Pharmacokinetics of acetaminophen after a single Oral administration of 20 or 40 mg/kg to 7-9 Day-old foals.
Authors: Gold Jenifer R, Grubb Tamara, Court Michael H, Villarino Nicolas F
Journal: Frontiers in veterinary science
Summary
# Acetaminophen Pharmacokinetics in Neonatal Foals: Establishing Baseline Data for Pain Management Acetaminophen presents a potential analgesic and antipyretic option for neonatal foals, yet safe and effective dosing protocols remain undefined for this age group. Researchers administered single oral doses of either 20 or 40 mg/kg to eight clinically healthy 7–9-day-old Quarter Horse foals, collecting plasma samples over 48 hours to characterise drug absorption, distribution and elimination, whilst monitoring haematological and biochemical safety markers before and seven days post-administration. Both doses reached peak plasma concentrations rapidly (median 1–1.5 hours), with the 20 mg/kg dose achieving 12 μg/mL and the 40 mg/kg dose reaching 14 μg/mL; the area under the plasma concentration-time curve showed proportional dose-dependent increases (46–100 h·μg/mL and 79–160 h·μg/mL respectively). Crucially, plasma disposition kinetics in neonatal foals proved comparable to adults, and all measured blood parameters remained within normal limits, suggesting oral acetaminophen does not produce immediate systemic toxicity in this population. Whilst these findings provide essential baseline pharmacokinetic data and reassurance regarding acute safety, determining clinically appropriate dosing regimens and therapeutic efficacy for pain and fever management in neonatal foals requires further investigation, particularly regarding optimal dosing intervals and potential hepatic metabolism considerations specific to immature equine livers.
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Practical Takeaways
- •Acetaminophen appears to be metabolized similarly in neonatal foals as in adults, suggesting potential for pain/fever management in this population, but clinical safety and optimal dosing protocols require further investigation
- •Single doses up to 40 mg/kg do not appear to cause acute hematologic or biochemical toxicity, though long-term safety data for neonates are needed
- •Peak plasma concentrations are achieved within 1-2 hours of oral administration, informing timing considerations if acetaminophen were to be used clinically in neonatal foals
Key Findings
- •Peak plasma acetaminophen concentrations occurred at 1.0-1.5 hours post-administration for both 20 and 40 mg/kg doses in 7-9 day-old foals
- •Maximum plasma concentrations were 12 µg/mL (20 mg/kg) and 14 µg/mL (40 mg/kg), with comparable disposition to adult horses
- •Hematology and biochemistry profiles remained within normal limits 7 days after acetaminophen administration at both dose levels
- •Dose-proportional increases in AUC were observed, with 40 mg/kg producing AUC of 79-160 h·µg/mL versus 46-100 h·µg/mL for 20 mg/kg