Pharmacokinetics of topically applied ciprofloxacin in equine tears.

The research evaluates how topically applied 0.3% ciprofloxacin, an antibiotic used in “eye drop” form, is distributed in horse tears. The study found that the drug’s distribution kinetics are akin to those seen in rabbits and humans.

Objective and Methodology

• The aim of the study was to investigate how ciprofloxacin 0.3%, used as an ophthalmic solution, behaves in the tears of healthy horses.
• Twenty adult, mixed-breed healthy horses, confirmed to be free of any eye diseases, were used for the study.
• 70 microliters of ciprofloxacin (Ciloxan) was placed in the lower pocket of the eye (ventral cul-de-sac) using a syringe and a 19-gauge cannula.
• To study the distribution and elimination (pharmacokinetics) of the drug, the tear film was sampled at different intervals post-administration (5, 10, 15, 30 mins and 1, 2, 4, 6 hrs).
• A total of five samples were taken at each time-point, with the sampling time being set at 15 seconds.
• Concentrations of ciprofloxacin in the tears were determined using a technique known as high-performance liquid chromatography, a method of separating and quantifying components of a mixture.

Results and Conclusion

• In terms of tear production as assessed by the Schirmer tear test, on average, there was 23.4 mm of wetting in 1 minute (standard deviation (SD): 4.8 mm).
• The mean concentration of ciprofloxacin in the tears 5 minutes after it was applied was 498.4 µg/g (SD: 266.8 µg/g).
• After this, the concentration rapidly declined and started to become steady at about 30 mins post administration.
• At 30 mins, and 1, 2, 4, and 6 hours post administration, the mean tear concentrations of ciprofloxacin were 66.6, 60.25, 42.25, 36.25, and 45.5 µg/g respectively (with varying SD).
• The study concluded that the pharmacokinetics of ciprofloxacin in healthy horses matches those observed in rabbits and humans. Applying ciprofloxacin topically resulted in a tear concentration that remained higher than the minimum inhibitory concentration (MIC90) for most disease-causing bacteria, for up to 6 hours after administration. This implies the dose was continually effective for this period.