Oral and intravenous administration of nimesulide in the horse: rational dosage regimen from pharmacokinetic and pharmacodynamic data.
Authors: Villa R, Cagnardi P, Belloli C, Zonca A, Zizzadoro C, Ferro E, Carli S
Journal: Equine veterinary journal
Summary
Nimesulide is frequently used off-label in equine practice as a selective COX-2 inhibitor, yet evidence-based dosing recommendations have been lacking. Villa and colleagues determined the pharmacokinetics of nimesulide following oral and intravenous administration in horses, measuring plasma protein binding and metabolite concentrations whilst correlating findings with in vitro COX isoform inhibition data to establish rational dosing. At the commonly used dose of 1.5 mg/kg, concentrations exceed the inhibitory threshold (IC50) for both COX-1 and COX-2, meaning the drug loses its selectivity and may cause adverse effects from non-selective prostaglandin inhibition affecting gastric protection and renal function. Although 1.5 mg/kg administered every 12–24 hours (depending on clinical severity) produces adequate therapeutic effects, practitioners should recognise that true COX-2 selectivity is not achieved at this dose, warranting cautious use and careful monitoring for gastrointestinal and renal complications. This work highlights a significant gap between clinical practice and the pharmacological reality of nimesulide in horses, necessitating either dose reduction, shorter treatment duration, or consideration of alternative NSAIDs with better selectivity profiles at equine therapeutic concentrations.
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Practical Takeaways
- •If using nimesulide in horses, dose at 1.5 mg/kg every 12-24 hours depending on inflammation severity, but recognize this is extra-label use without strong safety evidence
- •Be aware that nimesulide loses its COX-2 selectivity at clinical doses in horses, potentially increasing risk of gastrointestinal side effects compared to labeled use in other species
- •Consider administering oral doses with or without food consistently, as feeding status affects drug bioavailability and could impact efficacy
Key Findings
- •Nimesulide at 1.5 mg/kg bwt may produce adequate clinical anti-inflammatory effects in horses with a dosing interval of 12-24 hours depending on condition severity
- •At the recommended dose of 1.5 mg/kg bwt, plasma concentrations exceed the in vitro IC50 for both COX-1 and COX-2, resulting in loss of COX-2 selectivity
- •Pharmacokinetic analysis showed oral bioavailability was affected by feeding status, with implications for practical dosing protocols
- •The loss of COX-1/COX-2 selectivity at therapeutic doses raises concerns about gastrointestinal and other side effects associated with non-selective COX inhibition