Pharmacokinetics of 0.5 mg of a single and a multiple dose of intravitrealvancomycin in infected rabbit eyes

The purpose of this study was to determine the pharmacokinetics governing d istribution and elimination of 0.5 mg of intravitreal vancomycin in a singl e dose and in a multiple therapeutic regime in infected rabbit eyes. A total of 96 rabbits was injected with approximately 200 CFU of S. aureus intravitreally. Four days later, a single dose of 0.5 mg of vancomycin was administered to Group I (n = 36). Group II (n = 60) was injected with a max imum of 4 doses of 0.5 mg every 36 hr. Four animals were sacrificed at diff erent time points in each group. Samples of vitreous, aqueous and blood wer e taken from each animal for analyses by HPLC. These results were evaluated using the RSTRIP program. High vancomycin concentrations were demonstrated in the vitreous of Group I , with a calculated half-life of 12 hr. In Group II, vancomycin levels were within the therapeutic range during the entire experiment. There was minim al accumulation of the drug, and the half-life did not seem to be longer wi th multiple doses. In conclusion, the pharmacokinetics do not change significantly when a mult idose regime is used compared with a single dose. Therapeutic intravitreal concentrations of vancomycin can be achieved by using repeated doses of 0.5 mg of vancomycin.