c. Types of Emulsions. An emulsion usually consists of oil and water. When
the oil is the internal phase and the water is the external phase, the emulsion is said to
be an oil-in-water (o/w) emulsion. When the water is the internal phase and the oil is
the external phase, it is a water-in-oil (w/o) emulsion.
d. Creaming. Unhomogenized milk will separate into two layers while standing.
However, if it is shaken, the two layers will disappear. When an emulsion separates in
this manner, we say that it has creamed. The emulsion is still good since there is no
separated oil visible.
e. Cracking. When an emulsion separates into layers of oil and water and
shaking cannot restore the original emulsion, we say that the emulsion has cracked.
That is, it is no longer pharmaceutically useful as an emulsion.
THE USE OF EMULSIONS
Emulsions are used because they have some distinct advantages over other
types of dosage forms. Internally, the emulsion is a satisfactory form of dosage for
large quantities of unpleasant oily liquids, which cannot be given in capsules. These
doses are rapidly and completely-assimilated. Thus, an oil-in-water (o/w) emulsion of
cod liver oil can be prepared in which the flavored aqueous liquid surrounding the oil
globules masks the greasiness and the bad taste of the oil. Externally, an emulsion can
provide a homogenous ointment or lotion, which contains both oil and water soluble
ingredients. Emulsions provide palatable internal preparations and uniform dosages of
both internal and external preparations.
a. Overview. As you know, oil and water do not mix. Since oil and water do not
mix, how is it possible to form the two phases required for an emulsion? The answer is
b. Definition. An emulsifying agent, or emulsifier, is any substance that will
promote the formation of an emulsion. The chemical structure of an emulsifying agent
promotes the formation of an emulsion.
c. Examples of Emulsifying Agents. Acacia and tragacanth are used as
emulsifying agents. For specific information on the amount of an emulsifying agent that
must be used to prepare an emulsion, you should consult a reference such as
Remington's Pharmaceutical Sciences.