Emulsions are heterogeneous systems composed of at least two immiscible liquids, water (W) and oil (O), one of which (the dispersed phase) is finely and uniformly dispersed as globules throughout the second phase (the continuous phase). In addition to the two basic types (O/W and W/O) of emulsions, a relatively complex emulsion, called multiple emulsions can also be formulated. Emulsions are generally well documented as carriers for hydrophilic and lipophilic drugs. O/W and W/O/W emulsions are generally employed for the intravenous route. Lipid-based emulsions are used for parenteral nutrition, intravenous drug administration and as oxygen carriers. The main advantage of using the topical emulsions is to avoid the GI environment and first pass metabolic effect. Moreover, emulsions are also available for oral route. They are mainly used for enteric nutrition or laxative preparations. In addition, emulsions may also be used, to stabilize hydrolytically susceptible drugs for sustained release, reduction of irritation or toxicity, possible targeted delivery of drugs to various organs and possibly enhanced pharmacological effect. In conclusion, emulsion-based drug delivery systems have certain advantages over other dosage forms and the drug solubilized may be more bioavailable.

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