Endophthalmitis prophylaxis by intracameral antibiotics: In vitro model comparing vancomycin, cefuroxime, and moxifloxacin

Abstract

To compare the efficacy of intracameral vancomycin, cefuroxime, and moxifloxacin on postoperative bacterial endophthalmitis rates. Norwalk Hospital, Norwalk, Connecticut, USA. Experimental study. Bacteria and intraocular lenses (IOLs) were incubated with vancomycin, cefuroxime, moxifloxacin, or combinations. Antibiotic concentrations were high, corresponding to clinical maximum intracameral doses (1.0mg vancomycin or cefuroxime, 0.5mg moxifloxacin), or low (one third of clinicalmaximum dose). The following bacteria were isolated from patients with endophthalmitis: 18 strains including 6 staphylococci, 6 streptococci, 3 pseudomonad, and 3propionibacteria. Samples were diluted by half every 2hours to model the half-life of intracameral antibiotics. At 24hours, samples were vortexed to shake bacterial biofilms loose from the IOLs. The bacterial broth was plated and colonies were counted 24hours later. Efficacy against staphylococci was concentration dependent; all antibiotics were effective at high concentrations, while low concentrations were in general ineffective. Streptococci and propionibacteria were nearly eliminated by all antibioticsat low concentrations. Pseudomonads were most effectively treated by high-dose moxifloxacin and its combinations. Broadest coverage against common pathogens should be obtained by high-dose moxifloxacin (0.5mg intracameral). Submaximum dosing, which could occur if aqueous is released to lower intraocular pressure after injection, compromises the efficacy against staphylococci and pseudomonads. All antibiotics, even at low doses, were effective against streptococci and propionibacteria, suggesting that many of the worst endophthalmitis outcomes could be prevented by intracameral use of any of the 3 antibiotics used in this study.