Fentanyl, fentanyl analogs and novel synthetic opioids: A comprehensive review

High-throughput screening of fentanyl analogs

This study presents an analytical approach coupling novel ambient ionization sources with trapped ion mobility spectrometry (TIMS) and tandem mass spectrometry (MS/MS) for the rapid characterization of fentanyl analogs. Two ambient ionization sources were illustrated for minimal sample preparation and rapid analysis: electrospray ionization (nESI) and direct analysis in real time (DART). Fentanyl analogs can be separated using nESI-TIMS-MS/MS based on differences in their mobility and/or fragmentation pattern; reference mobility spectra are reported for 234 single standards. In contrast, DART-TIMS-MS/MS allowed for the characterization of 201 compounds due to differences in the protonation pattern and efficiency when compared to nESI. The TIMS high resolving power (R > 80) allowed baseline separation for most isomers and mobility trends were established for methylated and fluorinated isomers, with the more compact ortho-substituted analogs showing distinct separation from para- and meta-substituted species. This multi-dimensional strategy offers a comprehensive characterization of fentanyl analogs and other synthetic opioids with minimal sample preparation. This analysis shows significant potential for high-throughput screening (<5 min) and high sensitivity detection ( Collapse

Key Words

• DART
• Fentanyl
• Identification
• Isomers
• Mobility
• Screening

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MESH Headings

• Fentanyl/analogs & derivatives
• Fentanyl/analysis
• Fentanyl/chemistry
• High-Throughput Screening Assays/methods
• Tandem Mass Spectrometry/methods
• Ion Mobility Spectrometry/methods
• Spectrometry, Mass, Electrospray Ionization/methods
• Analgesics, Opioid/analysis
• Analgesics, Opioid/chemistry

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Grants

• R01 GM134247 NIGMS NIH HHS
• R35 GM153450 NIGMS NIH HHS

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Affiliation(s)

Samuel A Miller Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, United States
Andrew R Forero Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, United States
Lilian Valadares Tose Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, United States
Jordan E Krechmer Bruker Daltonics Inc., Billerica, MA, 01821, United States
Felician Muntean Bruker Daltonics Inc., Billerica, MA, 01821, United States
Francisco Fernandez-Lima Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, United States.

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"I still can feel the sickness": Withdrawal experiences of people on methadone maintenance treatment

INTRODUCTION

Opioid withdrawal is a regular occurrence for many people who use illicit opioids (PWUIO) involving acute physical and psychological pain. Yet, there is very little data on the withdrawal experience of people in methadone maintenance treatment (MMT) and almost none from the patients' experience. Learning more about patients' withdrawal experiences can help to inform policies and practices that are better suited to address withdrawal and may improve patient satisfaction as well as uptake and retention.

METHODS

This article is based on 29 semi-structured interviews with people who use illicit opioids who reported recent withdrawal experience. The study conducted interviews remotely via Zoom between April and August 2022 and later transcribed them professionally. The study team then coded data thematically using Atlas.ti, based on a combination of inductive and deductive coding strategies and informed by the literature and study aims.

RESULTS

Participants described withdrawal as a significant issue that negatively impacts their treatment experience and increases the likelihood of treatment cessation. Their accounts of withdrawal were complex and often involved multiple factors; however, feeling underdosed and missing clinic dosing hours were seen as important vectors that led to their withdrawal experiences. Importantly, participants framed feeling underdosed and missing clinic dosing hours as institutional problems, resulting primarily from clinic policies, practices, and culture rather than from patients' decisions or individual behavior. Specifically, they cited restricted access to take-home doses, limited hours of operation, and a punitive focus on complete abstinence as factors that made withdrawal difficult to avoid.

CONCLUSIONS

Patients' accounts demonstrate a disconnect between providers' focus on promoting complete abstinence and patients, who were often using MMT for more pragmatic reasons that did not include complete abstinence from all drugs. These findings support growing calls for the integration of MMT into the mainstream healthcare system by making it available via prescription from office-based medical settings and dispensed through pharmacies.

A Supramolecular-Quantum Dot System for Broad-Spectrum Detection of Fentanyl Analogs

Synthetic opioids, especially fentanyl and its analogs, have created an epidemic of abuse and significantly increased overdose deaths in the United States. Current detection methods have drawbacks in their sensitivity, scalability, and portability that limit field-based application to promote public health and safety. The need to detect trace amounts of fentanyl in complex mixtures with other drugs or interferents, and the continued emergence of new fentanyl analogs, further complicates detection. Accordingly, there is an urgent need to develop convenient, rapid, and reliable sensors for fentanyl detection. In this study, a sensor is prepared based on competitive displacement of a fluorescent dye from the cavity of a supramolecular macrocycle, with subsequent fluorescence quenching from graphene quantum dots. This approach can detect and quantify small quantities of fentanyl along with 58 fentanyl analogs, including highly potent variants like carfentanil that are of increasing concern. Detection of these agents is possible even at 0.01 mol% in the presence of common interferents. This simple, rapid, reliable, sensitive, and cost-effective approach couples supramolecular capture with graphene quantum dot nanomaterial quenchers to create a tool with the potential to advance public health and safety in the context of field-based detection of drugs in the fentanyl class.

Characteristics of Fentanyl Toxicity in Very Young Children

Children exposed to illicit fentanyl often experience severe toxicity and receive repeated naloxone doses and prolonged airway support. This retrospective study presents the clinical course and management of 4 cases, emphasizing the urgent need for prompt recognition and intervention to address the severe, extended effects of illicit fentanyl exposure in very young children.

Temporal and spatial trends of fentanyl co-occurrence in the illicit drug supply in the United States: a serial cross-sectional analysis

Background

Fentanyl and its analogs contribute substantially to drug overdose deaths in the United States. There is concern that people using drugs are being unknowingly exposed to fentanyl, increasing their risk of overdose death. This study examines temporal trends and spatial variations in the co-occurrence of fentanyl with other seized drugs.

Methods

We identified fentanyl co-occurrence (the proportion of samples of non-fentanyl substances that also contain fentanyl) among 9 substances or substance classes of interest: methamphetamine, cannabis, cocaine, heroin, club drugs, hallucinogens, and prescription opioids, stimulants, and benzodiazepines. We used serial cross-sectional data on drug reports across 50 states and the District of Columbia from the National Forensic Laboratory Information System, the largest available database on the U.S. illicit drug supply, from January 2013 to December 2023.

Findings

We analyzed data from 11,940,207 samples. Fentanyl co-occurrence with all examined substances increased monotonically over time (Mann-Kendall p < 0.0001). Nationally, fentanyl co-occurrence was highest among heroin samples (approx. 50%), but relatively low among methamphetamine (≤1%), cocaine (≤4%), and other drug samples. However, co-occurrence rates have grown to over 10% for cocaine and methamphetamine in several Northeast states in 2017-2023.

Interpretation

Fentanyl co-occurs most commonly with heroin, but its presence in stimulant supplies is increasing in some areas, where it may pose a disproportionately high risk of overdose.

Funding

This work was partly supported by FDA grant U01FD00745501. This article reflects the views of the authors and does not represent the views or policies of the FDA or US Department of Health and Human Services.

Use of fentanyl test strips by people who inject drugs: Baseline findings from the South Atlantic Fentanyl Test Strip Study (SAFTSS)

BACKGROUND

Research published during the early fentanyl period exposed a growing concern of unwitting fentanyl exposure and a general willingness to use fentanyl test strips (FTS). A paucity of FTS studies over the last several years has restricted our ability to understand FTS use in the late fentanyl era. The South Atlantic FTS Study (SAFTSS) was established to investigate contemporaneous changes in FTS use and drug use behavior among a rural cohort of PWID.

METHODS

Between June 2021 and March 2022, a total of 541 PWID completed an in-person survey. Baseline survey questions included demographics, socioeconomic characteristics, and drugs used. FTS questions covered lifetime use, past 6-months, and past 30-day use and included reasons for using FTS, levels of access, and confidence testing illicit opioids and stimulants. Multivariable analyses examined significant baseline correlates of lifetime and 30-day FTS use.

RESULTS

Overall, more than half (58%; N=315) used FTS in their lifetime. Among lifetime FTS users, almost half (47%) used FTS in the past 6 months and 30% in the past 30 days, with an average of 13 months from last FTS use and the baseline survey. The most common reason for not using FTS was "not having them with me when I use drugs." Less frequent reasons were "I already know it's fentanyl" followed by "FTS take too much time to use." Among past 30-day FTS users, 74% used FTS on heroin, 55% on methamphetamine, and 33% on fentanyl. Consumer confidence using FTS was higher with illicit opioids (66%) but lower for methamphetamine (43%). In both the lifetime and past 30-day models, PWID with FTS use were more likely than non-users to have witnessed an overdose in the past six months (lifetime aOR = 2.85, p<.001; 30-day aOR=2.57, p<.01). Virtually no differences in drug use behaviors were found when comparing past 30-days FTS use to no FTS use. Women (aOR=1.68, p<.05) and non-white PWID (aOR=2.43, p<.05) were more likely than men and white PWID to have used FTS.

CONCLUSIONS

Declines in FTS use are consistent with what syringe services programs have been signaling for years. Needs assessments to gauge interest in FTS before scaling up can help ensure funding better spent on naloxone and syringes is not allocated to idle FTS. Increased FTS among women and racial minorities presents opportunities for tailored interventions. Recognizing trauma associated with witnessing overdoses as a growing component of the opioid epidemic is a critical first step toward addressing the full spectrum of drug-related harm.

Reinforcing effects of fentanyl analogs found in illicit drug markets

RATIONALE

The potent synthetic opioid fentanyl, and its analogs, continue to drive opioid-related overdoses. Although the pharmacology of fentanyl is well characterized, there is little information about the reinforcing effects of clandestine fentanyl analogs (FAs).

OBJECTIVES

Here, we compared the effects of fentanyl and the FAs acetylfentanyl, butyrylfentanyl, and cyclopropylfentanyl on drug self-administration in male and female rats. These FAs feature chemical modifications at the carbonyl moiety of the fentanyl scaffold.

METHODS

Sprague-Dawley rats fitted with intravenous jugular catheters were placed in chambers containing two nose poke holes. Active nose poke responses resulted in drug delivery (0.2 mL) over 2 s on a fixed-ratio 1 schedule, followed by a 20 s timeout. Acquisition doses were 0.01 mg/kg/inj for fentanyl and cyclopropylfentanyl, and 0.03 mg/kg/inj for acetylfentanyl and butyrylfentanyl. After 10 days of acquisition, dose-effect testing was carried out, followed by 10 days of saline extinction.

RESULTS

Self-administration of fentanyl and FAs was acquired by both male and female rats, with no sex differences in acquisition rate. Fentanyl and FAs showed partial inverted-U dose-effect functions; cyclopropylfentanyl and fentanyl had similar potency, while acetylfentanyl and butyrylfentanyl were less potent. Maximal response rates were similar across drugs, with fentanyl and cyclopropylfentanyl showing maximum responding at 0.001 mg/kg/inj, acetylfentanyl at 0.01 mg/kg/inj, and butyrylfentanyl at 0.003 mg/kg/inj. No sex differences were detected for drug potency, efficacy, or rates of extinction.

CONCLUSIONS

Our work provides new evidence that FAs display significant abuse liability in male and female rats, which suggests the potential for compulsive use in humans.

Hyperalgesia in Patients With a History of Opioid Use Disorder: A Systematic Review and Meta-Analysis

Importance

Short-term and long-term opioid treatment have been associated with increased pain sensitivity (ie, opioid-induced hyperalgesia). Treatment of opioid use disorder (OUD) mainly involves maintenance with methadone and buprenorphine, and observations of heightened cold pain sensitivity among patients are often considered evidence of opioid-induced hyperalgesia.

Objective

To critically examine the evidence that hyperalgesia in patients with OUD is related to opioid use.

Data Sources

Web of Science, PubMed, and Embase between March 1, 2023, and April 12, 2024, were searched.

Study Selection

Studies assessing cold pressor test (CPT) pain responses during treatment seeking, pharmacological treatment, or abstinence in patients with OUD history were included.

Data Extraction and Synthesis

Multilevel random-effects models with robust variance estimation were used for all analyses. Study quality was rated with the JBI checklist. Funnel plots and Egger regression tests were used to assess reporting bias.

Main Outcomes and Measures

Main outcomes were pain threshold, tolerance, and intensity in patients and healthy controls, and unstandardized, standardized (Hedges g), and percentage differences (%Δ) in these measures between patients and controls. The association between pain sensitivity and opioid tolerance, withdrawal, and abstinence indices was tested with meta-regression.

Results

Thirty-nine studies (1385 patients, 741 controls) met the inclusion criteria. Most studies reported CPT data on patients undergoing opioid agonist treatment. These patients had a mean 2- to 3-seconds lower pain threshold (95% CI, -4 to -1; t test P = .01; %Δ, -22%; g = -0.5) and 29-seconds lower pain tolerance (95% CI, -39 to -18; t test P < .001; %Δ, -52%; g = -0.9) than controls. Egger tests suggested that these differences may be overestimated. There were some concerns of bias due to inadequate sample matching and participant dropout. Meta-regressions yielded no clear support for hyperalgesia being opioid related.

Conclusion and Relevance

Patients receiving opioid agonist treatment for OUD are hypersensitive to cold pain. It remains unclear whether hyperalgesia develops prior to, independent of, or as a result of long-term opioid treatment. Regardless, future studies should investigate the impact of hyperalgesia on patients' well-being and treatment outcomes.

Balancing acts: The dual faces of fentanyl in medicine and public health

Fentanyl is a potent synthetic opioid widely used in medicine for its effective analgesic properties, particularly in surgical procedures and in the treatment of severe, chronic pain. In recent decades, however, there has been a worrying increase in the illicit use of fentanyl, particularly in North America. This rise in illicit use is concerning because fentanyl is associated with polydrug abuse, which adds layers of complexity and dangerous. This review provides a comprehensive examination of fentanyl, focusing on its synthesis and medical use. It also discusses the significance of the piperidine ring in medicinal chemistry as well as the critical role of fentanyl in pain management and anesthesia. Furthermore, it addresses the challenges associated with the abuse potential of fentanyl and the resulting public health concerns. The study aims to strike a balance between the clinical benefits and risks of fentanyl by advocating for innovative uses while addressing public health issues. It examines the chemistry, pharmacokinetics and pharmacodynamics of fentanyl and highlights the importance of personalized medicine in the administration of opioids. The review underscores the necessity of continuous research and adaptation in both clinical use and public health strategies.

Development and validation of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method including 25 novel synthetic opioids in hair and subsequent analysis of a Swiss opioid consumer cohort

Major public health concern is raised by the evidence that common drugs like heroin are now frequently laced or replaced with highly potent novel synthetic opioids (NSOs). The objective of this study was to explore the prevalence and patterns of NSOs in a cohort of Swiss opioid users by hair analysis. Hair analysis is considered an ideal tool for retrospective consumption monitoring. Hair samples from 439 opioid users in Zurich were analyzed. Study inclusion required a previous positive hair test result for heroin metabolites, oxycodone, fentanyl, methadone, or tramadol. The samples were extracted with a two-step extraction procedure, followed by a targeted LC-MS/MS (QTRAP® 6500+) analysis in multiple reaction monitoring mode for a total of 25 NSOs. The method underwent full validation and demonstrated good selectivity and sensitivity with limits of detection (LOD) as low as 0.1 pg/mg. The analyzed sample cohort demonstrated a positivity rate for NSOs of 2.5%, including the following NSOs: butyrylfentanyl, acrylfentanyl, furanylfentanyl, methoxyacetylfentanyl, ocfentanil, U-47700, isobutyrylfentanyl and benzylfentanyl. Furthermore, we were able to identify specific consumption patterns among drug users. The results indicate that hair analysis is a valuable tool for investigating the prevalence of NSOs in drug-using populations, which seems to be low in the case of Swiss opioid users. Nevertheless, the results highlight the need for sensitive analytical detection methods in forensic toxicology to identify and monitor substance distribution in different populations.

How 3D printing technologies could undermine law enforcement strategies targeting the production and distribution of designer drugs

Countering the supply of counterfeit and designer drug pills laced with fentanyl or its analogues has long been a challenge with the potency of the drug and the ease with which it can be obtained impacting greatly on families and the wider society. The introduction of legislative measures to restrict access to the machinery that allows the production of the pills has yielded considerable gains with numerous seizures of pill presses reported. However, the increasing availability of bench top milling machines and advances in 3D printing could render this a short term victory where the technology may be set to outpace the capabilities of conventional law enforcement. While pill presses were once born from high specification industrial machining, low cost mills and 3D printing systems are already at the stage of producing small format presses within the domestic home. Here, a spotlight is trained on fentanyl (and its analogues) from the perspective of pill manufacture and their supply. An overview of pill press mechanics and the approaches presently taken to counter distribution is provided and the potential influence that both milling systems and 3D printing technologies could have in the future is critically evaluated.

75 years of forensic profiling: A critical review

The interest in characterization of drugs abused started in 1948 with the aim of determining the origin of opium. After 75 years there is still a great interest in this approach, called geo-profiling, chemical or forensic profiling in the following decades. Recently chemical attribution signatures (CAS) were proposed by the authors who studied "synthesis precursors and byproducts, impurities, degradation products, and metabolites in various biological matrices" of fentanyl. Forensic profiling evolved during these decades: new analytical approaches were tested and it was applied to more and more products, which threaten the health and security of citizens worldwide. In substances of natural origins (e.g. opium, cannabis and cocaine), it is possible to exploit the great variability of both elements and organic chemical compounds and to study chemical compounds such as reagents and solvents, by-products, and cutting agents used in the production chain. Profiles can be used to classify products from different seizures into groups of similar samples (tactical intelligence) or to determine the origin of samples (strategic intelligence). Chromatographic approaches coupled to mass spectrometry are very common to determine organic profiles, while elemental profiles are obtained by nuclear activation analysis, inductively coupled plasma mass spectrometry or ion beam analysis. A very important role in the field is played by isotope ratio analysis. Approaches to obtain forensic profiles are available also for chemical warfare agents, explosives, illegal medicines, doping agents, supplements, food. Chemometrics can be particularly useful to establish the authenticity of products and for the interpretation of large amount of forensic data. The future of forensic profiling is a challenge for forensic sciences. Organized crime is involved in the manufacturing of a large number of illegal products and forensic profiling is a very powerful tool to support the health of citizens and the administration of justice worldwide.

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 vivo pharmacokinetic, pharmacodynamic and brain concentration comparison of fentanyl and para-fluorofentanyl in rats

In 2022, para-fluorofentanyl (pFF) rose to the 6th most reported drug and the most reported fentanyl analog in the United States according to the Drug Enforcement Administration (DEA). pFF differs from fentanyl by the addition of a single fluorine group. To date, pFF has not been extensively evaluated in vivo and is frequently seen in combination with fentanyl. In the present study, the pharmacodynamic (PD) and pharmacokinetic (PK) properties and brain region-specific concentrations of pFF were evaluated in male Sprague-Dawley rats and compared to fentanyl. A 300 μg/kg subcutaneous dose of fentanyl or pFF was administered to assess PD and PK parameters as well as brain region concentrations. PD parameters were evaluated via a tail flick test to evaluate analgesia and core body temperature to measure hypothermia, a surrogate marker of overall opioid toxicity. Fentanyl and pFF were found to be equally active at the tested dose in terms of tail flick response with both compounds producing an analgesic response that lasted up to 240 min post-drug treatment. pFF induced a significantly greater hypothermic effect compared to fentanyl with a maximum temperature decrease of -5.6 ℃. Plasma PK parameters (T1/2, AUC, etc.) did not differ between fentanyl and pFF. However, pFF concentrations in the medulla, hippocampus, frontal cortex and striatum were more than two times the fentanyl concentrations. The increase in brain concentrations and greater hypothermic effect suggests that pFF is potentially more dangerous than fentanyl.

Identification of fentanyl analogs and potential biomarkers in urine using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-quadrupole/time of flight mass spectrometry (LC-Q/TOF-MS)

Novel synthetic opioids are a class of drugs abused for their potent analgesic effect and are responsible for many fatal intoxications, particularly within the United States. A targeted assay was developed and validated using LC-MS/MS, capable of identifying nineteen fentalogs. Solid phase extraction was used to isolate analytes of interest from urine. Limits of detection ranged from 0.05 to 0.1 ng/mL and the limit of quantitation was 0.5 ng/mL. Extraction efficiencies using the optimized procedure were 77-88 % for all targeted species. Bias, precision, matrix effects and interferences were within acceptable thresholds for all analytes. The validated assay was used to identify analytes of interest from thirty-seven individuals that had used fentanyl and related substances. In addition to quantitative analyses, a non-targeted liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q/TOF-MS) assay was also used to identify additional substances and potential biomarkers. Additional N-oxide and N-dealkylated species were identified using this approach, and the potential for biomarker use is presented, given the stability of some analytes within this class.

The Evolution of Illicit-Drug Detection: From Conventional Approaches to Cutting-Edge Immunosensors-A Comprehensive Review

The increasing use of illicit drugs has become a major global concern. Illicit drugs interact with the brain and the body altering an individual's mood and behavior. As the substance-of-abuse (SOA) crisis continues to spread across the world, in order to reduce trafficking and unlawful activity, it is important to use point-of-care devices like biosensors. Currently, there are certain conventional detection methods, which include gas chromatography (GC), mass spectrometry (MS), surface ionization, surface-enhanced Raman spectroscopy (SERS), surface plasmon resonance (SPR), electrochemiluminescence (ECL), high-performance liquid chromatography (HPLC), etc., for the detection of abused drugs. These methods have the advantage of high accuracy and sensitivity but are generally laborious, expensive, and require trained operators, along with high sample requirements, and they are not suitable for on-site drug detection scenarios. As a result, there is an urgent need for point-of-care technologies for a variety of drugs that can replace conventional techniques, such as a biosensor, specifically an immunosensor. An immunosensor is an analytical device that integrates an antibody-based recognition element with a transducer to detect specific molecules (antigens). In an immunosensor, the highly selective antigen-antibody interaction is used to identify and quantify the target analyte. The binding event between the antibody and antigen is converted by the transducer into a measurable signal, such as electrical, optical, or electrochemical, which corresponds to the presence and concentration of the analyte in the sample. This paper provides a comprehensive overview of various illicit drugs, the conventional methods employed for their detection, and the advantages of immunosensors over conventional techniques. It highlights the critical need for on-site detection and explores emerging point-of-care testing methods. The paper also outlines future research goals in this field, emphasizing the potential of advanced technologies to enhance the accuracy, efficiency, and convenience of drug detection.

Influence of carbon side chain length on the in vivo pharmacokinetic and pharmacodynamic characteristics of illicitly manufactured fentanyls

Since 2016, illicitly manufactured fentanyls and fentanyl analogs (referred to as IMFs) have contributed to an increase in drug overdoses. Although fentanyl has been characterized and evaluated extensively in animals and humans, many of the clandestinely synthesized analogs of fentanyl have not and users may unknowingly ingest these IMFs leading to overdose and potentially death. The pharmacodynamic (PD) and pharmacokinetic (PK) properties of four IMFs and fentanyl were evaluated in Sprague-Dawley rats. A 300-μg/kg subcutaneous dose of each compound (fentanyl, acetylfentanyl, cyclopropylfentanyl, butyrylfentanyl, and valerylfentanyl) was given. PD parameters were measured using a tail flick meter and core body temperature. Blood was drawn to evaluate PK parameters utilizing liquid chromatography tandem mass spectrometry (LC-MS/MS). Fentanyl displayed the greatest and longest lasting analgesia with a tail flick response of 10 s (the maximum cutoff). Additionally, fentanyl produced an average -4.9°C in core body temperature resulting in the greatest decrease in core body temperature. Acetylfentanyl, with the shortest carbon side chain, displayed the shortest T½, and lowest AUC and Cmax and resulted in an increase in body temperature. There were no other PK differences among the IMFs assessed. As IMFs are commonly seen on the streets and can pose significant risks to users (although these risks do depend on other factors such as dose and route of administration), there is a benefit to having the pharmacological properties of these compounds characterized to better understand the potential harm to humans.

Time Course of Reversal of Fentanyl-Induced Respiratory Depression in Healthy Subjects by Intramuscular Nalmefene and Intramuscular and Intranasal Naloxone

The increase in opioid overdose deaths, particularly involving potent, long-acting synthetic opioids, has led to calls for stronger, longer-acting opioid-overdose-reversal agents. Using an opioid-induced respiratory depression model, we investigated the onset and time course of action of naloxone and a long-acting opioid antagonist, nalmefene, in reversing the effects of an ongoing intravenous fentanyl infusion over a period of up to 100 min. Healthy, moderately experienced opioid users received intramuscular (IM) nalmefene 1 mg, IM naloxone 2 mg, or intranasal (IN) naloxone 4 mg after fentanyl-induced respiratory depression was established based on reduction in respiratory minute volume (MV). Each participant received each opioid antagonist twice per a randomized crossover schedule. Reversal of respiratory depression, pharmacokinetics, and safety were investigated. Participants showed rapid increases in plasma opioid antagonist concentrations, and meaningful reversal of depressed MV tended to occur earlier with IM nalmefene and IM naloxone than with IN naloxone. Compared to naloxone, nalmefene provided extended exposure, and mean MV was maintained at a higher level. All participants experienced treatment-related adverse events, but none were severe, serious, or led to study drug discontinuation. This study provides evidence that IM nalmefene 1 mg achieves reversal of fentanyl-induced respiratory depression similar to or better than that achieved with standard-of-care naloxone treatments. No new safety concerns were raised for IM nalmefene at the tested dose. The pharmacokinetic and pharmacodynamic properties of IM nalmefene position it as an important treatment option in opioid overdose reversal, particularly given the increasing prevalence of overdoses involving potent, long-acting synthetic opioids.

Effect of fentanyl on HIV expression in peripheral blood mononuclear cells

Introduction

Illicit drug use, particularly the synthetic opioid fentanyl, presents a significant global health challenge. Previous studies have shown that fentanyl enhances viral replication; yet, the mechanisms by which it affects HIV pathogenesis remain unclear. This study investigated the impact of fentanyl on HIV replication in CD4+ T lymphocytes.

Methods

CD4+ T lymphocytes from HIV-negative donors were activated, infected with HIVNL4-3, and treated with fentanyl. HIV proviral DNA and p24 antigen expression were quantified using real-time PCR and ELISA, respectively. Single-cell RNA libraries were analyzed to identify differentially expressed genes.

Results

Results indicated that fentanyl treatment increased HIV p24 expression and proviral DNA levels, and naltrexone mitigated these effects. Single-cell RNAseq analysis identified significantly altered gene expression in CD4+ T lymphocytes.

Discussion

The results of our findings suggest that fentanyl promotes HIV replication ex vivo, emphasizing the need for a deeper understanding of opioid-virus interactions to develop better treatment strategies for individuals with HIV and opioid use disorder.

A Review of Toxicological Profile of Fentanyl-A 2024 Update

Fentanyl and its analogues are synthetic opioids of varying potencies that are unfortunately heavily abused. Over the last 15 years, fentanyl and its analogues have contributed to the increasing prominence of hospitalisation and numerous deaths due to drug overdose. In this comprehensive literature review, the mechanism of toxicity of the drug in humans is evaluated. A systematic approach was used whereby the relevant literature has been detailed where the toxicity of fentanyl and/or its analogues to different organs/systems were investigated. Furthermore, the review covers the post-mortem toxicological data and demographic information from past fatal cases where fentanyl was believed to be involved. Such insight into fentanyl toxicity is useful as an aid to better understand the toxic doses of the drug and the suspected mechanism of action and the unexpected complications associated with overdose incidences involving the drug. Finally, the review offers an overview of the traditional and emerging test systems used to investigate the adverse effects of fentanyl on human health.

Contemporary burden and trends of opioid-overdose mortality in New York State

BACKGROUND

Limited research exists on contemporary opioid overdose mortality burden and trends in New York State, with most studies focusing on New York City. This study aimed to assess opioid overdose burden and death trends in New York State by age, sex, race/ethnicity, geographic area, opioid type, and overdose intent from 1999 to 2020.

METHODS

Mortality data were obtained from the Centers for Disease Control and Prevention's WONDER database. Opioid overdose decedents were identified using relevant International Classification of Diseases, 10th Revision codes. Joinpoint regression analyzed trends, estimating annual and average annual percentage changes in age-adjusted mortality rates (AAMR). 95% confidence intervals were derived using the Parametric Method.

RESULTS

From 1999 to 2020, New York State recorded 34,109 opioid overdose deaths (AAMR = 7.9 per 100,000 persons; 95% CI: 7.8-7.9). The overall trend increased by 12.6% per year (95% CI: 10.8, 14.4) from 2004 to 2020. Subgroups exhibited varying trends, with an 11.1% yearly increase among Non-Hispanic White persons from 2007 to 2020 (95% CI: 9.0, 13.2), a 24.6% annual rise among Non-Hispanic Black persons from 2012 to 2020 (95% CI: 17.7, 31.8), and an 18.3% increase yearly among Hispanic individuals from 2011 to 2020 (95% CI: 14.0, 22.9). Recent trends have worsened in both males and females, across all age groups, in both New York City (NYC) and areas outside NYC, and for heroin, natural and semisynthetic opioids, and synthetic opioids.

CONCLUSIONS

Opioid overdose mortality in New York State has worsened significantly in the last two decades. Further research is essential to identify driving factors for targeted public health interventions.

Dependency of fentanyl analogue protomer ratios on solvent conditions as measured by ion mobility-mass spectrometry

Recently, our group has shown that fentanyl and many of its analogues form prototropic isomers ("protomers") during electrospray ionization. These different protomers can be resolved using ion mobility spectrometry and annotated using mobility-aligned tandem mass spectrometry fragmentation. However, their formation and the extent to which experimental variables contribute to their relative ratio remain poorly understood. In the present study, we systematically investigated the effects of mixtures of common chromatographic solvents (water, methanol, and acetonitrile) and pH on the ratio of previously observed protomers for 23 fentanyl analogues. Interestingly, these ratios (N-piperidine protonation vs. secondary amine/O = protonation) decreased significantly for many analogues (e.g., despropionyl ortho-, meta-, and para-methyl fentanyl), increased significantly for others (e.g., cis-isofentanyl), and remained relatively constant for the others as solvent conditions changed from 100% organic solvent (methanol or acetonitrile) to 100% water. Interestingly, pH also had significant effects on this ratio, causing the change in ratio to switch in many cases. Lastly, increasing conditions to pH ≥ 4.0 also prompted the appearance of new mobility peaks for ortho- and para-methyl acetyl fentanyl, where all previous studies had only showed one single distribution. Because these ratios have promise to be used qualitatively for identification of these (and emerging) fentanyl analogues, understanding how various conditions (i.e., mobile phase selection and/or chromatographic gradient) affect their ratios is critically important to the development of advanced ion mobility and mass spectrometry methodologies to identify fentanyl analogues.

Machine Learning Discrimination and Ultrasensitive Detection of Fentanyl Using Gold Nanoparticle-Decorated Carbon Nanotube-Based Field-Effect Transistor Sensors

The opioid overdose crisis is a global health challenge. Fentanyl, an exceedingly potent synthetic opioid, has emerged as a leading contributor to the surge in opioid-related overdose deaths. The surge in overdose fatalities, particularly due to illicitly manufactured fentanyl and its contamination of street drugs, emphasizes the urgency for drug-testing technologies that can quickly and accurately identify fentanyl from other drugs and quantify trace amounts of fentanyl. In this paper, gold nanoparticle (AuNP)-decorated single-walled carbon nanotube (SWCNT)-based field-effect transistors (FETs) are utilized for machine learning-assisted identification of fentanyl from codeine, hydrocodone, and morphine. The unique sensing performance of fentanyl led to use machine learning approaches for accurate identification of fentanyl. Employing linear discriminant analysis (LDA) with a leave-one-out cross-validation approach, a validation accuracy of 91.2% is achieved. Meanwhile, density functional theory (DFT) calculations reveal the factors that contributed to the enhanced sensitivity of the Au-SWCNT FET sensor toward fentanyl as well as the underlying sensing mechanism. Finally, fentanyl antibodies are introduced to the Au-SWCNT FET sensor as specific receptors, expanding the linear range of the sensor in the lower concentration range, and enabling ultrasensitive detection of fentanyl with a limit of detection at 10.8 fg mL-1.

Opioid-Associated Nervous System Injuries

With the rise of the opioid epidemic, the practicing neurologist must recognize the patterns of a growing number of opioid-associated neurological injuries. This is in addition to the classic toxidrome of miosis, altered mental status, and respiratory depression, which must never be overlooked, as it is reversible and potentially lifesaving. Several other idiosyncratic syndromes due to opioid-related nervous system insults are defined by their characteristic imaging findings and portend variable functional recovery. Opioid toxicity can not only lead to brain injury, but also spinal cord and, rarely, peripheral nerve injury. As several newer synthetic opioids are undetectable by most assays, a low threshold to suspect opioid exposure must be maintained.

Stability of new psychoactive substances in crude wastewater

Those involved in drug testing continue to grapple with the dynamic nature of emerging psychoactive substances (NPS) and their rapid infiltration into society. The challenge extends beyond merely detecting and measuring NPS using analytical tools; it also encompasses the complexities arising from the formation and presence of metabolites and degradation products. This study utilises liquid chromatography time-of-flight mass spectrometry to investigate the stability of new psychoactive substances in wastewater. Seven NPS compounds including 25C-NBOMe, 5F-APINACA 4-hydroxyphenyl, AB-PINACA, APINACA 4-hydroxyphenyl, fentanyl, norfentanyl and MDPV, along with their corresponding internal standard, were examined. Reference material for each NPS compound was introduced into a wastewater sample from a Wessex water treatment plant. The sample was then exposed to four different environments: room temperature, refrigerator temperature, acidification to pH 2, and the introduction of sodium metabisulfite. The findings highlight the critical dependence of storage conditions on target analytes, emphasizing the paramount importance of the time elapsed between collection and analysis for NPS wastewater analysis. Notably, synthetic cannabinoids exhibit limited stability in wastewater whereas cathinone-like substances demonstrate greater stability. Furthermore, metabolites prove to be more stable in wastewater than the parent drug, suggesting that focusing on metabolite detection may be more favourable for future analysis.

Rapid and Sensitive Detection of Fentanyl and Its Analogs by a Novel Chemiluminescence Immunoassay

BACKGROUND

Abuse of fentanyl and its analogs is a major contributor to the opioid overdose epidemic in the United States, but detecting and quantifying trace amounts of such drugs remains a challenge without resorting to sophisticated mass spectrometry-based methods.

METHODS

A sensitive immunoassay with a sub-picogram limit of detection for fentanyl and a wide range of fentanyl analogs has been developed, using a novel high-affinity antibody fused with NanoLuc, a small-size luciferase that can emit strong and stable luminescence. When used with human urine samples, the assay has a sub-picogram limit of detection for fentanyl, with results fully concordant with LC-MS.

RESULTS

When applied to clinical samples, the novel chemiluminescence immunoassay can detect low positive fentanyl missed by routine screening immunoassays, with a limit of detection of 0.8 pg/mL in human urine. When applied to environmental samples, the assay can detect levels as low as 0.25 pg fentanyl per inch2 of environment surface. Assay turnaround time is less than 1 h, with inexpensive equipment and the potential for high-throughput automation or in-field screening.

CONCLUSIONS

We have established a novel assay that may have broad applications in clinical, environmental, occupational, and forensic scenarios for detection of trace amounts of fentanyl and its analogs.

Differentiating Structurally Similar Fentanyl Analogs by Comparing Density Functional Theory (DFT) Calculations and Surface-Enhanced Raman Spectroscopy (SERS) Results

Fentanyl and fentanyl analogs are the main cause of recent overdose deaths in the United States. The presence of fentanyl analogs in illicit drugs makes it difficult to estimate their potencies. This makes the detection and differentiation of fentanyl analogs critically significant. Surface-enhanced Raman spectroscopy (SERS) can differentiate structurally similar fentanyl analogs by yielding spectroscopic fingerprints for the detected molecules. In previous years, five fentanyl analogs, carfentanil, furanyl fentanyl, acetyl fentanyl, 4-fluoroisobutyryl fentanyl (4-FIBF), and cyclopropyl fentanyl (CPrF), gained popularity and were found in 76.4% of the fentanyl analogs trafficked. In this study, we focused on 4-FIBF, CPrF, and structurally similar fentanyl analogs. We developed methods to differentiate these fentanyl analogs using theoretical and experimental methods. To do this, a set of fentanyl analogs were examined using density functional theory (DFT) calculations. The DFT results obtained in this project permitted the assignment of spectral bands. These results were then compared with normal Raman and SERS techniques. Structurally similar fentanyl analogs show important differences in their spectra, and they have been visually differentiated from each other both theoretically and experimentally. Additional results using principal component analysis and soft independent modeling of class analogy show they can be distinguished using this technique. The limit of detection values for FIBF and CPrF were determined to be 0.35 ng/mL and 4.4 ng/mL, respectively, using SERS. Experimental results obtained in this project can be readily implemented in field applications and smaller laboratories, where inexpensive portable Raman spectrometers are often present and used in drug analysis.

Associations among drug acquisition and use behaviors, psychosocial attributes, and opioid-involved overdoses

AIMS

This study sought to develop and assess an exploratory model of how demographic and psychosocial attributes, and drug use or acquisition behaviors interact to affect opioid-involved overdoses.

DESIGN

We conducted exploratory and confirmatory factor analysis (EFA/CFA) to identify a factor structure for ten drug acquisition and use behaviors. We then evaluated alternative structural equation models incorporating the identified factors, adding demographic and psychosocial attributes as predictors of past-year opioid overdose.

SETTING AND PARTICIPANTS

We used interview data collected for two studies recruiting opioid-misusing participants receiving services from a community-based syringe services program. The first investigated current attitudes toward drug-checking (N = 150). The second was an RCT assessing a telehealth versus in-person medical appointment for opioid use disorder treatment referral (N = 270).

MEASUREMENTS

Demographics included gender, age, race/ethnicity, education, and socioeconomic status. Psychosocial measures were homelessness, psychological distress, and trauma. Self-reported drug-related risk behaviors included using alone, having a new supplier, using opioids with benzodiazepines/alcohol, and preferring fentanyl. Past-year opioid-involved overdoses were dichotomized into experiencing none or any.

FINDINGS

The EFA/CFA revealed a two-factor structure with one factor reflecting drug acquisition and the second drug use behaviors. The selected model (CFI = .984, TLI = .981, RMSEA = .024) accounted for 13.1% of overdose probability variance. A latent variable representing psychosocial attributes was indirectly associated with an increase in past-year overdose probability (β = .234, p = .001), as mediated by the EFA/CFA identified latent variables: drug acquisition (β = .683, p < .001) and drug use (β = .567, p = .001). Drug use behaviors (β = .287, p = .04) but not drug acquisition (β = .105, p = .461) also had a significant, positive direct effect on past-year overdose. No demographic attributes were significant direct or indirect overdose predictors.

CONCLUSIONS

Psychosocial attributes, particularly homelessness, increase the probability of an overdose through associations with risky drug acquisition and drug-using behaviors. Further research is needed to replicate these findings with populations at high-risk of an opioid-related overdose to assess generalizability and refine the metrics used to assess psychosocial characteristics.

Tropine exacerbates the ventilatory depressant actions of fentanyl in freely-moving rats

Our lab is investigating the efficacy profiles of tropine analogs against opioid-induced respiratory depression. The companion manuscript reports that the cell-permeant tropeine, tropine ester (Ibutropin), produces a rapid and sustained reversal of the deleterious actions of fentanyl on breathing, alveolar-arterial (A-a) gradient (i.e., index of alveolar gas exchange), and arterial blood-gas (ABG) chemistry in freely-moving male Sprague Dawley rats, while not compromising fentanyl analgesia. We report here that in contrast to Ibutropin, the injection of the parent molecule, tropine (200 μmol/kg, IV), worsens the adverse actions of fentanyl (75 μg/kg, IV) on ventilatory parameters (e.g., frequency of breathing, tidal volume, minute ventilation, peak inspiratory and expiratory flows, and inspiratory and expiratory drives), A-a gradient, ABG chemistry (e.g., pH, pCO2, pO2, and sO2), and sedation (i.e., the righting reflex), while not affecting fentanyl antinociception (i.e., the tail-flick latency) in freely-moving male Sprague Dawley rats. These data suggest that tropine augments opioid receptor-induced signaling events that mediate the actions of fentanyl on breathing and alveolar gas exchange. The opposite effects of Ibutropin and tropine may result from the ability of Ibutropin to readily enter peripheral and central cells. Of direct relevance is that tropine, resulting from the hydrolysis of Ibutropin, would combat the Ibutropin-induced reversal of the adverse effects of fentanyl. Because numerous drug classes, such as cocaine, atropine, and neuromuscular blocking drugs contain a tropine moiety, it is possible that their hydrolysis to tropine has unexpected/unintended consequences. Indeed, others have found that tropine exerts the same behavioral profile as cocaine upon central administration. Together, these data add valuable information about the pharmacological properties of tropine.

Searching for Synthetic Opioid Rescue Agents: Identification of a Potent Opioid Agonist with Reduced Respiratory Depression

While in the process of designing more effective synthetic opioid rescue agents, we serendipitously identified a new chemotype of potent synthetic opioid. Here, we report that conformational constraint of a piperazine ring converts a mu opioid receptor (MOR) antagonist into a potent MOR agonist. The prototype of the series, which we have termed atoxifent (2), possesses potent in vitro agonist activity. In mice, atoxifent displayed long-lasting antinociception that was reversible with naltrexone. Repeated dosing of atoxifent produced antinociceptive tolerance and a level of withdrawal like that of fentanyl. In rats, while atoxifent produced complete loss of locomotor activity like fentanyl, it failed to produce deep respiratory depression associated with fentanyl-induced lethality. Assessment of brain biodistribution demonstrated ample distribution of atoxifent into the brain with a Tmax of approximately 0.25 h. These results indicate enhanced safety for atoxifent-like molecules compared to fentanyl.

What's New on the Street?: An Update on New Opioids, Psychoactive Drugs, and Synthetic Marijuana

Substance abuse is a widespread problem in the United States and worldwide. This use within the pregnant population is thought to reflect a pattern similar to the general population, with estimates of 10% to 15% of pregnant women experiencing substance abuse. Illicit substance use during pregnancy has increased substantially during the past decade in the United States. During the past decade, novel or atypical substances have emerged and become increasingly popular. Occurrences of toxicity and untoward fetal effects from designer drug use must be kept high on the watch list for all who practice in maternal-fetal, newborn, and emergency departments.

Correlates of overdose among 2711 people who use drugs and live in 7 rural US sites

BACKGROUND

Overdose rates in rural areas have been increasing globally, with large increases in the United States. Few studies, however, have identified correlates of non-fatal overdose among rural people who use drugs (PWUD). The present analysis describes correlates of nonfatal overdose among a large multistate sample of rural PWUD.

METHODS

This is a cross-sectional analysis of data gathered via surveys with PWUD recruited through seven Rural Opioid Initiative (ROI) sites. Descriptive analyses were conducted to assess the prevalence of past 30-day overdose. Generalized estimating equations were used to estimate a series of multivariable models quantifying relationships of select factors to past-month overdose; factors were selected using the Risk Environment Framework.

RESULTS

The multisite sample included 2711 PWUD, 6% of whom reported overdosing in the past 30 days. In the fully adjusted model, houselessness (AOR=2.27, 95%CI[1.48, 3.48]), a positive test result for Hepatitis C infection (AOR=1.73 95%CI[1.18, 2.52]) and heroin/fentanyl use (AOR= 8.58 95%CI [3.01, 24.50]) were associated with an increased risk of reporting past 30-day overdose, while having a high-school education or less was associated with reduced odds of overdose (AOR=0.52, 95% CI[0.37, 0.74]).

CONCLUSION

As in urban areas, houselessness, Hepatitis C infection, and the use of heroin and fentanyl were significant correlates of overdose. Widespread access to overdose prevention interventions - including fentanyl test strips and naloxone - is critical in this rural context, with particular outreach needed to unhoused populations, people living with Hepatitis C, and people using opioids.

Development of fentanyl-specific monoclonal antibody (mAb) to antagonize the pharmacological effects of fentanyl

Fentanyl, a critical component of opioid analgesics, poses a severe threat to public health, exacerbating the drug problem due to its potential fatality. Herein, we present two novel haptens designed with different attachment sites conjugated to keyhole limpet hemocyanin (KLH), aiming to develop an efficacious vaccine against fentanyl. KLH-Fent-1 demonstrated superior performance over KLH-Fent-2 in antibody titer, blood-brain distribution, and antinociceptive tests. Consequently, we immunized mice with KLH-Fent-1 to generate fentanyl-specific monoclonal antibodies (mAbs) using the hybridoma technique to compensate for the defects of active immunization in the treatment of opioid overdose and addiction. The mAb produced by hybridoma 9D5 exhibited the ability to recognize fentanyl and its analogs with a binding affinity of 10-10 M. Subsequently, we developed a human IgG1 chimeric mAb to improve the degree of humanization. Pre-treatment with murine and chimeric mAb significantly reduced the analgesic effect of fentanyl and altered its blood-brain biodistribution in vivo. Furthermore, in a mouse model of fentanyl-induced respiratory depression, the chimeric mAb effectively reversed respiratory depression promptly and maintained a certain level during the week. The development of high-affinity chimeric mAb gives support to combat the challenges of fentanyl misuse and its detrimental consequences. In conclusion, mAb passive immunization represents a viable strategy for addressing fentanyl addiction and overdose.

Tackling new psychoactive substances through metabolomics: UHPLC-HRMS study on natural and synthetic opioids in male and female murine models

Novel psychoactive substances (NPS) represent a broad class of drugs new to the illicit market that often allow passing drug-screening tests. They are characterized by a variety of structures, rapid transience on the drug scene and mostly unknown metabolic profiles, thus creating an ever-changing scenario with evolving analytical targets. The present study aims at developing an indirect screening strategy for NPS monitoring, and specifically for new synthetic opioids (NSOs), based on assessing changes in endogenous urinary metabolite levels as a consequence of the systemic response following their intake. The experimental design involved in-vivo mice models: 16 animals of both sex received a single administration of morphine or fentanyl. Urine was collected before and after administration at different time points; the samples were then analysed with an untargeted metabolomics LC-HRMS workflow. According to our results, the intake of opioids resulted in an elevated energy demand, that was more pronounced on male animals, as evidenced by the increase in medium and long chain acylcarnitines levels. It was also shown that opioid administration disrupted the pathways related to catecholamines biosynthesis. The observed alterations were common to both morphine and fentanyl: this evidence indicate that they are not related to the chemical structure of the drug, but rather on the drug class. The proposed strategy may reinforce existing NPS screening approaches, by identifying indirect markers of drug assumption.

Fentanyl activates opposing opioid and non-opioid receptor systems that control breathing

Fentanyl elicits profound disturbances in ventilatory control processes in humans and experimental animals. The traditional viewpoint with respect to fentanyl-induced respiratory depression is that once the effects on the frequency of breathing (Freq), tidal volume (TV), and minute ventilation (MV = Freq × TV) are resolved, then depression of breathing is no longer a concern. The results of the present study challenge this concept with findings, as they reveal that while the apparent inhibitory effects of fentanyl (75 μg/kg, IV) on Freq, TV, and MV in adult male rats were fully resolved within 15 min, many other fentanyl-induced responses were in full effect, including opposing effects on respiratory timing parameters. For example, although the effects on Freq were resolved at 15 min, inspiratory duration (Ti) and end inspiratory pause (EIP) were elevated, whereas expiratory duration (Te) and end expiratory pause (EEP) were diminished. Since the effects of fentanyl on TV had subsided fully at 15 min, it would be expected that the administration of an opioid receptor (OR) antagonist would have minimal effects if the effects of fentanyl on this and other parameters had resolved. We now report that the intravenous injection of a 1.0 mg/kg dose of the peripherally restricted OR antagonist, methyl-naloxone (naloxone methiodide, NLXmi), did not elicit arousal but elicited some relatively minor changes in Freq, TV, MV, Te, and EEP but pronounced changes in Ti and EIP. In contrast, the injection of a 2.5 mg/kg dose of NLXmi elicited pronounced arousal and dramatic changes in many variables, including Freq, TV, and MV, which were not associated with increases in non-apneic breathing events such as apneas. The two compelling conclusions from this study are as follows: 1) the blockade of central ORs produced by the 2.5 mg/kg dose of NLXmi elicits pronounced increases in Freq, TV, and MV in rats in which the effects of fentanyl had apparently resolved, and 2) it is apparent that fentanyl had induced the activation of two systems with counter-balancing effects on Freq and TV: one being an opioid receptor inhibitory system and the other being a non-OR excitatory system.

Electrochemical Determination of Fentanyl Using Carbon Nanofiber-Modified Electrodes

In this work, we report the direct electrochemical oxidation of fentanyl using commercial screen-printed carbon electrodes (SPCEs) modified with carboxyl-functionalized carbon nanofibers (fCNFs). CNFs have surface chemistry and reactivity similar to carbon nanotubes (CNTs), yet they are easier to produce and are of a lower cost than CNTs. By monitoring the current produced during the electrochemical oxidation of fentanyl, variables such as fCNF loading, fentanyl accumulation time, electrolyte pH, and differential pulse voltammetry parameters were optimized. Under an optimized set of conditions, the fCNF/SPCEs responded linearly to fentanyl in the concentration range of 0.125-10 μM, with a limit of detection of 75 nM. The fCNF/SPCEs also demonstrated excellent selectivity against common cutting agents found in illicit drugs (e.g., glucose, sucrose, caffeine, acetaminophen, and theophylline) and interferents found in biological samples (e.g., ascorbic acid, NaCl, urea, creatinine, and uric acid). The performance of the sensor was also successfully tested using fentanyl spiked into an artificial urine sample. The straightforward electrode assembly process, low cost, ease of use, and rapid response make the fCNF/SPCEs prime candidates for the detection of fentanyl in both physiological samples and street drugs.

A quantitative LC-MS/MS analysis of Xylazine, p-Fluorofentanyl, Fentanyl and Fentanyl-Related compounds in postmortem blood

The purpose of this study was to develop and validate a method to quantitate the veterinary sedative xylazine as well as 4-anilino-N-phenethylpiperidine (4-ANPP), acetyl fentanyl, fentanyl, norfentanyl, and p-fluorofentanyl in blood utilizing liquid chromatography tandem mass spectrometry. This method also qualitatively monitors for the presence of o-fluorofentanyl and m-fluorofentanyl isomers. UCT Clean Screen® DAU extraction columns were utilized to isolate the analytes in postmortem blood samples. The extracts were eluted, evaporated, reconstituted, and then analyzed using a Waters Acquity™ UPLC coupled a triple quadrupole mass spectrometer. The lower limit of quantitation was determined to be 0.1 ng/mL for all analytes, except for xylazine (0.2 ng/mL). The upper limit of quantitation for all analytes was 100 ng/mL. No interferences from matrix, internal standard, or common drug analytes were observed. Bias (-13.1-4.6 %) and precision (-13.14-10.3 %) fell within the acceptable ± 20 % criteria range. Dilution integrity at x2, x10, and x100 was evaluated and all results were within ± 20 % of the target concentration. Processed extract stability was evaluated after 72 h and all results were within ± 20 % of the analyte initial concentration. Matrix effects were the most prominent with xylazine, but deemed acceptable as the deuterated internal standard also observed comparable enhancement. Analysis of 89 postmortem blood samples by this method resulted in positive results for fentanyl (0.27-66 ng/mL, n = 82), xylazine (0.24-958 ng/mL, n = 21), 4-ANPP (0.10-38 ng/mL, n = 72), acetyl fentanyl (0.18-1.5 ng/mL, n = 3), p-fluorofentanyl (0.11-33 ng/mL, n = 30), and norfentanyl (0.10-98 ng/mL, n = 73).

Identification of Unique Fragmentation Patterns of Fentanyl Analog Protomers Using Structures for Lossless Ion Manipulations Ion Mobility-Orbitrap Mass Spectrometry

The opioid crisis in the United States is being fueled by the rapid emergence of new fentanyl analogs and precursors that can elude traditional library-based screening methods, which require data from known reference compounds. Since reference compounds are unavailable for new fentanyl analogs, we examined if fentanyls (fentanyl + fentanyl analogs) could be identified in a reference-free manner using a combination of electrospray ionization (ESI), high-resolution ion mobility (IM) spectrometry, high-resolution mass spectrometry (MS), and higher-energy collision-induced dissociation (MS/MS). We analyzed a mixture containing nine fentanyls and W-15 (a structurally similar molecule) and found that the protonated forms of all fentanyls exhibited two baseline-separated IM distributions that produced different MS/MS patterns. Upon fragmentation, both IM distributions of all fentanyls produced two high intensity fragments, resulting from amine site cleavages. The higher mobility distributions of all fentanyls also produced several low intensity fragments, but surprisingly, these same fragments exhibited much greater intensities in the lower mobility distributions. This observation demonstrates that many fragments of fentanyls predominantly originate from one of two different gas-phase structures (suggestive of protomers). Furthermore, increasing the water concentration in the ESI solution increased the intensity of the lower mobility distribution relative to the higher mobility distribution, which further supports that fentanyls exist as two gas-phase protomers. Our observations on the IM and MS/MS properties of fentanyls can be exploited to positively differentiate fentanyls from other compounds without requiring reference libraries and will hopefully assist first responders and law enforcement in combating new and emerging fentanyls.

Fentanyl overdose: Temporal effects and prognostic factors in SKH1 mice

Fentanyl exposure and overdose are growing concerns in public health and occupational safety. This study aimed to establish parameters of fentanyl lethality in SKH1 mice for future overdose research. Lethality was determined using the up-down procedure, with subjects monitored post-administration using pulse oximetry (5 min) and then whole-body plethysmography (40 min). Following the determination of subcutaneous dose-response, [18F]Fluorodeoxyglucose positron emission tomography (18 F-FDG PET) was performed after LD10 fentanyl at 40 min, 6 h, 24 h or 7 days post-dose. LD10 and LD50 were observed to be 110 and 135 mg/kg, respectively, and consistent with four-parameter logistic fit values of 111.2 and 134.6 mg/kg (r2  = 0.9996). Overdose (LD10 or greater) yielded three distinct cardiovascular groups: survival, non-survival with blood oxygen saturation (SpO2) minimum ≥37% and non-survival with SpO2 <37%. Breaths per minute, minute volume and inspiratory quotient were significantly different between surviving and non-surviving animals for up to 40 min post-injection. 18 F-FDG PET revealed decreased glucose uptake in the heart, lungs and brain for up to 24 h. These findings provide critical insights into fentanyl lethality in SKH1 mice, including non-invasive respiratory effects and organ-specific impacts that are invaluable for future translational studies investigating the temporal effects of fentanyl overdose.

Exploring the topic structure and abuse trends of new psychoactive Substance since the 21st century from a bibliometric perspective

Nowadays, NPS abuse are continuing to expand in terms of harm and scope, due to its cheap and easy to manufacture anywhere in the world. This study reviewed articles related to seven heavily abused NPS to analyze the structure and trends of NPS abuse. A total of 2476 articles were retrieved based on the search strategy for bibliometric analysis. A significant trend of research in recent years was the increasing number of research on synthetic opioids and designer benzodiazepines, but synthetic cannabinoid and synthetic cathinone still dominate, which were mainly concerned with the development of metabolic models and determining methods as well as their abuse characteristics and reasons. However, with the introduction of class-wide ban on synthetic cannabinoid in China and a series of enhancements in other countries, the abuse of it might decrease to some extent, but more than 20 kinds of synthetic cannabinoid beyond the scope of ban in China still reminded researchers of their potential threats. As for synthetic cathinone, an important phenomenon was some of the drugs first identified during certain period might be more widely distributed in the future. Besides, several problems such as the regulation and prevention mode of emerging NPS, development of testing technologies as well as the interpretation and identification of multiple NPS combinations were also worth paying attention to. This study could help entrants better understand the structure of NPS abuse and provided direction for future research in forensic toxicology.

Acute opioid overdose in pediatric patients

Recent increases in pediatric and adolescent opioid fatalities mandate an urgent need for early consideration of possible opioid exposure and specific diagnostic and management strategies and interventions tailored to these unique populations. In contrast to adults, pediatric methods of exposure include accidental ingestions, prescription misuse, and household exposure. Early recognition, appropriate diagnostic evaluation, along with specialized treatment for opioid toxicity in this demographic are discussed. A key focus is on Naloxone, an essential medication for opioid intoxication, addressing its unique challenges in pediatric use. Unique pediatric considerations include recognition of accidental ingestions in our youngest population, critical social aspects including home safety and intentional exposure, and harm reduction strategies, mainly through Naloxone distribution and education on safe medication practices. It calls for a multifaceted approach, including creating pediatric-specific guidelines, to combat the opioid crisis among children and to work to lower morbidity and mortality from opioid overdoses.

Determining the manner of death in victims in drug-induced psychosis: a case of an atypical head stab wound

This case report presents a rare case of an atypical head stab wound suffered by a drug addict and inflicted with a screwdriver during drug-induced psychosis. It describes the diagnostic and treatment procedures in the hospital and the findings of the subsequent autopsy. It also analyzes the review of the interpretation of the CT scans made upon admission and the subsequent treatment by an independent medical review panel, which revealed signs of medical mismanagement. Therefore, it also discusses the legal consequences that the case may have involved for the attending physicians in addition to the consequences for the suspected perpetrator. The report raises many issues encountered in the case in terms of the clinical treatment and forensic determination of the manner of death in cases of injuries caused by sharp instruments and highlights the importance of comprehensive evaluation of the circumstantial evidence together with the clinical or autopsy findings, since such evidence may sometimes be overlooked in clinical practice.

The evolution of fentanyl-related substances: Prevalence and drug concentrations in postmortem biological specimens at the Miami-Dade Medical Examiner Department

Since 2014, the Miami-Dade Medical Examiner Department (MDME) has observed a drastic increase in the number of fentanyl and fentanyl analog (fentanyl-related substances (FRSs)) fatalities since its introduction into the heroin and cocaine supply. Due to the prevalence of FRS in Miami-Dade County, the MDME toxicology laboratory began documenting each case in which fentanyl and/or a fentanyl analog was identified. Additional information monitored included demographics (age, race and sex), other drugs identified, cause of death (COD) and manner of death (MOD). From 2014 to 2022, the MDME toxicology laboratory analyzed a total of 1,989 cases that tested positive for FRS, of which 1,707 had detectable and/or quantifiable fentanyl concentrations in postmortem cases. The majority of decedents were white males (62%), and the predominant age range was 25-34 years. The most prevalent MOD was accident (93%) with the most common COD listed as acute combined drug toxicity of fentanyl in combination with other drugs (79%). Other drugs found in combination with fentanyl included heroin, cocaine (most prevalent), synthetic cathinones and ethanol. Of all FRS cases, 9% (170 cases) involved fentanyl alone as a COD, while 2% (38 cases) included only fentanyl analogs. Fentanyl concentrations ranged from 1.0 to 1,646 ng/mL in peripheral blood, 1.2 to 449 ng/mL in central blood, 3.2 to 28 ng/mL in donor blood (obtained during tissue harvesting), 1.1 to 108 ng/mL in antemortem blood, 8.5 to 1,130 ng/g in liver and 2.0 to 471 ng/g in brain. Drug concentrations were also reported for an additional eight fentanyl analogs. Considering the prevalence, high potency and constant evolution of FRS, it is important to continuously monitor trends and report drug concentrations in complex medical examiner casework in an effort to educate pathologists, law enforcement and local governments.

In vitro μ-opioid receptor activation potential of U10 and β-U10, positional isomers of the synthetic opioid naphthyl U-47700

New synthetic opioids (NSOs) with diverse chemical structures continue to appear on recreational drug markets worldwide. U-type opioids have become one of the largest groups of non-fentanyl-related NSOs. Starting in 2020, a previously unreported U-compound coined "β-U10" (2-naphthyl U-47700; N-[2-(dimethylamino)cyclohexyl]-N-methylnaphthalene-2-carboxamide) was identified in Australia and the United States. β-U10 is a positional isomer of α-U10 (1-naphthyl U-47700), more commonly known as "U10." Here, the first comparative in vitro pharmacological characterization of naphthyl U-47700 (U10 and β-U10), together with the structural analogue U-47700 and fentanyl, is reported. Application of a cell-based μ-opioid receptor (MOR) activation (β-arrestin 2 recruitment) assay demonstrated β-U10 (EC50  = 348 nM; Emax  = 150% vs. hydromorphone) to be less potent than U-47700 (EC50  = 116 nM; Emax  = 154%) and fentanyl (EC50  = 9.35 nM; Emax  = 146%) but considerably more active than the α-isomer (EC50 value in the μM range). For the latter, maximum receptor activation could not be reached at 100 μM. The difference in MOR activation potential for U10 and β-U10 stresses the importance of (analytical) differentiation between closely related analytes. The emergence of β-U10 on the recreational drug market is an example of the continuing emergence of non-fentanyl-related NSOs and further emphasizes the need to closely monitor fluctuations in the drug supply.

Investigations on the in vitro and in vivo metabolic fate of the new synthetic opioid desmethylmoramide using HPLC-HRMS/MS for toxicological screening purposes

New synthetic opioids are an increasing challenge for clinical and forensic toxicologists that developed over the recent years. Desmethylmoramide (DMM), a structural analogue of methadone, is one of the most recent appearances on the drug market. This study investigated its metabolic fate in rat and pooled human liver S9 fraction (pHLS9) to allow the identification of suitable urinary screening targets beyond the parent compound. The analysis of rat urine after the administration of DMM revealed five metabolites, which were the result of pyrrolidine ring or morpholine ring hydroxylation and combinations of them. Additionally, an N',N-bisdesalkyl metabolite was formed. Incubations of DMM using pHLS9 revealed a pyrrolidine hydroxy metabolite, as well as an N-oxide. No Phase II metabolites were detected in either rat urine or incubations using pHLS9. The metabolism of DMM did in part comply with that of its archetype dextromoramide (DXM). Although morpholine ring hydroxylation and N-oxidation were described for DXM and detected for DMM, phenyl ring hydroxylation was not found for DMM but described for DXM. An analysis of 24 h pooled rat urine samples after DMM administration identified the hydroxy and dihydroxy metabolite as the most abundant excretion products, and they may, thus, serve as screening targets, as the parent compound was barely detectable.

Analysis of over 250 novel synthetic opioids and xylazine by LC-MS-MS in blood and urine

Novel Synthetic Opioids (NSO) are frequently found in postmortem (PM) and human performance (HP) forensic toxicology casework, resulting in impairment and fatal overdoses. Developing a broad NSO method benefits public health, as it can be used to identify trends in potent opioid use to develop risk management programs. This project aimed to design a comprehensive, rapid and routine method for the selective analysis of over 250 novel synthetic opioids in blood and urine. This method rapidly extracted 150 µL of blood or urine via protein precipitation followed by size-exclusion filtration, evaporation and reconstitution. Separation and data acquisition were achieved on a 12 min LC-MS-MS method using an F5 column. Data processing was expedited with a custom built-in query created in-house that automated processing and enhanced quality assurance. Validation according to ASB/ANSI Standard 036 was performed and applicability of the method was assessed using proficiency test and authentic casework samples. Assessed in blood and urine qualitatively were 261 unique analytes including fentanyl analogs (fentalogs), nitazenes and other miscellaneous synthetic opioids. As 59 isomeric target analytes were placed into groups due to co-elution, there were 202 distinct acquired targets or target - groups. To demonstrate applicability, 27 proficiency test blood samples received over an approximate 4-year period were analyzed with 126 expected results assessed comprising 25 unique target analytes. Additionally, 617 fatal accidental overdoses within San Francisco in 2022 were retroactively analyzed by this method with almost 10% of cases containing a new NSO substance(s). Such trends and NSO substances were previously unknown in this community.

Are carfentanil and acrylfentanyl naloxone resistant?

The rapid rise in deaths since 2012 due to opioid poisoning is correlated with the proliferation of potent synthetic opioid agonists such as fentanyl, acrylfentanyl, and carfentanil. The efficacy of frontline antidotes such as naloxone in reversing such poisoning events has been questioned, and the possibility of naloxone-resistant synthetic opioids has been raised. In this manuscript, we applied in vitro techniques to establish the median effective inhibitory concentrations for fentanyl, acrylfentanyl, and carfentanil and subsequently evaluate naloxone's ability to reverse agonist-receptor interactions.

Forecasting drug-overdose mortality by age in the United States at the national and county levels

The drug-overdose crisis in the United States continues to intensify. Fatalities have increased 5-fold since 1999 reaching a record high of 108,000 deaths in 2021. The epidemic has unfolded through distinct waves of different drug types, uniquely impacting various age, gender, race, and ethnic groups in specific geographical areas. One major challenge in designing interventions and efficiently delivering treatment is forecasting age-specific overdose patterns at the local level. To address this need, we develop a forecasting method that assimilates observational data obtained from the CDC WONDER database with an age-structured model of addiction and overdose mortality. We apply our method nationwide and to three select areas: Los Angeles County, Cook County, and the five boroughs of New York City, providing forecasts of drug-overdose mortality and estimates of relevant epidemiological quantities, such as mortality and age-specific addiction rates.

An automated group-housed oral fentanyl self-administration method in mice

RATIONALE AND OBJECTIVES

Social factors play a critical role in human drug addiction, and humans often consume drugs together with their peers. In contrast, in traditional animal models of addiction, rodents consume or self-administer the drug in their homecage or operant self-administration chambers while isolated from their peers. Here, we describe HOMECAGE ("Home-cage Observation and Measurement for Experimental Control and Analysis in a Group-housed Environment"), a translationally relevant method for studying oral opioid self-administration in mice. This setting reduces experimental confounds introduced by social isolation or interaction with the experimenter.

METHODS

We have developed HOMECAGE, a method in which mice are group-housed and individually monitored for their consumption of a drug vs. a reference liquid.

RESULTS

Mice in HOMECAGE preserve naturalistic aspects of behavior, including social interactions and circadian activity. The mice showed a preference for fentanyl and escalated their fentanyl intake over time. Mice preferred to consume fentanyl in bouts during the dark cycle. Mice entrained to the reinforcement schedule of the task, optimizing their pokes to obtain fentanyl rewards, and maintained responding for fentanyl under a progressive ratio schedule. HOMECAGE also enabled the detection of cage-specific and individual-specific behavior patterns and allowed the identification of differences in fentanyl consumption between co-housed control and experimental mice.

CONCLUSIONS

HOMECAGE serves as a valuable procedure for translationally relevant studies on oral opioid intake under conditions that more closely mimic the human condition. The method enables naturalistic investigation of factors contributing to opioid addiction-related behaviors and can be used to identify novel treatments.