Resident, Equine Internal Medicine Iowa State University Ames, Iowa, United States
Abstract:
Background: Acetaminophen is used in infants for antipyresis and analgesia. Neonatal foals might benefit from acetaminophen therapy, but effective and safe dosages for foals are unknown.
Objectives: To determine the pharmacokinetics and clinical safety of acetaminophen following oral administration of 40 mg/kg q12hr or 60 mg/kg q24hr for 14 days.
Methods: Foals received acetaminophen orally either at 40 mg/kg q12hr or 60 mg/kg q24hr for 14 days. Physical exams were performed daily. Plasma disposition of acetaminophen was determined after first and last drug administration and at the study midpoint. Hematology and serum chemistry analysis was performed prior to the study, at midpoint, and on the last day of administration. Plasma acetaminophen concentrations were determined by high performance liquid chromatography, and plasma pharmacokinetic parameters estimated using non-compartmental analysis.
Results: No statistically significant changes occurred on hematology and biochemistry profiles; elevations in GGT or SDH were seen in 4 foals at various timepoints. Cmax occurred within 2 hours for both doses. The 60 mg/Kg dose resulted in a larger median Cmax (range) at 28 mg/ml (22-32) than the 40 mg/kg dose at 23 mg/ml (19-27). The median AUC0-8 hr (range) was 100 h*ug/mL (82-100) at 40 mg/kg and 128 h*ug/mL (120-168) for 60 mg/kg. Trough concentrations decreased over time for both regimens.
Conclusions and Clinical Importance: Foals tolerate oral acetaminophen at 40 mg/kg q12hr or 60 mg/kg q24hr. Further analgesic and antipyretic studies will help to delineate optimal dosage regimens of acetaminophen to treat foals.
