Emulsions are preparations of two immiscible liquids, often water and oil, stabilized by an emulsifying agent to prevent separation. They serve to create a stable mixture for the administration of liquid drugs, can mask distasteful tastes, and are categorized into oil-in-water (o/w) and water-in-oil (w/o) types. Considerations for their preparation depend on intended use, drug solubility, and required absorption properties.

1. Emulsions
Md. Saiful Islam
BPharm, MPharm (PCP)
North South University
Fb Group: Pharmacy Universe

2. Emulsion
• Emulsion is a preparation consisting of two immiscible
liquids, usually water and oil, one of which is dispersed
as small globules in the other
• A third component, the emulsifying agent, is used to
make the dispersion stable
• In the absence of the emulsifying agent the globules
undergo coalescence to form two separate layers of
water and oil

3. Emulsion

4. Purpose of preparing emulsion or of emulsification
• To prepare a relatively stable and homogeneous mixture
of two immiscible liquids
• It permits administration of a liquid drug in the form of
minute globules rather than in bulk
• For orally administered emulsion, the o/w type permits
palatable administration of a distasteful oil by dispersing
in a sweetened, flavoured aqueous vehicle
• The reduced particle size of the oil globule permits the oil
more digestible and more readily absorbed

5. Distribution of formulation ingredients
between the phases of emulsion
The aqueous phase:
It contains- water soluble drugs
- preservatives
- coloring agent
- flavouring agent
It is desirable to use distilled or deionized water, since
Ca++ and Mg++ ions found in hard water may have
adverse effect on the stability of some emulsions

6. Distribution of formulation ingredients
between the phases of emulsion
The oil phase:
It consists of – fixed or volatile oils
- drugs that exist as oils, such as oil-soluble
vitamins and antiseptics
*** In order to keep the oil phase free from autoxidation and
consequent rancidity, an anti-oxidant and anti-microbial
agent must be used

7. Types of emulsion
Two types:
1. Oil-in-water or o/w emulsion: In which oil is dispersed
as globules in water
2. Water-in-oil or w/o emulsion: In which water is
dispersed as globules in oil
*** In o/w emulsion, oil is referred to as the “internal phase”
and water is referred to as the “external phase”
In w/o emulsion, water is referred to as the “internal
phase” and oil is referred to as the “external phase”

8. Types…

9. Uses of emulsions
Based on the use, emulsions are divided into two
groups:
1) Emulsions for internal use: Applied orally or by IV
injection
2) Emulsions for external use: Applied to the skin or the
mucous membranes

10. Orally administered emulsions
Properties:
• Oil-in-water type
• The medicinal oil enveloped in a film of emulsifying
agent aids in masking the disagreeable taste and the
oily sensation which makes a palatable drug
• Flavouring agent is added to the external aqueous phase

11. Considerations for selecting masking
agents for oral emulsions
• The distribution of drugs and flavours between the oil
and the water phases is an important consideration in
masking unpleasant taste.
• According to distribution principle, a substance will be
found in both phases of an emulsion but will concentrate
predominantly in the phase in which it is more soluble

12. Considerations for selecting masking
agents for oral emulsions
• The attempt to mask the distasteful drug by oil-in-water
emulsification will be defeated –
- if the drug possesses some water solubility and passes
partially into the external phase and
- if the flavour and the masking agent are predominantly
oil soluble and concentrate primarily in the internal phase

13. What will be the size of emulsion
globules?
• For better absorption of fats through the intestinal wall,
the emulsified fat globules should be kept less than 1μ in
diameter
• The most efficient absorption is attained for the globules
having the diameter about 0.5μ

14. Considerations for preparing IV
injections of emulsions
• The choice of emulsifying agent, the size and the
uniformity of globules are critical in the preparation for IV
use
• Sterile emulsifying agents are used and they are tested
for any untoward physiological effect.
• Initially coarse emulsions are prepared, then
homogenized, collected and sealed in sterile flask and
autoclaved
• Finally the product is tested for sterility and globule size

15. Considerations for preparing
emulsions for external use
Emulsion to be applied to the skin may be of both o/w and
w/o type. Factors considered before preparations are:
• Nature of the therapeutic agent
• The condition of the skin
***For the unbroken skin, a w/o emulsion can usually be
applied more evenly.
*** The medicinal agent causing skin irritation is better to
prepare as o/w type

16. Considerations for preparing
emulsions for external use
• The desirability of an emollient or tissue softening effect
*** The w/o emulsion is more softening to the skin, because
it resist drying and removal of the preparation by contact
with water
• If the easy removal from the skin with water is desired,
an o/w emulsion is preferred
• For getting better percutaneous absorption, particle size
of the internal phase should be critically controlled

17. Which type is suitable for better
percutaneous absorption?
• If the drug is water soluble, better percutaneous
absorption is obtained from the o/w type preparation
•
• And if the drug is oil soluble, better percutaneous
absorption is obtained from the w/o type preparation