DIFFERENT EFFECTS OF ABSORPTION PROMOTERS ON CORNEAL AND CONJUNCTIVAL PENETRATION OF OPHTHALMIC BETA-BLOCKERS

Purpose. The purpose of this study was to investigate the improvement in corneal penetration of ophthalmic beta-blockers of various lipophilicities afforded by absorption promoters and to compare the corneal against conjunctival penetration in response to absorption promoters. Methods. The penetration of the beta-blockers, atenolol, carteolol, tilisolol, timolol, and befunolol, in the presence of absorption promoters, across the isolated corneal and conjunctival membranes of albino rabbits was measured using a two-chamber glass diffusion cell. EDTA, taurocholic acid, capric acid, and saponin were used as the absorption promoters. Results. The absorption promoters significantly increased the corneal permeability of most beta-blockers, especially the hydrophilic agents. The absorption promoters also enhanced the conjunctival permeability of betablockers, although their effect in promoting conjunctival penetration was less than that on corneal penetration. There was a differing penetration of instilled beta-blockers in the cornea and conjunctiva in response to absorption promoters. Capric acid and saponin showed significant promoting action on corneal penetration, but not on conjunctival penetration. Taurocholic acid had a significant effect on conjunctival penetration but not on corneal penetration. Saponin caused slight irritation. Conclusions. Absorption promoters can improve the ocular delivery of beta-blockers and a selective use of absorption promoter can improve the extent and pathway of drug ocular absorption.