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Technology of Solid Dosage Forms &Disperse Systems
Pharmaceutical Emulsions
and Creams
National University
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General description
• Emulsions and creams are disperse systems
in which an insoluble liquid phase is dispersed
within a second liquid phase.
• Creams are emulsions that offer greater
consistency (viscosity) and are applied
topically.
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• Emulsions and creams are either oil in water
(o/w) in which oil is the disperse phase and
water the external phase, or water in oil (w/o),
in which water is the disperse phase and oil is
the external phase.
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• There are further more structurally complex
types, termed multiple emulsions. These are
termed water in oil in water (w/o/w) and oil in
water in oil (o/w/o) emulsions.
• However, the pharmaceutical uses of these are
extremely limited due to their possible reversion
to the parent primary emulsion.
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• The major use of emulsions is as cream
formulations (for external application);
however, they may also be administered
intravenously,rectally or orally.
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Advantages
• 1. Used to deliver drugs that exhibit a low
aqueous solubility.
• 2. Used to mask the taste of therapeutic
agents, by dissolving the drug in the internal
phase of an o/w emulsion.
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• 3.Commonly used to administer oils that have a
therapeutic effect.
• 4.If the therapeutic agent is irritant when
applied topically, the irritancy may be reduced
by formulation of the drug within the internal
phase of an o/w emulsion.
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• 5. Could be employed to administer drugs to
patients who have difficulty swallowing solid-
dosage forms.
• 6. Emulsions are employed for total parenteral
nutrition(TPN).
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Disadvantages
• 1. They are thermodynamically unstable and
so must be formulated to stabilise the
emulsion from separation of the two phases.
• 2. Difficult to manufacture.
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Theories of emulsification
• The system attempts to lose this excess free
surface energy to its surrounding by
coalescence of the droplets. Addition of
emulsifier which concentrates at an interface,
thereby altering the surface free energy.
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Go and read further for:
• The role of surface-active agents.
• The role of hydrophilic polymers.
• The role of adsorbed particles.
In emulsion stability.
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Determination of emulsion type
• When oil, water and the specified emulsifying
agents are mixed together, the resultant
emulsion type is defined by the stability of the
droplet phase; the phase of lower stability (i.e.
the greater rate of coalescence) coalesces to
form the external phase.
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Factors that determine
Emulsion Type prduced
(1) phase volume of the internal phase.
(2) the chemical properties of the film
surrounding the internal phase.
(3) viscosity of the internal and external phases.
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Tests for identification of
emulsion type
• Dilution test (miscibility test)
• Staining test (dye solubility test)
• Conductivity measurement
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Dilution test (miscibility test)
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Conductivity Test
• This test is based on the basic principle that
water is a good conductor of electricity.
Therefore in case of o/w emulsion , this test
will be positive as water is the external phase.
In this test.
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• An assembly consisting of a pair of electrodes
connected to a lamp is dipped into an
emulsion. If the emulsion is o/w type, the lamp
glows.
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Dye Solubility Test
• In this test, 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 and the dye will dissolve in it to
give color but if the scattered globules appear
red and continuous phase colorless, then it is
w/o type.
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• Similarly if an oil soluble dye such as Scarlet
red C or Sudan III is added to an emulsion and
the continuous phase appears red, then it w/o
emulsion.
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Emulsifying Agents
• 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 act by reducing the interfacial tension
between the two phases and forming a stable
interfacial film.
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• The selection of emulsifying agent plays a
very important role in the formulation of a
stable emulsion.
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Criteria For The Selection of
Emulsifying Agents
• It should be able to reduce the interfacial
tension between the two immiscible liquids.
• It should be physically and chemically stable ,
inert and compatible with the other ingredients
of the formulation.
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• It should be non irritant and non toxic in the
conc., used.
• It should be organoleptically inert i.e. should
not impart any color , odour or taste to the
preparation.
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• It should be able to produce and maintain the
required viscosity of the preparation.
• It should be able to form a coherent film
around the globules of the dispersed phase
and should prevent the coalescence of the
droplet of the dispersed phase.
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• No single emulsifying agent possesses all
the properties required for the formulation
of a stable emulsion therefore sometimes
blends of emulsifying agents have to be
taken.
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Instabilities In Emulsions
• An emulsion is a thermodynamically unstable
preparation so care has to be taken that the
chemical as well as the physical stability of the
preparation remains intact throughout the shelf
life.
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There should be
• No appreciable change in the mean particle
size or the size distribution of the droplets of
the dispersed phase.
• Droplets of the dispersed phase should remain
uniformly distributed throughout the system.
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Instabilities seen in emulsion
can be grouped as:
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1.Creaming
• This phenomenon occurs primarily as a result
of the density difference between the oil and
water phases and involves either the
sedimentation or elevation of the droplets of the
internal phase, producing a layer of
concentrated emulsion either at the top or
bottom of the container.
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• Patients often believe that an emulsion that
shows evidence of creaming has exceeded its
shelf-life.
• It is therefore important to understand the
physicochemical basis of creaming in
emulsions and, in so doing, reduce the rate of
or inhibit this phenomenon.
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The factors affecting creaming are best
described by stoke’€™s law:
V= 2r2 (d1-d2) g/9
• Where V= rate of creaming
• r=radius of globules
• d1= density of dispersed phase
• d2= density of dispersion medium
• g= gravitational constant
• = viscosity of the dispersion medium
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So,
• What will you do to decrease Creaming?
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2.Cracking
• It refers to the complete coalescence of the
internal phase, resulting in the separation of the
emulsion into two layers.It occurs due to the
destruction of the mono/multilayer film at the
interface between the droplet and external
phase.
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• If an emulsion has cracked it cannot be
recovered.
(irreversible instability)
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What are the possible reasons
of cracking?
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This phenomenon may be due to:
1. Incorrect selection of emulsifying agents.
2. Presence of incompatible excipients.
3. Temperature.
4. Microbial spoilage.
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3.Flocculation
• Although flocculation may stabilise the
formulation, there is also the possibility that
the close location of the droplets would enable
droplet coalescence to occur if the mechanical
properties of the interfacial film are
compromised.
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4.Phase inversion
• Phase inversion refers to the switching of an
o/w emulsion to a w/o emulsion (or vice
versa). This is a phenomenon that frequently
occurs whenever the critical value of the
phase volume ratio has been exceeded.
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• In o/w emulsions the frequently phase volume
ratio is 74:26 .
• For w/o emulsions this value is 40:60.
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Preparation of Emulsions
Preparation of emulsions depends on the scale
at which it is produced.
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• On small scale mortar and pestle can be
used but its efficiency is limited. To overcome
these drawback small electric mixers can be
used although care must be exercised to
avoid excessive entrapment of air.
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• For large scale production mechanical
stirrers are used to provide controlled
agitation and shearing stress to produce
stable emulsions.
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The methods commonly used to
prepare emulsions can be divided
into two categories:
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A- Trituration Method
This method consists of dry gum method
and wet gum method.
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1- Dry Gum Method
In this method the oil is first triturated with gum
with a little amount of water to form the
primary emulsion. The trituration is continued
till a characteristic ‘clicking’ sound is heard
and a thick white cream is formed. Once the
primary emulsion is formed, the remaining
quantity of water is slowly added to form the
final emulsion.
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2- Wet Gum Method
As the name implies, in this method first gum
and water are triturated together to form a
mucilage. The required quantity of oil is then
added gradually in small proportions with
thorough trituration to form the primary
emulsion.
Once the primary emulsion has been formed
remaining quantity of water is added to make
the final emulsion.
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B- Bottle Method
This method is employed for preparing
emulsions containing volatile and other non-
viscous oils. Both dry gum and wet gum
methods can be employed for the preparation.
As volatile oils have a low viscosity as
compared to fixed oils, they require
comparatively large quantity of gum for
emulsification.
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• In this method, oil or water is first shaken
thoroughly and vigorously with the calculated
amount of gum. Once this has emulsified
completely, the second liquid (either oil or
water) is then added all at once and the bottle
is again shaken vigorously to form the primary
emulsion. More of water is added in small
portions with constant agitation after each
addition to produce the final volume.
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Methods for preparing Emulsions
for External use:
• Emulsions meant for external application such
as creams, lotions and liniments contain in their
formula waxy solids which require melting
before mixing.
• Such emulsions may be prepared by melting
the oily components separately at 60 0C.
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• Similarly in another vessel, the aqueous
components are mixed and are warmed gently
to 60 C.
• The aqueous phase is then added to the oily
phase at the same temperature and stirred
until cold.
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Proportions of Oil, Water and Gum required for
formation of primary emulsion
Type of oil Oil Water Gum
Fixed oil 4 2 1
Mineral oil 3 2 1
Volatile oil 2 2 1
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Quality control tests for Emulsions
• 1.Determination of particle size and particle
count.
• 2.Determination of viscosity.
• 3.Determination of phase separation.
• 4.Determination of electrophoretic properties.
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Stability testing
Stability of emulsions is an important parameter for
the formulator.
Stability testing of emulsions involves determining
stability at long term storage conditions,
accelerated storage conditions, freezing and
conditions. Stress conditions are applied in order to
speed up the stability testing.
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The stress conditions used for speeding up
instability of emulsions include:
• Centrifugal force, Agitational force and
temperature
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• The following physical parameters are evaluated to
assess the effect of any of the above stress
conditions:
Phase separation
Viscosity
Electrophoretic properties
Particle size and particle count
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Packaging, Labeling and Storage
of Emulsions
• Depending on the use, emulsions should be
packed in suitable containers. Emulsions
meant for oral use are usually packed in well
filled bottles having an air tight closure.
• Light sensitive products are packed in amber
coloured bottles.
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• 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.
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• Emulsions should be stored in a cool place
but refrigeration should be avoided as this
low temperature can adversely effect the
stability of preparation.