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VANCOMYCIN LEVELS AFTER INTRAVITREAL INJECTION: Effects of Inflammation and Surgery

Objective: Vancomycin hydrochloride for intraocular injection is the drug of choice for the treatment of suspected gram‐positive endophthalmitis. To study its intraocular pharmacokinetics, we injected vancomycin into the vitreous cavity of phakic, aphakic, and aphakic‐vitrectomized rabbit eyes and determined its rate of clearance. Inflamed eyes were compared to control eyes in each group. Methods: Three groups of eyes were prepared. The eyes in Group 1 were phakic, the eyes in Group 2 had the lens removed, and the eyes in Group 3 had both the lens and central vitreous removed. Each group was subdivided into a control group and a group made inflamed by injection of heat‐killed Staphylococcus epidermidis. Vancomycin hydrochloride 1 mg in 0.1 cc of diluent was injected into the midvitreous cavity and samples obtained at 2 or 3, 8, 24, and 48 hours after injection. Vancomycin concentrations were measured and clearance rates were calculated for each of the groups. Results: Vancomycin was cleared substantially faster from aphakic‐vitrectomized eyes (half‐life 9.0 hours) and aphakic eyes (half‐life 8.9 hours) than phakic eyes (half‐life 25.1 hours). Inflammation increased the rate of elimination of vancomycin only in the aphakic group. Conclusions: Clearance of vancomycin from the phakic eye is prolonged compared to that of beta‐lactam antibiotics, an important pharmacokinetic advantage in treating endophthalmitis. Its clearance from aphakic‐vitrectomized eyes is dramatically faster than from phakic eyes and is similar to that of other antimicrobial agents.