Antibiotic levels in aqueous and vitreous humor after intraocular administration

Antibiotics poorly penetrate the vitreous humor after periocular or systemic administration. Sometimes a direct intravitreal injection is necessary for the treatment of bacterial endophthalmitis. The kinetics of the intravitreally injected antibiotics, netilmicin (500 micrograms/0.1 ml), piperacillin (2,000 micrograms/0.1 ml), ampicillin (2,000 micrograms/0.1 ml) and aztreonam (2,000 micrograms/0.1 ml), were examined in rabbits. Aqueous and vitreous antibiotic concentrations were assayed by microbiological methods. The results show that active levels of all drugs studied are present in the vitreous body for 48 h. In aqueous humor beta-lactam antibiotics are present in very small concentrations, whereas the aminoglycoside netilmicin (vitreous/aqueous ratio) have higher levels (%) than other drugs.