In vitro characterization of protonitazene metabolites, using human liver microsomes, and first application to two urines collected from death cases

Protonitazene, or N,N-diethyl-5-nitro-2-[(4-propoxyphenyl)methyl]-1H-benzimidazole-1-ethanamine, is a novel synthetic opioid, which belongs to the nitazene family. Over the last four years, nitazenes have re-emerged on the new psychoactive substances market and have been reported in several fatal intoxication cases. The metabolism of several nitazene analogues have already been studied, but to date, no data exists regarding protonitazene. The aim of the study was the detection of protonitazene and its metabolites in authentic human urine collected in two fatal intoxication cases, comparing the data after in vitro incubation with human liver microsomes, and subsequent analysis by ultra-performance liquid chromatography-tandem mass spectrometry and ultra-performance liquid chromatography-high-resolution mass spectrometry. Protonitazene metabolites, including N-desethyl-protonitazene, 5-amino-protonitazene and 4-hydroxy-nitazene, were characterized in vitro and were identified in the urine of both cases. The ratios between metabolites and parent protonitazene, higher than 1, were calculated to estimate the proportionality of metabolites. The results suggest that testing protonitazene metabolites should increase the window detection of exposure to protonitazene.