PURPOSE: To determine the penetration of gentamicin and amikacin into the rabbit vitreous cavity after their intravenous administration. METHODS: Gentamicin (1.6 mg/kg every 8 hours) and amikacin (6 mg/kg every 12 hours) were administered intravenously to 25 rabbits that had previously had the lens and vitreous removed from 43 eyes. For each drug, ocular inflammation was induced in one group of eyes by injection of heat-killed Staphylococcus epidermidis, while the other group was maintained as a control. Samples from the vitreous cavity were taken at regular intervals for 72 hours after beginning the intravenous medications and were analyzed for drug concentrations. RESULTS: The maximum intravitreal concentration ± SD achieved for gentamicin was 1.8 ± 0.5 μg/ml. The maximum intravitreal concentration for amikacin was 8.5 ± 3.2 μg/ml. Inflamed eyes demonstrated higher concentrations than did those without inflammation. CONCLUSIONS: In a rabbit model with conditions optimized to enhance penetration of antimicrobials into the vitreous cavity after intravenous administration, neither gentamicin nor amikacin penetrated sufficiently to reach potentially therapeutic concentrations consistently for either Pseudomonas or S epidermidis organisms.
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