Emulsions as drug carriers for ophthalmic use

The ocular bioavailability of drugs administered in standard aqueous vehicles is very poor. However, the ocular administration of lipophilic drugs also exhibits complex problems due to their low aqueous solubility. The wide and clinically well-accepted usage of emulsions for parenteral nutrition (see P.K. Hansrani, S.S. Davis and M.J. Groves, J. Parenter. Sci. Technol., 37 (1983) 145) has raised the possibility of using the oil phase of oil-in-water emulsions as a carrier of poorly water-soluble drugs. However, submicron emulsions are sensitive dispersed systems which need to be physically stabilized, especially following the incorporation of drug molecules into the oil dispersed globules, the sizes of which range from 100 to 300 nm. Two different drugs were incorporated into the original submicron emulsion which met ocular product requirements. The medicated emulsion formulation was stabilized by a combination of two emulsifying agents (phospholipids and an amphoteric emulsifier) following manufacturing process optimization. Emulsion formulations with extended physical shelf-life were therefore developed and fully characterized. The partition profile of the drugs in the various phases of the emulsions was also determined.