanced Pharmaceutical Bulletin 2011; 1:1: 48-53.
28) Kumar T., Gupta V., Jain A., Pandey A., Enhancement of solubility of aceclofenac by using different solubilization technique,
International Journal of Pharmacy and Life Sciences 2011;2:3: 620-24.
29) Jayakumar C., Morais A., Gandhi N., Solubility enhancement of theophylline drug using different solubilization techniques,
International Journal of Pharmaceutical and Clinical Science 2012:2:1: 7-10.
30) Reddy S., Rangaraju D., Kant A., Shankraiah M., et al. Solubility and dissolution enhancement of cefixime using natural
polymer by solid dispersion technique, International journal of research in pharmacy and chemistry 2011;1:2: 283-88.
31) Kulthe V., Chaudhari P., Solubility enhancement of etoricoxibby solid dispersions prepared by spray drying technique, Indian
Journal of Pharmaceutical Education and Research 2011;45:3: 248-258.
32) Lakshmi K., Kumar P., Kaza R. Dissolution enhancement of telmisartan by surface solid dispersion technology. International
Journal of Innovative Pharmaceutical Research.2012; 3:4:247-51.
33) Gunturu S., Amaravadi D., Preparation and evaluation of solid dispersions of nimesulide, International Journal of Pharmacy 2012;
2:4: 777-85.
34) Chawla G., Bansal K., Improved dissolution of a poorly water soluble drug in solid dispersions with polymeric and nonpolymeric hydrophilic additives, Acta Pharm 2008;58: 257–274.
35) Kumar S., Sushma M., Prasanna R., dissolution enhancement of poorly soluble drugs by using complexation technique – A
Review, Journal of pharmceuticals science and reaserch 2013:5:5: 120 – 24.
36) Shrikant M., Murali G., Sunil S., Murthy K., In- vitro dissoluation rate of poorly water soluble non-steroidal antiadrogen agent,
Bicalutamide, with hydrophilic carriears, Journal of scientific and industrial research 2010; 69: 629-34.
37) Nirav S., Patel J., Dissolution enhancement of anti-depressant escitalopram oxalate by solid dispersion technique.journal of
current pharmaceutical research 2012; 9:1: 26-32.
www.iajpr.com
5540
Sachin S. Gaikwad, et al.
Page
Vol 4, Issue 11, 2014.
Vol 4, Issue 11, 2014.
Sachin S. Gaikwad, et al.
ISSN NO: 2231-6876
38) Roul L., Manna N., Parhi R., Sahoo S., Dissolution rate enhancement of alprazolam by solid dispersion, Indian journal of
pharmaceutical education and research 2012; 46:1: 38-44.
39) Mirza S., Miroshnyk I., Muhammad H., Brauch J., Muhammad H., Enhanced dissolution and oral bioavailability of piroxicam
formulations: modulating effect of phospholipids, Pharmaceutics 2010; 2: 339-50.
40) Wagh V., Jagtap V., Shaikh T.. Nandedkar S., Formulation and evaluation of glimepiride solid dispersion tablets for their
solubility enhancement, Journal of Advanced Scientific Research 2012; 3:4: 36-41.
41) Murali K., Patel V., Valluru R., Hiremath J., Prathapreddy D., Solubility enhancement of amisulpride by solid dispersion
technique and preparation of fast dissolving tablets, Indo American Journal of Pharmaceutical Research 2012;1:5:616-28.
42) Patel C., Asija R., Asija S., Different methods of enhancement of solubilization and bioavailability of poorly soluble drugs: a
recent
review,
Pharmatutor-ART-1424.http://www.pharmatutor.org/articles/different-methods-enhancement-solubilizationbioavailability-poorly-soluble-drugs-review
43) Bajaj H., Bisht S., Yadav M., Singh V., Bioavailability enhancement: a review, International Journal of Pharma and Bio Sciences
2011; 2:2: 202 –16.
Page
5541
54878478451141124
www.iajpr.com
View publication stats