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

M. H. Barton, E. Paske, N. Norton, D. King, S. Giguère and S. Budsberg
January 2014
Equine Veterinary Journal

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.

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.

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.

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.

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.