Prospective and Challenges of Micro-Emulsion as a Novel Carrier for Drug Delivery

Micro-emulsions are isotropic, thermodynamically stable transparent (or translucent) systems of oil, water, and surfactant with a droplet size usually in the range of 20-200 nm. Micro-emulsions are currently of great technological and scientific importance to the researchers because of their potential to incorporate a wide range of drug molecules (hydrophilic and hydrophobic) due to the presence of both lipophilic and hydrophilic domains. These delivery systems provide protection against oxidation, enzymatic hydrolysis and improve the solubilization of lipophilic drugs and hence enhance their bioavailability. In addition to oral and intravenous delivery, they are amenable for sustained and targeted delivery through ophthalmic, dental, pulmonary, vaginal, and topical routes. They have been used to improve the oral bioavailability of various poorly soluble drugs. Furthermore, they can be employed for challenging tasks such as carrying chemotherapeutic agents to neo-plastic cells and oral delivery of insulin. In order to appreciate the potential of micro-emulsions as delivery vehicles, this review gives an overview of the formation and characterization of microemulsions. The use of microemulsions and closely related micro-emulsion-based systems as drug delivery vehicles is reviewed, with particular emphasis being placed on recent developments and future directions.