Objective: To determine the degree of ocular penetration and systemic absorption of commercially available topical ophthalmic solutions of 0.3% ciprofloxacin and 0.5% moxifloxacin following repeated topical ocular administration in ophthalmologically normal horses.
Animals: 7 healthy adult horses with clinically normal eyes as evaluated prior to each treatment.
Procedures: 6 horses were used for assessment of each antimicrobial, and 1 eye of each horse was treated with topically administered 0.3% ciprofloxacin or 0.5% moxifloxacin (n = 6 eyes/drug) every 4 hours for 7 doses. Anterior chamber paracentesis was performed 1 hour after the final dose was administered, and blood samples were collected at 24 (immediately after the final dose), 24.25, 24.5, and 25 hours (time of aqueous humor [AH] collection). Plasma and AH concentrations of ciprofloxacin or moxifloxacin were determined by use of high-performance liquid chromatography.
Results: Mean +/- SD AH concentrations of ciprofloxacin and moxifloxacin were 0.009 +/- 0.008 microg/mL and 0.071 +/- 0.029 microg/mL, respectively. The AH moxifloxacin concentrations were significantly greater than those of ciprofloxacin. Mean +/- SD plasma concentrations of ciprofloxacin were less than the lower limit of quantification. Moxifloxacin was detected in the plasma of all horses at all sample collection times, with a peak value of 0.015 microg/mL at 24 and 24.25 hours, decreasing to < 0.004 microg/mL at 25 hours.
Conclusions and clinical relevance: Moxifloxacin was better able to penetrate healthy equine corneas and reach measurable AH concentrations than was ciprofloxacin, suggesting moxifloxacin might be of greater value in the treatment of deep corneal or intraocular bacterial infections caused by susceptible organisms. Topical administration of moxifloxacin also resulted in detectable plasma concentrations.