Metonitazene is considered a new psychoactive substance (NPS) and emerging potent synthetic opioid, causing increased public health concern beginning in 2020. Metonitazene joins a growing list of new synthetic opioids (NSOs) contributing to deaths among people who use drugs in the United States and other parts of the world. Metonitazene (a 2‐benzylbenzimidazole analogue) first appeared in mid‐2020 in the recreational drug supply and subsequently began proliferating in death investigation casework towards the end of 2020. Screening and metabolite discovery were performed by liquid chromatography quadrupole time‐of‐flight mass spectrometry. Quantitative confirmation was performed by liquid chromatography tandem quadrupole mass spectrometry. Metonitazene was confirmed in 20 authentic forensic postmortem cases with an average concentration in blood at 6.3 ± 7.5 ng/ml (median: 3.8 ng/ml, range: 0.5–33 ng/ml, n = 18) and in urine at 15 ± 13 ng/ml (median: 11 ng/ml, range: 0.6–46 ng/ml, n = 14). Metonitazene was the only opioid identified in 30% of cases but was also found in combination with fentanyl (55%) and NPS benzodiazepines, opioids, and hallucinogens (45%). Medical examiners included metonitazene as a drug responsible for the cause of death, and the manner of death was always ruled to be an accident. The metabolism of metonitazene was found to be similar to that of isotonitazene, a closely related analogue. Toxicology laboratories and death investigators should ensure that metonitazene is included in forensic testing protocols, all while remaining vigilant for subsequent NSOs to emerge.

No abstract

Novel synthetic opioids continue to emerge on recreational drug markets worldwide. In response to legislative bans on fentanyl analogues, non-fentanyl structural templates, such as 2-benzylbenzimidazoles ('nitazenes'), are being exploited to create new -opioid receptor (MOR) agonists. Here, we pharmacologically characterize an emerging cyclic analogue of etonitazene, called N-pyrrolidino etonitazene (etonitazepyne), using in vitro and in vivo methods. A series of analytically confirmed fatalities is described to complement preclinical findings. Radioligand binding assays in rat brain tissue revealed that N-pyrrolidino etonitazene has high affinity for MOR (Ki=4.09 nM) over -opioid (Ki=959 nM) and -opioid (Ki=980 nM) receptors. In a MOR--arrestin2 activation assay, N-pyrrolidino etonitazene displayed high potency (EC50=0.348 nM), similar to etonitazene (EC50=0.360 nM), and largely exceeding the potencies of fentanyl (EC50=14.9 nM) and morphine (EC50=290 nM). When administered s.c. to male Sprague Dawley rats, N-pyrrolidino etonitazene induced opioid-like antinociceptive, cataleptic, and thermic effects. Its potency in the hot plate test (ED50=0.0017 mg/kg) was 10fold and 2,000-fold greater than fentanyl (ED50=0.0209 mg/kg) and morphine (ED50=3.940 mg/kg), respectively. Twenty-one overdose fatalities associated with N-pyrrolidino etonitazene were found to contain low blood concentrations of the drug (median=2.2 ng/mL), commonly in the context of polysubstance use. N-Pyrrolidino etonitazene was reported as a cause of death in at least two cases, demonstrating toxicity in humans. We demonstrate that N-pyrrolidino etonitazene is an extremely potent MOR agonist that is likely to present high risk to users. Continued vigilance is required to identify and characterize emergent 2benzylbenzimidazoles, and other non-fentanyl opioids, as they appear in the marketplace.

No abstract

Novel psychoactive substances (NPS) continue to represent a threat to public health and safety. The number of new drugs in the latest emergent synthetic opioid class—the 2-benzylbenzimidazole analogs—also called the nitazenes—has begun to dominate the current new synthetic opioid (NSO) subclass of NPS. We describe a liquid chromatography–tandem quadrupole mass spectrometry method for the quantification of nine analogs and/or metabolites of drugs in this series: isotonitazene, metonitazene, protonitazene, etonitazene, clonitazene, flunitazene, N-desethyl isotonitazene, 5-amino isotonitazene and 4ʹ-hydroxy nitazene in human whole blood, urine, and tissue. Samples were prepared for analysis using a basic liquid–liquid extraction. Chromatographic separation was achieved using a C-18 analytical column. Multiple reaction monitoring mode was used for detection. The calibration range for the analytes was 0.5–50 ng/mL (except for 5-amino isotonitazene, which was 1.0–50 ng/mL). The limit of detection was 0.1 ng/mL, and the limit of quantitation was 0.5 ng/mL. The method had no carryover or interferences. Ionization enhancement was observed but did not affect quantitation. All analytes passed the method validation assessment. Authentic human samples suspected of containing NSOs were obtained from a medical examiner and coroner offices, as well as partnering forensic toxicology laboratories. Isotonitazene was confirmed in 92 blood samples, and its metabolites were confirmed across various matrices. Metonitazene (n = 35), flunitazene (n = 5), protonitazene (n = 3), etodesnitazene (n = 2) and butonitazene (n = 1) were also detected in cases. These newly emerging 2-benzylbenzimidazole analogs were commonly found in combination with NPS benzodiazepines and opioids (e.g., flualprazolam, fentanyl). Nitazene analogs are potent esoteric drugs that may not be identified during routine toxicological screening, and specialized assays based on sensitive instrumentation are needed to accurately characterize these NSOs.