Doxycycline levels in preocular tear film of horses following oral administration.

The research conducted seeks to understand the concentration of an antibiotic, doxycycline, in horses’ tears after orally consumption. The purpose of this investigation is to determine if doxycycline could be used as a treatment for horse infectious and ulcerative cornea conditions (keratitis and keratomalacia).

Methods Employed

• Eight broodmares from a Thoroughbred breeding facility without any ocular disease were chosen for the study.
• The horses each received an oral doxycycline dose of 20 mg/kg every morning for five straight days.
• Tears were gathered 1 hour after the antibiotic consumption starting from the first administration day and lasting for 10 continuous days.
• A method called liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to measure the doxycycline levels in the horses’ tears.

Study Results

• Each horse had doxycycline present in their tears with low concentrations approximately ranging from 8.21 – 9.83 microg/mL. The highest concentration was observed between the third to fifth days.
• By the tenth day, the doxycycline levels had decreased below measurable ranges.
• None of the horses displayed any systemic side-effects within the study period.

Study Conclusions

• The findings suggest that doxycycline, after oral ingestion, is present in the tears of healthy horses with noninflamed eyes. This indicates it could potentially be used to treat cases of equine ulcerative keratomalacia (cornea damage and inflammation).
• The daily prescribed oral dose of 20 mg/kg doxycycline was well accepted by the horses.
• The antibiotic levels at the prescribed dosage may aid in the treatment of horse corneal ulceration, however, more research is required to validate these results.