Comparative penetration of moxifloxacin and gatifloxacin in rabbit aqueous humor after topical dosing

Purpose: To evaluate the aqueous penetration of the fourth-generation fluoroquinolones moxifloxacin and gatifloxacin. Setting: University of Arizona, Tucson, Arizona, USA. Methods: Forty eyes of 20 New Zealand white rabbits were divided into 2 experimental groups. In Experiment I rabbits (20 eyes), a commercial preparation of topical gatifloxacin 0.3% was administered to 9 eyes and moxifloxacin 0.5% to 9 eyes; 2 eyes served as a control. Eyes were dosed according to a keratitis protocol; ie, every 15 minutes for 4 hours. The aqueous humor was sampled 10 minutes after the last dose. Experiment II rabbits (20 eyes) were dosed according to a cataract prophylaxis protocol; ie, 4 times a day for 10 days. The aqueous humor was sampled 1 hour after the last dose of antibiotic in 12 eyes and 24 hours after the last dose in 8 eyes. High-performance liquid chromatography was used to determine the fluoroquinolone concentration. Results: In the keratitis dosing protocol, the mean concentration of moxifloxacin in the aqueous (n = 9) was 11.057 μg/mL (range 7.66 to 18.87 μg/mL), which was significantly higher than the mean concentration of gatifloxacin (n = 8) (7.570 μg/mL [range 4.75 to 10.86 μg/mL]) (P = .030). In the cataract prophylaxis dosing protocol, the mean aqueous concentration of moxifloxacin (n = 6) was 1.745 μg/mL (range 0.92 to 3.87 mg/mL). The mean concentration of gatifloxacin (n = 6) was 1.207 μg/mL (range 0.44 to 2.44 μg/mL). The difference was not statistically significant (P = .359). Conclusions: Higher mean levels (×1.46) of aqueous penetration were achieved with moxifloxacin than with gatifloxacin in the keratitis-dosing model. There was no statistically significant difference between the 2 drugs in the cataract prophylaxis dosing model. Both antibiotics had aqueous levels in excess of the minimum inhibitory concentration for most pathogenic organisms in both models.