Sodium hyaluronate as an ophthalmic vehicle: Some factors governing its effect on the ocular absorption of pilocarpine

Sodium hyaluronate, as an additive to aqueous ophthalmic formulations, has been claimed to increase the ocular contact time and, thereby, the drug bioavailability. In the present study, the effect of sodium hyaluronate on corneal residence time and drug absorption in rabbits was investiqated. Addition of sodium hyaluronate (0.125%) to a 3H-pilocarpine HC1 solution resulted in increased retention of radioactivity in tear fluid and a 2-fold increase in drug concentration in the cornea and aqueous humor. Further, the effects of concentration and molecular weight of sodium hyaluronate on the miosis induced by pilocarpine in rabbits were studied. A significant increase of miotic response was seen at concentrations just less than 0.1% sodium hyaluronate. Pilocarpine solutions prepared from high mol.wt. sodium hyaluronate exhibited a greater miotic response than those prepared from lower mol.wt. samples. This might indicate that other physicochemical properties of sodium hyaluronate influence drug bioavailability.