Microemulsions as ocular drug delivery systems: recent developments and future challenges

Eye drops are the most used dosage form by ocular route, in spite of low bioavailability and the pulsed release of the drug. However, due to their intrinsic properties and specific structures, the microemulsions are a promising dosage form for the natural defence of the eye. Indeed, because they are prepared by inexpensive processes through autoemulsification or supply of energy, and can be easily sterilized, they are stable and have a high capacity of dissolving the drugs. The in vivo results and preliminary studies on healthy volunteers have shown a delayed effect and an increase in the bioavailability of the drug. The proposed mechanism is based on the adsorption of the nanodroplets representing the internal phase of the microemulsion, which constitutes a reservoir of the drug on the cornea and should then limit their drainage.