To compare the efficacy of intravitreal gatifloxacin with intravitreal vancomycin in the treatment of Staphylococcus epidermidis endophthalmitis in a rabbit model.

Albino rabbits (n=30), infected with an intravitreal inoculum of S. epidermidis (10⁵ colony forming unit/0.1 mL), were divided into 6 groups (n=5). Groups I and IV received 200 µg/0.1 mL of intravitreal gatifloxacin, and groups II and V were injected 1000 µg/0.1 mL of vancomycin intravitreally. Intravitreal balanced salt solutions (untreated control) were given to Groups III and VI. Intravitreal antibiotic therapy commenced 24 hours after bacterial inoculation. The bactericidal efficacy was determined by electroretinography (ERG), clinical grading, bacterial culture of vitreous aspirates and histopathologic grading. ERGs and clinical gradings were performed only for groups I, II, and III and bacterial cultures were done only for groups IV, V, and VI.

Eyes in the gatifloxacin groups showed similar appearance to those in the vancomycin treated groups clinically, histologically, and functionally as proved with ERG. All aspirates from the gatifloxacin and vancomycin groups were culture negative at 5 days after bacterial inoculation, whereas all eyes in the untreated control group were culture positive.

This study demonstrated that intravitreal injection of 200 µg /0.1mL gatifloxacin appeared to be equally effective compared to intravitreal 1000 µg /0.1 mL vancomycin in the treatment of S. epidermidis endophthalmitis. If proven safe and efficacious after further study in humans, intravitreal injection of gatifloxacin could be considered an effective alternative to vancomycin for the treatment of S. epidermidis endophthalmitis.