Metabolism of highly potent synthetic opioid nitazene analogs: N‐ethyl‐N‐(1‐glucuronyloxyethyl) metabolite formation and degradation to N‐desethyl metabolites during enzymatic hydrolysis

Abstract

The metabolism of the highly potent synthetic opioids metonitazene, etonitazene, and protonitazene was investigated in fresh human hepatocytes. In the hydrolyzed culture medium, N‐desethyl‐, N,N‐di‐desethyl‐, O‐desalkyl‐, N‐desethyl‐O‐desalkyl‐, N,N‐di‐desethyl‐O‐desalkyl‐, and N‐oxidated metabolites were detected as phase I metabolites, whereas in the unhydrolyzed culture medium, O‐glucuronides of phase I metabolites with O‐dealkylation were detected as phase II metabolites. The detected phase I metabolites were identified by comparing their analytical data with those of synthesized authentic standards. In contrast, phase II metabolites were identified by comparing their analytical data with those of the glucuronidated products formed by the incubation of the corresponding substrates with human liver microsomes in the presence of uridine diphosphate glucuronic acid. In addition to the aforementioned metabolites, some putative N‐ethyl‐N‐(1‐glucuronyloxyethyl) metabolites were detected in the unhydrolyzed culture medium. Purification and hydrolysis experiments revealed that N‐ethyl‐N‐(1‐glucuronyloxyethyl) metabolites formed the corresponding N‐desethyl metabolites via unstable N‐ethyl‐N‐(1‐hydroxyethyl) metabolites during enzymatic hydrolysis.

In vitro structure–activity relationships and forensic case series of emerging 2-benzylbenzimidazole ‘nitazene’ opioids

“…N-Desethyl etonitazene and N-desethyl isotonitazene are metabolites of etonitazene and isotonitazene, respectively (Taoussi et al 2024;Kanamori et al 2024;Krotulski et al 2020). As previously discussed for N-piperidinyl 4′-OH nitazene, the highly potent N-desethyl metabolites may theoretically contribute to the toxicity of the parent drug.…”

“…4′-OH nitazene is a universal metabolite of all nitazenes with alkoxy chain modifications only (Taoussi et al 2024;Kanamori et al 2024;Walton et al 2021). Similarly, based on recent findings for N-piperidinyl etonitazene where the N-piperidinyl 4′-OH nitazene metabolite was identified in authentic urine samples from two patients that took this compound (Vandeputte et al 2022e;Berardinelli et al 2024), it can be hypothesized that N-pyrrolidino 4′-OH nitazene and N-piperidinyl 4′-OH nitazene are common O-dealkylated metabolites of the herein evaluated 'ring' nitazenes.…”