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The recent re-emergence and the increasing popularity of nitazenes, a group of new synthetic opioids (NSO) that belong to the benzimidazole chemical class, has raised public health concerns. As a class of potential opioid analgesic agents whose development was discontinued in the 1960s due to their high potential for abuse, very little is known about their metabolism and physiologic disposition. In the current study, three nitazenes-butonitazene, isotonitazene and protonitaze were incubated in human liver microsomes (HLM), human S9 (HS9) fractions and recombinant cytochrome P450 enzymes. All three nitazenes were rapidly metabolized in both HLM and HS9 with over 95% depletion within 60 min. In HLM, butonitazene, isotonitazene and protonitazene had in vitro intrinsic clearance (CLint) (µL/min/mg protein) values of 309, 221 and 216 respectively compared to 150 of verapamil, the positive control. In HS9, CLint values were 217, 139, and 150 for butonitazene, isotonitazene and protonitazene respectively compared to only 35 for testosterone, the control probe substrate. Putative metabolite identified from this study include products of hydroxylation, desethylation, dealkylation, desethylation followed by dealkylation, and desethylation followed by hydroxylation. The metabolic phenotyping showed CYP2D6, CYP2B6 and CYP2C8 and the major hepatic enzymes responsible for the metabolism of nitazenes. Within 30 min of incubation, CYP2D6 depleted butonitazene (99%), isotonitazene (72%) and butonitazene (100%) significantly. The rapid metabolism of nitazenes may be an important factor in accurate and timely detections and quantitation of the unchanged drugs in human matrices following intoxication or in forensic analysis. The involvement of multiple polymorphic CYPs in their metabolism may play important roles in the susceptibility to intoxication and/or addiction, depending on the activity of the metabolites. [ABSTRACT FROM AUTHOR]

Introduction: Protonitazene is an opioid belonging to the 2-benzylbenzimidazole structural class. We describe two cases of opioid toxicity involving the reported inhalation of a delta-9-tetrahydrocannabinol vape product in which protonitazene was detected. Case reports: Case 1 was a young male found unconscious after the reported use of a delta-9-tetrahydrocannabinol vape. He suffered two subsequent apnoeic episodes requiring bag-valve-mask ventilation before eventual recovery. Only protonitazene was detected in blood at a concentration of 0.74 µg/L. Case 2 was a young male who died shortly after being found unresponsive. The postmortem femoral blood concentrations of protonitazene and delta-9-tetrahydrocannabinol were 0.33 µg/L and 2 µg/L, respectively. Analysis of a pod vaping device found in the decedent's hand and a separate e-liquid bottle labelled as delta-9-tetrahydrocannabinol showed a mixture of protonitazene and delta-9-tetrahydrocannabinol. Discussion: The opioid effects of protonitazene are mediated through β-arrestin2 and mu opioid receptor signalling pathways. Benzimidazole opioids are lipophilic and, when mixed with a suitable solvent, can be used in a vape device. It is anticipated that naloxone would have provided effective reversal of toxicity in our cases. Conclusions: Novel routes of opioid administration, like vaping, may appear relatively innocuous in comparison to intravenous administration, but opioids may still be absorbed at high concentrations, resulting in severe opioid toxicity or death. [ABSTRACT FROM AUTHOR]

Abstract Since the early 2010s, synthetic opioids have significantly contributed to overall opioid-related overdose mortalities. For point of reference, of the 68,630 opioid-related deaths recorded in 2020, 56,516 involved synthetic opioids. During much of this period, fentanyl has been the most commonly used synthetic opioid. This time when fentanyl was the most popular opioid has been called the “third wave” of the opioid crisis, partly because it led to a sharp rise in deaths from overdoses. Other synthetic opioids, such as carfentanil, protonitazene, and isotonitazene, have also become more widely diverted for nonmedical used. Carfentanil is an even more potent fentanyl derivative that was initially used in the mid-1980s as a general anesthetic for large animals such as elephants. Related to its strong affinity for mu opioid receptors, carfentanil is still utilized in medicine and science today as a radiotracer for positron emission tomography imaging. Protonitazene and isotonitazene belong to a novel class of synthetic opioids called benzimidazoles that were manufactured in the 1950s as novel analgesics. These agents have come under recent scrutiny as designer synthetic opioids becoming more prevalent. However, to date, there is incomplete data regarding the prevalence of synthetic opioids, as traditional toxicology screenings may not be sensitive to detect these compounds at such low doses post-mortem, particularly when blood is drawn from the periphery instead of central tissues such as the brain, lung, or heart. This narrative review aims to highlight the clinical challenges presented by these new synthetic opioids.

Since the early 2010s, synthetic opioids have significantly contributed to overall opioid-related overdose mortalities. For point of reference, of the 68,630 opioid-related deaths recorded in 2020, 56,516 involved synthetic opioids. During much of this period, fentanyl has been the most commonly used synthetic opioid. This time when fentanyl was the most popular opioid has been called the "third wave" of the opioid crisis, partly because it led to a sharp rise in deaths from overdoses. Other synthetic opioids, such as carfentanil, protonitazene, and isotonitazene, have also become more widely diverted for nonmedical used. Carfentanil is an even more potent fentanyl derivative that was initially used in the mid-1980s as a general anesthetic for large animals such as elephants. Related to its strong affinity for mu opioid receptors, carfentanil is still utilized in medicine and science today as a radiotracer for positron emission tomography imaging. Protonitazene and isotonitazene belong to a novel class of synthetic opioids called benzimidazoles that were manufactured in the 1950s as novel analgesics. These agents have come under recent scrutiny as designer synthetic opioids becoming more prevalent. However, to date, there is incomplete data regarding the prevalence of synthetic opioids, as traditional toxicology screenings may not be sensitive to detect these compounds at such low doses post-mortem, particularly when blood is drawn from the periphery instead of central tissues such as the brain, lung, or heart. This narrative review aims to highlight the clinical challenges presented by these new synthetic opioids. [ABSTRACT FROM AUTHOR]

• Protonitazene is a novel synthetic opioid, which belongs to the nitazene family. • Nitazenes have re-emerged on the new psychoactive substances market and have been reported in several fatal intoxication cases. • Protonitazene metabolism was studied in vitro after drug incubation with human liver microsomes. • The identified metabolites were compared to the responses obtained in two authentic human urine specimens.. 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. [ABSTRACT FROM AUTHOR]

Protonitazene is a synthetic benzoimidazole opioid of the nitazenes class, developed in the 1950s as an effective analgesic, but never released on the market due to severe side effects and possible dependence. Despite its increasing use as a new psychoactive substance starting in 2019, its detection in human hair of intoxicated and deceased consumers has never been reported. We present the development and validation of a specific procedure to identify protonitazene in hair by LC-MS-MS. Drugs were incubated overnight at 40°C in 1 mL borate buffer, pH 9.5 with 20 mg pulverized hair and 1 ng/mg fentanyl-d5 used as internal standard. Drugs were then extracted with a mixture of organic solvents. The chromatographic separation was performed using a HSS C18 column with a 15 min gradient elution. Linearity was verified from 1 to 100 pg/mg. The limit of detection was estimated at 0.1 pg/mg. No interference was noted from a large panel of natural and synthetic opioids, fentanyl derivatives or other new synthetic opioids. Protonitazene was identified at 70 and at > 7600 pg/mg in the whole head hair specimens of two male subjects deceased from acute drug overdose in jail. Protonitazene was also identified at 14 and 54 pg/mg in two living co-prisoners. As nitazenes represent a growing threat to public health in various parts of the world, this method was developed in response to the challenges posed by the identification of this class of substances., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site–for further information please contact journals.permissions@oup.com.)