In situ gelling systems: a strategy to improve the bioavailability of ophthalmic pharmaceutical formulations.

The low therapeutic efficacy exhibited by conventional ophthalmic solutions owing to precorneal elimination of the drug, drainage by gravity, nasolacrimal drainage, conjunctival absorption, and the absence of controlled release and of bioadhesive properties, can be overcome by the use of in situ gelling systems. The combination in the same formulation of different in situ gelling polymers with different stimuli-responsiveness mechanisms exploiting the unique physicochemical characteristics of the ocular tissues is one such strategy that has produced improved results compared with conventional systems. As we discuss here, the recent use of biodegradable and biocompatible polymers in colloidal carrier systems has proved to be the most effective strategy, resulting in the exponential increase of the bioavailability of the ophthalmic drugs.