The efficacy of intravitreal vancomycin and dexamethasone in the treatment of experimental bacillus cereus endophthalmitis.

PURPOSE: Bacillus cereus causes the most virulent and refractory form of endophthalmitis. The authors analyzed effectiveness of intravitreal vancomycin with or without dexamethasone for experimental Bacillus cereus endophthalmitis.
METHODS: Rabbit eyes were injected intravitreally with 1x10(6) colony-forming units of Bacillus cereus organisms. At 24 hours after injection, eyes were injected intravitreally with 0.1 ml of balanced salt solution (group 1, n=10), 1 mg vancomycin (group 2, n=10), and antibiotic plus 0.4 mg dexamethasone (group 3, n=10). Inflammatory scores were assessed 7 days and 14 days after treatment. Furthermore, histologic grading was carried out at the conclusion of the clinical observations.
RESULTS: Eyes treated with vancomycin, with or without dexamethasone at 7 days and 14 days expressed significant less inflammation over iris and vitreous than the control group (p<0.05). Moreover, eyes treated with vancomycin with dexamethasone showed less inflammation over the conjunctiva and vitreous at 7 days and over the iris and vitreous at 14 days, compared to antibiotic treatment alone (p<0.05). Additionally, at 14 days, the histopathological changes of eyes treated with vancomycin with dexamethasone had less conjunctival inflammation, mild iridocyclitis, less vitreous cells, and less choroidal vasculitis and retinitis compared to control group and antibiotic treatment alone, respectively (p<0.05).
CONCLUSION: Intravitreal injection of vancomycin improved the therapeutic outcome of Bacillus cereus endophthalmitis. The addition of dexamethasone to antibiotic treatment provided a therapeutic benefit over antibiotic alone.