LC-MS/MS method for the simultaneous quantification of thiafentanil and naltrexone in bovine muscle, liver and kidney

Thiafentanil is a µ-opioid agonist used for the chemical immobilisation of a variety of ungulate species and is antagonised by the administration of naltrexone. The potential for these ungulates to be hunted for consumption by humans or predators raises concerns of drug residues in animal tissues. No analytical method to quantify tissue residue concentrations of thiafentanil has been previously reported. This research developed an LC-MS/MS method to quantify thiafentanil in bovine muscle, and both thiafentanil and naltrexone in bovine liver and kidney matrices. The analytical method was applied to quantify tissue residues in samples collected from goats 1, 2, 3, and 6 days post thiafentanil administration. The assay was validated over the calibration range 6.25-200 ng/mg for thiafentanil in muscle, and 3.13-400 ng/mg for thiafentanil and 57.8-7400 ng/mg for naltrexone in liver and kidney. No residues above the lowest limit of quantification were detected in the injection site, longissimus dorsi muscle, liver or kidney samples collected from the goats. The reported analytical method and residue depletion data provide a foundation for future thiafentanil and naltrexone residue depletion studies in wildlife species.