Pharmacokinetics of Intravitreal Bevacizumab (Avastin)

Purpose: To describe the pharmacokinetics of 1.25 mg of intravitreal bevacizumab (Avastin). Design: Experimental animal study. Participants: Twenty Dutch-belted rabbits. Methods: One eye of each of 20 rabbits was injected with 1.25 mg of intravitreal bevacizumab. Both eyes of each of 4 rabbits were enucleated at days 1, 3, 8, 15, and 29. Bevacizumab concentrations were measured in aqueous fluid, whole vitreous, and serum. Main Outcome Measures: Bevacizumab concentrations in the aqueous, vitreous, and serum. Results: Whereas vitreous concentrations of bevacizumab declined in a monoexponential fashion with a half-life of 4.32 days, concentrations of >10μg/ml bevacizumab were maintained in the vitreous humor for 30 days. Bevacizumab concentrations in the aqueous humor of the injected eye reached a peak concentration of 37.7 μg/ml 3 days after drug administration. A maximum serum concentration of 3.3 μg/ml was achieved 8 days after intravitreal injection and the concentration fell below 1 μg/ml 29 days after injection. Elimination of bevacizumab from the aqueous humor and serum paralleled that found in the vitreous humor, with half-life values of 4.88 days and 6.86 days, respectively. Very low concentrations of bevacizumab were detected in the fellow uninjected eye. Concentrations of bevacizumab in the vitreous of the fellow eye varied incrementally, from 0.35 ng/ml at 1 day to 11.17 ng/ml at 4 weeks. Concentrations of bevacizumab in the aqueous humor of the fellow eye reached their peak at 1 week, at 29.4 ng/ml, and declined to 4.56 ng/ml at 4 weeks. Conclusion: The vitreous half-life of 1.25 mg intravitreal bevacizumab is 4.32 days in a rabbit eye. Very small amounts of bevacizumab were detected in the serum and in the fellow uninjected eye.