Influence of ophthalmic ointments on the penetration of pilocarpine drops

To evaluate the influence of prior administered ointments upon the intraocular penetration of drops, we applied either a combination antibiotic ointment, a combination antibiotic-steroid ointment, or a lubricant ointment at different time periods before instillation of 2% pilocarpine drops into rabbit eyes. The level of pilocarpine measured in aqueous humor at one hour was compared to the level achieved in eyes without ointment application. No change was found in pilocarpine levels following application of the lubricant ointment. Pilocarpine concentrations were significantly lower (38%-48%) in animals receiving the antibiotic ointment at 5 or 15 minutes before pilocarpine drops. Pilocarpine levels also were decreased significantly when the steroid-antibiotic ointment was applied 15, 30 or 60 minutes before the drops. To verify these effects at other time periods, ointments were applied 15 minutes before pilocarpine drops and aqueous humor samples aspirated at 30 minutes or two hours. A 22% decrease in aqueous humor pilocarpine was found at 30 minutes with both the antibiotic and steroid-antibiotic combination; no effect was observed at two hours. To determine the influence of each drug component within the ointment on the penetration of pilocarpine, solutions of dexamethasone, neomycin, bacitracin and polymyxin B were mixed individually with pilocarpine drops and applied into the animal eyes. Bacitracin and polymyxin B significantly reduced one-hour pilocarpine levels in aqueous humor; however, no significant effect was observed with either neomycin or dexamethasone.