Ch10. pharmaceutical emulsion

Bule Hora University
College of Health and Medical Sciences
Department Of Pharmacy
INTEGRATED PHYSICAL PHARMACY AND PHARMACEUTICS I
CHAPTER 10
PHARMACEUTICAL EMULSIONS
By: Aliyi Gerina [B.pharm]
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Parmaceutical Emulsions by Aliyi G. Bule Hora University

Outline
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Parmaceutical Emulsions by Aliyi G. Bule Hora
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 Introduction
 Determination of emulsion type
 Theories of emulsification
 preparation of emulsion
 Preservation of emulsion
 Physical instabilities
 Rheology of emulsion
 Packaging, Labeling and storage

Introduction
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Dispersion System
Suspension
is a two phased system in which a
finely divided solid is dispersed in a
continuous phase .
Emulsion
is a dispersion in which the dispersed
phase is composed of small globules of a
liquid distributed throughout a vehicle in
which it is immiscible.

Emulsions (Definition)
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 An emulsion is a
thermodynamically unstable system consisting of at least
two immiscible liquid phases one of which is dispersed as
globules in the other liquid phase stabilized by a third
substance called emulsifying agent.
-OR-
 An emulsion is a
dispersion in which the dispersed phase is composed of small
globules of a liquid distributed throughout a vehicle in which
it is immiscible.

Cont’d,…
A.Two immiscible liquids not
emulsified.
B. An emulsion of phase B
dispersed in Phase A
C. Unstable emulsion slowly
separates.
D. The emulsifying agent ( black
film) places it self on interface
between phase A and phase B
and stabilizes the emulsion.
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Internal Phase or External Phase
in Emulsions
 The dispersed liquid is known as the
Internal or Discontinuous phase.
 The droplet phase is called the dispersed phase or
internal phase
 whereas the dispersion medium is
known as the External or Continuous
phase
 The liquid in which droplets are dispersed
is called the external or continuous phase.
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 Mask the Unpleasant taste.
 Improved Bio-availability.
 Sustained Release Medication.
 Nutritional supplement.
 Diagnostic purpose (x-rays
examination).
 External use preparation
(cream lotion foam aerosol).
 Economical.
 Short shelf-life.
 Unstable:- soluble phase
separate slowly
 Handling
 Storage
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Advantages Disadvantages

Types of emulsions:
 Based on dispersed
phase
 Single emulsions
 Oil in Water (O/W):
 Oil droplets dispersed in water.
 Water in Oil (W/O):
 Water droplets dispersed in oil.
 Multiple emulsions
 w/o/w emulsions
 o/w/o emulsions
 Based on Size of dispersed
phase
o Macroemulsions
o 0.2 – 50 mm
o Microemulsions
o 0.01 – 0.2 mm
o Nanoemulsions
o 50 – 1000 nm
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Oil-in water emulsion
o A system in which the oil droplets are dispersed throughout the
aqueous phase
o Fats or oils for oral administration are formulated as o/w
emulsions, either
 as medicaments in their own or
 as vehicles for oil-soluble drugs
o the inclusion of a suitable flavour in the aqueous
phase will mask any unpleasant taste.
(O/W)

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o Emulsions for intravenous administration must be of the o/w
type
 But IM injections can be formulated as w/o products
 if a water-soluble drug is required for depot therapy.
o O/w emulsions is used for the topical application of water-
soluble drugs
 Pleasant to use and easily washed from skin surfaces
 They do not have the greasy texture

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Water-in-oil (w/o) emulsion
o A system in which the water is dispersed throughout the oil
o useful for cleansing the skin of oil-soluble dirt
o cosmetically not acceptable
o Moisturizing creams are more efficient if formulated as w/o
emulsions
 produce a coherent, water-repellent film &
 prevent moisture loss from the skin and
 thus inhibit drying of the stratum corneum
(w/o)

DIFFERENCE BETWEEN O/W AND W/O EMULSIONS:
 Water is the dispersion medium and oil is the
dispersed phase.
 Water soluble drugs are more quickly
released from o/w emulsions.
 They are preferred for formulations meant for
internal use as bitter taste of oils can be
masked.
 They are non greasy and easily removable
from the skin surface.
 They are used externally to provide cooling
effect e.g. vanishing cream
 O/W emulsions give a positive conductivity
test as water is the external phase which is a
good conductor of electricity.
 Oil is the dispersion medium and
water is the dispersed phase.
 Oil soluble drugs are more quickly
released from w/o emulsions .
 They are preferred for formulations
meant for external use like creams.
 They are greasy and not water
washable.
 They are used externally to prevent
evaporation of moisture from the
surface of skin e.g. Cold cream.
 W/O emulsions go not give a positive
conductivity test as oil is the external
phase which is a poor conductor of
electricity.
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Oil in water emulsion (o/w) Water in oil emulsion (w/o)

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Multiple emulsion
 Multiple emulsions are the emulsion system in which the
dispersed phase contain smaller droplets that have the same
composition as the external phase.
 The multiple emulsions are also considered to be of two types:
Oil-in-Water-in-Oil:
 In O/W/O systems an aqueous phase (hydrophilic) separates
internal and external oil phase.
 In other words, O/W/O is a system in which water droplets may
be surrounded in oil phase,
 which in true encloses one or more oil droplets.
Water-in-Oil-In-Water:
 In W/O/W systems, an organic phase (hydrophobic) separates
internal and external aqueous phases.
 In other words, W/O/W is a system in which oil droplets may be
surrounded by an aqueous phase,
 which in turn encloses one or several water droplets.
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o Multiple emulsions
 are potential candidates for a sustained DFs.
 can be used to separate two incompatible hydrophilic
substances in the inner and outer aqueous phases by the
middle oil phase.

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o Preparation of multiple emulsion involves two stages
 w/o/w emulsion is prepared by
 First forming a w/o emulsion and
 Then dispersing this primary emulsion in a secondary aqueous
phase
 o/w/o emulsion is prepared by
 First forming a o/w emulsion and
 Then dispersing this primary emulsion in a secondary oily
phase

Determination of emulsion type
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a. Dilution test (Miscibility tests with oil or water)
based on the solubility of external phase of emulsion.
- o/w emulsion can be diluted with water.
- w/o emulsion can be diluted with oil.

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b. Conductivity test
 water is good conductor of electricity whereas oil
is nonconductor.
 Therefore, continuous phase of water runs electricity
more than continuous phase of oil.

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c. Dye solubility test (staining tests)
 when an emulsion is mixed with a water soluble dye such as
amaranth and observed under the microscope.
if the continuous phase appears red, then it means that the
emulsion is o/w type as water is the external phase
if the scattered globules appear red and continuous phase
colorless, then it is w/o type.
 Similarly if an oil soluble dye (Scarlet red C or Sudan III) is
added to an emulsion and the continuous phase appears
red,then it is w/o emulsion.

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d. Cobalt chloride paper test:
 When a filter paper soaked in cobalt chloride solution is
dipped in to an emulsion and dried, it turns from blue to pink,
 indicating that the emulsion is o/w type .

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e. Fluorescence test
 If a drop of an emulsion is exposed to UV radiation
and observed under a microscope,
 show continuous Fluorescence it is W/O emulsion type
 show only spotty fluorescence then it is O/W type

Theories of emulsification
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o There are many theories to explain how
o emulsifying agents promote emulsification and
o maintain the stability of the emulsion.
o Certain of these theories apply rather specifically
 to certain types of emulsifying agents and
 to certain conditions

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o The most prevalent theories are
 The surface tension theory
 by lowering of interfacial tension.
 The oriented-wedge theory and
 mono molecular layers of emulsifying agents are curved around a
droplet of the internal phase of the emulsion.
 The plastic or interfacial film theory
 A film of emulsifying agent prevents the contact and coalescing of
the dispersed phase.

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Surface tension theory
o According to the surface tension theory of emulsification
 The surface-active agents as emulsifiers lowers the
interfacial tension of the two immiscible liquids
 reducing the repellent force between the liquids and
diminishing each liquid’s attraction for its own molecules.

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The oriented-wedge theory
o The theory is based on the presumption that certain emulsifying
agents orient themselves about and within a liquid in a manner
reflective of their solubility in that particular liquid
o Many molecules of substances upon which this theory is based
have a hydrophilic portion and a hydrophobic portion
 the molecules position or orient themselves into each phase.

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o Depending on their orientation
 either oil globules or water globules can be surrounded
o An emulsifying agent having a greater hydrophilic than hydrophobic
character will promote an o/w emulsion, and
o w/o emulsion results from use of an emulsifying agent is more
hydrophobic than hydrophilic

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The plastic or interfacial film theory
o Places the emulsifying agent at the interface between the oil
and water, surrounding the droplets of the internal phase as a
thin layer of film adsorbed on the surface of the drops
o The film prevents contact and coalescing of the dispersed
phase
 the tougher and more pliable the film, the greater the
stability of the emulsion.

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o It is more than likely that even within a given emulsion
system, more than one of the theories play a part
 For instance, lowering of the interfacial tension is important
in the initial formation of an emulsion,
 but the formation of a protective wedge of molecules or film
of emulsifier is important for continued stability.
 Certain emulsifiers are capable of both tasks.

Preparation of emulsions
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Additives For Formulation Of Emulsion
A. Emulsifying agent
B. Preservative
C. Antioxidants
D. Flavoring agent

A.Emulsifying Agents
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 They are the substances added to an emulsion
 to prevent the coalescence of the globules of the dispersed phase.
 They are also known as emulgents or emulsifiers.
 They help in formation of emulsion by three mechanisms.
- Reduction in interfacial tension – thermodynamic stabilization
- Formation of a rigid interfacial film – mechanical barrier to
coalescence
- Formation of an electrical double layer – electrical barrier to
approach of particles.

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 Pharmaceutically acceptable emulsifiers must also :
Be stable .
Be compatible with other ingredients .
Be non – toxic .
Possess little odor , taste , or color .
Not interfere with the stability of efficacy of the active
agent .

Classification of Emulsifiers
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Synthetic Surface active
agents( Monomolecular
films)
Semi synthetic and natural
Hydrophilic colloids
( Multi-molecular films)
Finely divided solid
particles(Particulat
e film)

1. Synthetic surface active
agents
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Reduce interfacial tension and
make the emulsion thermodynamically more stable.
To reduce the interfacial tension Oil droplets are surrounded by a
coherent monolayer of the surfactant which prevents coalescence.
If the emulsifier is ionized , the presence of strong charge may
lead to repulsion in droplets and
hence increasing stability.
Adsorbed at oil/water interface to form.
Form protective monomolecular film
Micelle formation

Classification of Surfactants
 Cationic
 Quaternary ammonium
compounds
e.g. benzalkonium chloride,
cetrimide.
 Anionic
 Soaps
-Mono valent
-Polyvalent
-Organic
 Sulphates
 Sulphonates
 Nonionic
 Polyoxy ethylene fatty alcohol
ethers
 Sorbitan fatty acid esters
 Polyoxyethylene sorbitan fatty
acid esters
 Lanolin alcohols and
ethoxylated lanolin alcohols
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2.Semi synthetic and natural
surface active agents
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 Also known as Hydrocolloid Emulsifying agents
 Provide a protective sheath (Multi-molecular films )around
the droplets
 Impart a charge to the dispersed droplets
 so that they repel each other.
 Swell to increase the viscosity of the system
 so that droplets are less likely to change.

Classification of Hydrocolloidals
 Includes mainly cellulose derivatives
like
 sodium carboxymethyl cellulose,
 hydroxyl propyl cellulose and
methyl cellulose.
 They are used for formulating o/w type
of emulsions.
 They primarily act by increasing the
viscosity of the system.
 e.g., methyl cellulose,
hydroxypropyl cellulose and sodium
carboxy methyl cellulose.
-Plant origin
 Polysaccharides
(Acacia, starch,tragacanth,
agar, pectin, lecithin)
-Animal origin
 Proteins ( Gelatin)
 Cholesterol
 Wool fat
 Egg yolk
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Semi synthetic Natural

3. Finely divided solid particles
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 Also known as Particulate films
 Form a particulate "film“ around dispersed particles.
 These particles rely on adsorption to interfaces and like the
hydrophilic colloids,
 function by forming a physical barrier to coalescence.
 Finely divided solid particles that are wetted to some degree
by both oil and water act as emulsifying agents.
 This results from their being concentrated at interface,
 where they produce a particulate film around the dispersed droplets to
prevent coalescence.

Classification of Particulate films
• Bentonite,
• Veegum
• Magnesium trisilicate
• Magnesium hydroxide
• Aluminium hydroxide
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Colloidal Clays Metallic hydroxides

B. Preservatives
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 Number of ingredients in emulsion support the growth of
microorganism
 which result into change in colour, odour and taste of emulsion.
 Therefore there is need to include the preservative.
 Microbial contamination may occur due to:
 contamination during development or production
 Usage of impure raw materials
 Poor sanitation conditions
 Invasion by an opportunistic microorganisms.
 Contamination by the consumer during use of the product.
 Precautions to prevent microbial growth ;
o Use of uncontaminated raw materials
o Careful cleaning of equipment with steam .

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 The preservative must be :
 Less toxic
 Stable to heat and storage
 Chemically compatible
 Reasonable cost
 Acceptable taste, odor and color.
 Effective against fungus, yeast, bacteria.
 Available in oil and aqueous phase at effective level concentration.
 Preservative should be in unionized state to penetrate the
bacteria.
 Preservative must no bind to other components of the emulsion

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- Examples
 Acids and acid derivatives - Benzoic acid – Antifungal agent
 Aldehydes – Formaldehyde – Broad spectrum
 Phenolics - Phenol - Broad spectrum
Propyl hydroxy benzoate
 Quaternaries -Chlorhexidine and salts - Broad spectrum
Benzalkonium chloride
Cetyl trimethyl ammonium bromide
 Mercurials -Phenyl mercuric acetate – Broad spectrum

C . Antioxidants
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 Many organic compound subjected to autoxidation upon
 exposure to light and air and
 result on decomposition.
 Emulsified lipid are particularly sensitive to attach.
 Unsaturated oils become rancid on autoxidation
 result in change in taste, odour and appearance.
 Autoxidation occurs by
 free radical reaction
 Can be prevented by
 absence of oxygen,
 a free radical chain breaker
 by reducing agent

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 The Antioxidants must be
 Nontoxic,
 Nonirritant,
 effective at low concentration under the expected conditions
of storage and use,
 soluble in the medium and stable.
 Antioxidants for use in oral preparation should also be
odorless and tasteless.

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Examples:
 Gallic acid, Propyl gallate - pharmaceuticals and cosmetics - Bitter
taste
 Ascorbic acid – Suitable for oral use products
 Sulphites - Suitable for oral use products
 Tocopherol - pharmaceuticals and cosmetics -Suitable for oral
preparations
 Butylated hydroxytolune (BHT) and
 Butylated hydroxyanisol (BHA)

D. Flavouring agent
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 Flavouring agent is incorporated in the formulation
 to impart the taste to it.
 Example:
Vanillin – in liquid paraffin emulsion.
Benzaldehyde – in cod-liver oil emulsion.

Methods of Emulsion
Preparation
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o Emulsions may be prepared by several methods, depending
upon the nature of the components and the equipment
o On a small scale emulsions may be prepared using
 Porcelain mortar and pestle
 a mechanical blender or mixer, such as milkshake mixer, a
hand homogenizer,
 sometimes a simple prescription bottle

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o In the small-scale extemporaneous preparation of emulsions,
there are three commonly used methods
 the continental or dry gum method
 the English or wet gum method and
 the bottle or Forbes bottle method
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Dry Gum Method / Continental Method
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 In dry gum method the oil is first triturated with
gum & then water is added.
 “4:2:1" Method
4 parts (volumes) of oils
2 parts of water
1 part of gum

Wet Gum Method / English Method
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 In wet gum method the first gum triturated with water to
form a mucilage & then oil added in small quantities.
 “4:2:1" Method
4 parts (volumes) of oil
2 parts of water
1 part of gum

Bottle Method/ Forbes Bottle Method
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 This method useful for the volatile & other non-viscous oils.
 Because of low viscosity the volatile oils it requires greater amount
of gum.
 4 : 4: 2 method.
 4 parts (volumes) of oil
4 parts of water
2 part of gum
 Oil is put in large bottle + Gum (shaken until mixed) + Water (to
form primary emulsion) then volume make up with water.

Table shows Proportions of oil, water & Gum acacia
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Proportion of Oil : Water: Gum
Fixed Oils 4 : 2 : 1
Volatile Oils 4 : 4 : 2
Fixed Oils:
- Castor oil, Cod liver oil, Shark liver oil, Olive oil, Almond oil,
Liquid paraffin.
Volatile Oils:
- Turpentine oil, Sandal wood oil, Cinnamon oil, Peppermint oil

Physical Stability of emulsions
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o A stable emulsion may be defined as a system in which the
• Globules retain their initial character
• Remain uniformly distributed throughout the continuous phase.
o Different instability problems
• Reversible: such as creaming and flocculation
• Irreversible: such as coalescence and breaking

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FLOCCULATION
 Neighboring globules come closer to each other and form
colonies in the continuous phase.
 This aggregation of globules is not clearly visible.
 This is the initial stage that leads to instability.
 Flocculation of the dispersed phase may take place
 before,during or after creaming.

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 Flocculation is due to the interaction of attractive and repulsive
forces, whereas
 creaming is due to density differences in the two phases.
 flocs slowly move either upward or downward
 leading to creaming.

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 The reversibility of flocculation depends upon strength of
interaction between particles as determined by:
a. the chemical nature of emulsifier,
b. the phase volume ratio,
c. the concentration of dissolved substances.
 The extent of flocculation of globules depends on
(a) globule size distribution.
(b) charge on the globule surface.
(c) viscosity of the external medium.
 This can be obtained by adding viscosity improving agents
(bodying agents or thickening agents) such as
 hydrocolloids or waxes.

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CREAMING
 It is the concentration of the floccules of the internal phase form
upward or downward layer
 according to the density of internal phase.
 Droplets larger than 1 mm may settle preferentially to the top or
the bottom under gravitational forces.
 It can be observed by a difference in color shade of the layers.
 It is a reversible process, i.e., cream can be re-dispersed easily
by agitation,
 this is possible because the oil globules are still surrounded by the
protective sheath of the emulsifier.

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 Creaming is of two types, upward creaming and downward
creaming:
 Upward creaming, is due to the dispersed phase is less dense than
the continuous phase.
 This is normally observed in o/w emulsions.
 The velocity of sedimentation becomes negative.
 Downward creaming occurs if the dispersed phase is heavier than
the continuous phase.
 Due to gravitational pull, the globules settle down.
 This is normally observed in w/o emulsions.

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 Since creaming involves the movement of globules in an emulsion,
Stokes’ law can be applied.
dx/dt=d2 (pi-pe)g
18n
 dx/dt=rate of setting
 D=diameter particle
 p=density of internal phase and external phase
 g=gravitational constant
 n=viscosity of medium

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Factors affect creaming:
 Globule size:
↑globule size => ↑creaming
 The density of the internal phase and External phases:
pi-pe=0 => dx/dt=0
pi-pe=-ve => [i.e.-ve velocity ,upward creaming]
pi-pe=+ve => [downward creaming]
 Gravity:
Constant, however centrifugation is applied
 Velocity:
↑ => ↓creaming

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The rate of creaming can be increased
 If the density difference is greater
 By increasing the force of gravity through centrifugation
 By increasing the diameter of the globule
Following are ways in which creaming may be
minimised:
– reduction in the globule size (eg by homogenizing the emulsion)
– increasing viscosity of continuous phase (eg. by the use of
thickening agents such as tragacanth or methyl cellulose)
– decrease in the density difference between the two phases.

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Creaming is undesirable from a pharmaceutical point
of view:
– Creamed emulsion is inelegant in appearance,
– Possibility of inaccurate dosage,
– Increases the likelihood of coalescence as the globules are close
together in the cream.

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COALESCENCE
 It is the process by which dispersed phase droplets merge with
each to form large particles.
 This type of closed packing induces greater cohesion which
leads to coalescence
 In this process, the emulsifier film around the globules is
destroyed to a certain extent.
 This step can be recognized by increased globule size and reduced
number of globules.

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 Factors:
• Relative magnitude of forces between droplets
• Disruption of interface
• Dehydration, freezing
 Strategies to reduce coalescence
– Adding thickening or gelling agent
– Increase thickness of interface
– Increase repulsion or reduce Attraction

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CRACKING or BREAKING
• Separation of an emulsion into its constituent phases
– Due to coalescence and creaming combined , the oil separates
completely from water so that it floats at the top in a single,
continuous layer.
– Re-dispersion cannot be achieved by shaking and the preparation
is no longer an emulsion.

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Cracking of emulsion can be due to:
 Addition of a chemical that is incompatible with the emulsifying
agent, thus destroying its emulsifying ability
 The addition of surface active agents of opposite ionic charge
e.g. the addition of cetrimide (cationic) to an emulsion
stabilized with sodium oleate (anionic)
 The addition of large ions of opposite charge
e.g. neomycin sulphate (cationic) to aqueous cream (anionic).

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 Bacterial growth: protein materials and non-ionic surface-
active agents are excellent media for bacterial growth;
 Temperature change:
– rise in temperature: protein emulsifying agents may be
denatured and the solubility characteristics of non-ionic
emulsifying agents change
– Freezing: ice formed disrupt the interfacial film around the
droplets

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Precipitation or Decomposition of Emulsifying agent:
Gums, Gelatin & casein are insoluble in alcohol
If this solvent is transferred to prepared emulsion, that time the
emulgent precipitate &
cracking was caused.
Anion emulgent are incompatible with large cations &
cation emulgent are incompatible with large anions.
By addition of Common Solvent:
- If common solvent was added in prepared emulsion that time
cracking was showed.
- E.g. alcohol is added in turpentine oil liniment,
- alcohol is soluble with turpentine oil, soft soap &
water are soluble in alcohol that time destroying the emulsion.

Cont’d,…
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Phase inversion
 In phase inversion o/w type emulsions changes into w/o type and
vice versa.
 It is a physical instability.

Cont’d,…
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It may be brought about by:
 by addition of an electrolyte
 e.g. addition of calcium chloride into o/w emulsion formed by sodium
stearate can be inverted to w/o.
 by changing the phase volume ratio.
– For stability of an emulsion, the optimum range of concentration of
dispersed phase is 30–60% of the total volume.
– If the disperse phase exceeds this the stability of the emulsion is
questionable.
– As the concentration of the disperse phase approaches a
theoretical maximum of 74% of the total volume, phase inversion is more
likely to occur.
 by temperature changes.
 by changing the emulsifying agent.

Cont’d,…
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Phase inversion can be minimized by:
 using the proper emulsified agent in adequate
concentration.
 keeping the concentration of dispersed phase between 30 to
60%.
 storing the emulsion in a cool place.

Rheological considerations
71
o Flow property of the product will be vital for proper performance
of the emulsion under the conditions of use or preparation.
o The need for correct flow characteristics is indicated by
 The flow of parenteral emulsion through a hypodermic needle
 removal of emulsion from bottle or a tube, and
 the behavior of emulsion in varies milling operations employed in large
scale manufacture .
o Factors that influence the flow properties of emulsions
 Factors related to dispersed phase includes
 The phase volume ratio
 The particle size distribution
 The viscosity of the internal phase
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Cont’d,…
72
o Most emulsion, except the dilute ones,
 exhibit non-Newtonian flow.
o When the volume concentration of the dispersed phase is low (< 0.05),
 the system exhibit Newtonian behavior
o As the volume concentration increased
 Pseudoplastic flow
o At sufficiently higher concentration
 Plastic flow
o Reduction in particle size increases the viscosity
 The wider PSD the lower is the viscosity
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Cont’d,…
73
o Another components that may influence the viscosity of an
emulsion is
o the emulsifying agent.
 The greater the concentration of emulsifying agent,
 the greater the viscosity of the product.
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Packaging, Labeling and storage
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 Depending on the use, emulsions should be packed in suitable
containers.
 for oral use : usually packed in well filled bottles having an air tight
closure.
 Light sensitive products : packed in amber colored bottles.
 For viscous emulsions : wide mouth bottles should be used.
 The label on the emulsion
 should mention that these products have to be shaken thoroughly before use.
 External use products should clearly mention on their label that
 they are meant for external use only.
 Emulsions should be stored in a cool place but refrigeration should be
avoided
 as this low temperature can adversely effect the stability of preparation.

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Thank you!!

Ch10. pharmaceutical emulsion

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