Post-Mortem Identification and Toxicological Findings of Fluetonitazepyne and Isotonitazepyne

Nitazepyne-type substances, such as fluetonitazepyne and isotonitazepyne, are among the latest additions to the group of nitazenes-highly potent and dangerous opioids that have emerged on the illicit drug market in recent years. In early 2025, five death cases in Finland tested positive for fluetonitazepyne and one for isotonitazepyne in urine drug screening. The median (range) concentration of fluetonitazepyne in post-mortem femoral blood was 1.7 (0.4-9.5) μg/L, and the concentration of isotonitazepyne was 1.4 μg/L. Other psychoactive substances were detected in all cases. A peak corresponding to O-dealkylated fluetonitazepyne, the 4-OH-nitazepyne metabolite, was present in all fluetonitazepyne-positive urine samples and was later used in the identification of isotonitazepyne in one fatal case. This metabolite proved useful as a marker compound for nitazepyne-type benzimidazole opioids in a urine screening.