Assessment of the Antinociceptive, Respiratory-Depressant, and Reinforcing Effects of the Low pKa Fluorinated Fentanyl Analogs, FF3 and NFEPP

RATIONALE

Recent studies report that fentanyl analogs with relatively low pKa values produce antinociception in rodents without other mu opioid-typical side effects due to the restriction of their activity to injured tissue with relatively low pH values. However, it is unclear if and to what degree these compounds may produce mu opioid-typical side effects (respiratory depression, reinforcing effects) at doses higher than those required to produce antinociception.

OBJECTIVES

The present study compared the inflammatory antinociceptive, respiratory-depressant, and reinforcing effects of fentanyl and two analogs of intermediate (FF3) and low (NFEPP) pKa values in terms of potency and efficacy in male and female Sprague-Dawley rats.

METHODS

Nociception was produced by administration of Complete Freund's Adjuvant into the hind paw of subjects, and antinociception was measured using an electronic Von Frey test. Respiratory depression was measured using whole-body plethysmography. Reinforcing effects were measured in self-administration using a progressive-ratio schedule of reinforcement. The dose ranges tested for each drug encompassed no effect to maximal effects.

RESULTS

All compounds produced full effects in all measures but varied in potency. FF3 and fentanyl were equipotent in antinociception and self-administration, but FF3 was less potent than fentanyl in respiratory depression. NFEPP was less potent than fentanyl in every measure. The magnitude of potency difference between antinociception and other effects was greater for FF3 than for NFEPP or fentanyl, indicating that FF3 had the widest margin of safety when relating antinociception to respiratory-depressant and reinforcing effects.

CONCLUSIONS

Low pKa fentanyl analogs possess potential as safer analgesics, but determining the optimal degree of difference for pKa relative to fentanyl will require further study due to some differences between the current results and findings from prior work with these 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.

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.

On the challenge of unambiguous identification of fentanyl analogs: Exploring measurement diversity using standard reference mass spectral libraries

Fentanyl analogs are a class of designer drugs that are particularly challenging to unambiguously identify due to the mass spectral and retention time similarities of unique compounds. In this paper, we use agglomerative hierarchical clustering to explore the measurement diversity of fentanyl analogs and better understand the challenge of unambiguous identifications using analytical techniques traditionally available to drug chemists. We consider four measurements in particular: gas chromatography retention indices, electron ionization mass spectra, electrospray ionization tandem mass spectra, and direct analysis in real time mass spectra. Our analysis demonstrates how simultaneously considering data from multiple measurement techniques increases the observable measurement diversity of fentanyl analogs, which can reduce identification ambiguity. This paper further supports the use of multiple analytical techniques to identify fentanyl analogs (among other substances), as is recommended by the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG).

The rise and rise of fentanyl in postmortem casework

Forensic toxicology laboratories are navigating a period of time with increasing drug overdose deaths, an opioid epidemic, the impact of the COVID-19 pandemic, and the illicit drug market flooded with novel psychoactive substances. In New York City, the Department of Forensic Toxicology has experienced a 56% increase in postmortem casework in the past decade with fentanyl detected in 80% of all overdose deaths. Over a period of 2.5 years, 15,638 postmortem cases were tested for the presence of fentanyl and fentanyl analogs using liquid-chromatography tandem mass spectrometry (LCMSMS). Fentanyl was detected in approximately one third of cases and of these 4447 cases with femoral blood. A twofold increase in cases with high concentrations of fentanyl (>100 ng/mL) was observed between 2021 and 2022. The minor metabolite and precursor chemical, 4-ANPP (4-anilino-N-phenethylpiperidine) may help differentiate between illicit and licit fentanyl. 4-ANPP blood concentrations were <10 ng/mL in 98% of the cases and the 4-ANPP:fentanyl ratio was <0.67 for 99.1% of blood specimens. Only six cases had 4-ANPP concentrations higher than the corresponding fentanyl blood concentration. This study also highlights, the changing fentanyl analogs found in postmortem cases since 2016 in NYC with the emergence of fluorofentanyl initially identified in 2020 and continuing to dominate in comparison with the prevalence of other analogs, many of which are no longer detected in casework. The detection of one of the latest drugs to be mixed with fentanyl, namely xylazine, has also increased in prevalence by 36.7% in 2022 compared with 2021.

Field-portable detection of fentanyl and its analogs: A review

The need to detect fentanyl and its analogs in the field is an important capability to help prevent unintentional exposure or overdose on these substances, which may result in death. Many portable methods historically used in the field by first responders and other field users to detect and identify other chemical substances, such as hazardous materials, have been applied to the detection and identification of these synthetic opioids. This paper describes field portable spectroscopic methods used for the detection and identification of fentanyl and its analogs. The methods described are automated colorimetric tests including lateral flow assays; vibrational spectroscopy (mid-infrared and Raman); gas chromatography-mass spectrometry; ion mobility spectrometry, and high-pressure mass spectrometry. In each case the background and key details of these technologies are outlined, followed by a discussion of the application of the technology in the field. Attention is paid to the analysis of complex mixtures and limits of detection, including the required spectral databases and algorithms used to interrogate these types of samples. There is also an emphasis on providing actionable information to the (likely) non-scientist operators of these instruments in the field.

Identifying reliable ions for the statistical differentiation of structurally similar fentanyl analogs

Definitive identification of fentanyl analogs based on mass spectral comparison is challenging given the high degree of structural and, hence, spectral similarity. To address this, a statistical method was previously developed in which two electron-ionization (EI) mass spectra are compared using the unequal variance t-test. Normalized intensities of corresponding ions are compared, testing the null hypothesis (H0 ) that the difference in intensity is equal to zero. If H0 is accepted at all m/z values, the two spectra are statistically equivalent at the specified confidence level. If H0 is not accepted at any m/z value, then there is a significant difference in intensity at that m/z value between the two spectra. In this work, the statistical comparison method is applied to distinguish EI spectra of valeryl fentanyl, isovaleryl fentanyl, and pivaloyl fentanyl. Spectra of the three analogs were collected over a 9-month period and at different concentrations. At the 99.9% confidence level, the spectra of corresponding isomers were statistically associated. Spectra of different isomers were statistically distinct, and ions responsible for discrimination were identified in each comparison. To account for inherent instrument variations, discriminating ions for each pairwise comparison were ranked based on the magnitude of the calculated t-statistic (tcalc ) value. For a given comparison, ions with higher tcalc values are those with the greatest difference in intensity between the two spectra and, therefore, are considered more reliable for discrimination. Using these methods, objective discrimination among the spectra was achieved and ions considered most reliable for discrimination of these isomers were identified.

Review of analytical methods for screening and quantification of fentanyl analogs and novel synthetic opioids in biological specimens

Fentanyl, fentanyl analogs, and other novel synthetic opioids (NSO), including nitazene analogs, prevail in forensic toxicology casework. Analytical methods for identifying these drugs in biological specimens need to be robust, sensitive, and specific. Isomers, new analogs, and slight differences in structural modifications necessitate the use of high-resolution mass spectrometry (HRMS), especially as a non-targeted screening method designed to detect newly emerging drugs. Traditional forensic toxicology workflows, such as immunoassay and gas chromatography mass spectrometry (GC-MS), are generally not sensitive enough for detection of NSOs due to observed low (sub-μg/L) concentrations. For this review, the authors tabulated, reviewed, and summarized analytical methods from 2010-2022 for screening and quantification of fentanyl analogs and other NSOs in biological specimens using a variety of different instruments and sample preparation approaches. Limits of detection or quantification for 105 methods were included and compared to published standards and guidelines for suggested scope and sensitivity in forensic toxicology casework. Methods were summarized by instrument for screening and quantitative methods for fentanyl analogs and for nitazenes and other NSO. Toxicological testing for fentanyl analogs and NSOs is increasingly and most commonly being conducted using a variety of liquid chromatography mass spectrometry (LC-MS)-based techniques. Most of the recent analytical methods reviewed exhibited limits of detection well below 1 μg/L to detect low concentrations of increasingly potent drugs. In addition, it was observed that most newly developed methods are now using smaller sample volumes which is achievable due to the sensitivity increase gained by new technology and new instrumentation.

Does occupational exposure to fentanyl cause illness? A systematic review

INTRODUCTION

The opioid epidemic in the United States continues to result in an increasing number of deaths and is increasingly dominated by fentanyl and fentanyl analogs. As a result, first responders are likely to come into contact with fentanyl-containing substances daily. Concerns persist regarding occupational exposure resulting in intoxication. We performed a systematic review to describe occupational illnesses from fentanyl and its analogs.

METHODS

We conducted a systematic review of the literature following the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to assess the danger of occupational exposure to fentanyl. The PubMed, EMBASE, Google Scholar, SCOPUS, CINAHL, and National Institute for Occupational Safety and Health databases were queried to identify occupational fentanyl exposures. Studies included were single case reports, case series, observational studies, controlled studies, and abstracts from scientific presentations. We reviewed articles meeting the eligibility criteria and abstracted outcome data. Outcomes included study design, number of study subjects and study demographics, description of exposure, personal protective equipment used, duration of symptoms, illness developed, medical evaluation performed, treatment provided, hospitalizations, deaths, drug testing performed, and any situation review performed to prevent illness, analytical confirmation of the identity of culprit agent, and concentrations of drug in serum/blood.

RESULTS

Our search yielded 454 citations after deduplication. After abstract and text review, 12 unique reports met the inclusion criteria. All identified studies were observational studies. Ten of the 12 were Health Hazard Evaluation reports from the National Institute for Occupational Safety and Health; two reports describe the same exposure case. There were no reported instances of comprehensive drug testing using liquid chromatography-mass spectrometry or gas chromatography-mass spectrometry in exposed first responders. Among first responders possibly exposed to fentanyl or fentanyl analogs, none were admitted to the hospital, and only three first responders received naloxone. The three officers who received naloxone lacked recommended personal protective equipment and had subjective improvement of symptoms following naloxone. There were no instances of severe respiratory depression requiring assisted ventilation or hospital admission. Among forensic laboratory technicians, only one instance of detectable concentrations of fentanyl in urine was reported, and there were no instances of symptomatic cases.

CONCLUSIONS

Among published reports of 27 first responders with symptoms after possible ambient fentanyl exposure, symptoms, recorded physical findings, and vital signs were inconsistent with acute opioid toxicity. Breaches in the recommended use of personal protective equipment appeared common. Only three persons received naloxone, although none had plausible effects of fentanyl. No suspected exposure to fentanyl led to hospitalization or death. Based on these low-quality data, there were no plausible opioid effects from ambient exposure to suspected fentanyl.

In vitro metabolite identification of acetylbenzylfentanyl, benzoylbenzylfentanyl, 3-fluoro-methoxyacetylfentanyl, and 3-phenylpropanoylfentanyl using LC-QTOF-HRMS together with synthesized references

Acetylbenzylfentanyl, benzoylbenzylfentanyl, 3-fluoro-methoxyacetylfentanyl, and 3-phenylpropanoylfentanyl are fentanyl analogs that have been reported to the European Monitoring Centre for Drugs and Drug Addiction in recent years. The aim of this study was to identify metabolic pathways and potential biomarker metabolites of these fentanyl analogs. The compounds were incubated (5 μM) with cryopreserved hepatocytes for up to 5 h in vitro. Metabolites were analyzed with liquid chromatography-quadrupole time of flight-high-resolution mass spectrometry (LC-QTOF-HRMS). The experiments showed that acetylbenzylfentanyl, benzoylbenzylfentanyl, and 3-phenylpropanoylfentanyl were mainly metabolized through N-dealkylation (forming nor-metabolites) and 3-fluoro-methoxyacetylfentanyl mainly through demethylation. Other observed metabolites were formed by mono-/dihydroxylation, dihydrodiol formation, demethylation, dehydrogenation, amide hydrolysis, and/or glucuronidation. The experiments showed that a large number of metabolites of 3-phenylpropanoylfentanyl were formed. The exact position of hydroxy groups in formed monohydroxy metabolites could not be established solely based upon recorded MSMS spectra of hepatocyte samples. Therefore, potential monohydroxy metabolites of 3-phenylpropanoylfentanyl, with the hydroxy group in different positions, were synthesized and analyzed together with the hepatocyte samples. This approach could reveal that the β position of the phenylpropanoyl moiety was highly favored; β-OH-phenylpropanoylfentanyl was the most abundant metabolite after the nor-metabolite. Both metabolites have the potential to serve as biomarkers for 3-phenylpropanoylfentanyl. The nor-metabolites of acetylbenzylfentanyl, benzoylbenzylfentanyl, and 3-fluoro-methoxyacetylfentanyl do also seem to be suitable biomarker metabolites, as do the demethylated metabolite of 3-fluoro-methoxyacetylfentanyl. Identified metabolic pathways and formed metabolites were in agreement with findings in previous studies of similar fentanyl analogs.

Insights from biosurveillance: non-fatal opioid overdoses in Rhode Island 2019-21

BACKGROUND AND AIMS

Opioids biosurveillance is a new approach to public health surveillance of non-fatal overdoses that relies upon laboratory analysis of residual biospecimens from hospitals treating opioids overdoses. In Rhode Island (RI), USA, hospitals report suspected opioid overdoses to the Department of Health. Residual specimens associated with these overdoses are submitted to the State Health Laboratories for further characterization. This surveillance project aimed to characterize non-fatal overdoses through toxicological testing of urine specimens associated with non-fatal overdoses during the initial 2-year period of biosurveillance implementation in RI to assess the feasibility and public health utility of this approach.

METHODS

This study included individuals who presented for treatment for a suspected opioid overdose in 10 RI hospitals between July 2019 and June 2021. Urine samples were received for 1354 unique overdose encounters corresponding to reported overdoses. Some individuals experienced multiple overdoses during this time. Urine samples were extracted and then analyzed by liquid chromatography tandem mass spectrometry with a panel consisting of 1033 opiates, synthetic opioids, fentanyl analogs and select metabolites. Temporal and spatial trends were evaluated for the studied population.

RESULTS

A total of 1354 samples were tested for the presence of opioids in urine collected from individuals who experienced a suspected overdose. Fentanyl (and/or norfentanyl) was present in 79% of all samples in which opioids were found (n = 1033). Fentanyl analogs varied in their contribution to these totals, with observations ranging as high as 35% of all opioid-containing samples in August 2019 and May 2021.

CONCLUSIONS

Laboratory identification of opioids involved in suspected overdoses shows that fentanyl and its analogs are the main drivers of the opioids overdose epidemic in Rhode Island, USA. The biosurveillance approach is unique in its ability to quantify contributions of novel fentanyl analogs to the burden of overdoses.

[Analysis of 29 fentanyl analogs and their fragmentation mechanism by liquid chromatography-quadrupole time-of-flight mass spectrometry]

Given the wide variety of fentanyl analogs, the test for this entire group tends to be crucial and particularly difficult since all fentanyl-like substances are listed as controlled substances in China. This study meticulously analyzed the fragmentation pathways and mechanisms of 29 fentanyl analogs and summarized the fragmentation pathways and features for the entire group of fentanyl analogs, thus providing a reference for related screening tests. Fentanyl, thiofentanyl, and sufentanil were selected as the representative compounds in this study, and the fragmentation mechanism of their fragment ions was interpreted. The general fragmentation rules for fentanyl analogs were summarized as well. The fragment ions of the three compounds formed by induced cleavage (i) came with high abundance ratios, such as fragment ions of m/z 188, 105, 194, 111, and 238, while the induced cleavage was due to the amide and piperidinyl groups. Moreover, the induction ability of amide group was significantly stronger than that of the piperidinyl group, and induced cleavage was the main fragmentation pathway for most of the fentanyl analogs. Furthermore, the fragment ions with m/z 281 and 287 for fentanyl and thiofentanyl were formed by loss of the propionyl group after single H rearrangement (rH). The fragment ions with m/z 216, 146, and 132 for fentanyl and thiofentanyl were formed by double H rearrangement (r2H). Although their abundance ratios were not high, they still had specificity and regularity. Elimination reaction (re) was also a very common fragmentation pathway for these compounds, leading to fragment ions with m/z 134 and 140. Phenylethyl substituents were more prone to the elimination reaction with a higher abundance ratio than thiophenethyl substituents. Compounds such as sufentanil with methoxy substituents at the piperidinyl para-position could produce a large number of fragment ions, which were more susceptible to the rH pathway and loss of methanol neutral molecules, leading to the formation of ions with m/z 355. Similarly, compounds such as remifentanil bearing a methyl formate substituent at the piperidine para-position also produced numerous fragment ions, which were more prone to the rH pathway to lose methyl formate or methanol neutral molecules and furnish fragment ions with m/z 317 or 345. Compounds containing hydroxyl substituents, such as β-hydroxyfentanyl and β-hydroxythiofentanyl, produce significant dehydration ions and formed fragment ions with m/z 335 (β-hydroxyfentanyl) and m/z 341 (β-hydroxythiofentanyl). A method based on liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) for the qualitative and quantitative determination of the 29 fentanyl analogs was developed. Drugs and white powder samples were extracted by acetonitrile, as well as protein and milk beverage samples. Sugar-containing solids or powders, drinking water, fruit and vegetable drinks, health drinks, tea drinks, and alcohol samples were extracted by 10% acetonitrile aqueous solution. Following vortexing, centrifugation, and membrane separation, the target compounds were separated on a Kinetex C18 column (100 mm×2.1 mm, 2.6 μm) with gradient elution at a flow rate of 0.4 mL/min. The mobile phases were composed of acetonitrile and 0.08% formic acid aqueous solution. The target compounds were quantified by LC-QTOF-MS using an external standard method in positive ion mode. The 29 fentanyl analogs showed good linear relationships in the range of 1-20 μg/L, and the correlation coefficients were greater than 0.995. The limits of detection (LODs) and limits of quantification (LOQs) were 0.01 mg/kg and 0.05, respectively. The average recoveries were 85.2%-112.9% for hypoglycemic drugs, Lulu drinks, glucose powder, Zhenlu health drink and chocolate, with RSDs of 1.9%-19.8% (n=6). This method is rapid, simple, time-saving, highly sensitivity and stable, and it is applicable to a wide variety of samples. Hence, it is suitable for the identification, confirmation, and quantitative detection of the 29 fentanyl analogs in drugs, solids or powders containing sugar, beverages, drinking water, wine samples, etc.

Novel Synthetic Opioids (NSO) Use in Opioid Dependents Entering Detoxification Treatment

INTRODUCTION

Over the last decade, the use of New/Novel Synthetic Opioids (NSO) has emerged as an increasing problem, and especially so in the USA. However, only little is known about the prevalence and history of NSO use in European heroin dependents.

METHOD

A cross-sectional multicenter study, carried out with the means of both standardized interviews and urine toxicology enhanced screening, in a sample of opioid addicted patients referred for an in-patient detoxification treatment.

RESULTS

Sample size included here n = 256 patients; prior to admission, 63.7% were prescribed with an opioid maintenance treatment. Lifetime use of heroin and opioid analgesics was reported by 99.2 and 30.4%, respectively. Lifetime NSO/fentanyl use was reported by 8.7% (n = 22); a regular use was reported by 1.6% (n = 4), and ingestion over the 30 days prior to admission by 0.8% (n = 2). Most typically, patients had started with a regular consumption of heroin, followed by maintenance opioids; opioid analgesics; and by NSO. Self-reported data were corroborated by the toxicology screenings carried out; no evidence was here identified for the presence of heroin being contaminated by fentanyl/derivatives.

DISCUSSION

NSO and also opioid analgesics did not play a relevant role in the development and the course of opioid/opioid use disorders in German patients referred for an inpatient detoxification treatment.

Improvements in Toxicology Testing to Identify Fentanyl Analogs and Other Novel Synthetic Opioids in Fatal Drug Overdoses, Connecticut, January 2016-June 2019

OBJECTIVES

Drug overdose deaths in Connecticut increasingly involve a growing number of fentanyl analogs and other novel nonfentanyl synthetic opioids (ie, novel synthetics). Current postmortem toxicology testing methods often lack the sophistication needed to detect these compounds. We examined how improved toxicology testing of fatal drug overdoses can determine the prevalence and rapidly evolving trends of novel synthetics.

METHODS

From 2016 to June 2019, the Connecticut Office of the Chief Medical Examiner increased its scope of toxicology testing of suspected drug overdose deaths in Connecticut from basic to enhanced toxicology testing to detect novel synthetics. The toxicology laboratory also expanded its testing panels during this time. We analyzed toxicology results to identify and quantify the involvement of novel synthetics over time.

RESULTS

From 2016 to June 2019, 3204 drug overdose deaths received enhanced toxicology testing; novel synthetics were detected in 174 (5.4%) instances. Ten different novel synthetics were detected with 205 total occurrences. Of 174 overdose deaths with a novel synthetic detected, most had 1 (n = 146, 83.9%) or 2 (n = 26, 14.9%) novel synthetics detected, with a maximum of 4 novel synthetics detected. Para-fluorobutyrylfentanyl/FIBF, furanylfentanyl, and U-47700 were most identified overall, but specific novel synthetics came in and out of prominence during the study period, and the variety of novel synthetics detected changed from year to year.

CONCLUSIONS

Enhanced toxicology testing for drug overdose deaths is effective in detecting novel synthetics that are not identified through basic toxicology testing. Identifying emerging novel synthetics allows for a timely and focused response to potential drug outbreaks and illustrates the changing drug market.

Novel chimeric monoclonal antibodies that block fentanyl effects and alter fentanyl biodistribution in mice

The prevalence and societal impact of opioid use disorder (OUD) is an acknowledged public health crisis that is further aggravated by the current pandemic. One of the devastating consequences of OUD is opioid overdose deaths. While multiple medications are now available to treat OUD, given the prevalence and societal burden, additional well-tolerated and effective therapies are still needed. To this point, we have developed chimeric monoclonal antibodies (mAb) that will specifically complex with fentanyl and its analogs in the periphery, thereby preventing them from reaching the central nervous system. Additionally, mAb-based passive immunotherapy offers a high degree of specificity to drugs of abuse and does not interfere with an individual’s ability to use any of the medications used to treat OUD. We hypothesized that sequestering fentanyl and its analogs in the periphery will mitigate their negative effects on the brain and peripheral organs. This study is the first report of chimeric mAb against fentanyl and its analogs. We have discovered, engineered the chimeric versions, and identified the selectivity of these antibodies, through in vitro characterization and in vivo animal challenge studies. Two mAb candidates with very high (0.1–1.3 nM) binding affinities to fentanyl and its analogs were found to be effective in engaging fentanyl in the periphery and blocking its effects in challenged animals. Results presented in this work constitute a major contribution in the field of novel therapeutics targeting OUD.

Illicitly Manufactured Fentanyl Entering the United States

The 'third wave' of the ongoing opioid overdose crisis in the United States (US) is driven in large measure by illicitly manufactured fentanyl (IMF), a highly potent synthetic opioid or an analog developed in clandestine laboratories primarily in China and Mexico. It is smuggled into this country either as IMF or as precursors. The southern border of the US is a frequent point of entry for smuggled IMF and the amounts are increasing year over year. IMF is also sometimes mixed in with other substances to produce counterfeit drugs and dealers as well as end-users may not be aware of IMF in their products. IMF is inexpensive to produce and when mixed with filler materials can be used to cut heroin, vastly expanding profitability. It is an attractive product for smuggling as very tiny amounts can be extremely potent and highly profitable. Drug trafficking over the border also involves the tandem epidemic of money laundering as drugs enter the country and cash payments exit. While drug smuggling in and out of the US (and other nations) has been going on for decades, the patterns are changing. Highly potent and potentially lethal IMF is a dangerous new addition to the illicit drug landscape and one with disastrous consequences.

Quantification of fentanyl analogs in oral fluid using LC-QTOF-MS

Oral fluid is a valuable alternative matrix for forensic toxicologists due to ease of observed collection, limited biohazardous exposure, and indications of recent drug use. Limited information is available for fentanyl analog prevalence, interpretation, or analysis in oral fluid. With increasing numbers of fentanyl-related driving under the influence of drug (DUID) cases appearing in the United States, the development of detection methods is critical. The purpose of the present study was to develop and validate a quantitative method for fentanyl analogs in oral fluid (collected via Quantisal™) using liquid chromatography-quadrupole-time-of-flight-mass spectrometry (LC-QTOF-MS). Validation resulted in limits of detection and quantification ranging from 0.5 to 1 ng/mL. Established linear range was 1-100 ng/mL for all analytes, except acetyl fentanyl at 0.5-100 ng/mL (R²  > 0.994). Within- and between-run precision and bias were considered acceptable with maximum values of ±15.2%CV and ±14.1%, respectively. Matrix effects exhibited ionization enhancement for all analytes with intensified enhancement at a low concentration (9.3-47.4%). No interferences or carryover was observed. Fentanyl analogs were stable in processed extracts stored in the autosampler (4^⁰ C) for 48h. The validated method was used to quantify fentanyl analogs in authentic oral fluid samples (n=17) from probationers/parolees. Fentanyl and 4-ANPP concentrations were 1.0-104.5 ng/mL and 1.2-5.7 ng/mL, respectively.

Wooden Chest syndrome: The atypical pharmacology of fentanyl overdose

WHAT IS KNOWN AND OBJECTIVE

A large percentage of opioid overdose fatalities involve fentanyl or one of its legal or illegal analogs (F/FAs). Is there something about the pharmacology of these drugs that make them unusually dangerous in an overdose?

COMMENT

Some of the reasons for the dangers of overdose of F/FAs is their high potency and low cost (that leads to wide distribution). But it is rarely asked if the basic pharmacology of F/FAs differ in some fundamental way from conventional opioids such as morphine and heroin. In addition to centrally mediated respiratory depression via opioid receptors, F/FAs cause rigidity in the key respiratory muscles of the chest, upper airway and diaphragm ("wooden chest syndrome," WCS) by a non-opioid mechanism.

WHAT IS NEW AND CONCLUSION

WCS is an atypical pharmacology of F/FAs. Because of its rapid onset and non-opioid mechanism, WCS makes F/FA overdose particularly dangerous.

Acute Intoxications Involving Valerylfentanyl Identified at the New York City Office of Chief Medical Examiner

The detection of novel fentanyl analogs in both seized drugs and toxicological specimens has presented a significant challenge to laboratories with respect to identification, sourcing reference drug standards, time required for method development and ensuring sufficient method sensitivity. The New York City Office of Chief Medical Examiner (NYC OCME) has included testing for valerylfentanyl as part of a panel of synthetic opioids since May 2017 but did not identify the first valerylfentanyl positive case until July 2018. Unlike many other illicit fentanyl analogs that were briefly identified before being replaced with a new analog, valerylfentanyl has persisted over time and continues to be identified in New York City acute polydrug intoxications. Since July 2018, a total of 69 cases were identified with valerylfentanyl present, but there were no cases where it was the sole intoxicant. 84% of decedents were male, with the majority between the ages of 50 and 59 years (39%) and were predominantly Hispanic (49%). The cause of death in all 69 cases involved acute polydrug intoxication, while the manner of death was deemed an accident in 68 cases and undetermined in one case. Concentrations of valerylfentanyl in postmortem blood ranged from < 0.10 to 21 ng/mL with 44.9% (N = 31) of the concentrations at or below the lower limit of quantification (0.10 ng/mL) but above the limit of detection (0.05 ng/mL). Fentanyl was present in 100% of the cases and in higher concentrations (1.6-116 ng/mL). The most common drug classes detected with valerylfentanyl were other opiates (76.8%), cocaine/metabolites (50.7%), benzodiazepines (29%), and ethanol (21.7%). Valerylfentanyl is a relatively unknown fentanyl analog with limited information in the scientific literature. This study presents the first publication detailing a series of postmortem cases involving valerylfentanyl in acute intoxications and includes key demographic information and femoral blood concentrations for improved interpretation and analysis.

Opioid epidemic spread from Northern and Eastern Europe to Mediterranean Area

Abstract

The addiction to illicit opioid and the misuse of prescription synthetic opioids pain relievers and fentanyl analogs generated an opioid epidemic in North America over the last two decades that affected public health with a constantly rising number of overdoses deaths. This health treat moved to Europe with a significant increase starting from 2015 involving mainly norther and eastern countries and finally also the Mediterranean area. The "lock down" isolation and economic recession caused by COVID-19 pandemic showed a resurgence in opioid use and harms.

Untargeted Metabolic Profiling of 4-Fluoro-Furanylfentanyl and Isobutyrylfentanyl in Mouse Hepatocytes and Urine by Means of LC-HRMS

The diffusion of new psychoactive substances (NPS) is highly dynamic and the available substances change over time, resulting in forensic laboratories becoming highly engaged in NPS control. In order to manage NPS diffusion, efficient and innovative legal responses have been provided by several nations. Metabolic profiling is also part of the analytical fight against NPS, since it allows us to identify the biomarkers of drug intake which are needed for the development of suitable analytical methods in biological samples. We have recently reported the characterization of two new analogs of fentanyl, i.e., 4-fluoro-furanylfentanyl (4F-FUF) and isobutyrylfentanyl (iBF), which were found for the first time in Italy in 2019; 4F-FUF was identified for the first time in Europe and was notified to the European Early Warning System. The goal of this study was the characterization of the main metabolites of both drugs by in vitro and in vivo experiments. To this end, incubation with mouse hepatocytes and intraperitoneal administration to mice were carried out. Samples were analyzed by means of liquid chromatography-high resolution mass spectrometry (LC-HRMS), followed by untargeted data evaluation using Compound Discoverer software with a specific workflow, designed for the identification of the whole metabolic pattern, including unexpected metabolites. Twenty metabolites were putatively annotated for 4-FFUF, with the dihydrodiol derivative appearing as the most abundant, whereas 22 metabolites were found for iBF, which was mainly excreted as nor-isobutyrylfentanyl. N-dealkylation of 4-FFUF dihydrodiol and oxidation to carbonyl metabolites for iBF were also major biotransformations. Despite some differences, in general there was a good agreement between in vitro and in vivo samples.

First Polish case of fatal single-substance poisoning with cyclopropylfentanyl, a new synthetic opioid

The article presents the first Polish case of fatal single-substance poisoning with cyclopropylfentanyl, a representative of fentanyl derivatives, whose victim was a 37-year-old man. This opioid was detected in biological material collected during medicolegal autopsy and in the syringe found near the deceased. Blood and urine samples were analyzed using liquid chromatography with mass spectrometry. The concentration of cyclopropylfentanyl was 24 ng/mL in blood and 73 ng/mL in urine.

Activation of the μ-opioid receptor by alicyclic fentanyls: Changes from high potency full agonists to low potency partial agonists with increasing alicyclic substructure

Fentanyl analogs represent an important group of new psychoactive substances and knowing their efficacy and potency might assist in interpreting observed concentrations. The potency of fentanyl analogs can be estimated from in vitro studies and can be used to establish structure–activity relationships. In this study, recombinant CHO‐K1 cells (AequoScreen) expressing the human μ‐opioid receptor were used to establish dose–response curves via luminescent analysis for cyclopropyl‐, cyclobutyl‐, cyclopentyl‐, cyclohexyl‐, and 2,2,3,3‐tetramethylcyclopropylfentanyl (TMCPF), on three separate occasions, using eight different concentrations in an eight‐fold serial dilution in triplicates starting at ~60 μM. Fentanyl was used as a full agonist reference while morphine and buprenorphine were included for comparison. Cyclopropylfentanyl (EC₅₀ = 4.3 nM), cyclobutylfentanyl (EC50 = 6.2 nM), and cyclopentylfentanyl (EC₅₀ = 13 nM) were full agonists slightly less potent than fentanyl (EC₅₀ = 1.7 nM). Cyclohexylfentanyl (EC₅₀ = 3.1 μM, efficacy 48%) and TMCPF (EC₅₀ = 1.5 μM, efficacy 65%) were partial agonists less potent than morphine (EC₅₀ = 430 nM). Based on the results, cyclopropyl‐, cyclobutyl‐, and cyclopentylfentanyl would be expected to induce intoxication or cause fatal poisonings at similar concentrations to fentanyl, while the toxic or fatal concentrations of cyclohexylfentanyl and TMCPF would be expected to be much higher.

Novel Opioids: Systematic Web Crawling Within the e-Psychonauts' Scenario

Background

A wide range of novel psychoactive substances (NPSs) are regularly searched and discussed online by e-psychonauts. Among NPSs, the range of prescription/non-prescription opioids (fentanyl and non-fentanyl analogs) and herbal derivatives currently represents a challenge for governments and clinicians.

Methods

Using a web crawler (i.e., NPS.Finder^®), the present study aimed at assessing psychonaut fora/platforms to better understand the online situation regarding opioids.

Results

The open-web crawling/navigating software identified some 426 opioids, including 234 fentanyl analogs. Of these, 176 substances (162 were very potent fentanyls, including two ohmefentanyl and seven carfentanyl analogs) were not listed in either international or European NPS databases.

Conclusion

A web crawling approach helped in identifying a large number, indeed higher than that listed by European/international agencies, of unknown opioids likely to possess a significant misuse potential. Most of these novel/emerging substances are still relatively unknown. This is a reason of concern; each of these analogs potentially presents with different toxicodynamic profiles, and there is a lack of docking, preclinical, and clinical observations. Strengthening multidisciplinary collaboration between clinicians and bioinformatics may prove useful in better assessing public health risks associated with opioids.

Metabolic Pathways and Potencies of New Fentanyl Analogs

Up to now, little is known about the metabolic pathways of new fentanyl analogs that have recently emerged on the drug markets worldwide with high potential for producing addiction and severe adverse effects including coma and death. For some of the compounds, limited information on the metabolism has been published, however, for others so far no information is available. Considering the well characterized metabolism of the pharmaceutically used opioid fentanyl and the so far available data, the metabolism of the new fentanyl analogs can be anticipated to generally involve reactions like hydrolysis, hydroxylation (and further oxidation steps), N- and O-dealkylation and O-methylation. Furthermore, phase II metabolic reactions can be expected comprising glucuronide or sulfate conjugate formation. When analyzing blood and urine samples of acute intoxication cases or fatalities, the presence of metabolites can be crucial for confirmation of the uptake of such compounds and further interpretation. Here we present a review on the metabolic profiles of new fentanyl analogs responsible for a growing number of severe and fatal intoxications in the United States, Europe, Canada, Australia, and Japan in the last years, as assessed by a systematic search of the scientific literature and official reports.

Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry Assay for Quantifying Fentanyl and 22 Analogs and Metabolites in Whole Blood, Urine, and Hair

Recently, synthetic opioid-related overdose fatalities, led by illicitly manufactured fentanyl and analogs, increased at an alarming rate, posing a global public health threat. New synthetic fentanyl analogs have been constantly emerging onto the drug marked for the last few years, to circumvent the laws and avoid analytical detection. Analytical methods need to be regularly updated to keep up with the new trends. In this study, we aimed to develop a new method for detecting the newest fentanyl analogs with a high sensitivity, in whole blood, urine, and hair. The method is intended to provide to clinical and forensic toxicologists a tool for documenting consumption. We developed a comprehensive ultra-high-performance liquid chromatography-tandem mass spectrometry method for quantifying fentanyl and 22 analogs and metabolites. Urine samples were simply diluted before injection; a liquid-liquid extraction was performed for blood testing; and a solid phase extraction was performed in hair. The chromatographic separation was short (8 min). The method was validated with a high sensitivity; limits of quantifications ranged from 2 to 6 ng/L in blood and urine, and from 11 to 21 pg/g in hair. The suitability of the method was tested with 42 postmortem blood, urine, or hair specimens from 27 fatalities in which fentanyl analogs were involved. Average blood concentrations (±SD) were 7.84 ± 7.21 and 30.0 ± 18.0 μg/L for cyclopropylfentanyl and cyclopropyl norfentanyl, respectively (n = 8), 4.08 ± 2.30 μg/L for methoxyacetylfentanyl, (n = 4), 40.2 ± 38.6 and 44.5 ± 21.1 μg/L for acetylfentanyl and acetyl norfentanyl, respectively (n = 3), 33.7 and 7.17 μg/L for fentanyl and norfentanyl, respectively (n = 1), 3.60 and 0.90 μg/L for furanylfentanyl and furanyl norfentanyl, respectively (n = 1), 0.67 μg/L for sufentanil (n = 1), and 3.13 ± 2.37 μg/L for 4-ANPP (n = 9). Average urine concentrations were 47.7 ± 39.3 and 417 ± 296 μg/L for cyclopropylfentanyl and cyclopropyl norfentanyl, respectively (n = 11), 995 ± 908 μg/L for methoxyacetylfentanyl, (n = 3), 1,874 ± 1,710 and 6,582 ± 3,252 μg/L for acetylfentanyl and acetyl norfentanyl, respectively (n = 5), 146 ± 318 and 300 ± 710 μg/L for fentanyl (n = 5) and norfentanyl (n = 6), respectively, 84.0 and 23.0 μg/L for furanylfentanyl and furanyl norfentanyl, respectively (n = 1), and 50.5 ± 50.9 μg/L for 4-ANPP (n = 10). Average hair concentrations were 2,670 ± 184 and 82.1 ± 94.7 ng/g for fentanyl and norfentanyl, respectively (n = 2), and 10.8 ± 0.57 ng/g for 4-ANPP (n = 2).

Opioids in the Frame of New Psychoactive Substances Network: A Complex Pharmacological and Toxicological Issue

BACKGROUND

New psychoactive substances (NPS), often referred to as "legal highs" or "designer drugs", are derivatives and analogues of existing psychoactive drugs that are introduced in the recreational market to circumvent existing legislation on drugs of abuse.

OBJECTIVE

This systematic review aims to gather the state of the art regarding chemical, molecular pharmacology and toxicological information of opioid class of NPS.

METHODS

Chemical, pharmacological, toxicological and clinical effects of opioid class of NPS were searched in books and in PubMed (U.S. National Library of Medicine) without a limiting period.

RESULTS

Within this class, fentanyl analogues are among the most frequently abused and pose several clinical concerns and therefore will be thoroughly discussed. Other opioid sub-categories of NPS frequently misused include AH-7921, MT-45, U-47700, U-50488, desomorphine, mitragynine, tramadol, tapentadol, salvinorin A and its analogue herkinorin.

CONCLUSION

Due to inefficient monitoring techniques, as well as limited knowledge regarding the acute and long-term effects of opioids NPS, further clinical and forensic toxicological studies are required.

Drug Interactions With New Synthetic Opioids

Fentanyl, fentanyl analogs, and other new synthetic opioids (NSO) have burst onto the illegal drug market as new psychoactive substances (NPS). They are often sold as heroin to unsuspecting users and produce euphoria through their agonist action on μ- opioid receptors. Their high consumption, often combined with other substances, has led to multiple intoxications during recent years. In some countries, such as the United States, the consumption of opioids, whether for medical or recreational purposes, has become epidemic and is considered a public health problem. Fentanyl analogs are more potent than fentanyl which in turn is 50 times more potent than morphine. Furthermore, some fentanyl analogs have longer duration of action and therefore interactions with other substances and medicines can be more serious. This review is focused on the potentially most frequent interactions of opioid NPS taking into account the drugs present in the reported cases of poly-intoxication, including other illegal drugs of abuse and medication. Substances involved are mainly antidepressants, antihistamines, antipsychotics, benzodiazepines, analgesics, anesthetics, psychostimulants, other opioids, alcohol, and illegal drugs of abuse. The interactions can be produced due to pharmacokinetic and pharmacodynamic mechanisms. Naloxone can be used as an antidote, although required doses might be higher than for traditional opioid intoxications. It is crucial that doctors who habitually prescribe opioids, which are often misused by patients and NPS users, be aware of designer opioids' potentially life-threatening drug-drug interactions in order to prevent new cases of intoxication.

Detectability of fentanyl and designer fentanyls in urine by 3 commercial fentanyl immunoassays

In recent times, structural variants of fentanyl (designer fentanyls) have appeared on the recreational drug market for new psychoactive substances (NPS). These potent opioids have caused harmful intoxications and increased opioid-related mortality in many countries. This work evaluated 3 commercial immunoassays for fentanyl screening in urine and investigated whether they are useful also for screening of designer fentanyls. The assays examined were the Thermo DRI® Fentanyl Enzyme Immunoassay, the ARK™ Fentanyl Assay homogeneous enzyme immunoassay, and the Immunalysis® Fentanyl Urine SEFRIA™ Drug Screening Kit. A liquid chromatography-high-resolution mass spectrometry method was used as reference. The DRI fentanyl immunoassay generated somewhat higher assay imprecision values (%CV) compared with the ARK™ and SEFRIA™ assays, but all assays showed %CV values acceptable for routine use. The 3 assays showed overall good detectability (33%-95% cross-reactivity) for blank urine samples spiked with acetylfentanyl, acrylfentanyl, butyrfentanyl, 4-chloroisobutyrfentanyl, 4-fluorobutyrfentanyl, 4-fluorofentanyl, 4-fluoroisobutyrfentnyl, isobutyrfentanyl, methoxyacetylfentanyl, or tetrahydrofuranfentanyl, whereas 4-methoxybutyrfentanyl (all assays) and 2-fluorofentanyl (DRI assay) showed low cross-reactivity. A good detectability of designer fentanyls was confirmed in urine samples from authentic acute intoxications. In conclusion, the present results demonstrate that the urinary fentanyl immunoassays are generally useful also for preliminary screening of fentanyl analogs sold as NPS. When the SEFRIA™ assay was applied for testing of 980 urine samples from patients treated for drug dependence in Sweden, only 1 sample was confirmed positive for fentanyl.

In Vitro and In Vivo Metabolite Identification Studies for the New Synthetic Opioids Acetylfentanyl, Acrylfentanyl, Furanylfentanyl, and 4-Fluoro-Isobutyrylfentanyl

New fentanyl analogs have recently emerged as new psychoactive substances and have caused numerous fatalities worldwide. To determine if the new analogs follow the same metabolic pathways elucidated for fentanyl and known fentanyl analogs, we performed in vitro and in vivo metabolite identification studies for acetylfentanyl, acrylfentanyl, 4-fluoro-isobutyrylfentanyl, and furanylfentanyl. All compounds were incubated at 10 μM with pooled human hepatocytes for up to 5 h. For each compound, four or five authentic human urine samples from autopsy cases with and without enzymatic hydrolysis were analyzed. Data acquisition was performed in data-dependent acquisition mode during liquid chromatography high-resolution mass spectrometry analyses. Data was analyzed (1) manually based on predicted biotransformations and (2) with MetaSense software using data-driven search algorithms. Acetylfentanyl, acrylfentanyl, and 4-fluoro-isobutyrylfentanyl were predominantly metabolized by N-dealkylation, cleaving off the phenethyl moiety, monohydroxylation at the ethyl linker and piperidine ring, as well as hydroxylation/methoxylation at the phenyl ring. In contrast, furanylfentanyl's major metabolites were generated by amide hydrolysis and dihydrodiol formation, while the nor-metabolite was minor or not detected in case samples at all. In general, in vitro results matched the in vivo findings well, showing identical biotransformations in each system. Phase II conjugation was observed, particularly for acetylfentanyl. Based on our results, we suggest the following specific and abundant metabolites as analytical targets in urine: a hydroxymethoxy and monohydroxylated metabolite for acetylfentanyl, a monohydroxy and dihydroxy metabolite for acrylfentanyl, two monohydroxy metabolites and a hydroxymethoxy metabolite for 4-fluoro-isobutyrylfentanyl, and a dihydrodiol metabolite and the amide hydrolysis metabolite for furanylfentanyl.

Synthesis and biological evaluation of some novel 1-substituted fentanyl analogs in Swiss albino mice

Fentanyl [N-(1-phenethyl-4-piperidinyl)propionanilide] is a potent opioid analgesic agent, but a has narrow therapeutic index. We reported earlier on the synthesis and bioefficacy of fentanyl and its 1-substituted analogs (1–4) in mice. Here we report the synthesis and biological evaluation of four additional analogs, viz. N-isopropyl-3-(4-(N-phenylpropionamido)piperidin-1-yl)propanamide (5), N-t-butyl-3-(4-(N-phenylpropionamido)piperidin-1-yl)propanamide (6), isopropyl 2-[4-(N-phenylpropionamido)piperidin-1-yl]propionate (7) and t-butyl 2-[4-(N-phenylpropionamido)piperidin-1-yl]propionate (8). The median lethal dose (LD₅₀) determined by intravenous, intraperitoneal and oral routes suggests these analogs to be comparatively less toxic than fentanyl. On the basis of observational assessment on spontaneous activities of the central, peripheral, and autonomic nervous systems, all the analogs were found to be similar to fentanyl. Naloxone hydrochloride abolished the neurotoxic effects of these analogs, thereby ascertaining their opioid receptor-mediated effects. All the analogs displayed significant analgesic effects, measured by formalin-induced hind paw licking and tail immersion tests at their respective median effective dose (ED₅₀). They also exhibited 8–12 fold increase in therapeutic index over fentanyl. However, 5 and 6 alone produced lower ED₅₀ (20.5 and 21.0 µg/kg, respectively) and higher potency ratio (1.37 and 1.33, respectively) compared to fentanyl. They could thus be considered for further studies on pain management.