Vancomycin concentration in the vitreous after intravenous and intravitreal administration for postoperative endophthalmitis

Objectives: To measure the concentrations of vancomycin in the vitreous of patients with postoperative endophthalmitis after administration of 1 g of vancomycin hydrochloride intravenously and injection of 1 mg of vancomycin hydrochloride into the vitreous, and to determine whether these concentrati ons are adequate for treatment of gram-positive infections. Methods: Patients with acute postoperative endophthalmitis were treated wit h intravenous administration of 1 g of vancomycin hydrochloride folio-wed b y vitrectomy and collection of vitreous samples 1 to 5 hours later. Intravi treal vancomycin and ceftazidime were given. Vitreous samples were cultured and their vancomycin concentrations assayed. Minimal inhibitory concentrat ions of vancomycin for the isolated vitreal pathogens, and serum and vitreo us cidal activity were determined. Results: Eighteen patients with acute postoperative endophthalmitis were st udied. Fourteen vitreous samples were available after intravenous vancomyci n administration, and 4 vitreous samples were available after intravitreal vancomycin administration. After intravenous injection, vitreous vancomycin concentrations ranged from 0.4 to 4.5 mu g/mL. Minimal inhibitory concentr ations in these samples, obtained from 10 bacterial isolates, were below th e therapeutic levels for most causative organisms, including staphylococci. Vitreous cidal activity values were negative at a dilution of 1:2 in 9 of 10 patients examined. After a l-mg intravitreal injection, vancomycin conce ntrations in vitreous samples obtained by a second tap from 4 patients 44 t o 72 hours later were 182, 138, 58, and 25 mu g/mL. In 2 patients in whom m easurements were obtained, vitreous cidal activity values were 1:512 and 1. 32. Conclusion: Vitreous vancomycin concentrations for the treatment of gram-po sitive endophthalmitis were nontherapeutic after intravenous administration but therapeutic after intravitreal administration.