STABILITY TESTING , BY DR. UMESH KUMAR SHARMA AND ARATHY SA

1. STABILITY TESTING,
THEORIES OF DISPERTION,
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By : Dr. Umesh Kumar Sharma and Arathy .S.A
Department of Pharmaceutics,
Mar Dioscorus College of Pharmacy,
Alathara, Sreekariyam,
Thiruvananthapuram, Kerala, India

2. A study of drug stability and of stability testing
techniques is essential for the following main reason
 Patient safety
 Drug Activity
 Legal Requirement
 Bad image for the Manufacture
 Patient economy
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3.  The most common causes of instability or
decomposition of drug are hydrolysis and oxidation.
 Photochemical decompositions and isomerisation
also lead to instability of drug.
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4.  This problems is most important in system containing
water such as emulsion, suspension and solution etc.
 Hydrolysis is usually catalysed by H ions or OH ions.
 Hydrolytic reactions in solid drug products such as
tablet, capsules, powders, and granules may be
prevented by avoiding their contact with moisture at
the time of their manufacture
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5.  Oxidation involves either addition of oxygen or
removal of hydrogen.
 Autoxidation is a most common form of oxidation
degradation that occurs in many of the
pharmaceutical preparations and involves a free
radical chain process.
 Heavy metals such as cobalt, Nickel, copper and iron
usually catalyses the degradation.
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Include suitable antioxidants in the preparation.
Ascorbic acid, sodium sulphide, sodium meta bisulphite
are usually used.
Effect of antioxidants can be increased through the use
of synergists such as chelating agents like EDTA, citric
acid etc.
Photolysis
Exposure to light may cause oxidation, reduction, ring
rearrangement or modification and polymerisation.
This can be reduced by use of amber coloured bottles.

7.  Isomerisation is the conversion of a drug into its
geometrical or optical isomers.
 Since different isomers of a drug have different
activities, such conversions may cause serious loss of
therapeutic activity.
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8.  Accelerated stability studies is designed to predict
stability and hence shelf life of formulations under or
recommended storage conditions by carrying out the
study under accelerated conditions of temperature,
moisture, and light.
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Shelf life is the time period during which the
dosage form is supposed to retain its original
qualities.
The prediction of shelf life is based on applying
Arrhenius equation which gives the effect of
temperature on rate constant, k, of a chemical
reaction.

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From the slopes of lines the reaction rate constant k for
the degradation at each of the elevated temperature is
calculated

11.  Dispersed system consist of at least two phases, the
substance that is dispersed known as the
dispersed/internal phase and continuous/external
phase.
 Based on the particle size of the dispersed phase,
dispersions are generally classified as:
 Molecular dispersions
 Colloidal dispersions
 Coarse dispersions
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Colloidal dispersions having other various
pharmaceutical dispersion system. It includes:
• Microemulsions
• Microspheres
• Micelles
• Liposome
• Nanoparticles
• Nanosuspension

13.  Micro emulsion as a system of water, oil and
amphiphile which is optically isotropic and
thermodynamically stable liquid solution.
 Micro emulsions have droplets typically in the size
range 10–100nm.
 Three different theories have been proposed to
explain the micro emulsion formation and stability.
They are the interfacial mixed film theory,
solubilisation theory and thermodynamic theory.
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Characterization
o Particle size in micro emulsions can be elucidated by
small- angle x- ray scattering, small-angle neutron
scattering, dynamic and static light scattering, freeze
fracture electron microscopy, neutron scattering
techniques.
Evaluation
1. Physical appearance
2. Scattering Techniques
3. Drug stability
4. Globule size and zeta potential measurements
5. Electrical conductivity

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Uses
• Dry cleaning processes
• Floor polishers and cleaners
• Personal care products
• Drugs
• Synthesis of polymers

16. Microspheres:
 Microspheres are solid, spherical devices containing
the drug in a polymer matrix.
 Size ranging from 1 to 1,000 mm.
Characterization :
 Particle size of microspheres can be determined by
light microscopy and coulter counter.
 Shape and surface morphology can be examined
using scanning electron microscopy and atomic force
microscopy.
 The porosity of the microspheres can be measured by
air permeability (for pores ranging from 10 to 75
mm) and mercury porosimetry 16

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Evaluation
• Particle size and shape
• Chemical analysis
• Density
• Isoelectric point
• Angle of contact
Uses
• Cosmetics
• Thickening agent
• Retro reflective
• Drug delivery

18.  Micelles are attractive candidates as drug carriers for
delivering poorly water-soluble drugs.
 Micelles are self-assembling colloidal systems with
particle size normally ranging from 5 to 100 nm.
 Micelles are spontaneously formed when amphiphilic
molecules are placed in water at a certain
concentration and temperature.
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Property of micellization is generally displayed by
molecules that possess two distinct regions with
opposite affinities toward a particular solvent.
 At a low concentration, the molecules exist
separately in a solution.
The hydrophobic portions of the molecules condense
to form the core, whereas the hydrophilic portions
constitute the shell or corona of the micelle.

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Evaluation
• Morphological characterization.
• Particle size and zeta potential.
• Solubility.
• Drug loading.
• Differential scanning calorimetry.
Uses
• Electrophoresis and chromatography.
• Gene delivery.
• Removal of complex lipids and fat soluble vitamins
from human body.

22. LIPOSOMES:
 Liposomes is a spherical vesicle having at least one
lipid bilayer MLV.
 Liposomes range from 5 to 50 mm in size,
Mechanism
 Liposomes can hence loaded with hydrophobic /
hydrophilic molecules.
 To deliver the molecules to a site of action, the lipid
bilayer.
 Can fuse with other bilayers such as the cell membrane.
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Evaluation
• Vesicle shape.
• Vesicle size and size distribution.
Uses
• Can be formulated as gels, creams, aerosol
suspension.
• Detection of tumours.
• Application in nutrients and in cosmetics.

25. Nanoparticles
 Particles between 1 and 100nm in size with a
surrounding interfacial layer.
Characterization
 Tunable resistive pulse sensing.
Synthesis
 Several methods are gas condensation, attrition,
chemical precipitation etc.
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Evaluation
• Zeta potential
• Particle shape
• Particle size
Uses
• Deliver drugs to tumour.
• Treatment chronic bacterial infection.

27. Nanosuspension
 Is a submicron colloidal dispersion of drug particles.
 Size below 1um.
Preparation
 Produced by bottom up and top down techniques.
Characterization
 Particle size can be determined by photon correlation
spectroscopy, laser diffraction coulter counter.
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Evaluation
• Colour, odour, taste.
• Particle size distribution.
• Zeta potential.
• Density.
• PH value.

29. EMULSIONS
An emulsion is a biphasic liquid preparations containing
two immiscible liquids, one of which is dispersed as minute
globules into the other.
 The liquid phase is converted into minute globules is
called the ‘dispersed phase’ and the liquid in which the
globules are dispersed is called the ‘continuous phase’.
 Normally, two immiscible liquids cannot be dispersed for
a long period.
 So an emulsifying agent is added to the system.
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It forms a film around the globules in order to scatter
them indefinitely in the continuous phase, so that a stable
emulsion is formed.
The globule size in emulsions varies from 0.25 to 25um.
Classification of emulsions
1. Based on the nature of dispersed phase
a. Oil in water(O/W)
b. Water in oil(W/O)
2. Based on the globule size of liquid droplets
a. Macro emulsions
b. Micro emulsions

31. Identification test of emulsions systems
Dye test
 The scarlet red dye is mixed with the emulsion.
 If the disperse globules appear red and the ‘ground’
colourless, the emulsion is o/w type.
 The reverse condition occurs in w/o type emulsion ie,
the disperse globules appear colourless in the red
‘ground’ .
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32. Dilution test
 The emulsion is diluted with water.
 In case the emulsion remains stable after its dilution,
it is o/w emulsions.
 The w/o emulsions breaks on its dilution with water
but remains stable when diluted with oil.
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33. Conductivity test
 Water is a good conductor of electricity, whereas oil
is non-conductor of electricity.
 The conductivity test can be performed by dipping a
pair of electrodes connected through a low voltage
bulb in the emulsion.
 If the bulb glows on passing the electric current the
emulsion is o/w type, because water is in the
continuous phase.
 In case the bulb does not glow, the emulsion is w/o
type, because oil is in the continuous phase.
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34. Fluorescence test
 Certain fixed oils possess the physical property of
fluorescing in the presence of ultraviolet radiation.
 On microscopic observation of emulsion under
ultraviolet radiation, the whole field fluorescence
indicates that oil present in continuous phase(w/o
type emulsion) and droplets fluorescence indicates
that oil is present in dispense phase(o/w type
emulsion).
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35. Theories of emulsification
 There is no universal theory of emulsification,
because emulsions can be prepared using several
different types of emulsifying agent, each of which
depends for its action on a different principle to
achieve a stable product.
 When two immiscible liquids are agitated together,
so that one is dispersed as small droplets in the other,
the liquid separates rapidly into clearly defined layers
expect in very dilute o/w emulsion.
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36. Emulsifying agents
The emulsifying agents reduce the interfacial tension
between two phases i.e. oily phase and aqueous phase
and thus make them miscible with each other and form
a stable emulsion.
Emulsifying agents can be classified into three groups.
 Surfactants.
 Hydrophilic colloids.
 Finely divided solids.
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Emulsifying agents assists in the formation of
emulsions by 3 mechanism.
a. Reduced interfacial tension
When two immiscible liquids are mixed, the oil droplets
will disperse in the continuous phase which leads to
increase in surface area which in turn increase the
surface free energy according to the equation.
∆G= ᵞ*∆A

38. b. Formation of rigid interfacial film-
 The absorbed emulsifier at the interface surrounds the
dispersed droplets forming a coherent
monomolecular or multimolecular film.
 The stability of emulsion depends on the
characteristics of the film formed at the interface
which in turn depends upon the type of emulsifier.
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39. c. Formation of electrical double layer-
 Interfacial films formed can produce repulsive forces
between approaching droplets. Such repulsion is due
to an electrical double layer, which arise from
electrically- charged groups oriented on the surface of
emulsified globules.
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40. Formulation of Emulsion
Emulsifying agent
 To reduce the interfacial tension between two phases.
Emulsifying agent, sometimes used singly, are
preferably a combination of two emulsifying agents.
Surfactants
 Molecules and ions that are absorbed at interface are
termed surface active agents.
 which will given a weighed HLB of 8 to 16 which is
satisfactory for o/w emulsions and an HLB 3to 8 for
w/o emulsions.
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41. Hydrophilic colloids-
 Naturally occurring gums and synthetic hydrophilic
polymers.
Finely divided solid particles-
 They act as a good emulsifiers, especially in
combination with surfactants.
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42. Methods of preparation of emulsion
Continental method (Dry gum):
In a mortar, the 1-part gum is levigated with the 4 parts oil until
the powder is thoroughly wetted; then the 2 parts water are
added all at once, and the mixture is vigorously and continually
triturated until the primary emulsion formed is creamy white and
produces a crackling sound as it is triturated.
English method (wet gum):
• In this method, the 1 part gum is triturated with 2 parts water
to form a mucilage; then the 4 parts oil is added slowly, in
portions, while triturating.
• After all the oil is added, the mixture is triturated for several
times to form the primary emulsion.
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Bottle method:
• This method is suitable for oleaginous substance of
very low viscosities.
• One part of powdered gum is placed in a dry bottle and
four parts oil are added.
•The bottle is capped and thoroughly shaken. To this, the
required volume of water is added all at once, and the
mixture is shaken thoroughly until the primary
emulsion forms.

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Phase inversion method:
•In this method, the aqueous phase is first added to
the oil phase so as to form a W/O emulsion.
• At the inversion point, the addition of more water
results in the inversion of emulsion which gives rise
to an O/W emulsion.

45. Stability of emulsions
Flocculation and creaming-
• Flocculation of dispersed phase may take place before or after
creaming.
• Creaming occurs when the aggregated droplets rise through the
medium or sink to the bottom (sedimentation).
• Creaming depends upon the radius of the droplets, the relative
difference in the densities of the two phases, and the viscosity of
the continuous phase. The rate of creaming can be assessed by
Stokes' equation.
V=d2(ps–po)g/18no
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46. Coalescence or breaking-
• Coalescence occurs when two or more droplets fuse
together to form a single larger droplet, which leads
to the complete separation of the two immiscible
phases.
Ostwald ripening
• Ostwald ripening is a process that involves the
growth of large particles at the expense of smaller
ones because of high solubility of the smaller droplets
and molecular diffusion through the continuous
phase.
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47. Phase inversion-
 Emulsions can invert from an O/W to a W/O
emulsion or vice versa during homogenization or
sterilization procedures. This phenomenon is called
as phase inversion and can be regarded as a form of
instability.
 The temperature at which phase inversion occurs is
called phase inversion temperature (PIT).
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49. Evaluation of emulsion:
Stress Condition-
Stress conditions normally employed for evaluating the
stability of emulsions.
a. Aging and temperature
It is a routine to determine the shelf life of all types of
preparations by storing them for varying periods of time at
temperature.
b. Centrifugation
It is commonly accepted that shelf life under normal
storage conditions can be predicted rapidly by observing
the separation of the dispersed phase due to either creaming
when the emulsion is expected to centrifugation.
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c. Agitation
• Simple mechanical agitation can contribute to the energy
with which two droplets impinge upon each other.
•Excessive shaking of an emulsion or excessive
homogenization may interfere with the formation of an
emulsion.
•Agitations can break emulsions.
Parameters commonly measured to assess the effect of
stress conditions include
1. Phase separation- By measuring the volume of the
separated phase.
2. Viscosity -Viscometers of cone plate type or
penetrometer are used.

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3. Electrophoretic properties
• Zeta potential- By observing movement of particle
under the influence of electric current.
•Electrical conductivity- With the aid of pt electrodes

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THANK YOU
Dr. Umesh Kumar Sharma and Arathy .S.A
Department of Pharmaceutics,
Mar Dioscorus College of Pharmacy,
Alathara, Sreekariyam,
Thiruvananthapuram, Kerala, India