Efficacy of cyclo-oxygenase inhibition by two commercially available firocoxib products in horses.

Abstract

REASONS FOR PERFORMING STUDY: Two firocoxib preparations for oral use are approved for use in animals in many countries: a chewable canine tablet and an equine paste. In order to reduce costs, many veterinarians use the canine product in horses even though this is an off-label use of the preparation. OBJECTIVE: To determine the relative efficacy of 2 commercially available firocoxib products to inhibit prostaglandin E₂ (PGE2) synthesis after oral dosing in horses. STUDY DESIGN: A crossover design using 8 adult horses (n = 4 for each preparation during each treatment period). Body weight range 532-614 kg. METHODS: Horses received 57 mg of the assigned firocoxib preparation orally once daily for 7 days, with a 14 day washout period between drug crossover. Ten healthy adult light breed horses were used as no-treatment controls. During each treatment period, blood was taken before dosing on Days 0 and 7 and on Day 7 1 h after dosing for ex vivo lipopolysaccharide (LPS) stimulation to induce (PGE₂ ) synthesis. Heparinised plasma was also collected on Day 7 immediately prior to and 1 h after dosing to determine plasma firocoxib concentrations. RESULTS: In the control group, there was no significant change in LPS-induced PGE2 over time. In contrast, immediately prior to and 1 h after treatment on Day 7, the mean LPS-induced PGE₂ concentration decreased significantly compared to Day 0 values in all treated horses. There was no difference in PGE₂ or plasma firocoxib concentrations between firocoxib treatment groups. CONCLUSION: In this model, the canine chewable preparation of firocoxib was as effective as the equine paste formulation at reducing LPS-induced PGE₂ synthesis. POTENTIAL RELEVANCE: The canine chewable preparation of firocoxib may be a suitable alternative to the paste formulation in horses for situations where extra-label drug use can be legally justified. The Summary is available in Chinese - see Supporting information.