Pharmacokinetics and in vitro efficacy of salicylic acid after oral administration of acetylsalicylic acid in horses.
Authors: Buntenkötter Kathrin, Osmers Maren, Schenk Ina, Schänzer Wilhelm, Machnik Marc, Düe Michael, Kietzmann Manfred
Journal: BMC veterinary research
Summary
# Salicylic acid pharmacokinetics following acetylsalicylic acid administration in horses Salicylic acid (SA) presents a unique challenge in equine sport because it accumulates naturally through dietary plant intake, yet sport organisations enforce regulatory thresholds for urinary and plasma concentrations; this study sought to clarify how oral acetylsalicylic acid (ASA) dosing translates to measurable SA levels. Eight horses received three escalating single doses (12.5, 25, and 50 mg/kg) of ASA in a crossover design, with plasma and urine SA concentrations monitored systematically. Peak plasma concentrations and urinary excretion increased proportionally with dose, establishing clear pharmacokinetic parameters that distinguish therapeutic SA levels from those accumulated through routine feeding. These findings enable veterinarians and equine professionals to predict which ASA doses risk breaching competition thresholds, and provide sport organisations with evidence-based guidance for differentiating between dietary SA accumulation and intentional medication use. For practitioners managing pain or inflammation in competition horses, the dose-dependent SA profiles offer critical reference points for informed decision-making regarding both efficacy and regulatory compliance.
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Practical Takeaways
- •Horses competing under sport organizations with SA thresholds should avoid ASA administration due to doping violation risk, even at therapeutic doses
- •Be aware that common plant-based feeds naturally contain salicylates that may elevate urinary SA levels independent of medication use
- •If using ASA therapeutically, allow adequate washout time (several days minimum based on urinary kinetics) before competitions with SA testing
Key Findings
- •Salicylic acid plasma concentrations increased dose-dependently after oral ASA administration at 12.5, 25, and 50 mg/kg
- •Urinary SA concentrations exceeded established sport organization thresholds at all three ASA dosages tested
- •SA peak plasma concentrations were reached within 1-2 hours post-administration across all dose groups
- •Natural dietary sources of salicylates may contribute to background SA levels detectable in equine urine and plasma