Page 25 - Reference Guide For Foreign Pharmacy Licensing Exam Theory

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a. O/W emulsion: In this type of emulsion, water is continuous phase and oil is dispersed phase. Emulsion for
oral administration is generally O/W type to hide taste and increase palatability of medicinal oil.

b. W/O emulsion: Oil is present as continuous phase, while water is present as dispersed phase.

c. O/W/O or W/O/W emulsion: It is also known as multiple-emulsion.

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d. Microemulsion: They are W/O or O/W emulsions with a particle size ranging from 100 A to 600 A. Unlike
emulsion, they are clear and thermodynamically stable. Sodium lauryl sulfate or Potassium oleate is normally
used as an emulsifying agent. They are generally used to solubilize drugs in the pharmaceutical industry.

e. Nanoparticle emulsion: It is similar in size and shape to the globule of microemulsion. It is prepared by the
process of polymerization, and is used to solubilize drugs, globulins and toxoids.

The total surface free energy in emulsion can be calculated by the following:

F = 6 V/d

V = volume of dispersed phase in ml,
d = mean diameter of the particle,
 = interfacial tension between dispersed phase and dispersion medium and
F = surface free energy.

The formulation of emulsion requires the following agents:

a. Emulsifying agent
b. Preservative
c. Antioxidant
d. Viscosity enhancer

Creaming and cracking are the major problems with the stability of emulsion.

Creaming: The concentrated layer of dispersed phase particles in the form of loosely attached floccules is
defined as creaming. The emulsion can be redispersed by vigorously shaking the bottle. The rate of creaming can
be calculated by Stoke’s equation:

= 2 2 ( 1− 2)
9 

V = sedimentation rate in cm/sec
r = radius of suspended particles
1 = density of dispersed phase
2 = density of dispersion medium
 = viscosity of continuous phase in poise
2
g = gravitational constant = 980 cm/sec

Cracking: It is more severe of a problem compare to creaming. In cracking, emulsion is destroyed and separated
into two phases. High temperatures and the addition of electrolytes, microorganisms or an opposite type of
emulsifying agent may cause cracking.

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