VEHICLE EFFECTS IN OPHTHALMIC BIOAVAILABILITY - AN EVALUATION OF POLYMERIC INSERTS CONTAINING PILOCARPINE

A series of polymeric ophthalmic inserts containing pilocarpine were formulated with 4 different types of polyvinyl alcohol, PVA and 2 types of hydroxypropylcellulose. Pilocarpine was present as the nitrate, or as the salt with polyacrylic acid, PAA. In vivo miosis vs. time experiments on albino rabbits, showed that all inserts increased significantly the bioavailability of pilocarpine, with respect to a standard solution of pilocarpine nitrate. Two PVA inserts, containing the PAA-salt of pilocarpine, were particularly effective. The preparations were also submitted to in vitro release tests and to differential scanning calorimetry, to ascertain the release mechanism, and to verify, via the thermal behavior, possible interactions between drug and polymers. The chemical and physicochemical factors, most likely to influence the ophthalmic bioavailability of pilocarpine from the present preparations, are briefly reviewed.