Pharmacokinetics of single dose administration of three increasing doses of acetaminophen per os in 1-3-month-old foals.
Authors: Gold Jenifer Robin, Grubb Tamara, Court Michael, Villarino Nicolas Francisco
Journal: Equine veterinary journal
Summary
# Acetaminophen Pharmacokinetics in Young Foals: Early Evidence for Dose-Dependent Plasma Disposition Acetaminophen has potential as an analgesic and antipyretic agent in foals, offering a possible non-NSAID alternative for pain and fever management in this age group, yet its pharmacokinetic behaviour and safety profile remain largely uncharacterised in neonatal equine patients. Gold and colleagues administered three ascending single oral doses (10, 20, and 40 mg/kg) to six Quarter Horse foals aged 1–3 months in a randomised cross-over design, measuring plasma concentrations over 64 hours using liquid chromatography and assessing haematological and biochemical parameters before and seven days post-administration. Peak plasma concentrations increased dose-dependently, ranging from 4.4 to 14 µg/ml across the three doses, with corresponding AUC values of 25–105 h × µg/ml; notably, when normalised to dose, the pharmacokinetic parameters showed no significant differences, suggesting linear kinetics across this range. Terminal half-life remained consistent at 2.7–2.8 hours regardless of dose, and aside from expected physiological elevations in blood urea nitrogen and alkaline phosphatase (attributed to foal growth), safety markers appeared unremarkable. Whilst this foundational pharmacokinetic data establishes that acetaminophen is absorbed and eliminated predictably in young foals, the clinical utility remains speculative—the study's small sample size, single-dose design, lack of repeated-dosing protocols, and absence of efficacy data mean practitioners cannot yet determine optimal dosing intervals or therapeutic thresholds for pain relief or fever control, leaving important questions about hepatic metabolism and long-term safety in this age group un
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Practical Takeaways
- •Acetaminophen shows linear pharmacokinetic behaviour in 1-3 month old foals across the doses tested, but clinical effectiveness for pain and fever management has not yet been demonstrated
- •The short half-life of 2.7-2.8 hours suggests frequent dosing intervals would be required if this drug were to be used therapeutically in foals
- •Current safety data from this small study is insufficient to recommend acetaminophen as a practical alternative to NSAIDs for foal pain management without further efficacy and safety research
Key Findings
- •Median plasma acetaminophen concentrations were dose-dependent: 4.4 µg/ml (10 mg/kg), 6.3 µg/ml (20 mg/kg), and 14 µg/ml (40 mg/kg)
- •AUC0-∞ values increased proportionally with dose: 25, 41, and 105 h×µg/ml for 10, 20, and 40 mg/kg doses respectively
- •Terminal half-life was consistent across all doses at 2.7-2.8 hours
- •Haematology and biochemistry profiles remained normal except for blood urea nitrogen and alkaline phosphatase concentrations; analgesic and antipyretic efficacy in foals remains unknown