Penetration of norfloxacin into the aqueous humor of the human eye

Forty six patients received a topical application of a 0.3% norfloxacin (Zoroxin; MSD, Austria) solution into the lower fornix at different time intervals and frequencies before undergoing planned extracapsular cataract extraction. Aqueous humor was sampled at the beginning of surgery and assayed for the level of the antibiotic with high performance liquid chromatography. The highest aqueous humor level observed 30 min after the administration of the last drop in four patients who received five drops of norfloxacin into the lower fornix was 660.25 +/- 378.2 ng/ml. These concentrations are above the minimum inhibitory concentration of norfloxacin for 90% (MIC90) of most of the gram-negative microorganisms, but below the MIC90 of most of the staphylococci (coagulase negative Staph. and Staphylococcus aureus range between 0.25-1 mg/ml).