Ocular penetration of pilocarpine in rabbits

K. Green and S. J. Downs

Aqueous humor pilocarpine hydrochloride concentration was measured at 15, 30, 60, and 120 minutes after instillation in the rabbit eye of a radioactively labeled 2% pilocarpine solution in various vehicles. Maximum concentrations were found with a vehicle containing 1.67% polyvinylpyrrolidone and other water-soluble polymers (Adsorbotears) and 1% hydroxypropyl methylcellulose. These produced pilocarpine concentrations during the first two hours after administration three times greater than those found with either saline, 1.4% polyvinyl alcohol, or 0.5% hydroxypropyl methylcellulose. Benzalkonium chloride, 0.01%, enhanced pilocarpine penetration into the aqueous by as much as 50% at all time intervals. The vehicle viscosity was unrelated to efficacy of pilocarpine penetration into the aqueous. The equally effective 1% hydroxypropyl methylcellulose and Adsorbotears have viscosities of 112 and 20 centistokes, respectively, while 0.5% hydroxypropyl methylcellulose (13 centistokes), 1.4% polyvinyl alcohol (3 centistokes), and sodium chloride solution (0.85 centistokes) are much less efficacious.