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SOLUILITY ENHANCEMENT TECHNIQUES
1
MALLA REDDY COLLEGE OF PHARMACY
Maisammaguda, Dhulapally (post via Hakimpet),Sec-bad-14
Presented by
M.SHIVA KUMAR
256213885015
M. Pharmacy 1st Year
Pharmaceutical Analysis & Quality Assurance
Guided by
Mrs. Yasmin Begum
M.pharm

CONTENTS
• INTRODUCTION
• IMPORTANCE OF SOLUBILITY
• NEED OF IMPROVING SOLUBILITY
• TECHNIQUES OF SOLUBILITY
ENHANCEMENT
• APPLICATIONS
• CONCLUSIONS
• REFERENCES
2

INTRODUCTION
Solubility:
• The term ‘Solubility’ is defined as maximum
amount of solute that can be dissolved in a given
amount of solvent to form a homogenous system
at specified temperature.
• The solubility of a drug is represented through
various concentration expressions such as parts,
percentage, molarity, molality, volume fraction,
mole fraction.
3

 The pharmacopoeia lists solubility in terms of
number of millilitres of solvent required to
dissolve 1g of solute.
The indian pharmacopoeia provides general
terms to describe a given range. These
descriptive terms are given as:
Definition
Parts of solvent required for one part of
solute
Very soluble < 1
Freely soluble 1 - 10
Soluble 10 - 30
Sparingly soluble 30 - 100
Slightly soluble 100 - 1000
Very slightly soluble 1000 - 10,000
Insoluble > 10,000 4

IMPORTANCE OF SOLUBILITY
• Therapeutic effectiveness of a drug depends upon
the bioavailability and ultimately upon the
solubility of drug molecules.
• Solubility is one of the important parameter to
achieve desired concentration of drug in systemic
circulation for pharmacological response to be
shown.
• Currently only 8% of new drug candidates have
both high solubility and permeability.
• Nearly 40% of the new chemical entities
currently being discovered are poorly water
soluble.
5

Contd..
6
• More than one-third of the drugs listed in the U.S.
Pharmacopoeia fall into the poorly water-soluble
or water-insoluble categories.
• Low aqueous solubility is the major problem
encountered with formulation development of new
chemical entities.
• Any drug to be absorbed must be present in the
form of an aqueous solution at the site of
absorption. Water is the solvent of choice for
liquid pharmaceutical formulations.
• Most of drugs are weakly acidic and weakly basic
with poor aqueous solubility. Hence various
techniques are used for the improvement of the
solubility of poorly water-soluble drugs.

NEED FOR SOLUBILITY
ENHANCEMENT
• There are variety of new drugs & their derivatives
are available. But less than 40% of lipophilic
drugs candidates fail to reach market due to
poor bioavailability, even though these drugs
might exhibit potential pharmaco-dynamic
activities.
• The lipophilic drug that reaches market requires
a high dose to attain proper pharmacological
action.
• The basic aim of the further formulation &
development is to make that drug available at
proper site of action within optimum dose.
7

Solubility of drug is largely due to,
1. Polarity of the solvents, that is, to its dipole moment. A polar
solvent dissolves ionic solutes and other polar substances.
2. The ability of solute to form hydrogen bond with solvent.
3. Also depends on the ratio of the polar to non polar groups of
the molecule.
 As the length of a non-polar chain of an aliphatic alcohol
increases, the solubility of the compound in water decreases.
 Straight chain monohydric alcohols, aldehyde, ketones, and
acids with more than four or five carbons cannot enter into the
hydrogen bonded structure of water and hence are only slightly
soluble.
8

• When additional polar groups are present in the
molecule, as found in tartaric acid,propylene
glycol, glycerin, water solubility increases greatly.
• Branching of the carbon chain reduces the non-polar
effect and leads to increased water
solubility.
• Tertiary butyl alcohol is miscible in all proportions
with water, where as n-butyl alcohol is slightly
dissolved.
9

Process of Solubilization
Step 1: Holes opens in the solvent
Step2: Molecules of the solid breaks away from the bulk
Step 3:The freed solid molecule is intergrated into the hole in
the solvent
10

Techniques Of Solubility
Enhancement
I. Physical Modifications
A. Particle size reduction
a. Micronization c.Sonocrystalisation
b. Nanosuspension d.Supercritical fluid process
B. Modification of the crystal habit
a. Polymorphs
b. Pseudopolymorphs
C. Drug dispersion in carriers
a. Eutectic mixtures
b. Solid dispersions
c. Solid solutions
D. Complexation
a. Use of complexing agents
E. Solubilization by surfactants
a. Microemulsions
11

II. Chemical Modifications
a. Change in the pH
b. Use of buffer
c. Derivatization
III. Other methods
a. Co-crystallisation
b. Co-solvency
c. Hydrotrophy
d. Solubilizing agents
e. Solvent deposition
f. Selective adsorption on insoluble carrier
g. Using soluble prodrug
h. Functional polymer technology
i. Precipatation
j. Porous microparticle technology
k. Nanotechnology approaches 12

A. Particle size reduction:
• Particle size reduction can be achieved by
a.Micronization
b.nanosuspension
c.Sonocrystalisation
d.Supercritical fluid process
Colloidal mill
a. Micronization:
• Micronization increases the dissolution rate of drugs through
increased surface area.
• Micronization of drugs is done by milling techniques using jet
mill, rotor stator colloid mills etc.
• Micronization is not suitable for drugs having a high dose
number because it does not change the saturation solubility of
the drug.
• The process involves reducing the size of the solid drug
particles to 1 to 10 microns commonly by spray drying or by
use of attrition methods (fluid energy or jet mill).The process is
13
also called micro-milling.

b. Nanosuspension:
• A pharmaceutical nanosuspension is biphasic system consisting of
nano sized drug particles stabilized by surfactants for either oral and
topical use or parenteral and pulmonary administration.
• Nanosuspension technology has been developed as a promising
candidate for efficient delivery of hydrophobic drugs . This technology
is applied to poorly soluble drugs that are insoluble in both water and
oils. The particle size distribution of the solid particles in
nanosuspensions is usually less than one micron with an
average particle size ranging between 200 and 600 nm.
• The advantages offered by nanosuspension is increased dissolution rate
is due to larger surface area exposed.
• Nanosuspension approach has been employed drugs like
paclitaxel,tarazepide,amphotericin B which are still on research stage.
14

• Techniques for the production of nanosuspensions:
a) Homogenization.
b) Wet milling.
Homogenization:
 The suspension is forced under pressure through a
valve that has nano aperture. This causes bubbles of
water to form which collapses as they come out of
valves. This mechanism cracks the particles.
Wet milling:
 Active drug in the presence of surfactant is
defragmented by milling.
15

Other techniques for reduction of the
particle size
1.Sonocrystallisation
2. Supercritical fluid process
1. Sonocrystallisation:
• The novel approach for particle size reduction on the basis of
crystallisation by using ultrasound is Sonocrystallisation.
• Sonocrystallisation utilizes ultrasound power for inducing
crystallisation.
• It not only enhances the nucleation rate but also an effective
means of size reduction and controlling size distribution of the
active pharmaceutical ingredients.
• Most applications use ultrasound in the range 20 kHz-5 MHz
16

2. Supercritical fluid process:
• Novel nanosizing and solubilization technology whose
application has increased particle size reduction via
supercritical fluid (SCF) processes.
• A supercritical fluid (SF) can be defined as a dense
noncondensable fluid.
• Supercritical fluids are fluids whose temperature and pressure
are greater than its critical temperature (Tc) and critical
pressure (Tp).
• A SCF process allows micronisation of drug particles within
narrow range of particle size, often to sub-micron levels.
Current SCF processes have demonstrated the ability to create
nanoparticulate suspensions of particles 5 to 2,000 nm in
diameter .
17

Supercritical fluid region
18

• The most widely employed methods of SCF processing for
micronized particles are.
1. rapid expansion of supercritical solutions (RESS)
2. and gas antisolvents recrystallisation (GAS)
both of which are employed by the pharmaceutical industry
using carbon dioxide (CO2) .
due to its favourable processing characteristics like its low
critical temperature(Tc = 31.1oC) and pressure (Pc = 73.8
bar).
19

B. Modification of the crystal habit:
• Broadly polymorphs can be classified as enantiotropes and
monotropes based on thermodynamic properties.
• In the case of an enantiotropic system, one polymorphs
form can change reversibly into another at a definite
transition temperature below the melting point, while no
reversible transition is possible for monotropes.
• Metastable forms are associated with higher energy and
thus higher solubility.
• Similarly the amorphous form of drug is always more suited
than crystalline form due to higher energy associated and
increase surface area.
• The anhydrous form of a drug has greater solubility than
the hydrates. This is because the hydrates are already in
interaction with water and therefore have less energy for
crystal breakup in comparison to the anhydrates.
20

• Some drugs can exist in amorphous form (i.e. having no
internal crystal structure).
• Such drugs represent the highest energy state and can be
considered as super cooled liquids.
• They have greater aqueous solubility than the crystalline
forms because they require less energy to transfer a
molecule into solvent. Thus, the order for dissolution of
different solid forms of drug is
Amorphous >Metastable polymorph >Stable polymorph
• Melting followed by a rapid cooling or recrystallization from
different solvents can be produce metastable forms of a
drug.
21

C.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, frequently prepared by the
1.Hotmelt method.
2.solvent evaporation method.
3.Hotmelt extrusion method.
1. Hot melt method:
Sekiguchi and Obi,used a hot melt method to prepare
solid dispersion. Sulphathiazole and urea were melted
together and then cooled in an ice bath. The resultant solid
mass was then milled to reduce the particle size. Cooling
leads to supersaturation, but due to solidification the
dispersed drug becomes trapped within the carrier matrix.
22

• A molecular dispersion can be achieved or not, depends on
the degree of supersaturation and rate of cooling used in
the process.
2. Solvent Evaporation Method:
• An important prerequisite for the manufacture of a solid
dispersion using the solvent method is that both the drug
and the carrier are sufficiently soluble in the solvent. The
solvent can be removed by various methods like by spray-drying
or by freeze-drying.
• Temperatures used for solvent evaporation generally lie in
the range 23-65 oC.
• These techniques have problems such as negative effects of
the solvents on the environment and high cost of
production , hot melt extrusion method is preferred in
preparing solid solutions.
23

3.Hot-melt Extrusion:
• Melt extrusion was used as a manufacturing tool in the
pharmaceutical industry as early as 1971.
• It has been reported that melt extrusion of miscible
components results in amorphous solid solution formation,
whereas extrusion of an immiscible component leads to
amorphous drug dispersed in crystalline excipient.
• The process has been useful in the preparation of solid
dispersions in a single step.
24

D. Complexation:
• Complexation is the reversible association between two or more
molecules to form a nonbonded entity with a well defined
stiochiometry.
• Complexation relies on relatively weak forces such as vanderwaal
forces, hydrogen bonding and hydrophobic interactions.
• There are many types of complexing agents and a partial list can be
found in table.
25

Inclusion complexation:
• Inclusion complexes are formed by the insertion of the
nonpolar molecule or the nonpolar region of one molecule
(known as guest) into the cavity of another molecule or
group of molecules (known as host).
• The most commonly used host molecules are cyclodextrins.
• Cyclodextrins are non-reducing,crystalline, water soluble,
cyclic, oligosaccharides. Cyclodextrins consist of glucose
monomers arranged in a donut shape ring.
26

• Three naturally occurring CDs are α-Cyclodextrin, β-
Cyclodextrin, and γ- Cyclodextrin.
• The internal surface of cavity is hydrophobic and external is
hydrophilic, this is due to the arrangement of hydroxyl group
within the molecule.
27

Staching complexation :
• Staching complexes are formed by the overlap of
the planar regions of aromatic molecules.
• Nonpolar moieties tend to be squeezed out of
water by the strong hydrogen bonding
interactions of water.
• This causes some molecules to minimize the
contact with water by aggregation of their
hydrocarbon moieties.
• This aggregation is favored by large planar
nonpolar regions in the molecule.
• Stached complexes can be homogeneous or
mixed. The former is known as self association
and latter as complexation.
28

E. Solubilization by surfactants:
• Surfactants are molecules with distinct polar and nonpolar
regions. Most surfactants consist of a hydrocarbon segment
connected to a polar group. The polar group can be anionic,
cationic, zwitter ionic or nonionic.
• The presence of surfactants may lower the surface tension
and increase the solubility of the drug within an organic
solvent
Microemulsion:
• A microemulsion is a four-component system composed of
external phase, internal phase, surfactant and cosurfactant.
• The addition of surfactant, which is predominately soluble in
the internal phase unlike the cosurfactant, results in the
formation of an optically clear, isotropic, thermodynamically
stable emulsion. It is termed as microemulsion because of
the internal phase is <0.1 micron droplet diameter.
29

• The formation of microemulsion is spontaneous and does not
involve the input of external energy as in case of coarse
emulsions.
• The surfactant and the cosurfactant alternate each other and form
a mixed film at the interface, which contributes to the stability of
the microemulsion.
• Non-ionic surfactants, such as Tweens (polysorbates) and
Labrafil (polyoxyethylated oleic glycerides), with high
hyrophile-lipophile balances are often used to ensure immediate
formation of oil-in-water droplets during production.
• Advantages of microemulsion over coarse emulsion ,It’s ease of
preparation due to spontaneous formation, thermodynamic
stability, transparent and elegant appearance, enhanced
penetration through the biological membranes, increased
bioavailability and less inter- and intra-individual variability in
drug pharmacokinetics.
30

B. CHEMICAL MODIFICATIONS
1) By change of pH:
For organic solutes that are ionizable,changing the pH of
the system is the simplest and most effective means of
increasing aqueous solubility.
2) Use of buffer:
Buffer maintains the pH of the solution overtime
and it reduces or eliminate the potential for precipitation
upon dilution. On dilution pH alteration occurs that
decrease solubility .
31
Change of pH by 1 fold increase solubility by 10 fold
If it changes by one pH unit ,that decrease ionization of
the drug and solubility decreases by 10 fold.

3) Derivatization:
 It is a technique used in chemistry which
transforms a chemical compound into a product
of similar chemical structure, called derivative.
 Derivatives have different solubility as that of
adduct.
 It is used for quantification of adduct formation
of esters and amides via acyl chlorides.
32

III. Other methods
a. Co-crystallisation
b. Co-solvency
c. Hydrotrophy
d. Solubilizing agents
e. Solvent deposition
f. Selective adsorption on insoluble carrier
g. Using soluble prodrug
h. Functional polymer technology
i. Precipatation
j. Porous microparticle technology
k. Nanotechnology approaches
33

1.Co-crystallization:
• A co-crystal may be defined as a crystalline material that
consists of two or more molecular (and electrically neutral)
species held together by non-covalent forces.
• Co-crystals are more stable, particularly as the co-crystallizing
agents are solids at room temperature.
• Only three of the co-crystallizing agents are classified as
generally recognised as safe (GRAS) it includes saccharin,
nicotinamide and acetic acid limiting the pharmaceutical
applications.
• Co-crystals can be prepared by evaporation of a heteromeric
solution or by grinding the components together. Another
technique for the preparation of co-crystals includes
sublimation, growth from the melt, and slurry preparation.
34

2. Cosolvency:
• The solubilisation of drugs in co-solvents is an another
technique for improving the solubility of poorly soluble
drug.
• It is well-known that the addition of an organic cosolvent to
water can dramatically change the solubility of drugs.
• Weak electrolytes and nonpolar molecules have poor water
solubility and it can be improved by altering polarity of the
solvent.
• This can be achieved by addition of another solvent. This
process is known as cosolvency. Solvent used to increase
solubility known as cosolvent.
• Cosolvent system works by reducing the interfacial tension
between the aqueous solution and hydrophobic solute. It is
also commonly referred to as solvent blending.
35

SOME PERANTRALPRODUCT THAT CONTAIN COSOLVENT
36
PRODUCT COSOLVENT
Diazepam (Valium) 10% ethanol + propyline
glycol
Digoxin( Lanolin) 10% ethanol + propyline
glycol
Epinephrine(susphrin) 32.5% glycerin

3. Hydrotrophy:
• Hydrotrophy designate the increase in solubility in water
due to the presence of large amount of additives.
• The mechanism by which it improves solubility is more
closely related to complexation involving a weak interaction
between the hydrotrophic agents (sodium benzoate,
sodium acetate, sodium alginate, and urea) .
4. Solubilizing agents:
• The solubility of poorly soluble drug can also be improved
by various solubilizing materials.
• PEG 400 is improving the solubility of hydrochlorthiazide85.
Modified gum karaya (MGK), a recently developed excipient
was evaluated as carrier for dissolution enhancement of
poorly soluble drug, nimodipine.
37

5.Solvent deposition:
• In this method,the poorly aqueous soluble drug such as
Nifedipine is dissolved in an organic solvent like alcohol and
deposited on an inert ,hydrophylic,solid matrix such as starch
or microcrystalline cellulose and evoporation of solvent is
done.
6.Selective adsorption on insoluble carriers:
• A highly active adsorbent such as inorganic clays like
Bentonite can enhance the dissolution rate of poorly water-soluble
drugs such as griseofulvin,indomethacin and
prednisone by maintaining the concentration gradient at its
maximum.
• 2 reasons suggested for rapid release of drugs from the
surface of clays :-
1. weak physical bonding between adsorbate and adsorbent.
2. hydration and swelling of the clay in the aqueous media.
38

7. Use of soluble prodrug:
• The most common prodrug stratergy involves the
incorporation of polar or ionizable moiety into the parent
compound to improve aqueous solubility.
Example : prodrug of established drugs has been successfully
used to improve water solubility of corticosteroids
benzodiazepines.
8.Functional Polymer Technology:
• Functional polymer enhaces the dissolution rate of poorly
soluble drugs by avoiding the lattice energy of the drug
crystal,which is the main barrier to rapid dissolution in
aqueous media.
• The dissolution rate of poorly soluble ,ionizable drug like
cationic,anionic and amphoteric actives can be enhanced by
this technology.
• Applied to heat sensitive materials and oils also.
39

9.Precipitation:
• In this method, the poorly aqueous soluble drug such as
cyclosporine is dissolved in a suitable organic solvent followed
by its rapid mixing with a non-solvent to effect precipitation of
drug in nano size particles. The product so prepared is also
called as hydrosol.
10. Porous microparticle technology:
• The poorly water soluble drug is embedded in a microparticle
having a porous, water soluble,sponge like matrix,dissolves
wetting the drug and leaving a suspension of rapidly dissolving
drug particles.
• These drug particles provide large surface area for increased
dissolution rate.
• This is the core technology applied as HDDSTM(Hydrophobic
Drug Delivery System).
40

11. Nanotechnology approaches:
For many new chemical enteties of very low solubility ,oral
bioavailability enhancement by micronization is not sufficeint
because micronized product has a tendency of
agglomeration,which leads to decreased effective surface area for
dissolution .
• Nanotechnology refers broadly to the study and use of materials
and structures at the nanoscale level of approximately 100
nanometers (nm) or less.
NANOCRYSTAL: Size: 1-1000 nm
• Crystalline material with dimensions measured in nanometers.
• There are two distinct methods used for producing nanocrystals .
1. bottom-up.
2. top-down.
• The top-down methods (i.e. Milling and High pressure
homogenization) start milling down from macroscopic level, e.g.
from a powder that is micron sized.
• In bottom-up methods (i.e. Precipitation and Cryo-vacuum
method), nanoscale materials are chemically composed from
atomic and molecular components.
41

NanoMorph:
• The NanoMorph technology is to convert drug substances
with low water-solubility from a coarse crystalline state into
amorphous nanoparticles.
• A suspension of drug substance in solvent is fed into a
chamber, where it is rapidly mixed with another solvent.
• Immediately the drug substance suspension is converted
into a true molecular solution. The admixture of an aqueous
solution of a polymer induces precipitation of the drug
substance
• The polymer keeps the drug substance particles in their
nanoparticulate state and prevents them from aggregation
or growth. Using this technology the coarse crystalline drug
substances are transformed into a nanodispersed
amorphous state, without any physical milling or grinding
procedures. It leads to the preparation of amorphous
nanoparticles.
42

Other novel Nanotechnology approaches:
• Nanocrystal technology
• Nanoedge technology
• Nanopure technology
• Nnocochelate technology
43

APPLICATION OF
SOLUBILITY
• Solubility is of fundamental importance in a large
number of scientific disciplines and practical
applications, to the use of medicines, and the transport
of pollutants.
• Solubility is represents a fundamental concept in fields
of research such as chemistry,physics, food science,
pharmaceutical, and biological sciences.
• The solubility of a substance becomes specially
important in the pharmaceutical field because it often
represents a major factor that controls the bioavailability
of a drug substance.
44

• Solubility is commonly used to describe the
substance, to indicate a substance's polarity,to
help to distinguish it from other substances, and
as a guide to applications of the substance.
• Solubility of a substance is useful when
separating mixtures.
• Moreover, solubility and solubility-related
properties can also provide important information
regarding the structure of drug substances, and
in their range of possible intermolecular
interactions.
45

Conclusion
• A drug administered in solution form immediately available
for absorption.
• Solubility is a most important parameter for the oral
bioavailability of poorly soluble drugs.
• Dissolution of drug is the rate determining step for oral
absorption of the poorly water soluble drugs, which can
subsequently affect the in vivo absorption of drug.
• Currently only 8% of new drug candidates have both high
solubility and permeability.
• Because of solubility problem of many drugs the
bioavailability of them gets affected and hence solubility
enhancement becomes necessary.
• It is now possible that to increase the solubility of poorly
soluble drugs with the help of various techniques. 46

References
1. International Journal Of Pharma Professional’s Research Review Article SOLUBILITY
ENHANCEMENT TECHNIQUES WITH SPECIAL EMPHASIS O N HYDROTROPHY-Volume
1, Issue 1, July 2010 available at www.ijppronline.com
2. SOLUBILITY ENHANCEMENT TECHNIQUES -Volume 5, Issue 1, November –
December 2010; Article-007 available at www.pharmainfo.net
3. Journal of Global Pharma Technology TECHNIQUES TO ENHANCE SOLUBILITY OF
POORLY SOLUBLE DRUGS: A REVIEWavailable at www.jgpt.co.in
4. PHARMACIE GLOBALE -INTERNATIONAL JOURNAL OF COMPREHENSIVE PHARMACY-REVIEW
ON SOLUBILITY ENHANCEMENT TECHNIQUES FOR HYDROPHOBIC DRUGS
available at www.pharmacie-globale.info
5. International Journal of PharmTech ResearchVol.2, No.3, pp 2007-2015, July-Sept
2010 . Solubility Enhancement of Poorly Water Soluble Drug by Solid Dispersion
47
Techniques

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