Pharmacokinetics of topically applied ciprofloxacin in equine tears

Diane Hendrix, University of Tennessee - Knoxville
Jamie Stuffle, University of Tennessee - Knoxville
Sherry Cox, University of Tennessee - Knoxville

Abstract

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

Animal studied:  Twenty healthy, adult, mixed-breed horses.

Procedures:  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.

Results:  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 µg/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 µg/g, respectively.

Conclusions:  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 MIC90 levels for most pathogenic bacteria for 6 h post administration.