Synthesis, Chemical Characterization, and μ-Opioid Receptor Activity Assessment of the Emerging Group of "Nitazene" 2-Benzylbenzimidazole Synthetic Opioids

In vitro, in vivo metabolism and quantification of the novel synthetic opioid N-piperidinyl etonitazene (etonitazepipne)

OBJECTIVES

N-piperidinyl etonitazene (etonitazepipne) is a newly synthesized opioid related to the 2-benzylbenzimidazole analog class. Etonitazepipne has been formally notified and placed under intensive monitoring in Europe in January 2022. Nitazenes have high affinity at µ-opioid receptor (MOR). Etonitazepipne, specifically shows a EC50 of 2.49 nM, suggesting about 50 times higher potency combined with higher efficacy compared to morphine. Antinociceptive potency l ('hot plate test' with rats) was 192-fold greater than that of morphine.

METHODS

Here we report on a post-mortem case involving etonitazepipne and its quantification using a standard addition method (SAM) through liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, characterization and identification of phase I human metabolites using in vitro assay based on pooled human liver microsomes (pHLM) was performed along with the analysis of authentic urine samples by means of high-performance liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS).

RESULTS

The concentration of etonitazepipne in post-mortem blood and urine was 8.3 and 11 ng/mL, respectively. SAM was validated by assessing the following parameters: intraday and interday repeatability, matrix effect and recovery rate in post-mortem blood. A total of 20 and 14 metabolites were identified after pHLM incubation and urine analysis, respectively. Most pronounced in vitro and in vivo transformations were O-deethylation, hydroxylation, ketone reduction, and combinations thereof.

CONCLUSIONS

Considering small traces of the parent drug often found in real cases, the identification of metabolic biomarkers is crucial to identify exposure to this drug. O-deethylated, oxidated metabolites, and combination thereof are proposed as urinary biomarkers along with the parent compound.

Using forensic intelligence as a model for determining future toxicology methods: TBI forensic toxicology and forensic drug chemistry nitazene identification

The Tennessee Bureau of Investigation (TBI) serves all 95 counties of Tennessee, but the data included in this article are primarily focused in Upper East and East Tennessee (the parts of the state included in the eastern time zone). The forensic chemistry (seized drug) unit of the TBI began reporting nitazene analogues in late 2019. The primary analogues found in forensic chemistry cases were isotonitazene and metonitazene. After discussion and review of reporting statistics, the forensic toxicology unit began to monitor for these compounds in toxicology samples by using ion characteristics with the nitazene analogues. Between March 2021 and December 2023, TBI toxicology received 49,639 cases statewide. Of those, 20,105 (40.5%) received toxicology testing. Approximately 95% of TBI toxicology cases are related to Driving Under the Influence (DUI)/motor vehicle-related incidents. Fatal overdoses and cases from the medical examiner office comprise <5% of TBI toxicology caseload. The toxicology section utilizes the SCIEX 3200 Qtrap with a SCIEX Exion LC AC autosampler system to monitor multiple reaction monitoring transition of nitazene analogues. The ion monitoring for two nitazene analogues, isotonitazene and metonitazene, started in March 2021. Ion monitoring should not be construed as a confirmed result but rather as an indication that a drug may be present. A comparison of this data from the forensic toxicology and forensic chemistry units revealed the rise of new drugs that required a more in-depth review to understand the magnitude and scope. This article is also intended to encourage collaboration between forensic toxicology and forensic chemistry (seized drug) units.

Elucidating the Gas-Phase Behavior of Nitazene Analog Protomers Using Structures for Lossless Ion Manipulations Ion Mobility-Orbitrap Mass Spectrometry

2-Benzylbenzimidazoles, or "nitazenes", are a class of novel synthetic opioids (NSOs) that are increasingly being detected alongside fentanyl analogs and other opioids in drug overdose cases. Nitazenes can be 20× more potent than fentanyl but are not routinely tested for during postmortem or clinical toxicology drug screens; thus, their prevalence in drug overdose cases may be under-reported. Traditional analytical workflows utilizing liquid chromatography-tandem mass spectrometry (LC-MS/MS) often require additional confirmation with authentic reference standards to identify a novel nitazene. However, additional analytical measurements with ion mobility spectrometry (IMS) may provide a path toward reference-free identification, which would greatly accelerate NSO identification rates in toxicology laboratories. Presented here are the first IMS and collision cross section (CCS) measurements on a set of fourteen nitazene analogs using a structures for lossless ion manipulations (SLIM)-orbitrap MS. All nitazenes exhibited two high intensity baseline-separated IMS distributions, which fentanyls and other drug and druglike compounds also exhibit. Incorporating water into the electrospray ionization (ESI) solution caused the intensities of the higher mobility IMS distributions to increase and the intensities of the lower mobility IMS distributions to decrease. Nitazenes lacking a nitro group at the R1 position exhibited the greatest shifts in signal intensities due to water. Furthermore, IMS-MS/MS experiments showed that the higher mobility IMS distributions of all nitazenes possessing a triethylamine group produced fragment ions with m/z 72, 100, and other low intensity fragments while the lower mobility IMS distributions only produced fragment ions with m/z 72 and 100. The IMS, solvent, and fragmentation studies provide experimental evidence that nitazenes potentially exhibit three gas-phase protomers. The cyclic IMS capability of SLIM was also employed to partially resolve four sets of structurally similar nitazene isomers (e.g., protonitazene/isotonitazene, butonitazene/isobutonitazene/secbutonitazene), showcasing the potential of using high-resolution IMS separations in MS-based workflows for reference-free identification of emerging nitazenes and other NSOs.

Human metabolism of four synthetic benzimidazole opioids: isotonitazene, metonitazene, etodesnitazene, and metodesnitazene

Following isotonitazene scheduling in 2019, the availability of alternative 2-benzylbenzimidazole opioids (nitazenes) on the global drug market increased, resulting in many fatalities worldwide. Nitazenes are potent µ-opioid receptor agonists with strong narcotic/analgesic effects, and their concentrations in biological matrices are low, making the detection of metabolite biomarkers of consumption crucial to document use in clinical and forensic settings. However, there is little to no data on the metabolism of the most recently available nitazenes, especially desnitro-analogues. The aim of the research was to assess isotonitazene, metonitazene, etodesnitazene, and metodesnitazene human metabolism and identify specific metabolite biomarkers of consumption. The four analogues were incubated with 10-donor-pooled human hepatocytes, and the incubates were analyzed by liquid chromatography-high-resolution tandem mass spectrometry and data mining with Compound Discoverer (Thermo Scientific); the analysis was supported by in silico metabolite predictions with GLORYx open-access software. Metabolites were identified in postmortem blood and/or urine samples from two metonitazene-positive and three etodesnitazene-positive cases following the same workflow, with and without glucuronide hydrolysis in urine, to confirm in vitro results. Twelve, nine, twenty-two, and ten metabolites were identified for isotonitazene, metonitazene, etodesnitazene, and metodesnitazene, respectively. The main transformations were N-deethylation at the N,N-diethylethanamine side chain, O-dealkylation, and further O-glucuronidation. In vitro and autopsy results were consistent, demonstrating the efficacy of the 10-donor-pooled human hepatocyte model to predict human metabolism. We suggest the parent and the corresponding O-dealkyl- and N-deethyl-O-dealkyl metabolites as biomarkers of exposure in urine after glucuronide hydrolysis, and the corresponding N-deethyl metabolite as additional biomarker in blood.

Identification of N-piperidinyl etonitazene in alternative keratinous matrices from a decomposing cadaver

This short report describes research on N-piperidinyl etonitazene, also known as etonitazepipne, in keratinous matrices (hair and nails) after death related to a suspected opioid overdose. Etonitazepipne belongs to the family of benzimidazole opioids, a class of new synthetic opioids that has penetrated the illicit drug market. Analysis in the case under study showed the presence of etonitazepipne in both hair and nails, confirming that the substance accumulates in the body with repeated intake.

In vitro structure-activity relationships and forensic case series of emerging 2-benzylbenzimidazole 'nitazene' opioids

2-Benzylbenzimidazole 'nitazene' opioids are presenting a growing threat to public health. Although various nitazenes were previously studied, systematic comparisons of the effects of different structural modifications to the 2-benzylbenzimidazole core structure on μ-opioid receptor (MOR) activity are limited. Here, we assessed in vitro structure-activity relationships of 9 previously uncharacterized nitazenes alongside known structural analogues. Specifically, we focused on MOR activation by 'ring' substituted analogues (i.e., N-pyrrolidino and N-piperidinyl modifications), 'desnitazene' analogues (lacking the 5-nitro group), and N-desethyl analogues. The results from two in vitro MOR activation assays (β-arrestin 2 recruitment and inhibition of cAMP accumulation) showed that 'ring' modifications overall yield highly active drugs. With the exception of 4'-OH analogues (which are metabolites), N-pyrrolidino substitutions were generally more favorable for MOR activation than N-piperidine substitutions. Furthermore, removal of the 5-nitro group on the benzimidazole ring consistently caused a pronounced decrease in potency. The N-desethyl modifications showed important MOR activity, and generally resulted in a slightly lowered potency than comparator nitazenes. Intriguingly, N-desethyl isotonitazene was the exception and was consistently more potent than isotonitazene. Complementing the in vitro findings and demonstrating the high harm potential associated with many of these compounds, we describe 85 forensic cases from North America and the United Kingdom involving etodesnitazene, N-desethyl etonitazene, N-desethyl isotonitazene, N-pyrrolidino metonitazene, and N-pyrrolidino protonitazene. The low-to-sub ng/mL blood concentrations observed in most cases underscore the drugs' high potencies. Taken together, by bridging pharmacology and case data, this study may aid to increase awareness and guide legislative and public health efforts.

Intoxications involving methoxyacetylfentanyl and U-47700: a study of 3 polydrug fatalities

Novel synthetic opioids (NSOs) represent an emerging group of novel psychoactive substances, acting as agonists at the opioid receptors. NSOs include fentanyl-related compounds, e.g. methoxyacetylfentanyl (MeACF), and non-fentanyl analogs, e.g. "U compounds" including U-47700. Here we present three cases of death involving MeACF and U-47700, with particular reference to preliminary data on pharmacokinetics and tissue distribution.After a complete post-mortem examination, general unknown screenings and analysis of drugs of abuse were performed on postmortem samples by immunoassays, gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. To quantify the analytes of interest in post-mortem blood and tissues, the standard addition method was used. A toxicological significance score (TSS), weighing the role of the NSO in each death case, was assigned.Case 1 died at the hospital after consumption of U-47700, methadone (serum levels: 2,600 ng/ml and 37 ng/ml), tilidine and benzodiazepines. In case 2, U-47700 (204 ng/ml) together with methadone (290 ng/ml), flubromazepam (480 ng/ml) and diazepam (300 ng/ml) were detected in peripheral blood. In case 3, methoxyacetylfentanyl (266 ng/ml), furanylfentanyl (4.3 ng/ml) 4-ANPP (15 ng/ml) and alprazolam (69 ng/ml) were quantified in femoral blood. In all cases, the NSO likely contributed to the death (TSS = 3).NSOs appear to be often consumed in the setting of polydrug intoxications, especially in combination with other opioids and benzodiazepines, which often exert synergistic effects. The standard addition method remains the most reliable in post-mortem analysis and toxicological results should always be evaluated together with circumstantial and autopsy data.

Study of metabolism and potential toxicity of nine synthetic opioid analogs using the zebrafish larvae model

The use of novel psychoactive substances (NPSs) has dramatically increased worldwide, and among them, synthetic opioids are one of the fastest growing groups, where cinnamylpiperazines and 2-benzylbenzimidazoles represent two of the most relevant subclasses. However, the data on their toxicity and metabolism are still limited. The aim of the present study was to evaluate the toxicity and metabolic pathways of some compounds belonging to these families, namely, AP-237, 2-methyl AP-237, isotonitazene, flunitazene, etodesnitazene, metonitazene, metodesnitazene, N-pyrrolidino etonitazene, and butonitazene. The study was performed using a zebrafish early life stages model. In fact, zebrafish (Danio rerio) embryos and larvae have recently been recognized as a suitable animal model in alternative to mammals, because they require less time and resources and do not need complex procedures for ethics approval. The cellular toxicity after a single administration was assessed at the fourth day post-fertilization with acridine orange staining. Possible morphological defects were evaluated with a light microscope after 24 h of exposure to 1 μmol/L concentration of each drug. Subsequently, the larvae were euthanized and underwent analysis of drug metabolites using UPLC coupled to an Orbitrap high-resolution mass spectrometer. High rates of morphological defects, as well as of cellular death, were detected, but no significant difference in mortality between treatment and control groups was observed. In addition, several metabolites, mainly produced through monohydroxylation, N-dealkylation, and O-dealkylation, were identified in the larvae extracts.

Metabolism of highly potent synthetic opioid nitazene analogs: N-ethyl-N-(1-glucuronyloxyethyl) metabolite formation and degradation to N-desethyl metabolites during enzymatic hydrolysis

The metabolism of the highly potent synthetic opioids metonitazene, etonitazene, and protonitazene was investigated in fresh human hepatocytes. In the hydrolyzed culture medium, N-desethyl-, N,N-di-desethyl-, O-desalkyl-, N-desethyl-O-desalkyl-, N,N-di-desethyl-O-desalkyl-, and N-oxidated metabolites were detected as phase I metabolites, whereas in the unhydrolyzed culture medium, O-glucuronides of phase I metabolites with O-dealkylation were detected as phase II metabolites. The detected phase I metabolites were identified by comparing their analytical data with those of synthesized authentic standards. In contrast, phase II metabolites were identified by comparing their analytical data with those of the glucuronidated products formed by the incubation of the corresponding substrates with human liver microsomes in the presence of uridine diphosphate glucuronic acid. In addition to the aforementioned metabolites, some putative N-ethyl-N-(1-glucuronyloxyethyl) metabolites were detected in the unhydrolyzed culture medium. Purification and hydrolysis experiments revealed that N-ethyl-N-(1-glucuronyloxyethyl) metabolites formed the corresponding N-desethyl metabolites via unstable N-ethyl-N-(1-hydroxyethyl) metabolites during enzymatic hydrolysis.

Pharmacologic Characterization of Substituted Nitazenes at μ, κ, and Δ Opioid Receptors Suggests High Potential for Toxicity

The benzimidazole opioids (substituted nitazenes) are highly potent μ opiod receptor (MOR) agonists with heroin- or fentanyl-like effects. These compounds have caused hospitalizations and fatal overdoses. We characterized the in vitro pharmacology and structure-activity relationships of 19 nitazenes with substitutions at three positions of the benzimidazole core. Affinities were assessed using agonist radioligand binding assays at human μ, κ, and Δ opioid receptors (MOR, KOR, and DOR, respectively) heterologously expressed in CHO cells. Notably, for MOR binding, nine substituted nitazenes had significantly higher affinities than fentanyl including N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, and N-desethyl isotonitazene; 13 had subnanomolar affinities. Only metodesnitazene and flunitazene had significantly lower affinities than fentanyl. Affinities for the substituted nitazenes at KOR and DOR relative to MOR were 46- to 2580-fold and 180- to 1280-fold lower, respectively. Functional activities were assessed using [35S]GTPγS binding assays. Four nitazenes had subnanomolar potencies at MOR: N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, N-pyrrilidino protonitazene and N-desethyl isotonitazene. Ten substituted nitazenes had significantly higher potencies than fentanyl. All tested nitazenes were full MOR agonists. Potencies at KOR and DOR relative to MOR were 7.3- to 7920-fold and 24- to 9400-fold lower, respectively. Thus, many of these compounds are high affinity/high potency MOR agonists with elevated potential to elicit toxicity and overdose at low doses. SIGNIFICANCE STATEMENT: Substituted nitazenes are a growing public health threat. Although the 19 nitazenes tested vary in their opioid receptor pharmacology, a number are very high affinity, high potency, and high efficacy compounds- higher than fentanyl. Their pharmacology suggests high potential for harm.

Wastewater-based monitoring of the nitazene analogues: First detection of protonitazene in wastewater

Synthetic opioids, particularly the nitazene analogues class, have become a public health concern due to their high potency. Wastewater-based epidemiology can detect community use of these compounds. The objective of this work was to detect nitazene analogues in wastewater from samples collected from eight sites in the United States. Influent wastewater samples were collected from eight sites in seven states (Arizona, Oregon, New Mexico, Illinois, New Jersey, Washington and Georgia) in the United States. Samples were collected from each site on three days between 27 December 2022 and 4 January 2023, acidified on collection, stored frozen and shipped to Arizona State University (Tempe, AZ) for sample processing. Samples were then shipped to The University of Queensland (Brisbane, Australia) for sample analysis. Protonitazene was found in samples collected from two sites in Washington and Illinois. The concentration was estimated up to 0.5 ng/L, with estimated excreted mass loads up to 0.3 mg/day/1000 people. This work has shown that it is possible to detect nitazene analogues in wastewater using a combination of sample pre-concentration and sensitive instrumentation, thereby further expanding the utility of wastewater-based epidemiology.

In Vitro Functional Profiling of Fentanyl and Nitazene Analogs at the μ-Opioid Receptor Reveals High Efficacy for Gi Protein Signaling

Novel synthetic opioids (NSOs), including both fentanyl and non-fentanyl analogs that act as μ-opioid receptor (MOR) agonists, are associated with serious intoxication and fatal overdose. Previous studies proposed that G-protein-biased MOR agonists are safer pain medications, while other evidence indicates that low intrinsic efficacy at MOR better explains the reduced opioid side effects. Here, we characterized the in vitro functional profiles of various NSOs at the MOR using adenylate cyclase inhibition and β-arrestin2 recruitment assays, in conjunction with the application of the receptor depletion approach. By fitting the concentration-response data to the operational model of agonism, we deduced the intrinsic efficacy and affinity for each opioid in the Gi protein signaling and β-arrestin2 recruitment pathways. Compared to the reference agonist [d-Ala2,N-MePhe4,Gly-ol5]enkephalin, we found that several fentanyl analogs were more efficacious at inhibiting cAMP production, whereas all fentanyl analogs were less efficacious at recruiting β-arrestin2. In contrast, the non-fentanyl 2-benzylbenzimidazole (i.e., nitazene) analogs were highly efficacious and potent in both the cAMP and β-arrestin2 assays. Our findings suggest that the high intrinsic efficacy of the NSOs in Gi protein signaling is a common property that may underlie their high risk of intoxication and overdose, highlighting the limitation of using in vitro functional bias to predict the adverse effects of opioids. In addition, the extremely high potency of many NSOs now infiltrating illicit drug markets further contributes to the danger posed to public health.

In Support of Community Drug Checking Programs: Position Statement of AMERSA, Inc. (Association for Multidisciplinary Education and Research in Substance use and Addiction)

BACKGROUND

Position statements clarify key issues that are in alignment with the vision, mission, and values of the AMERSA, Inc. (Association for Multidisciplinary Education and Research in Substance use and Addiction). This Position Statement, endorsed by the AMERSA Board of Directors on October 3, 2023, amplifies the position of the organization, guides their activities, and informs the public and policymakers on the organization's stance on this issue.

ISSUE

The unregulated drug supply in the United States evolves constantly, leaving those who use drugs potentially unaware of new adulterants in their drugs. Not knowing that information can leave people vulnerable to serious adverse events such as fatal overdoses, wounds, and other health consequences. Without real-time data on the composition of drugs available in a community, healthcare providers and public health practitioners are left with insufficient data, making it increasingly difficult to know how to best serve people who use drugs. In this context, community-based drug checking has become recognized as an important harm reduction strategy with the potential to provide those who use drugs with more information about their supply.

RECOMMENDATIONS

It is imperative to expand funding and increase access to drug checking programs in communities across the United States. Key policy changes, such as those related to decriminalizing drug and drug paraphernalia possession, are needed to increase the utilization of drug checking programs. Protection of persons who use drugs through harm reduction strategies, including drug checking programs needs to be widely available and accessible.

Alkoxy chain length governs the potency of 2-benzylbenzimidazole 'nitazene' opioids associated with human overdose

RATIONALE

Novel synthetic opioids (NSOs) are emerging in recreational drug markets worldwide. In particular, 2-benzylbenzimidazole 'nitazene' compounds are problematic NSOs associated with serious clinical consequences, including fatal respiratory depression. Evidence from in vitro studies shows that alkoxy chain length can influence the potency of nitazenes at the mu-opioid receptor (MOR). However, structure-activity relationships (SARs) of nitazenes for inducing opioid-like effects in animal models are not well understood compared to relevant opioids contributing to the ongoing opioid crisis (e.g., fentanyl).

OBJECTIVES

Here, we examined the in vitro and in vivo effects of nitazene analogues with varying alkoxy chain lengths (i.e., metonitazene, etonitazene, isotonitazene, protonitazene, and butonitazene) as compared to reference opioids (i.e., morphine and fentanyl).

METHODS AND RESULTS

Nitazene analogues displayed nanomolar affinities for MOR in rat brain membranes and picomolar potencies to activate MOR in transfected cells. All compounds induced opioid-like effects on locomotor activity, hot plate latency, and body temperature in male mice, and alkoxy chain length markedly influenced potency. Etonitazene, with an ethoxy chain, was the most potent analogue in MOR functional assays (EC50 = 30 pM, Emax = 103%) and across all in vivo endpoints (ED50 = 3-12 μg/kg). In vivo SARs revealed that ethoxy, isopropoxy, and propoxy chains engendered higher potencies than fentanyl, whereas methoxy and butoxy analogues were less potent. MOR functional potencies, but not MOR affinities, were positively correlated with in vivo potencies to induce opioid effects.

CONCLUSIONS

Overall, our data show that certain nitazene NSOs are more potent than fentanyl as MOR agonists in mice, highlighting concerns regarding the high potential for overdose in humans who are exposed to these compounds.

The in vitro functional profiles of fentanyl and nitazene analogs at the μ-opioid receptor - high efficacy is dangerous regardless of signaling bias

Novel synthetic opioids (NSOs), including both fentanyl and non-fentanyl analogs that act as the μ-opioid receptor (MOR) agonists, are associated with serious intoxication and fatal overdose. Previous studies proposed that G protein biased MOR agonists are safer pain medications, while other evidence indicates that low intrinsic efficacy at MOR better explains reduced opioid side effects. Here, we characterized the in vitro functional profiles of various NSOs at MOR using adenylate cyclase inhibition and β-arrestin2 recruitment assays, in conjunction with the application of the receptor depletion approach. By fitting the concentration-response data to the operational model of agonism, we deduced the intrinsic efficacy and affinity for each opioid in the Gi protein signaling and β-arrestin2 recruitment pathways. Compared to the reference agonist DAMGO, we found that several fentanyl analogs were more efficacious at inhibiting cAMP production, whereas all fentanyl analogs were less efficacious at recruiting β-arrestin2. In contrast, the non-fentanyl 2-benzylbenzimidazole (i.e., nitazene) analogs were highly efficacious and potent in both the cAMP and β-arrestin2 assays. Our findings suggest that the high intrinsic efficacy of the NSOs in Gi protein signaling is a common property that may underlie their high risk of intoxication and overdose, highlighting the limitation of using in vitro functional bias to predict the adverse effects of opioids. Instead, our results show that, regardless of bias, opioids with sufficiently high intrinsic efficacy can be lethal, especially given the extremely high potency of many of these compounds that are now pervading the illicit drug market.

Responding to changes in the unregulated drug supply: the need for a dynamic approach to drug checking technologies

Drug checking services provide individuals who use drugs with the ability to test samples of their drugs for the presence of highly potent substances. However, there has been recent concern about whether the existing repertoire of point-of-care drug checking technologies, such as immunoassay strips and Fourier-transform infrared spectroscopy (FTIR), are adequate in identifying substances in the unregulated drug supply. Carfentanil and nitazene opioids, substances that are even more potent than fentanyl in vitro, have been found in the unregulated supply in North America and pose a challenge to our existing drug checking strategy. For example, etizolam has recently permeated the unregulated drug supply in North America, and has demonstrated the ability to evade point-of-care drug checking technologies. In response to the incessantly changing nature of the unregulated supply, we argue that drug checking technologies and service delivery models must continuously adapt alongside constantly changing drug markets. We provide two examples of emerging technologies, paper spray-mass spectrometry and surface-enhanced Raman spectroscopy, which address many of the shortcomings of existing technologies. For both technologies, we discuss their feasibility, where they can be offered, their advantages, and how they address gaps in our existing technologies. We contend that these technologies, and other emerging technologies, can be integrated into a future approach to drug checking that flexibly uses different technologies and service delivery methods to adapt to changes in the drug supply.

Buprenorphine Dose and Time to Discontinuation Among Patients With Opioid Use Disorder in the Era of Fentanyl

Importance

Buprenorphine treatment for opioid use disorder (OUD) has more than doubled since 2009. However, current US Food and Drug Administration buprenorphine dosing guidelines are based on studies among people using heroin, prior to the emergence of fentanyl in the illicit drug supply.

Objective

To estimate the association between buprenorphine dose and time to treatment discontinuation during a period of widespread fentanyl availability.

Design, Setting, and Participants

This retrospective cohort study used statewide Rhode Island Prescription Drug Monitoring Program data. Participants were Rhode Island residents initiating buprenorphine treatment for OUD between October 1, 2016, and September 30, 2020. Data analysis was performed from December 9, 2022, to August 10, 2023.

Exposure

Daily dose of buprenorphine (16 mg and 24 mg) defined starting on the day of initiation based on total quantity and days' supply dispensed. Patients were censored on any dose change.

Main Outcomes and Measures

Buprenorphine treatment discontinuation in the 180 days following initiation, defined as a gap in treatment of more than 27 days based on prescription fill dates and days' supply. Kaplan-Meier and Cox regression survival analyses were conducted to estimate the association between buprenorphine dose and time to treatment discontinuation, controlling for potential informative censoring and measured potential confounders.

Results

Among 6499 patients initiating buprenorphine treatment for OUD, most were aged 25 to 44 years (57%; n = 3682), were male (61%; n = 3950), and had private (47%; n = 3025) or Medicaid (33%; n = 2153) insurance. More than half of patients were prescribed a daily dose of interest at initiation (16 mg: 50%; n = 3264; 24 mg: 10%; n = 668). In Kaplan-Meier analyses, 58% of patients discontinued buprenorphine treatment within 180 days (16 mg: 59% vs 24 mg: 53%; log-rank test P = .005). In Cox regression analyses, patients prescribed a dose of 16 mg had a greater risk of treatment discontinuation than those prescribed 24 mg (adjusted hazard ratio, 1.20; 95% CI, 1.06-1.37).

Conclusions and Relevance

In this cohort study of patients initiating buprenorphine treatment from 2016 to 2020, patients prescribed a 24 mg dose of buprenorphine remained in treatment longer than those prescribed 16 mg. The value of higher buprenorphine doses than currently recommended needs to be considered for improving retention in treatment.

Naloxone Use in Novel Potent Opioid and Fentanyl Overdoses in Emergency Department Patients

Importance

Synthetic opioids, such as the fentanyl analogue and nitazene drug class, are among the fastest growing types of opioids being detected in patients in the emergency department (ED) with illicit opioid overdose (OD). However, clinical outcomes from OD of novel potent opioids (NPOs), specifically nitazenes, are unknown aside from small case series.

Objective

To determine naloxone administration and clinical sequelae of patients who were in the ED with NPO overdose compared with fentanyl OD.

Design, Setting, and Participants

This is a cohort study subgroup analysis of adults admitted to the ED and tested positive for NPOs among in the ongoing nationwide ToxIC Fentalog cohort study from 2020 to 2022. Patients who were in the ED with a presumed acute opioid OD and residual blood samples were included, and those testing positive for NPOs were analyzed. Patients were included in this analysis if their confirmatory testing was positive for an NPO analyte, such as brorphine, isotonitazene, metonitazene, and/or N-piperidinyl etonitazene. A comparison group included patients that were positive for fentanyl and devoid of any other analytes on toxicologic analysis.

Exposures

Patients were exposed to NPOs, including brorphine, isotonitazene, metonitazene and/or N-piperidinyl etonitazene.

Main Outcomes and Measures

The primary outcome was the total number of naloxone doses and total cumulative naloxone dose administered as part of routine clinical care following the OD. Naloxone requirements and clinical sequelae of NPO-positive patients were compared with those testing positive for fentanyl only.

Results

During the study period, 2298 patients were screened, of whom 717 met inclusion criteria, 537 had complete laboratory testing data, with 11 (2.0%) positive for only fentanyl and 9 (1.7%) positive for NPOs (brorphine, isotonitazene, metonitazene, or N-piperidinyl etonitazene). The age range of patients was aged 20 to 57 years (4 males [44.4%] and 5 females [55.6%]). The NPO group received a statistically significantly higher mean (SD) number of naloxone boluses in-hospital (1.33 [1.50]) compared with the fentanyl group (0.36 [0.92]) (P = .02), which corresponded to a moderately large effect size (Cohen d = 0.78). Metonitazene overdose was associated with cardiac arrest and more naloxone doses overall. Metonitazene cases had a mean (SD) number of 3.0 (0) naloxone doses, and 2 of 2 patients (100%) with metonitazene overdoses were administered cardiopulmonary resuscitation.

Conclusions and Relevance

In this cohort study of patients admitted to the ED with confirmed opioid overdose testing positive for NPOs, in-hospital naloxone dosing was high compared with patients who tested positive for fentanyl alone. Further study is warranted to confirm these preliminary associations.

Non-fentanyl new synthetic opioids - An update

BACKGROUND

New synthetic opioids (NSO) constitute one of the fastest-growing group of New Psychoactive Substances, which emerged on the illicit drug marker in the second half of 2000's. The most popular and the largest NSO subgroup are high potency fentanyl and its analogs. Subsequent to core-structure scheduling of fentanyl-related substances many opioids with different chemical structures are now emerging on the illicit drug market, rendering the landscape highly complex and dynamic.

METHODS

PubMed, Scopus and Google Scholar were searched for appropriate articles up to December 2022. Moreover, a search for reports was conducted on Institutional websites to identify documentation published by World Health Organization, United Nations Office on Drugs and Crime, United States Drug Enforcement Administration, and European Monitoring Centre for Drugs and Drug Addiction. Only articles or reports written in English were selected.

RESULTS

Non-fentanyl derived synthetic opioids, i.e., 2-benzylbenzimidazoles (nitazenes), brorphine, U-compounds, AH-7921, MT-45 and related compounds are characterized, describing them in terms of available forms, pharmacology, metabolism as well as their toxic effects. Sample procedures and analytical techniques available for detection and quantification of these compounds in biological matrices are also presented. Finally, as overdoses involving highly potent NSO may be difficult to reverse, the effectiveness of naloxone as a rescue agent in NSO overdose is discussed.

CONCLUSIONS

Current review presents key information on non-fentanyl derived NSO. Access to upto-date data on substances of abuse is of great importance for clinicians, public health authorities and professionals performing analyses of biological samples.

Mu-opioid receptor selective superagonists produce prolonged respiratory depression

Synthetic opioids are increasingly challenging to combat the opioid epidemic and act primarily at opioid receptors, chiefly the G protein-coupled receptor (GPCR) μ-opioid receptor (MOR), which signals through G protein-dependent and β-arrestin pathways. Using a bioluminescence resonance energy transfer (BRET) system, we investigate GPCR-signaling profiles by synthetic nitazenes, which are known to cause overdose and death due to respiratory depression. We show that isotonitazene and its metabolite, N-desethyl isotonitazene, are very potent MOR-selective superagonists, surpassing both DAMGO G protein and β-arrestin recruitment activity, which are properties distinct from other conventional opioids. Both isotonitazene and N-desethyl isotonitazene show high potency in mouse analgesia tail-flick assays, but N-desethyl isotonitazene shows longer-lasting respiratory depression compared to fentanyl. Overall, our results suggest that potent MOR-selective superagonists may be a pharmacological property predictive of prolonged respiratory depression resulting in fatal consequences and should be examined for future opioid analgesics.

Quantification of the benzimidazole opioid analog isotonitazene in human hair using liquid chromatography-tandem mass spectrometry

Benzimidazole opioids were originally developed from the late 1950s to 1970s as analgesics for medical use, although a lot of them could not be approved as licit medicines because of their severe side effects and physical dependence. Such benzimidazole opioid analogs as abused drug, however, have recently been found in illicit drug markets throughout the world. Isotonitazene is one such benzimidazole opioids, whose analgesic potency can be as much as 500 times greater than that of morphine, according to previous animal studies. In line with this potency, a couple of hundred fatalities related to it were reported to date. In this study, a well validated method for the quantification of isotonitazene in human hair samples using liquid chromatography (LC)-tandem mass spectrometry (MS/MS) was established, and could be applied to authentic samples which were seized by the police security bureau. Isotonitazene concentrations in the seized hair averaged 6.11 pg/mg. The LLOQ and LOD of this method were 1.25 and 2.5 pg/mg, respectively; the calibration curve of the substance in hair samples showed a good linearity in the concentration range of 2.5-250 pg/mg (r > 0.999); the extraction recovery rates were 87.3-105% in the tested range; the inter- and intra-day precisions and accuracies (%biases) were not greater than 9.09% for each determination. Isotonitazene in human hair showed good stability at room temperature and under dark storage conditions for 30 days. As for matrix effect in hair samples, moderate ion suppression of target substances could be found. This is the first report for the analysis of isotonitazene in human hair samples.

Evaluation of fentanyl immunoassay test strips for rapid in-situ detection of fentanyl and fentanyl analogs in seized samples and alternative matrices

BACKGROUND

Ion mobility spectrometry is used for the rapid detection of drugs at points of security but are unable to differentiate some drugs leading to the instrument alarming for a drug not present in the sample. This can be particularly problematic for samples that alarm for fentanyl. In this study, fentanyl immunoassay strips were evaluated for use as a secondary test for fentanyl, including for the testing of alternative matrices, such as powders, e-liquids, and infused papers and textiles.

METHODS

The limit of detection of fentanyl immunoassay strips was examined along with their selectivity to 18 fentanyl analogsand 72 other drugs and cutting agents. The effectiveness of the test strips at the detection of fentanyl in the presence of other drugs was examined by testing a series of concentrations of fentanyl in solution in combination with other drugs. The testing of alternative matrices was explored with laboratory prepared samples through sampling with cotton buds and extraction in water.

RESULTS

The fentanyl immunoassay strips detected fentanyl at concentrations of 45 ng/mL and reacted with 16 of 18 tested fentanyl analogs with carfentanil and norfentanyl being the only analogs to not react. There was no reactivity with other drugs or cutting agents. The effectiveness of the fentanyl test strips was not reduced when fentanyl was mixed with other drugs. Fentanyl was successfully detected with high sensitivity in all alternative matrices.

CONCLUSION

The fentanyl immunoassay strips were found to be an effective secondary test for fentanyl and at least 16 fentanyl analogs in seized drug samples, including when mixed with other drugs. The effectiveness of the sampling methods for alternative matrices should be further evaluated using fentanyl and fentanyl analog casework samples. The use of this method by law enforcement and other agencies should be examined to assess its effectiveness and ease of use in operational settings.

Old Drugs and New Challenges: A Narrative Review of Nitazenes

Nitazenes are a group of compounds developed in the 1950s as opioid analgesics, but they were never approved to market. As such, they are not well known outside of academic research laboratories. A characteristic of nitazenes is their high potency (e.g., hundreds to thousands fold more potent than morphine and other opioids and tenfold more potent than fentanyl). In the past few years, several nitazenes, including "designer analogs," have been detected in the illicit drug supply and have been implicated in overdose mortality, primarily due to their exceptionally high potency. In the street drug supply, nitazenes are often found mixed with fentanyl or other agents but their presence is not always disclosed to drug buyers, who may not even be familiar with nitazenes. These drugs pose a particular challenge since there is little experience in how to reverse a nitazene overdose or potential drug-drug or drug-alcohol interactions. Public health efforts are needed to better inform street drug consumers, first responders, healthcare professionals, and the general public about these "new old drugs" that are infiltrating the recreational drug supply.

Comparative neuropharmacology of structurally distinct non-fentanyl opioids that are appearing on recreational drug markets worldwide

BACKGROUND

The emergence of novel synthetic opioids (NSOs) is contributing to the opioid overdose crisis. While fentanyl analogs have historically dominated the NSO market, a shift towards non-fentanyl compounds is now occurring.

METHODS

Here, we examined the neuropharmacology of structurally distinct non-fentanyl NSOs, including U-47700, isotonitazene, brorphine, and N-desethyl isotonitazene, as compared to morphine and fentanyl. Compounds were tested in vitro using opioid receptor binding assays in rat brain tissue and by monitoring forskolin-stimulated cAMP accumulation in cells expressing the human mu-opioid receptor (MOR). Compounds were administered subcutaneously to male Sprague-Dawley rats, and hot plate antinociception, catalepsy score, and body temperature changes were measured.

RESULTS

Receptor binding results revealed high MOR selectivity for all compounds, with MOR affinities comparable to those of morphine and fentanyl (i.e., nM). All drugs acted as full-efficacy MOR agonists in the cyclic AMP assay, but nitazene analogs had greater functional potencies (i.e., pM) compared to the other drugs (i.e., nM). When administered to rats, all compounds induced opioid-like antinociception, catalepsy, and body temperature changes, but nitazenes were the most potent. Similar to fentanyl, the nitazenes had faster onset and decline of in vivo effects when compared to morphine. In vivo potencies to induce antinociception and catalepsy (i.e., ED₅₀s) correlated with in vitro functional potencies (i.e., EC₅₀s) but not binding affinities (i.e., K_is) at MOR.

CONCLUSIONS

Collectively, our findings indicate that non-fentanyl NSOs pose grave danger to those individuals who use opioids. Continued vigilance is needed to identify and characterize synthetic opioids as they emerge in clandestine drug markets.

Detection, chemical analysis, and pharmacological characterization of dipyanone and other new synthetic opioids related to prescription drugs

The emergence of structurally diverse new synthetic opioids (NSOs) has caused the opioid crisis to spiral to new depths. Little information is available about the pharmacology of most novel opioids when they first emerge. Here, using a β-arrestin 2 recruitment assay, we investigated the in vitro μ-opioid receptor (MOR) activation potential of dipyanone, desmethylmoramide, and acetoxymethylketobemidone (O-AMKD) - recent NSOs that are structurally related to the prescription opioids methadone and ketobemidone. Our findings indicate that dipyanone (EC₅₀=39.9 nM; E_max=155% vs. hydromorphone) is about equally active as methadone (EC₅₀=50.3 nM; E_max=152%), whereas desmethylmoramide (EC₅₀=1335 nM; E_max=126%) is considerably less active. A close structural analogue of ketobemidone (EC₅₀=134 nM; E_max=156%) and methylketobemidone (EC₅₀=335 nM; E_max=117%), O-AMKD showed a lower potency (EC₅₀=1262 nM) and efficacy (E_max=109%). Evaluation of the opioid substitution product buprenorphine and its metabolite norbuprenorphine confirmed the increased in vitro efficacy of the latter. In addition to in vitro characterization, this report details the first identification and full chemical analysis of dipyanone in a seized powder, as well as a postmortem toxicology case from the USA involving the drug. Dipyanone was quantified in blood (370 ng/mL), in which it was detected alongside other NSOs (e.g., 2-methyl AP-237) and novel benzodiazepines (e.g., flualprazolam). While dipyanone is currently not commonly encountered in forensic samples worldwide, its emergence is worrisome and representative of the dynamic NSO market. Graphical Abstract.

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.

Intoxications in an Australian Emergency Department Involving 'Nitazene' Benzylbenzimidazole Synthetic Opioids (Etodesnitazene, Butonitazene and Protonitazene)

Benzimidazole synthetic opioids are highly potent μ-opioid receptor agonists with heroin-like effects, including dose-dependent respiratory depression and a high risk of abuse and toxicity. Benzimidazoles were first detected in 2019 in Europe and Canada, with analytical confirmation of etodesnitazene, protonitazene and butonitazene in 2021. We report the first detections of these compounds in Australia, in two patients presenting with drug toxicity to Emergency Departments (EDs) in the state of Victoria. Case 1 was a female in her 20s who rectally administered etodesnitazene and was found unconscious with respiratory depression and hypotension. Case 2 was a female in her 30s who presented to the ED in a sedated state after taking a formulation of protonitazene that also contained butonitazene, in addition to methylamphetamine. She responded positively to naloxone. Novel synthetic opioids were used with prior experience of the formulations purchased; however, the unpredictability of their effects was demonstrated by the acute toxicity experienced with this occasion of use. Toxicosurveillance of ED presentations with analytical confirmation of drugs is crucial in identifying emerging drugs in the community and informing harm reduction strategies.

New Psychoactive Substances Intoxications and Fatalities during the COVID-19 Epidemic

In January 2020, the World Health Organization (WHO) issued a Public Health Emergency of International Concern, declaring the COVID-19 outbreak a pandemic in March 2020. Stringent measures decreased consumption of some drugs, moving the illicit market to alternative substances, such as New Psychoactive Substances (NPS). A systematic literature search was performed, using scientific databases such as PubMed, Scopus, Web of Science and institutional and government websites, to identify reported intoxications and fatalities from NPS during the COVID-19 pandemic. The search terms were: COVID-19, SARS-CoV-2, severe acute respiratory syndrome coronavirus 2, coronavirus disease 2019, intox*, fatal*, new psychoactive substance, novel psychoactive substance, smart drugs, new psychoactive substance, novel synthetic opioid, synthetic opioid, synthetic cathinone, bath salts, legal highs, nitazene, bath salt, legal high, synthetic cannabinoid, phenethylamine, phencyclidine, piperazine, novel benzodiazepine, benzodiazepine analogue, designer benzodiazepines, tryptamine and psychostimulant. From January 2020 to March 2022, 215 NPS exposures were reported in Europe, UK, Japan and USA. Single NPS class intoxications accounted for 25, while mixed NPS class intoxications represented only 3 cases. A total of 130 NPS single class fatalities and 56 fatalities involving mixed NPS classes were published during the pandemic. Synthetic opioids were the NPS class most abused, followed by synthetic cathinones and synthetic cannabinoids. Notably, designer benzodiazepines were frequently found in combination with fentalogues. Considering the stress to communities and healthcare systems generated by the pandemic, NPS-related information may be underestimated. However, we could not define the exact impacts of COVID-19 on processing of toxicological data, autopsy and death investigations.

New Psychoactive Substances: Major Groups, Laboratory Testing Challenges, Public Health Concerns, and Community-Based Solutions

Across communities worldwide, various new psychoactive substances (NPSs) continue to emerge, which worsens the challenges to global mental health, drug rules, and public health risks, as well as combats their usage. Specifically, the vast number of NPSs that are currently available, coupled with the rate at which new ones emerge worldwide, increasingly challenges both forensic and clinical testing strategies. The well-established NPS detection techniques include immunoassays, colorimetric tests, mass spectrometric techniques, chromatographic techniques, and hyphenated types. Nonetheless, mitigating drug abuse and NPS usage is achievable through extensive community-based initiatives, with increased focus on harm reduction. Clinically validated and reliable testing of NPS from human samples, along with community-driven solution, such as harm reduction, will be of great importance, especially in combating their prevalence and the use of other illicit synthetic substances. There is a need for continued literature synthesis to reiterate the importance of NPS, given the continuous emergence of illicit substances in the recent years. All these are discussed in this overview, as we performed another look into NPS, from differentiating the major groups and identifying with laboratory testing challenges to community-based initiatives.

Identification of etazene (etodesnitazene) metabolites in human urine by LC-HRMS

Etazene (or etodesnitazene) is a novel and highly active synthetic opioid belonging to the rapidly evolving and emerging group of "nitazenes." Etazene metabolites were identified through analysis of a human urine sample. The sample was obtained from a 25-year-old man who attempted suicide by taking a new psychoactive substances (NPS) cocktail purchased online and was analyzed by ultrahigh performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). Etazene metabolites were predicted with BioTransformer 3.0, and the exact masses were added to the inclusion list. Eight possible metabolites were identified in the urine sample. N- and O-deethylation were identified as the predominant metabolism routes, resulting in M1 (O-deethylated etazene; most abundant metabolite based on the peak area), M2 (N-deethylated etazene), and M3 (N,O-dideethylated etazene) metabolites. Less abundant hydroxylated products of these deethylated metabolites and etazene were also found. Additionally, in the analysis without β-glucuronidase treatment, M1- and M3-glucuronide phase II metabolites were found. As N- and O-deethylated products seem to be the predominant urinary metabolites, the detection of these metabolites in urine can be useful to demonstrate etazene exposure.

Heteroaromatic Diazirines Are Essential Building Blocks for Material and Medicinal Chemistry

In materials (polymer) science and medicinal chemistry, heteroaromatic derivatives play the role of the central skeleton in development of novel devices and discovery of new drugs. On the other hand, (3-trifluoromethyl)phenyldiazirine (TPD) is a crucial chemical method for understanding biological processes such as ligand-receptor, nucleic acid-protein, lipid-protein, and protein-protein interactions. In particular, use of TPD has increased in recent materials science to create novel electric and polymer devices with comparative ease and reduced costs. Therefore, a combination of heteroaromatics and (3-trifluoromethyl)diazirine is a promising option for creating better materials and elucidating the unknown mechanisms of action of bioactive heteroaromatic compounds. In this review, a comprehensive synthesis of (3-trifluoromethyl)diazirine-substituted heteroaromatics is described.

Tentative Identification of Etazene (Etodesnitazene) Metabolites in Rat Serum and Urine by Gas Chromatography-Mass Spectrometry and Accurate Mass Liquid Chromatography-Mass Spectrometry

2-Benzylbenzimidazole derivatives comprise a small but forensically significant group of synthetic opioids. In humans, the metabolism of some members of this group is extensive, with little or none of the parent compound remaining. The recent detection of the 2-benzylbenzimidazole derivative, etazene (etodesnitazene), in products seized in Russia required the detection of its metabolites in biofluids for forensic toxicology purposes. Using gas chromatography--mass spectrometry (GC-MS) and high resolution accurate mass (HRAM) liquid chromatography-mass spectrometry (LC-MS), eight etazene metabolites were found in the urine and serum of rats. These were tentatively identified as products of N-deethylation, O-deethylation, hydroxylation or N-oxidation of benzimidazole moiety and combinations of these processes. The parent substance and its O-deethylated metabolite prevailed in rat serum, while in urine, the level of etazene was low compared to N,O-deethylated and N-deethylated with hydroxylation metabolites. Glucuronidated, sulfonated and glutathionated forms were not found. Taking into account reports on the study of the metabolism of other 2-benzylbenzimidazole derivatives in humans, it may be concluded that the mono-deethylated and mono-hydroxylated metabolites are suitable as target analytes in urine.

Rapid screening of 2-benzylbenzimidazole nitazene analogs in suspect counterfeit tablets using Raman, SERS, DART-TD-MS, and FT-IR

Developing methods to rapidly screen for novel synthetic 2-benzylbenzimidazole opioids, also known as nitazenes, has become increasingly important due to their high potency. These compounds have potency comparable or exceeding that of fentanyl by up to 10 times and have been implicated in approximately 5% of all drug overdose deaths in the United States in 2021. This paper details the authenticity determination of suspect tablets and the identification of three nitazene analogs (N-pyrrolidino etonitazene, isotonitazene, and etodesnitazene) in suspect tablets seized at a mail facility using Raman and surface-enhanced Raman scattering (SERS) with handheld devices, portable Fourier transform infrared spectrometer (FT-IR), and a direct analysis in real-time ambient ionization coupled to a thermal desorption unit and a mass spectrometer (DART-TD-MS). These methods are rapid and excellent for screening opioids in suspect tablets but could not fully determine the exact structure of some of the nitazene analogs present due to spectral similarities or similar fragmentation patterns. Liquid chromatography-mass spectrometry (LC-MS) confirmed the presence of these nitazene compounds in addition to other opioids/drugs that were in trace quantities. The quantitative high-performance liquid chromatography coupled with ultraviolet (HPLC-UV) detection experiments determined that the suspect tablets contained an average of 0.817 mg of N-pyrrolidino etonitazene per tablet. The results obtained reveal that the simultaneous deployment of these complementary and orthogonal portable analytical techniques as part of a workflow allows suspect tablets to be screened and nitazene-type drugs to be identified in suspect counterfeit tablets at remote sampling sites.

Plasma pharmacokinetics and pharmacodynamic effects of the 2-benzylbenzimidazole synthetic opioid, isotonitazene, in male rats

RATIONALE

Isotonitazene is an illicit synthetic opioid associated with many intoxications and fatalities. Recent studies show that isotonitazene is a potent µ-opioid receptor (MOR) agonist in vitro, but little information is available about its in vivo effects.

OBJECTIVES

The aims of the present study were to investigate the pharmacokinetics of isotonitazene in rats, and relate pharmacokinetic parameters to pharmacodynamic effects.

METHODS

Isotonitazene and its metabolites were identified and quantified by liquid chromatography tandem quadrupole mass spectrometry (LC-QQQ-MS). Male Sprague-Dawley rats with jugular catheters and subcutaneous (s.c.) temperature transponders received isotonitazene (3, 10, 30 µg/kg, s.c.) or its vehicle. Blood samples were drawn at 15, 30, 60, 120, and 240 min post-injection, and plasma was assayed using LC-QQQ-MS. At each blood draw, body temperature, catalepsy scores, and hot plate latencies were recorded.

RESULTS

Maximum plasma concentrations of isotonitazene rose in parallel with increasing dose (range 0.2-9.8 ng/mL) and half-life ranged from 23.4 to 63.3 min. The metabolites 4'-hydroxy nitazene and N-desethyl isotonitazene were detected, and plasma concentrations were below the limit of quantitation (0.5 ng/mL) but above the limit of detection (0.1 ng/mL). Isotonitazene produced antinociception (ED₅₀ = 4.22 µg/kg), catalepsy-like symptoms (ED₅₀ = 8.68 µg/kg), and hypothermia (only at 30 µg/kg) that were significantly correlated with concentrations of isotonitazene. Radioligand binding in rat brain tissue revealed that isotonitazene displays nM affinity for MOR (Ki = 15.8 nM), while the N-desethyl metabolite shows even greater affinity (Ki = 2.2 nM).

CONCLUSIONS

In summary, isotonitazene is a potent MOR agonist whose pharmacodynamic effects are related to circulating concentrations of the parent drug. The high potency of isotonitazene portends substantial risk to users who are exposed to the drug.

Proliferation of Novel Synthetic Opioids in Postmortem Investigations After Core-Structure Scheduling for Fentanyl-Related Substances

ABSTRACT

New generations of novel synthetic opioids (NSOs) have emerged to fill a void in the illicit drug markets left by the decline in popularity of fentanyl analogs subsequent to core-structure scheduling of fentanyl-related substances in the United States and China. These new opioids include members of the 2-benzyl benzimidazole (eg, isotonitazene, metonitazene, N -pyrrolidino etonitazene, protonitazene, etodesnitazene), benzimidazolone (eg, brorphine), and cinnamylpiperazine (eg, AP-238, 2-methyl AP-237) subclasses. Novel synthetic opioids continue to be detected in opioid-related fatal overdoses, demonstrating the harms associated with exposure to these drugs. Between January 2020 and December 2021, 384 casework blood samples were reported by our laboratory to contain 1 or more of the prior listed 8 NSOs. Isotonitazene (n = 144), metonitazene (n = 122), and brorphine (n = 91) were the 3 most prevalent substances, with positivity for isotonitazene and brorphine peaking just before the announcement of emergency scheduling. These NSOs have been documented as significant drivers of drug mortality, and this case series described here highlights the challenges medical examiners and coroners face in staying current with emerging drugs. Challenges include regional differences, rapid turnover, short lifecycles, variable toxicology testing, and difficulty in assessing individual drug toxicity in polydrug cases.

Pharmacological characterization of novel synthetic opioids: Isotonitazene, metonitazene, and piperidylthiambutene as potent MU opioid receptor agonists

Recent trends of opioid abuse and related fatalities have highlighted the critical role of Novel Synthetic Opioids (NSOs). We studied the μ-opioid-like properties of isotonitazene (ITZ), metonitazene (MTZ), and piperidylthiambutene (PTB) using different approaches. In vitro studies showed that ITZ and MTZ displayed a higher potency in both rat membrane homogenates (EC₅₀: 0.99 and 19.1 nM, respectively) and CHO-MOR (EC₅₀: 0.71 and 10.0 nM, respectively) than [D-Ala², NMe-Phe⁴, Gly-ol⁵]-enkephalin (DAMGO), with no difference in maximal efficacy (Emax) between DAMGO and NSOs. ITZ also has higher affinity (Ki: 0.06 and 0.05 nM) at the MOR than DAMGO in both systems, whilst MTZ has higher affinity in CHO-MOR (Ki = 0.23 nM) and similar affinity in rat cerebral cortex (Ki = 0.22 nM). PTB showed lower affinity and potency than DAMGO. In vivo, ITZ displayed higher analgesic potency than fentanyl and morphine (ED₅₀: 0.00156, 0.00578, 2.35 mg/kg iv, respectively); ITZ (0.01 mg/kg iv) and MTZ (0.03 mg/kg iv) reduced behavioral activity and increased dialysate dopamine (DA) in the NAc shell (max. about 200% and 170% over basal value, respectively. Notably, ITZ elicited an increase in DA comparable to that of higher dose of morphine (1 mg/kg iv), but higher than the same dose of fentanyl (0.01 mg/kg iv). In silico, induced fit docking (IFD) and metadynamic simulations (MTD) showed that binding modes and structural changes at the receptor, ligand stability, and the overall energy score of NSOs were consistent with the results of the biological assays.

Designer Benzodiazepines' Activity on Opioid Receptors: A Docking Study

BACKGROUND

Previous studies have reported that benzodiazepines (BZDs) seem to enhance euphoric and reinforcing properties of opioids in opioid users so that a direct effect on opioid receptors has been postulated, together with a possible synergistic induction of severe side effects due to co use of BDZs and opioids. This is particularly worrisome given the appearance on the market of designer benzodiazepines (DBZDs), whose activity/toxicity profiles are scarcely known.

OBJECTIVES

This study aimed to evaluate, through computational studies, the binding affinity (or lack thereof) of 101 DBZDs identified online on the kappa, mu, and delta opioid receptors (K, M, DOR); and to assess whether their mechanism of action could include activation of the latter.

METHODS

MOE® was used for the computational studies. Pharmacophore mapping based on strong opioids agonist binders' 3D chemical features was used to filter the DBZDs. Resultant DBZDs were docked into the crystallised 3D active conformation of KOR (PDB6B73), DOR (PDB6PT3) and MOR (PDB5C1M). Co-crystallised ligands and four strong agonists were used as reference compounds. A score (S, Kcal/mol) representative of the predicted binding affinity, and a description of ligand interactions were obtained from MOE®.

RESULTS

The docking results, filtered for S < -8.0 and the interaction with the Asp residue, identified five DBZDs as putative binders of the three ORs : ciclotizolam, fluloprazolam, JQ1, Ro 48-6791, and Ro 48-8684.

CONCLUSION

It may be inferred that at least some DBZDs may have the potential to activate opioid receptors. This could mediate/increase their anxiolytic, analgesic, and addiction potentials, as well as worsen the side effects associated with opioid co-use.

Identification of a novel opioid, N-piperidinyl etonitazene (etonitazepipne), in patients with suspected opioid overdose

BACKGROUND

Novel opioids in the illicit drug supply, such as the "nitazene" group of synthetic opioids, present an ongoing public health problem due to high potency and respiratory depressant effects. We describe three patients in whom N-piperidinyl etonitazene, a compound not previously reported in human exposure, was detected after suspected opioid overdose. Other substances that these patients tested for included fentanyl, cocaine, levamisole, phenacetin, benzoylecgonine, para-fluorofentanyl, presumptive heroin (tested as 6-monoacetylmorphine (6-MAM), morphine, and codeine), and tramadol.

METHODS

This is a case series of patients with acute opioid overdose enrolled in an ongoing multicenter prospective cohort study. Data collected included reported substance use, clinical course, naloxone dose and response, outcome, and analytes detected in biological samples.

RESULTS

Between October 6, 2020 and October 31, 2021, 1006 patients were screened and 412 met inclusion criteria. Of these, three patients (age 33-55) tested positive for N-piperidinyl etonitazene at one site in New Jersey over a period of three days in July 2021. Two patients reported the use of cocaine; one reported the use of heroin and alprazolam. All three patients received naloxone with improvement in their mental status (2 milligrams (mg) intranasally (IN); 8 mg IN; 0.08 mg intravenous (IV)). Two of three received subsequent doses for recurrence of opioid toxicity (0.4-0.6 mg IV). One patient was diagnosed with pneumonia and admitted to the intensive care unit, one was discharged from the Emergency Department (ED), and one used additional drug while in the ED and required admission for a naloxone infusion. None developed organ damage or sequelae.

CONCLUSION

These cases represent a local outbreak of a novel "nitazene" opioid. Public health toxicosurveillance should incorporate routine testing of this emerging class of synthetic compounds in the illicit drug supply.

Acute Intoxications and Fatalities Associated With Benzimidazole Opioid (Nitazene Analog) Use: A Systematic Review

BACKGROUND

Synthetic benzimidazole opioids (BOs) are highly potent µ-opioid receptor agonists with heroin-like effects. Isotonitazene was first available in 2019 in the drug market, although new analogs have multiplied recently. The authors aimed to identify BO use trends and gather toxicological data from BO-related cases to assist in clinical and forensic investigations.

METHODS

A systematic literature search was conducted according to the PRISMA guidelines. PubMed and Scopus databases were accessed in October 2021 to identify scientific reports of BO-related intoxication and fatalities. Publication dates, case descriptions, symptoms, autopsy findings, and concentrations of BOs and metabolites in biological matrices were compiled.

RESULTS

Data from 8 case reports with 93 fatalities involving isotonitazene ( n = 65), metonitazene ( n = 20), etonitazepyne ( N -pyrrolidino etonitazene) ( n = 8), flunitazene ( n = 4), and/or butonitazene ( n = 1), and 1 acute intoxication involving etonitazepyne were collected. Autopsy findings included pulmonary congestion/high lung weight (66%), cardiomegaly/high cardiac weight (39%), cerebral edema (22%), gastric contents in the airways (22%), and organ congestion (22%). Median peripheral blood concentrations were 1.7 ng/mL for isotonitazene (0.4-9.5 ng/mL, n = 13), 5.4 ng/mL for metonitazene (0.52-33 ng/mL, n = 17), 5.4 ng/mL for etonitazepyne (2.4-8.3 ng/mL, n = 2), 1.3 ng/mL for flunitazene (0.58-2.1 ng/mL, n = 2), and 3.2 ng/mL for butonitazene ( n = 1). Central nervous system depressants were almost always coadministered.

CONCLUSIONS

Isotonitazene was predominant in cases from 2019 to mid-2020 and was replaced by metonitazene after scheduling in the United States. Typical findings on opioid overdoses have been reported. Peripheral blood concentrations were consistent with a potency similar to that of fentanyl. These results must be interpreted carefully, considering the scarcity of reports on BO-related cases and drug co-exposures.

Development of a non-radioactive mass spectrometry-based binding assay at the μ-opioid receptor and its application for the determination of the binding affinities of 17 opiates/opioids as well as of the designer opioid isotonitazene and five further 2-benzylbenzimidazoles

Radioactive ligand binding assays are the most commonly applied method for the determination of binding affinities of compounds at a particular receptor. While they are highly sensitive and high-throughput capable they come with major disadvantages due to the radioactive ligands utilized. Here we present the development of a mass-spectrometry-based binding assay for the determination of binding affinities at the human μ-opioid receptor using non-labelled DAMGO ([D-Ala², N-MePhe⁴, Gly⁵-ol]-enkephalin). The runtime of the LC-MS/MS method was 5.5 min per data point and allowed for the highly sensitive detection of 38.5 fg DAMGO on column. The assay shows low non-specific binding and the equilibrium dissociation constant of DAMGO was 0.57 nM. The assay was applied to determine the K_i values of 17 opiates/opioids and the results were in good agreement with the data from radioactive receptor binding assays published in the literature. Additionally, the K_i value of six 2-benzylbenzimidazoles, including the widely abused designer opioid isotonitazene, were determined ranging from 0.654 to 72.9 nM. Consequently, the developed assay provides a suitable alternative to radioactive binding assays as it allows for a reliable and rapid determination of receptor binding affinities of e.g. newly emerging designer opioids.

Identification of the synthetic cannabinoid-type new psychoactive substance, CH-PIACA, in seized material

Synthetic cannabinoids (SCs) remain the largest class of new psychoactive substances (NPS), and while the number of NPS that are reported to the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) for the first time each year declines, the number of newly reported SCs still exceeds other NPS classes. This decline can be seen as a result of legislative changes by different jurisdictions which have sometimes transitioned to a more generalized approach when controlling substances by defining common structural scaffolds rather than explicit structures. While the consequences of such legislative changes have been expected over the years, the introduction of so‐called “class‐wide” bans puts further pressure on clandestine laboratories to synthesize compounds which are out of the scope of the legislation, and thus, these compounds are initially harder to detect and/or identify in the absence of analytical data. Recently, a SC with an indole‐3‐acetamide core‐linker scaffold, AD‐18 (i.e., ADB‐FUBIATA or ADB‐FUBIACA), was reported for the first time in China in 2021. Here, an additional cannabinoid with the indole‐3‐acetamide scaffold, N‐cyclohexyl‐2‐(1‐pentyl‐1H‐indol‐3‐yl)acetamide (CH‐PIACA), is reported which was identified for the first time in a seized material in Denmark. Structural characterization was performed using gas chromatography–mass spectrometry (GC–MS), liquid chromatography‐high‐resolution mass spectrometry (LC‐HRMS), and nuclear magnetic resonance (NMR) spectroscopy.

Cannabinoid receptor activation potential of the next generation, generic ban evading OXIZID synthetic cannabinoid receptor agonists

In recent years, several nations have implemented various measures to control the surge of new synthetic cannabinoid receptor agonists (SCRAs) entering the recreational drug market. In July 2021, China put into effect a new generic legislation, banning SCRAs containing one of 7 general core scaffolds. However, this has driven manufacturers towards the synthesis of SCRAs with alternative core structures, exemplified by the recent emergence of "OXIZID SCRAs". Here, using in vitro β-arrestin2 recruitment assays, we report on the CB₁ and CB₂ potency and efficacy of five members of this new class of SCRAs: BZO-HEXOXIZID, BZO-POXIZID, 5-fluoro BZO-POXIZID, BZO-4en-POXIZID and BZO-CHMOXIZID. All compounds behaved as full agonists at CB₁ and partial agonists at CB₂ . Potencies ranged from 84.6 - 721 nM at CB₁ and 2.21 - 25.9 nM at CB₂ . Shortening the n-hexyl tail to a pentyl tail enhanced activity at both receptors. Fluorination of this pentyl analog did not yield a higher receptor activation potential, whereas an unsaturated tail resulted in decreased potency and efficacy at CB₁ . The cyclohexyl methyl analog BZO-CHMOXIZID was the most potent compound at both receptors, with EC₅₀ values of 84.6 and 2.21 nM at CB₁ and CB₂ , respectively. Evaluation of the activity of a seized powder containing BZO-4en-POXIZID suggested a high purity, in line with HPLC-DAD, GC-MS, LC-QTOF-MS and FTIR and NMR analysis. Furthermore, all tested compounds showed a preference for CB₂ , except for BZO-POXIZID. Overall, these findings inform public health officials, law enforcement agencies and clinicians on these newly emerging SCRAs.

Pharmacological evaluation and forensic case series of N-pyrrolidino etonitazene (etonitazepyne), a newly emerging 2-benzylbenzimidazole 'nitazene' synthetic opioid

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 μ-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 δ-opioid (Ki = 959 nM) and κ-opioid (Ki = 980 nM) receptors. In a MOR-β-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 tenfold 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 2-benzylbenzimidazoles, and other non-fentanyl opioids, as they appear in the marketplace.

Reports of Adverse Events Associated with Use of Novel Psychoactive Substances, 2017-2020: A Review

An important role of modern forensic and clinical toxicologists is to monitor the adverse events of novel psychoactive substances (NPS). Following a prior review from 2013 to 2016, this critical literature review analyzes and evaluates published case reports for NPS from January 2017 through December 2020. The primary objective of this study is to assist in the assessment and interpretation of these cases as well as provide references for confirmation methods. Chemistry, pharmacology, adverse events and user profiles (e.g., polypharmacy) for NPS are provided including case history, clinical symptoms, autopsy findings and analytical results. Literature reviews were performed in PubMed and Google Scholar for publications using search terms such as NPS specific names, general terms (e.g., ‘designer drugs’ and ‘novel psychoactive substances’), drug classes (e.g., ‘designer stimulants’) and outcome-based terms (e.g., ‘overdose’ and ‘death’). Government and website drug surveillance databases and abstracts published by professional forensic science organizations were also searched. Toxicological data and detailed case information were extracted, tabulated, analyzed and organized by drug category. Case reports included overdose fatalities (378 cases), clinical treatment and hospitalization (771 cases) and driving under the influence of drugs (170 cases) for a total of 1,319 cases providing details of adverse events associated with NPS. Confirmed adverse events with associated toxidromes of more than 60 NPS were reported including synthetic cannabinoid, NPS stimulant, NPS hallucinogen, NPS benzodiazepine and NPS opioid cases. Fifty of these NPS were reported for the first time in January 2017 through December 2020 as compared to the previous 4 years surveyed. This study provides insight and context of case findings described in the literature and in digital government surveillance databases and websites during a recent 4-year period. This review will increase the awareness of adverse events associated with NPS use to better characterize international emerging drug threats.

First identification, chemical analysis and pharmacological characterization of N-piperidinyl etonitazene (etonitazepipne), a recent addition to the 2-benzylbenzimidazole opioid subclass

N-Piperidinyl etonitazene ('etonitazepipne') represents a recent addition to the rapidly expanding class of 2-benzylbenzimidazole 'nitazene' opioids. Following its first identification in an online-sourced powder and in biological samples from a patient seeking help for detoxification, this report details its in-depth chemical analysis and pharmacological characterization. Analysis of the powder via different techniques (LC-HRMS, GC-MS, UHPLC-DAD, FT-IR) led to the unequivocal identification of N-piperidinyl etonitazene. Furthermore, we report the first activity-based detection and analytical identification of N-piperidinyl etonitazene in authentic samples. LC-HRMS analysis revealed concentrations of 1.21 ng/mL in serum and 0.51 ng/mL in urine, whereas molecular networking enabled the tentative identification of various (potentially active) urinary metabolites. In addition, we determined that the extent of opioid activity present in the patient's serum was equivalent to the in vitro opioid activity exerted by 2.5-10 ng/mL fentanyl or 10-25 ng/mL hydromorphone in serum. Radioligand binding assays in rat brain tissue revealed that the drug binds with high affinity (K_i = 14.3 nM) to the µ-opioid receptor (MOR). Using a MOR-β-arrestin2 activation assay, we found that N-piperidinyl etonitazene is highly potent (EC₅₀ = 2.49 nM) and efficacious (E_max = 183% versus hydromorphone) in vitro. Pharmacodynamic evaluation in male Sprague Dawley rats showed that N-piperidinyl etonitazene induces opioid-like antinociceptive, cataleptic, and thermic effects, its potency in the hot plate assay (ED₅₀ = 0.0205 mg/kg) being comparable to that of fentanyl (ED₅₀ = 0.0209 mg/kg), and > 190 times higher than that of morphine (ED₅₀ = 3.940 mg/kg). Taken together, our findings indicate that N-piperidinyl etonitazene is a potent opioid with the potential to cause harm in users.

A Vaccine against Benzimidazole-Derived New Psychoactive Substances That Are More Potent Than Fentanyl

New psychoactive substance (NPS) opioids have proliferated within the international drug market. While synthetic opioids are traditionally composed of fentanyl analogues, benzimidazole-derived isotonitazene and its derivatives are the current NPS opioids of concern. Hence, in this study, we implement immunopharmacotherapy wherein antibodies are produced with high titers and nanomolar affinity to multiple benzimidazole-derived NPS opioids (BNO). Notably, these antibodies blunt psychoactive and physiological repercussions from BNO exposure, which was observed through antinociception, whole-body plethysmography, and blood-brain biodistribution studies. Moreover, we detail previously unreported pharmacokinetics of these drugs, which explains the struggle of traditional pharmaceutical opioid antagonists against BNO substances. These findings provide further insight into the in vivo effects of BNO drugs and the development of effective broad-spectrum therapeutics against NPS opioids.