Pharmaceutical Considerations of Microemulsion as a Drug Delivery System
Microemulsions were recognized after the work of Hoar and Schulman in 1943, which revealed the use of strong surface-active agent leading to spontaneous emulsification; however, it was in 1959 when Schulman first used the term “microemulsion” for such emulsion system. Microemulsions are optically transparent, thermodynamically stable colloidal systems, 10–100 nm diameters that form spontaneously upon mixing of oil, water, and emulsifier. After its discovery in 1943 to till date, more than 1200 publications have been reported and development of O/W type of microemulsions has been the priority for the researchers, mostly using non-ionic surfactants. Although microemulsions seem to be one of the most promising candidates in pharmaceuticals because of relative ease in the formulation and distinct characteristics when compared to other dispersion systems, its commercial success as a drug delivery system has been very little. Much of the time after its discovery has been exhausted in failure to understand correct formulation requisites or confusing it with other similar systems. In the face of increasing the number of publication year after year, its formulation has been generally based on trial-and-error. Efficient strategies for excipient selection and detailed understanding of microstructures contributing to its formulation is still required which may serve as the foundation for attaining greater success in this field.
Keywords: Microemulsion, Surfactants. Spontaneous emulsification, Solubilization.
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