Pharmacokinetics of single-dose oral acetaminophen with and without concurrent administration of silymarin or N-acetylcysteine in orange-winged Amazon parrots (Amazona amazonica).

OBJECTIVE

To determine the pharmacokinetics of acetaminophen (N-acetyl-para-aminophenol [APAP]) and its metabolites after oral administration of a single dose of APAP, with or without silymarin or N-acetylcysteine (NAC), to orange-winged Amazon parrots (Amazona amazonica).

METHODS

Eight parrots received, in 3 separate studies, 1 of the following oral treatments: (1) APAP (100 mg/kg) with silymarin (50 mg/kg, twice, q 12 h); (2) APAP (100 mg/kg) with NAC (400 mg/kg); or (3) APAP (100 mg/kg) alone. For each study, blood samples were collected over 24 hours after drug administration to evaluate plasma concentrations of APAP, APAP-glucuronide, and APAP-sulfate. Pharmacokinetic parameters were calculated. Plasma biochemistry panels were performed before and after each study. In a fourth study, a single oral dose of APAP (100 mg/kg) was administered to 8 additional parrots for adverse effects evaluation alone.

RESULTS

Pharmacokinetic parameters for APAP, APAP-glucuronide, and APAP-sulfate were established. The APAP maximum plasma concentration, time of maximal plasma concentration, and half-life across studies ranged from 2,016.9 to 2,917.2 ng/mL, 1.13 to 2.1 hours, and 1.3 to 1.45 hours, respectively. Acetaminophen had marked metabolism to APAP-glucuronide and negligible to APAP-sulfate. Concurrent administration of APAP with silymarin resulted in a mild but significant elevation in glutamate dehydrogenase.

CONCLUSIONS

Acetaminophen plasma concentrations were lower than in other avian species despite a relatively high dose. Acetaminophen has fast absorption, short half-life, and marked glucuronidation. Single oral dose administration of APAP, alone or with NAC, appears safe based on plasma biochemistries. Multidose and pharmacodynamic studies are needed.

CLINICAL RELEVANCE: This is the first pharmacokinetic study of APAP in psittacines, which has the potential to be an effective and safe component of multimodal analgesia in these species.