Comparison of the Metabolic Profiles Associated with Protonitazene and Protonitazepyne in Two Severe Poisonings

Nitazenes represent an emerging class of new synthetic opioids characterized by a high-potency μ-opioid receptor (MOR) agonist activity. Background: We report two 20-year-old males who presented with severe neurorespiratory depression with typical opioid syndrome, but no opioid identification based on routine blood and urine screening tests. The first patient recovered with supportive care, mechanical ventilation, and naloxone infusion, whereas the second patient developed post-anoxic cardiac arrest and died from brain death. Methods: A complementary comprehensive toxicological screening using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) was performed, and data were processed using a dedicated molecular network strategy to profile the metabolites. Results: Protonitazene and protonitazepyne, two nitazenes differing in their ethylamine moieties (i.e., a diethyl versus a pyrrolidine substitution, respectively), were identified. We found an extensive metabolism of protonitazene, leading to the identification of multiple phase I (resulting from hydroxylation, N-desethylation, and O-despropylation) and phase II (resulting from glucuronidation) metabolites. By contrast, protonitazepyne metabolism appeared limited, with one metabolite annotated confidently, protonitazepyne acid, which resulted from the oxidative pyrrolidine ring cleavage. Concusions: To conclude, nitazene detection is highly challenging due to its extensive structural and metabolic diversity. Our findings highlight the contribution of the untargeted LC-HRMS screening approach and suggest that diagnostic product ions can serve as robust markers for nitazene identification.