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D.V. Hendrix, S.K. Cox; Pharmacokinetics of Topically Applied Ciprofloxacin in Equine Tears . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4897.
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Purpose: To evaluate the pharmacokinetics of topically applied ciprofloxacin 0.3% ophthalmic solution in tears of healthy horses. Methods: Twenty study horses were confirmed free of ophthalmic disease by complete ophthalmic examination including Schirmer tear test, slit lamp biomicroscopy, and indirect ophthalmoscopy. Seventy µL of 0.3% ciprofloxacin (CiloxanTM) was placed in the ventral cul de sac of both eyes of each horse using a microliter syringe and 19 g cannula. The conjunctiva was not touched with the cannula. The horses were randomized into groups. Population kinetics were carried out by sampling the tear film from the lower cul de sac of each eye one time with tear test strips at 5, 10, 15, 30 minutes and 1, 2, 4, 6 hours post administration for a total of 5 samples at each time point. Sample collection time was 15 seconds. Strips were stored at –80 degrees Centigrade. Concentrations of ciprofloxacin were determined from tears extracted from the tear test strips using HPLC. Results: Mean (± SD) Schirmer tear test result was 23.4 ± 4.8 mm wetting in one minute. The mean concentration of ciprofloxacin in the tears at 5 minutes post administration was 59.6 ± 21 µg/g. Mean concentration rapidly declined and began to plateau at 1 hour. The mean tear concentrations of ciprofloxacin at 1, 2, 4 and 6 hours were 5.7 ± 3.7, 3.5 ± 1.5, 3.9 ± 1.9, 3.4 ± 1.9 µg/g, respectively. Conclusions: The pharmacokinetics of ciprofloxacin in normal horses are similar to those in rabbits and human beings. Topical application of ciprofloxacin resulted in a mean tear concentration of ciprofloxacin that remained above the MIC levels for Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa, and Staphylococcus sp which are the more commonly isolated bacteria from horses with bacterial keratitis for 6 hours post administration.
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