Pharmacokinetics of topically applied ciprofloxacin in equine tears

To evaluate the pharmacokinetics of topically applied ciprofloxacin 0.3% ophthalmic solution in tears of healthy horses.

Twenty healthy, adult, mixed-breed horses.

Twenty study horses were confirmed free of ophthalmic disease by complete ophthalmic examination. Seventy microliters of 0.3% ciprofloxacin (Ciloxan) was placed in the ventral cul-de-sac of each eye using a microliter syringe and 19-g cannula. Population kinetics were carried out by sampling the tear film from the lower cul-de-sac of each eye with tear test strips at 5, 10, 15 and 30 min and 1, 2, 4 and 6 h post administration for a total of five samples at each time-point. Sample collection time was 15 s. Concentrations of ciprofloxacin were determined using high performance liquid chromatography.

Mean (+/-SD) of the Schirmer tear test results from all eyes was 23.4 +/- 4.8 mm wetting in 1 min. Mean concentration of ciprofloxacin in the tears at 5 min post administration was 498.4 +/- 266.8 microg/g. Mean concentration rapidly declined and began to plateau at 30 min. The mean tear concentrations of ciprofloxacin at 30 min and at 1, 2, 4 and 6 h were 66.6 +/- 56.0, 60.25 +/- 55.7, 42.25 +/- 30.9, 36.25 +/- 32.0, and 45.5 +/- 46.5 microg/g, respectively.

The pharmacokinetics of ciprofloxacin in normal horses are similar to those in rabbits and humans. Topical application of ciprofloxacin resulted in a mean tear concentration of ciprofloxacin that remained above the MIC(90) levels for most pathogenic bacteria for 6 h post administration.