PREFORMULATION STUDIES

Pharmacy

www.DuloMix.com 1

CONTENTS

➢ Introduction

➢ Major area of preformulation research

❑ Organoleptic characters

❑ Bulk characterization

❑ Solubility characters

❑ Stability characters

➢ Conclusion

www.DuloMix.com 2

PREFORMULATION

➢It is defined as the phase of research and development in

which preformulation studies characterize physical and

chemical properties of a drug molecule in order to develop safe,

effective and stable dosage form.

www.DuloMix.com 3

OBJECTIVES

➢ To establish the physico-chemical parameters of a new

drug entity.

➢ To determine its kinetics and stability.

➢ To establish its compatibility with common excipients.

➢ It provides insights into how drug products should be

processed and stored to ensure their quality.

www.DuloMix.com 4

Major Area of Preformulation
Research

➢ ORGANOLEPTIC CHARACTERS

➢ BULK CHARACTERS

❑ Crystallinity and polymorphism

❑ Hygroscopicity

❑ Fine particle characterization

❑ Powder flow properties

www.DuloMix.com 5

➢ SOLUBILITY ANALYSIS

❑ ionization constant-PKa

❑ pH solubility profile

❑ Common ion effect-Ksp

❑ Thermal effects

❑ Solubilization

❑ Partition co-efficient

❑ Dissolution

www.DuloMix.com 6

➢ STABILITYANALYSIS

❑ Stability in toxicology formulations

❑ Solution stability

❑ pH rate profile

❑ Solid state stability

❑ Bulk stability

❑ Compatibility

www.DuloMix.com 7

ORGANOLEPTIC CHARACTERS

❖ Colour,odour, taste of the new drug must be recorded

COLOUR ODOUR TASTE

❑Off-white ❑pungent ❑Acidic

❑Cream yellow ❑sulphurous ❑Bitter

❑tan ❑Fruity ❑Bland

❑shiny ❑Aromatic ❑Intense

❑Odourless ❑Sweet

❑Tasteless

www.DuloMix.com 8

BULK CHARACTERIZATION

Crystallinity

➢ Crystal habit & internal structure of drugcan affect bulk&

physicochemical property of molecule.

➢ Crystal habit is description of outer appearance of crystal.

➢ Internal structure is molecular arrangement within the solid.

➢ Change with internal structure usually alters crystal habit.

•Eg. Conversion of sodium salt to its free acid form produce both

change in internal structure & crystal habit.

www.DuloMix.com 9

Different shapes of crystals

www.DuloMix.com 10

Different shapes of crystals

➢ Depending on internal structure compounds is classified as

❑ Crystalline

❑ Amorphous

➢ Crystalline compounds are characterized by repetitious spacing of constituent
atom or molecule in three dimensional array.

➢ In amorphous form atom or molecule are randomly placed.

➢ Solubility & dissolution rate are greater for amorphous form than crystalline, as
amorphous form has higher thermodynamic energy.

Eg. Amorphous form of Novobiocin is well absorbed whereas
crystalline form results in poor absorption.

www.DuloMix.com 11

Polymorphism

➢ It is the ability of the compound to crystallize as more than one

distinct crystalline species with different internal lattice.

➢ Different crystalline forms are called polymorphs.

➢ Polymorphs are of 2 types

• Enatiotropic

• Monotropic

➢ The polymorph which can be changed from one form into another

by varying temp or pressure is called as Enantiotropic polymorph.

Eg. Sulphur.

www.DuloMix.com 12

Polymorphism

➢ One polymorph which is unstable at all temp. & pressure is called as
Monotropic polymorph. Eg. Glyceryl stearate.

➢ Polymorphs differ from each other with respect to their physical
property such as

• Solubility

• Melting point

• Density

• Hardness

• Compression characteristic

Eg. Chloromphenicol exist in A,B & C forms, of these B form is more
stable & most preferable.

www.DuloMix.com 13

ANALYTICAL METHODS FOR THE
CHARACTERIZATION OF SOLID FORMS

➢ Microscopy

➢ Hot stage microscopy

➢ Thermal analysis

➢ X-ray diffraction

➢ Infrared (IR) spectroscopy

➢ Proton magnetic resonance (PMR)

➢ Nuclear magnetic resonance (NMR)

➢ Scanning electron microscopy (SEM)

www.DuloMix.com 14

Microscopy

➢ Material with more than one refractive index are anisotropic &

appear bright with brilliant colors against black polarized

background.

➢ The color intensity depends upon crystal thickness.

➢ Isotropic material have single refractive index and this substance

do not transmit light with crossed polarizing filter and appears

black.

www.DuloMix.com 15

Microscopy

➢ Advantage :

By this method, we can study crystal morphology & difference

between polymorphic form.

➢ Disadvantage :

This require a well trained optical crystallographer, as there are

many possible crystal habit & their appearance at different

orientation.

www.DuloMix.com 16

Hot stage microscopy

➢ The polarizing microscope fitted with hot stage is useful for
investigating polymorphism, melting point & transition temp.

Disadvantage :

➢ In this technique, the molecules can degrade during the melting
process.

www.DuloMix.com 17

Thermal analysis

➢ Differential scanning calorimetry (DSC) & Differential thermal analysis
are (DTA) are particularly useful in the investigation of polymorphism.

➢ It measures the heat loss or gain resulting from physical or chemical
changes within a sample as a function of temp.

➢ For characterizing crystal forms , the heat of fusion can be obtained from
the area under DSC- curve for melting endotherms.

➢ Similarly, heat of transition from one polymorph to another may be
calculated.

➢ A sharp symmetric melting endotherm can indicate relative purity of
molecule.

➢ A broad asymmetric curve indicates presence of impurities.

www.DuloMix.com 18

X-ray diffraction

Working :

➢ When beam of nonhomogenous X-ray is allow to pass through the crystal, X-ray
beam is diffracted & it is recorded by means of photographic plate.

➢ Diffraction is due to crystal which acts as 3 dimensional diffraction grating toward
X-ray.

www.DuloMix.com 19

➢ Random orientation of crystal lattice in the powder causes the X-ray

to scatter in a reproducible pattern of peak intensities.

➢ The diffraction pattern is characteristic of a specific crystalline

lattice for a given compound.

➢ An amorphous form does not produce a pattern mixture of different

crystalline forms.

➢ Single – Crystal x-ray provide the most complete information

about the solid state.

www.DuloMix.com 20

HYGROSCOPICITY

➢ Many drug substances, particularly water –soluble salt forms, have a

tendency to adsorb atmospheric moisture.

➢ Adsorption and moisture content depend upon the atmospheric humidity,

temperature, surface area, exposure and the mechanism of moisture uptake.

➢ The degree of Hygroscopicity is classified into four classes:

❑ Slightly hygroscopic: increase in weight is ≥ 0.2% w/w and < 2% w/w

❑ Hygroscopic : increase in weight is ≥ 0.2 % w/w and < 15 % w/w

❑ Very hygroscopic : increase in weight is ≥ 15% w/w

❑ Deliquescent : sufficient water is adsorbed to form a solution

www.DuloMix.com 21

Hygroscopicity is tested by:

Samples are exposed to the moisture

exposed to controlled relative humidity environments

moisture uptake is monitored at different time points

Analytical methods which is used are :

❑ Gravimetry

❑ Karl Fischer Titration

❑ Gas chromatography

www.DuloMix.com 22

PARTICLE SIZE

➢ Particle size is characterized using these terms :

Very coarse, Coarse, Moderately coarse, Fine,Very fine .

➢ Particle size can influence variety of important factors :

– Dissolution rate

– Suspendability

– Uniform distribution

– Penetrability

– Lack of grittiness

www.DuloMix.com 23

Methods to Determine
Particle Size

➢Sieving (5µ-150µ)

➢Microscopy(0.2µ-100µ)

➢Sedimentation rate method(1µ-200µ)

➢Light energy diffraction(0.5µ-500µ)

➢Laser holography(1.4µ-100µ)

www.DuloMix.com 24

POWDER FLOW PROPERTIES

➢ Powder flow properties can be affected by change in particle size,
shape & density.

➢ The flow properties depends upon following-
❑ Force of friction.
❑ Cohesion between one particle to another.

➢ Fine particle posses poor flow by filling void spaces between
larger particles causing packing & densification of particles.

➢ By using glident we can alter the flow properties.
Eg. Talc

www.DuloMix.com 25

Determination of Powder Flow
Properties

Angle of Type of Flow
➢ By determining Angle of Repose.

Repose
➢ A greater angle of repose indicate ( In degree)

poor flow.

➢ It should be less than 30°. & can be <25 Excellent

determined by following equation.

25-30 Good
tan θ = h/r.

where, θ = angle of repose.
30-40 Passable

h=height of pile.

>40 Very poor
r= radius.

www.DuloMix.com 26

Methods to determine angle
of repose

➢Static angle of
repose

▪ Fixed-funnel
method

▪ Fixed-cone method

➢Kinetic or dynamic
method

▪ Rotating cylinder
method

▪ Tilting box method

www.DuloMix.com 27

Determination of Powder
Flow Properties

➢Measurement of free flowing powder by compressibility.

➢Also known as Carr’s index.

CARR’S INDEX(%) =(TAPPED DENSITY – POURED DENSITY)
X 100

TAPPED DENSITY

➢ It is simple, fast & popular method of predicting
powder flow characteristics.

www.DuloMix.com 28

Determination of Powder
Flow Properties

Carr’s Index Type of flow
5-15 Excellent

12-16 Good

18-21 Fair To Passable

23-35 Poor

33-38 Very Poor

>40 Extremely Poor

www.DuloMix.com 29

SOLUBILITY STUDIES

➢ Solution phase equilibrium with solid phase at a stated

temperature and pressure .

➢ Determines amount of drug dissolved, amount of drug

available for absorption.

➢ Solubility reduction is carried out in certain conditions:

❑ Enhancement of chemical stability.

❑ taste masking products.

❑ Production of sustained release products.

www.DuloMix.com 30

Descriptive Term Parts of solvent required
for 1 part of solute

Very Soluble Less than 1

Freely Soluble From 1 to 10

Soluble From 10 to 30

Sparingly Soluble From 30 to 100

Slightly Soluble From 100 to 1000

Very Slightly Soluble From 1000 to 10,000

Practically insoluble 10,000 and Over

www.DuloMix.com 31

➢The equilibrium solubility is based on the phase-solubility
technique proposed by Higuchi-Connors .

Method:

Drug dispersed in solvent in a closed container

agitated at a constant temperature using shakers

samples of the slurry are withdrawn as a function of time

clarified by centrifugation and assayed by HPLC, UV, GC etc

www.DuloMix.com 32

General Method of Increasing the Solubility:
➢ Addition of co-solvent

➢ pH change method

➢ Reduction of particle size

➢ Temperature change method

➢ Hydotrophy

➢ Addition of Surfactant

➢ Dielectrical Constant

➢ Complexation

www.DuloMix.com 33

pKa determination

➢ pKa is the dissociation constant of a drug.

➢ The un-ionized drug is lipid soluble thus permeates through lipid membrane.

➢ The ionized substance is lipid insoluble therefore permeation is slow.

➢ Degree of ionization depends on pH.

Henderson-Hasselbalch equation

For basic compounds: [ionized]
pH = pKa +

[un− ionized]

[un− ionized]
pH = pKa +

For acidic compounds: [ionized]

( p H − p K a )
% i o n i z e d = 1 0

( p H − p K a )
1 +1 0

➢ Determined by uv spectroscopy, potentiometric titration, titrimetric method.

www.DuloMix.com 34

Partition Coefficient

➢A measurement of drug lipophilicity i,e the ability to cross the cell
membrane

p c
= organic

o / a c aque ous

Distribution coefficient
( pH − pKa)

➢For acids: log D = log P − log (1 +10 )
10 10 10

p K a − p H

➢For bases : l o g D = l o g P − l o g (1 + 1 0 )
1 0 1 0 1 0

➢ The octanol-water system is widely accepted to explain these phenomenon.

➢ Buccal membrane : butanol-pentanol system

➢ Blood-Brain barrier: chloroform-cyclohexane

➢ Determined by SHAKE FLASK METHOD

www.DuloMix.com 35

SHAKE FLASK METHOD :
➢ Drug is shaken between octanol and water.

➢ Aliquot is taken and analyzed for drug content.

RULE OF FIVE : for drug permeates through passive diffusion

1. Log P is greater than 5

2. Molecular weight >500

3. There are more than 5 hydrogen bond donors (number of NH + OH)

4. There are more than 10 hydrogen bond acceptors (number of hydrogen +oxygen )

5. Molar refractivity should be between 40-130

www.DuloMix.com 36

DISSOLUTION

Rate constant Rate constant

of of absorption

Kdissolution K a
d

Solid drug in Drug in solution Drug systemic
the G.I Fluid in the G.I fluid circulation

➢ When Kd << Ka ,dissolution is significantly slower and the absorption is described
as dissolution-rate limited.

dC/dt=dissolution rate
➢The dissolution rate of drug

h=diffusion layer thickness
Substance in which surface area is C=solute concentration in bulk solution
Constant during dissolution is V=volume of the dissolution medium

described by Noyes-Whitney equation. D=diffusion coefficient
A=surface area of the dissolving solid

dC DA
= (CS Cs=solute conc. in the diffusion layer

=
dt h C )

V

www.DuloMix.com 37

➢ Constant surface area is obtained by compressing powder into a disc of known

area with a die and punch apparatus.

➢ Hydrodynamic conditions are maintained with Static-disc dissolution apparatus

and Rotating disc apparatus.

Fig : static dissolution apparatus and rotating disc apparatus

www.DuloMix.com 38

STABILITY ANALYSIS

1. Solution stability

2. Solid state stability

SOLUTION STABILITY

The decomposition of drug occurs through hydrolysis, oxidation, photolysis.

Hydrolysis (anaesthetics, vitamins etc )

Ester hydrolysis
R’-COOR + H+ + OH- RCOOH + ROH

ester acid alcohol

Amide hydrolysis

RCONHR’ + H+ + OH- RCOOH + H2N-R’

amide acid amine

www.DuloMix.com 39

Oxidation

➢ Used to evaluate the stability of pharmaceutical preparations

Eg : steroids, vitamins, antibiotics, epinephrine

Autoxidation

Materials + molecular oxygen

homolytic fission

Free radicals are produced.

➢Oxygen sensitivity is measured by bubbling air through the compound or

adding hydrogen peroxide.

www.DuloMix.com 40

Photolysis :

pharmaceutical compounds

exposure to uv light

absorbs the radiant energy

undergoes degradative reactions

www.DuloMix.com 41

SOLID-STATE STABILITY

➢ Objective:

❑ identification of stable storage conditions.

❑ identification of compatible excipients.

➢ Solid-state stability depends on the temperature, light,

humidity, polymorphic changes, oxidation.

www.DuloMix.com 42

Solid-State Stability profile of a new compound:
➢ Samples are placed in open vials and are exposed directly to a variety of

temperatures, humidities, and light intensities for up to 12 weeks.

➢ Vials exposed to oxygen and nitrogen to study the surface oxidation and

chemical stability , polymorphic changes and discolouration.

➢ Stability data obtained at various humidities may be linearized with respect to

moisture using the following apparent decay rate constant (KH )

k [gpl].
H = k 0

gpl= Conc. of water in atmosphere in units of grams of water per liter of dry air .

ko = Decay rate constant at zero relative humidity

www.DuloMix.com 43

Drug- excipient compatibility

➢ Compatibility test play a very important role in the preformulation studies of oral

dosage forms

➢ An incompatibility in the dosage form can result in any of the following changes:

❑ Changes in organoleptic properties

❑ Changes in dissolution performance

❑ Physical form conversion

❑ An decrease in potency

www.DuloMix.com 44

www.DuloMix.com 45

CONCLUSION

➢Preformulation studies on a new drug molecule provide useful

information for subsequent formulation of a physicochemically

stable and biopharmaceutically suitable dosage form.

➢Preformulation work is the foundation of developing efficacious

and economical formulations.