Ocular penetration of intravenously administered enrofloxacin in the horse.

The study investigates how the antibiotic enrofloxacin, when administered intravenously, penetrates the eye of the horse. It finds that enrofloxacin concentrations increase in the eye when the blood-aqueous barrier is disrupted and that these concentrations exceed the minimum inhibitory concentration for Leptospira pomona, a bacteria often found in horses with recurrent eye inflammation.

Objectives and Methods

• The study aimed to establish whether enrofloxacin, when given intravenously, leads to antibiotic concentrations in the aqueous humour (the clear fluid in the front of the eye) greater than the minimum amount required to inhibit the growth of the bacteria Leptospira pomona, which commonly affects horses with recurrent uveitis (eye inflammation).
• The second objective was to understand if paracentesis, a procedure to remove fluid from the eye, disrupts the blood-aqueous barrier sufficiently to cause an increase in aqueous humour protein and enrofloxacin concentrations.
• The researchers collected samples from six horses after administering enrofloxacin via injection into a vein. Paracentesis was performed on the left eye on two consecutive days, an hour after giving the enrofloxacin, to measure the concentrations of the antibiotic in healthy eyes and in eyes where the blood-aqueous barrier had been mechanically disrupted. Paracentesis was also done on the right eye a day after the enrofloxacin treatment. Blood samples were taken at the same time to define the ratio of enrofloxacin in the aqueous humour to the plasma.

Results

• The average concentration of enrofloxacin in the aqueous humour an hour after administration was .32 mg/l, with a range from .18 to .47.
• The concentration of enrofloxacin, the total protein, and the ratio of enrofloxacin in the aqueous humour to the plasma were all higher on the second day of the experiment than on the first day.

Conclusion

• The results indicate that when the blood-aqueous barrier is disrupted, the concentrations of enrofloxacin increase beyond the minimum amount required to inhibit the Leptospira pomona bacteria.