The Rise and Fall of Isotonitazene and Brorphine: Two Recent Stars in the Synthetic Opioid Firmament

Elucidating the harm potential of brorphine analogues as new synthetic opioids: Synthesis, in vitro, and in vivo characterization

The emergence of new synthetic opioids (NSOs) has added complexity to recreational opioid markets worldwide. While NSOs with diverse chemical structures have emerged, brorphine currently remains the only NSO with a piperidine benzimidazolone scaffold. However, the emergence of new generations of NSOs, including brorphine analogues, can be anticipated. This study explored the pharmaco-toxicological, opioid-like effect profile of brorphine alongside its non-brominated analogue (orphine) and three other halogenated analogues (fluorphine, chlorphine, iodorphine). In vitro, radioligand binding assays in rat brain tissue indicated that all analogues bind to the μ-opioid receptor (MOR) with nM affinity. While analogues with smaller-sized substituents showed the highest MOR affinity, further in vitro characterization via two cell-based (HEK 293T) MOR activation (β-arrestin 2 and mini-Gαi recruitment) assays indicated that chlorphine, brorphine, and iodorphine were generally the most active MOR agonists. None of the compounds showed significant in vitro biased agonism compared to hydromorphone. In vivo, we investigated the effects of intraperitoneal (IP) administration of the benzimidazolones (0.01-15 mg/kg) on mechanical and thermal antinociception in male CD-1 mice. Chlorphine and brorphine overall induced the highest levels of antinociception. Furthermore, the effects on respiratory changes induced by a fixed dose (15 mg/kg IP) of the compounds were investigated using non-invasive plethysmography. Fluorphine-, chlorphine-, and brorphine-induced respiratory depressant effects were the most pronounced. For some compounds, pretreatment with naloxone (6 mg/kg IP) could not reverse respiratory depression. Taken together, brorphine-like piperidine benzimidazolones are opioid agonists that have the potential to cause substantial harm to users should they emerge as NSOs. This article is part of the Special Issue on "Novel Synthetic Opioids (NSOs)".

Fluorofentanyl and novel synthetic opioids in accidental overdose deaths

One of the quickest-growing subclasses of novel psychoactive substances is novel synthetic opioids (NSOs), which are categorized as fentanyl analogs (fentalogs) or nonfentanyl opioids that bind to the mu-opioid receptor. Increased detections of NSOs have been observed in the USA. However, limited information on their prevalence outside of the East Coast is available. This study details the prevalence of NSOs, specifically fluorofentanyl, in the biological and drug paraphernalia specimens of accidental overdose deaths in San Francisco in 2022. A recently developed and validated liquid chromatography with tandem mass spectrometry method was utilized for the analysis of >250 NSOs. Out of the 649 accidental overdose deaths in 2022, 617 cases were available for blood analysis, with at least 1 NSO detected in 48 cases (7.8%). Fentalogs were detected in all 48 cases, with fluorofentanyl being detected in 40 cases. In postmortem femoral blood, estimated concentrations of fluorofentanyl ranged from 0.1 to 8.9 ng/mL, and 0.05 to 85 ng/mL in urine. Polysubstance use with NSO was seen with fentanyl (89.6%), methamphetamine (70.8%), cocaine (33.3%), and heroin (18.8%). NSOs, mainly fluorofentanyl, were observed in matched drug paraphernalia. This report documents the migration of fluorofentanyl to the West Coast, specifically California.

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.

Nitazene test strips: a laboratory evaluation

BACKGROUND

2-Benzylbenzimidazole 'nitazene' opioids pose a growing threat to public health. Nitazene analogues are increasingly found mixed with or (mis)sold as heroin and in falsified (non-)opioid medications, posing a great risk of intoxication in users (un)knowingly exposed to these potent opioids. Lateral flow immunoassay nitazene test strips (NTS; BTNX Rapid Response™) became commercially available in Q1 2024, with the aim to enable rapid detection of nitazene analogues in drug samples. As only limited independent data is available on the performance of these strips, this lab-based study aimed at evaluating their potential for drug checking applications.

METHODS

Following dilution of drug standards in water, the NTS readouts were analyzed independently by two individuals and by ImageJ. The limit of detection for isotonitazene was determined using two manufacturing lots of NTS. Cross-reactivity with 32 other nitazene analogues was evaluated. Six sourced drug samples were tested to explore the ability of NTS to detect the presence of a nitazene analogue in authentic samples.

RESULTS

The limits of detection for isotonitazene were 2000 or 3000 ng/mL, depending on the lot. Twenty-four of the 33 tested nitazene analogues cross-reacted with the NTS at concentrations ≤ 9000 ng/mL. Structural analysis indicated that either substitution or removal of the 5-nitro group, or lengthening the linker between the two aromatic rings, generally hampered detection. All six authentic drug samples consistently tested positive, with no observed false negatives.

CONCLUSIONS

This study provides a better understanding of the potential of NTS for drug checking purposes. Our findings indicate that NTS can theoretically alert to the presence of most nitazene analogues that have emerged on recreational drug markets. However, 'desnitazenes' (lacking the 5-nitro group) may yield false negative results due to low cross-reactivity. Although factors like specificity, lot-to-lot variability, nitazene analogue content in drug samples, solubility, and different testing conditions should be considered, our study results indicate that, at least under the conditions evaluated here (using reference standards and sourced powders), NTS are capable of detecting the presence of a wide range of nitazene analogues. Hence, NTS may alert users of the presence of nitazene analogues in drug samples.

Method development for the quantification of nine nitazene analogs and brorphine in Dried Blood Spots utilizing liquid chromatography - tandem mass spectrometry

The detection of nitazenes in biological fluids is increasingly needed as they are repeatedly reported in intoxication and overdose cases. A simple method for the quantification of low levels of nine nitazene analogs and brorphine in Dried Blood Spots (DBS) was developed and validated. 10 μL of spiked whole blood is deposited on a Capitainer®B card and allowed to dry. The spot is punched out, and extracted with 500 μL methanol:acetonitrile (3:1 v/v) added with 1.5 μL of fentanyl-D5 as the internal standard. After stirring, sonication, and centrifugation of the vial, the solvent is dried under nitrogen, the extract is reconstituted in 30 μL methanol, and 1 μL is injected into a UHPLC-MS/MS instrument. The method validation showed linear calibration in the 1-50 ng/mL range, LOD values ranging between 0.3 ng/mL (isotonitazene) and 0.5 ng/mL (brorphine), average CV% and bias% within 15 % and 10 % for all compounds, respectively. The matrix effect due to blood and filter paper components was within 85-115 % while recovery was between 15-20 %. Stability tests against time and temperature showed no significant variations for storage periods up to 28 days. Room temperature proved to represent the best samples storage conditions. UHPLC-MS/MS proved capable to reliably identify all target analytes at low concentration even in small specimen volumes, as those obtained from DBS cards, which in turn confirmed to be effective and sustainable micro-sampling devices. This procedure improves the efficiency of toxicological testing and provides an innovative approach for the identification of the nitazene class of illicit compounds.

Plasma drug screening using paper spray mass spectrometry with integrated solid phase extraction

Drug overdoses have risen dramatically in recent years. We developed a simple nontargeted method using a disposable paper spray cartridge with an integrated solid phase extraction column. This method was used to screen for ~160 fentanyl analogs, synthetic cannabinoids, other synthetic drugs, and traditional drugs of abuse in over 300 authentic overdose samples collected at emergency departments in Indianapolis. A solid phase extraction step was implemented on the paper spray cartridge to enable subnanograms per milliliter synthetic drugs screening in plasma. Analysis was performed on a quadrupole orbitrap mass spectrometer using the sequential window acquisition of all theoretical fragment ion spectra approach in which tandem mass spectrometry was performed using 7 m/z isolation windows in the quadrupole. Calibration curves with isotopically labeled internal standards were constructed for 35 of the most frequently encountered synthetic and traditional illicit drugs by US toxicology labs. Additional qualitative-only drugs in a suspect screening list were also included. Limits of detection in plasma for synthetic cannabinoids ranged from 0.1 to 0.5 and 0.1 to 0.3 ng/mL for fentanyl and its analogs and between 1 and 5 ng/mL for most other drugs. Relative matrix effects were evaluated by determining the variation of the calibration slope in 10 different lots of biofluid and found to be between 3% and 20%. The method was validated on authentic overdose samples collected from two emergency departments in Indianapolis, Indiana, from suspected or known overdoses. Commonly detected synthetic drugs included fentanyl related substances, designer benzodiazepines such as flubromazolam, and the synthetic cannabinoid 5F-PB-22.

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.

Bibliometric evaluation of Journal of Analytical Toxicology as a scholarly publication according to the Web-of-Science citation database

Soon approaching its 50th anniversary, Journal of Analytical Toxicology (JAT) is an international scholarly publication specializing in analytical and forensic aspects of toxicology. Science Citation Index (SCI) and Journal Citation Reports (JCR), both of which are part of the Web-of-Science (WOS) database, were used to make a bibliometric evaluation of JAT articles. Between 1977 (volume 1) and 2023 (volume 47), a total of  n = 4,785 items were published in JAT; the top-ten most highly cited articles and the most prolific authors were identified. Changes in the journal impact factor (JIF) were studied between 1997 and 2022, and this metric varied from a low of 1.24 (2006) to a high of 3.36 (2020).The most recent JIF (2022) dropped to 2.5 and the corresponding 5 year JIF was 2.6. JAT's most highly cited article (590 cites) was a working group (SWGTOX) report dealing with standard practices for the validation of analytical methods in forensic toxicology laboratories. JAT published 62 articles each of which were cited over 100 times and the H-index for JAT was 89. The most prolific author of JAT articles was credited with 119 items, the first in 1980 (volume 4) and the latest in 2023 (volume 47). JAT articles were cited 4,537 times in 2022 by all journals in the JCR database, although 520 of these were self-citations (11.5%). Bibliometric methods are increasingly used to evaluate the published work of individual scientists, university departments, entire universities and whole countries. Highly cited articles are considered more influential and authoritative compared with papers that are seldom or never cited.

Rapid Analysis of Fentanyl and Fentanyl Analogues from Whole Blood Using SPME Coupled to the Microfluidic Open Interface

Fentanyl and its analogues are potent opioids that pose a significant threat to society. Over the last several years, considerable focus has been on the concerning trend of increasing fentanyl usage among drug users. Fentanyl analogues are mainly synthesized to evade analytical detection or increase their potency; thus, very low concentrations are sufficient to achieve a therapeutic effect. In an effort to help combat the synthetic opioid epidemic, developing targeted mass spectrometric methods for quantifying fentanyl and its analogues at ultralow concentrations is incredibly important. Most methods used to analyze fentanyl and its analogues from whole blood require manual sample preparation protocols (solid-phase extraction or liquid-liquid extraction), followed by chromatographic separation and mass spectrometric detection. The main disadvantages of these methods are the tedious sample preparation workflows, resulting in lengthy analysis times. To mitigate these issues, we present a targeted method capable of analyzing 96 samples containing fentanyl, several fentanyl analogues, and a common fentanyl (analogue) precursor simultaneously in 2.4 min per sample. This is possible by using a high-throughput solid phase microextraction workflow on the Concept96 autosampler followed by manual coupling of solid-phase microextraction fibers to the microfluidic open interface for tandem mass spectrometry analysis. Our quantitative method is capable of extremely sensitive analysis, with limits of quantification ranging from 0.002 to 0.031 ng mL-1 and linearity ranging from 0.010 to 25.0 ng mL-1. The method shows very good reproducibility (1-18%), accuracy (81-100%) of calibration and validation points, and good interday reproducibility (6-15%).

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.

Are the NPS commonly used? An extensive investigation in Northern Italy based on hair analysis

New psychoactive substances (NPS) are present on the Italian illicit markets, but data from the analysis of biological samples to evaluate their real consumption are rare. For this reason, an epidemiological study was carried out by means of a ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method for the determination of 115 NPS on the keratin matrix. A total of 847 hair samples were collected in 2020 and 2021 and analyzed. The sample donors were in the age range of 18-40 years, from both genders, and were tested either for driving relicensing or for drug withdrawal monitoring. The UPLC-MS-MS system consisted of a Waters ACQUITY UPLC® I-Class, coupled with a Waters XEVO TQ-XS triple quadrupole mass spectrometer. The method was developed and fully validated according to international guidelines. Limits of detection were set as the minimum criterion to identify positive samples. Overall, 56 samples resulted positive for ketamine, 35 for norketamine, 6 for fentanyl, 3 for norfentanyl, 3 for 4-ANPP, 3 for MDMB-4en-PINACA, 2 for N,N-DMT, 2 for 5-chloro AB-PINACA, 1 for α-PHP and 1 for methcathinone. NPS were detected in a small part of samples (8.4%), which seems in contrast with their apparent wide diffusion in Italy, yet it is congruent with similar investigations based on hair analysis. Future studies will be performed to expand the investigated population, especially in terms of age and origin.

Detection of fentanyl, synthetic opioids, and ketamine in hair specimens from purposive samples of American and Italian populations

With the current crisis related to the diffusion of fentanyl and other novel opioids in several countries and populations, new and effective approaches are needed to better elucidate the phenomenon. In this context, hair testing offers a unique perspective in the investigation of drug consumption, producing useful information in terms of exposure to psychoactive substances. In this research, we applied targeted ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analytical methods to detect novel synthetic and prescription opioids and other common controlled psychoactive drugs in the keratin matrix. A total of 120 hair samples were analyzed from the United States (US) and Italy, segmented when longer than 6 cm, and then analyzed. In the 60 samples (83 segments in total) analyzed from a purposive sample of data collected in the US, fentanyl was detected in 14 cases (16.9%), with no detection of nitazens or brorphine. We also detected fentanyl metabolites, despropionyl-p-fluorofentanyl, and prescription opioids. In the 60 samples collected in Italy (91 segments in total), ketamine was the most prevalent compound detected (in 41 cases; 45.1%), with ketamine demonstrating a strong correlation with detection of amphetamines and MDMA, likely due to co-use of these substances in recreational contexts. Several common drugs were also detected but no exposure to fentanyl or its analogs were detected. Results of this retrospective exploration of drug use add to increasing evidence that hair testing can serve as a useful adjunct to epidemiology studies that seek to determine biologically confirmed use and exposure in high-risk populations.

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.

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., Kis) 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.

Current attitudes toward drug checking services and a comparison of expected with actual drugs present in street drug samples collected from opioid users

BACKGROUND

The opioid epidemic continues to be associated with high numbers of fatalities in the USA and other countries, driven mainly by the inclusion of potent synthetic opioids in street drugs. Drug checking by means of various technologies is being increasingly implemented as a harm reduction strategy to inform users about constituent drugs in their street samples. We assessed how valued drug checking services (DCS) would be for opioid street drug users given the ubiquity of fentanyl and related analogs in the drug supply, the information they would most value from drug checking, and compared expected versus actual constituent drugs in collected samples.

METHODS

A convenience sample of opioid street drug users (N = 118) was recruited from two syringe service exchange programs in Chicago between 2021 and 2022. We administered brief surveys asking about overdose history, whether fentanyl was their preferred opioid, and interest in DCS. We also collected drug samples and asked participants what drug(s) they expected were in the sample. Provided samples were analyzed using LC-MS technology and the results compared to their expected drugs.

RESULTS

Participants reported an average of 4.4 lifetime overdoses (SD = 4.8, range = 0-20) and 1.1 (SD = 1.8, range = 0-10) past-year overdoses. A majority (92.1%) believed they had recently used drugs containing fentanyl whether intentionally or unintentionally. Opinions about the desirability of fentanyl were mixed with 56.1% indicating they did not and 38.0% indicating they did prefer fentanyl over other opioids, mainly heroin. Attitudes toward DCS indicated a general but not uniform receptiveness with a majority indicating interest in DCS though sizeable minorities believed DCS was "too much trouble" (25.2%) or there was "no point" in testing (35.4%). Participants were especially inaccurate identifying common cutting agents and potentiating drugs such as diphenhydramine in their samples (sensitivity = .17).

CONCLUSIONS

Results affirmed street drug users remain interested in using DCS to monitor their drugs and such services should be more widely available. Advanced checking technologies that provide information on the relative quantities and the different drugs present in a given sample available at point-of-care, would be most valuable but remain challenging to implement.

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.

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.

Public health and medical preparedness for mass casualties from the deliberate release of synthetic opioids

The large amounts of opioids and the emergence of increasingly potent illicitly manufactured synthetic opioids circulating in the unregulated drug supply in North America and Europe are fueling not only the ongoing public health crisis of overdose deaths but also raise the risk of another type of disaster: deliberate opioid release with the intention to cause mass harm. Synthetic opioids are highly potent, rapidly acting, can cause fatal ventilatory depression, are widely available, and have the potential to be disseminated for mass exposure, for example, if effectively formulated, via inhalation or ingestion. As in many other chemical incidents, the health consequences of a deliberate release of synthetic opioid would manifest quickly, within minutes. Such an incident is unlikely, but the consequences could be grave. Awareness of the risk of this type of incident and preparedness to respond are required to save lives and reduce illness. Coordinated planning across the entire local community emergency response system is also critical. The ability to rapidly recognize the opioid toxidrome, education on personal protective actions, and training in medical management of individuals experiencing an opioid overdose are key components of preparedness for an opioid mass casualty incident.

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.

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.

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.

Application of Fabric Phase Sorptive Extraction (FPSE) Engaged to Tandem LC-MS/MS for Quantification of Brorphine in Oral Fluid

Brorphine (1-[1-[1-(4-bromophenyl) ethyl]-piperidin-4-yl]-1,3-dihydro-2H-benzo [d]imidazol-2-one) is one of the most recent novel synthetic opioids (NSOs) on the novel psychoactive substances (NPSs) market, involved in over 100 deaths in 2020. Brorphine is a substituted piperidine-benzimidazolone analogue that retains structural similarities to fentanyl, acting as a full agonist at the μ-opioid receptor. Oral Fluid (OF) is an alternative matrix, frequently analyzed for the detection of NPS. Fabric phase sorptive extraction (FPSE) is a superior, green-sample -preparation technology recently applied for drug analysis. This contribution presents the development and validation of a method, based on the application of FPSE and liquid chromatography-tandem mass spectrometry (LC-MS/MS), to determine/quantitate brorphine in OF. The method's linearity ranged between 0.05 and 50 ng/mL (R² = 0.9993), the bias ranged between 12.0 and 16.8%, and inter- and intra-day precisions ranged between 6.4 and 9.9%. Accuracy and extraction efficiency lied between 65 and 75%. LOD/LOQ were 0.015 ng/mL/0.05 ng/mL. Analyte's post-preparative stability was higher than 95%, while no matrix interferences and carryover between runs were observed. This is the first report introducing the application of FPSE for NPS determination, specifically, the quantification of brorphine in OF, thereby presenting a simple, rapid, sensitive, specific, effective, and reliable procedure engaged to LC-MS/MS that is suitable for routine application and the analysis of more NPSs.

Discussion on the molecular mechanism of Duhuo Jisheng decoction in treating osteoarthritis based on network pharmacology and molecular docking

In this study, network pharmacology and molecular docking technology were used to explore the molecular mechanisms of the Duhuo Jisheng decoction in the treatment of osteoarthritis (OA). The chemical composition of the prescriptions was obtained from the traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP) database and the retrieved literature. Targets for the active ingredients were obtained using TCMSP and the Swiss Target Prediction Database. Disease targets were obtained from GeneCards and DisGeNET databases. The online tool, Venny, was used to obtain common targets for drugs and diseases. Protein-protein interactions (PPI) between common targets were analyzed using the search tool for the retrieval of interacting genes/proteins (STRING) database. Common targets were analyzed for gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment using the database for annotation, visualization and integrated discovery (DAVID) database. Molecular docking of the first 10 targets and first 10 components was verified using AutoDock Tools software, and the docking diagram was visualized using PyMOL software. After screening, 210 chemical components of the Duhuo Jisheng decoction (DHJSD) were identified. The 253 common targets of drugs and diseases were combined by eliminating repeat values. Based on PPI network analysis, the top ten targets were SRC, STAT3, MAPK3, MAPK1, RELA, PIK3R1, HSP90AA1, TP53, EP300, and AKT1. KEGG analysis showed that DHJSD could regulate the HIF-1, PI3K-Akt, and JAK-STAT signaling pathways. The biological processes involved include inflammatory reactions, the negative regulation of apoptosis, and the positive regulation of cell proliferation. Molecular docking results showed that all targets, except the RELA protein, showed good binding to the compounds, indicating that the 10 components might exert therapeutic effects by binding to the above targets. DHJSD can treat OA by regulating the HIF-1, PI3K-Akt, and JAK-STAT signaling pathways. The proteins involved were SRC, STAT3, MAPK3, MAPK1, and PIK3R1. In this study, network pharmacology was used to predict the mechanism of DHJSD in OA treatment, which was verified by molecular docking to provide experimental research ideas and scientific basis for OA treatment.

Retrospective identification of new psychoactive substances in patient samples submitted for clinical drug analysis

New psychoactive substances (NPS) are life-threatening through unpredictable toxicity and limited analytical options for clinicians. We present the retrospective identification of NPS in raw data from a liquid chromatography-high resolution mass spectrometry (LC-HRMS) based multidrug panel analysis on 14,367 clinical oral fluid samples requested during 2019 mainly by psychiatric and addiction care clinics. Retrospectively analysed NPS included 48 notified originally in 2019 by the European Union Early Warning System (EU-EWS) and 28 frequently reported in Sweden. Of 88 included NPS, 34 (mitragynine, flualprazolam, 3F/4F-α-P(i)HP, etizolam, 4F-MDMB-BINACA, cyproheptadine, 5F-MDMB-PICA, isotonitazene, isohexedrone, MDPEP, N-ethylpentedrone, tianeptine, flubromazolam, 4'-methylhexedrone, α-P(i)HP, eutylone, mephedrone, N-ethylhexedrone, 5F-MDMB-PINACA, ADB-BUTINACA, 3-methoxy PCP, 4F-furanylfentanyl, 4F-isobuturylfentanyl, acrylfentanyl, furanylfentanyl, clonazolam, norfludiazepam, 3F-phenmetrazine, 3-MMC, 4-methylpentedrone, BMDP, ethylphenidate, methylone, α-PVP) were identified as 219 findings in 84 patients. Eight NPS notified in 2019 were identified, five before EWS release. NPS occurred in 1.20% of all samples and 1.53% of samples containing traditional drugs, and in 1.87% of all patients and 2.88% of patients using traditional drugs. NPS use was more common in men and polydrug users. Legal (not scheduled) NPS were more used than comparable illegal ones. Retrospective identification could be useful when prioritizing NPS for clinical routine analysis and when studying NPS epidemiology.

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.

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.

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.

Pharmacological and metabolic characterization of the novel synthetic opioid brorphine and its detection in routine casework

After their first emergence in 2009, Novel synthetic opioids (NSO) have become an emerging class of New Psychoactive Substances (NPS) on the market for these new drugs. So far, 67 NSO have been reported to the Early Warning system of the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA). It is presumed that NSO mainly target the four known opioid receptors, i.e. the μ-opioid (MOR), the δ-opioid (DOR), the κ-opioid (KOR) and nociceptin receptors and that their consumption can result in serious adverse effects such as massive respiratory depression or death. In the present study we investigated the in vivo and in vitro metabolism of brorphine, a NSO that was first identified on the NPS market in August 2019 in the United States, using both a pooled human liver microsome assay and real forensic case samples. For the detection of metabolites LC-HR-MS/MS was used and quantification of brorphine was performed using an LC-MS/MS method. Additionally, we pharmacologically characterized brorphine regarding its activation of the MOR and KOR via G protein recruitment using the [³⁵S]-GTPγS assay. In forensic urine samples, 14 distinct metabolites were identified, whereas in blood only four metabolites could be found. The pooled human liver microsome assay generated six distinct in vitro phase I metabolites. The most prominent in vivo metabolite was formed by N-oxydation, whereas the main in vitro metabolite was formed by hydroxylation. The pharmacological characterization at the MOR and KOR revealed brorphine to be a potent MOR agonist and a weak, partial KOR agonist in the [³⁵S]-GTPγS assay.