Detection and pharmacokinetics of three formulations of firocoxib following multiple administrations to horses.
Authors: Knych H K, Stanley S D, Arthur R M, Mitchell M M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Firocoxib Pharmacokinetics in Horses Firocoxib, a selective cyclooxygenase-2 inhibitor commonly used for pain and inflammation management in equine practice, poses regulatory challenges because it can mask lameness and potentially allow compromised horses to compete; Knych and colleagues therefore investigated how three marketed formulations accumulate and clear from the bloodstream following multiple doses. Nine horses received intravenous injection (0.09 mg/kg daily for 5 days), oral paste (0.1 mg/kg daily for 14 days), or oral tablets (57 mg daily for 14 days), with plasma samples analysed using liquid chromatography-mass spectrometry to track drug elimination. All three formulations demonstrated similar plasma half-lives of approximately 1.7 days, with concentrations falling below the Racing Medication and Testing Consortium's racehorse threshold of 20 ng/ml by day 7 post-final dose; notably, no formulation exceeded the 240 ng/ml threshold established for US Equestrian Federation competitions. For equine professionals involved in competition horses, these findings establish evidence-based withdrawal times—a minimum of 7 days following cessation of any firocoxib formulation for racehorses—whilst recognising that regulatory thresholds differ between sporting disciplines, underscoring the importance of understanding your relevant governing body's specific requirements before administering this medication.
Read the full abstract on PubMed
Practical Takeaways
- •If treating competition horses with firocoxib, observe a 7-day withdrawal period before racing to comply with regulatory thresholds; non-racing disciplines have higher tolerance thresholds
- •Injectable, paste, and tablet formulations show comparable pharmacokinetic profiles, so choice can be based on practical administration factors rather than regulatory clearance timing
- •This data supports evidence-based withdrawal guidelines and helps prevent inadvertent regulatory violations in performance horses
Key Findings
- •Mean plasma half-life of firocoxib was approximately 1.6-1.7 days across all three formulations (injectable, paste, tablet)
- •All formulations achieved plasma concentrations below the Racing Medication and Testing Consortium threshold of 20 ng/ml by 7 days post-final dose
- •No formulation exceeded the 240 ng/ml threshold for US Equestrian Federation competition events at any measured time point
- •Provides withdrawal time guidance: minimum 7 days recommended for racehorses across all firocoxib formulations