Biotransformation and kinetics of selected benzimidazole synthetic opioids in human hepatocytes

Pius S Fasinu^*Gajanan Jadhav

• The University of Alabama at Birmingham, Birmingham, United States

Background/Objectives: The reemergence of the 2-benzylbenzimidazole opioids, also called nitazenes, in the illicit drug market constitute a serious threat to public health. One of the major challenges in handling exposures and managing intoxications in humans is the poor understanding of the kinetics and biotransformation pathways of these drugs. While the schedule status of nitazenes limits interventional clinical studies in humans, liver-based in vitro studies can provide insights into their metabolism and pharmacokinetics. Methods: Three nitazene analogues - butonitazene, isotonitazene and protonitaze, were incubated in primary human hepatocytes. The depletion rate was profiled against time for metabolic kinetic analysis. Qualitative and quantitative analysis of the incubates was conducted using liquid chromatography-high-resolution tandem mass spectrometry. Results: All three analogs were rapidly metabolized in hepatocytes with intrinsic clearance values of 2.4, 3.0 and 3.9 mL/min/g liver for butonitazene, isotonitazene and protonitazene respectively, yielding products of multiple metabolic r eactions including hydroxylation, N-dealkylation, glucuronidation and acetylation. The extrapolated in vivo clearance [(mL/min)/kg body mass] values of butonitazene, isotonitazene and protonitazene were 14.4, 15.2 and 16 respectively compared to 15.5 and 18 for 7-hydroxycoumarin and testosterone respectively. Conclusions: Nitazenes are susceptible to hepatic metabolism through hydroxylation, N-dealkylation and conjugations. Extrapolated in vivo metabolic clearance is similar to 7-hydroxycoumarin and testosterone. For practical purposes, these findings can provide useful estimations in clinical toxicology and forensic pathology.