Microemulsions: an overview and pharmaceutical applications

Microemulsions are potential drug carrier systems for oral, topical, and parenteral administration. They offer the advantage of spontaneous formation, ease of manufacturing and scale-up, thermodynamic stability, and improved drug solubilization and bioavailability. Preparing a pharmaceutically acceptable dosage form demands a clear understanding of the microemulsion structure, phase behavior, factors leading to its thermodynamic stability, factors influencing drug release from the formulation, requirements of ideal microemulsion excipients, and the potential uses and limitations of the microemulsion system. Knowledge of the various methods available to thoroughly characterize a microemulsion system is essential. An overview of these factors is presented in this review. While microemulsion is used in several fields, in this review the pharmaceutical applications are emphasized. Several references are cited, but the list is by no means exhaustive. The review is written so that a newcomer to the field can easily grasp the important facts pertaining to this novel delivery system.