Postmortem examination and toxicological analysis for acute metonitazene intoxication in Japan: A case report

Benzoimidazole analgesics (Nitazenes, NZs) are opioid receptor agonists that exhibit very strong pharmacological effects at minute doses, and their abuse has recently become a concern worldwide. Although no deaths involving NZs had been reported in Japan to date, we recently experienced an autopsy case of a middle-aged man who was determined to have died from poisoning by metonitazene (MNZ), a type of NZs. There were traces of suspected illegal drug use around the body. Autopsy findings were consistent with acute drug intoxication as the cause of death, but it was difficult to identify the causative drugs by simple qualitative drug screening. Analysis of compounds recovered from the scene where the body was found identified MNZ, and its abuse was suspected. Quantitative toxicological analysis of urine and blood was performed using a liquid chromatography high-resolution tandem mass spectrometer (LC-HR-MS/MS). Results showed that MNZ concentrations in blood and urine were 6.0 and 5.2 ng/mL, respectively. Other drugs detected in blood were within therapeutic ranges. Quantitated blood MNZ concentration in the present case was in the similar range as those reported in overseas NZs-related deaths. There were no other findings that could have contributed to the cause of death, and the decedent was judged to have died of acute MNZ intoxication. Emergence of NZs distribution has been recognized in Japan similarly to overseas; early investigation of their pharmacological effects as well as crackdown on their distribution is strongly desired.