Development of a liquid chromatography-tandem mass spectrometry method for the analysis of plasma naltrexone and its active metabolite in patients with AUD

Naltrexone, an FDA-approved mu-opioid receptor antagonist for alcohol dependence, requires therapeutic drug monitoring due to its pharmacokinetic variability. This study developed a liquid chromatography-electrospray ionization-tandem mass spectrometry method for accurately quantifying naltrexone and its active metabolite, 6β-naltrexol, using deuterated internal standards (naltrexone-d₃ and 6β-naltrexol-d₃). Sample preparation involved solid-phase extraction with a Strata-X cartridge followed by elution. Separation was performed on a C18 column with gradient elution at 0.3 mL/min. Detection in dynamic multiple reaction monitoring mode used ion transitions at m/z 342 > 324 for naltrexone and m/z 344 > 161 for 6β-naltrexol. The calibration curves were linear over the range of 0.0152-33.3 ng/mL for naltrexone and 0.410-100. ng/mL for 6β-naltrexol, both with a correlation coefficient of 1.0000 and 0.9998, individually. Intraday and interday variations were below 9.2% for naltrexone and 6.6% for 6β-naltrexol. The recovery was 99.5% for naltrexone and 95.0% for 6β-naltrexol. Applied to plasma samples from five patients receiving 50 mg oral naltrexone daily for 12 weeks, average concentrations were 3.30 ± 4.40 ng/mL (naltrexone) and 48.5 ± 23.4 ng/mL (6β-naltrexol). The developed assay method effectively quantifies naltrexone and its metabolite in alcohol-dependent patients in Taiwan.