A lot testing protocol for quality assurance of fentanyl test strips for harm reduction applications.

Fentanyl test strips (FTS) are lateral flow immunoassays that were originally designed and validated for detecting low concentrations of fentanyl in urine. Some FTS are now being marketed for the harm reduction purpose of testing street drugs for the presence of fentanyl. This manuscript provides a simple protocol to assess whether different brands and lots of fentanyl test strips perform adequately for use in drug checking. The results gathered from this protocol will document problems with particular lots or brands of FTS, help buyers choose from among the array of products, provide feedback to manufacturers to improve their products, and serve as an early warning system for ineffective products.

Fentanyl Test Strips for Harm Reduction: A Scoping Review.

BACKGROUND: High potency synthetic opioids like fentanyl have continued to replace or contaminate the supply of illicit drugs in North America, with fentanyl test strips (FTSs) often used as a harm reduction tool for overdose prevention. The available evidence to support FTS for harm reduction has yet to be summarized. METHODS: A search of PubMed, Ovid Embase, and Web of Science was conducted in March 2023. A 2-stage review was conducted to screen by title and abstract and then by full text by 2 reviewers. Data were extracted from each study using a standardized template. RESULTS: A total of 91 articles were included, mostly from North America, predominantly reporting on FTS along with other harm reduction tools, and all conducted after 2016. No randomized controlled trials are reported. Robust evidence exists supporting the sensitivity and specificity of FTS, along with their acceptability and feasibility of use for people who use drugs and as a public health intervention. However, limited research is available on the efficacy of FTS as a harm reduction tool for behavior change, engagement in care, or overdose prevention. CONCLUSIONS: Though FTSs are highly sensitive and specific for point of care testing, further research is needed to assess the association of FTS use with overdose prevention. Differences in FTS efficacy likely exist between people who use opioids and nonopioid drugs, with additional investigation strongly needed. As drug testing with point-of-care immunoassays is embraced for nonfentanyl contaminants such as xylazine and benzodiazepines, increased investment in examining overdose prevention is necessary.

An urgent need for community lot testing of lateral flow fentanyl test strips marketed for harm reduction in Northern America.

BACKGROUND: Fentanyl test strips (FTS) are lateral flow immunoassay strips designed for detection of ng/mL levels of fentanyl in urine. In 2021, the US Centers for Disease Control and the Substance Abuse and Mental Health Administration stated that federal funds could be used for procurement of FTS for harm reduction strategies approved by the government such as drug checking. The market for FTS has expanded rapidly in the US and Canada. However, there is no regulatory oversight by either government to ensure proper function of FTS that are being marketed for drug checking. MAIN BODY: Many brands of FTS have rapidly entered the harm reduction market, creating concerns about the reproducibility and accuracy of their performance from brand to brand and lot to lot. Some examples are provided in this Comment. Similar problems with product quality were observed in the mid 2000's when lateral flow immunoassays for malaria were funded in many countries and again in 2020, when COVID-19 tests were in huge demand. The combination of high demand and low levels of regulation and enforcement led some manufacturers to join the goldrush without adequate field testing or quality assurance. We argue that the harm reduction community urgently needs to set a lot checking program in place. A set of simple protocols for conducting the tests and communicating the results have been developed, and are described in the following Perspectives paper in this issue. CONCLUSION: In the absence of governmental regulation and enforcement, the harm reduction community should implement a FTS lot checking program. Based on previous experience with the malaria diagnostic lot checking program, this inexpensive effort could identify products that are not suitable for harm reduction applications and provide valuable feedback to manufacturers. Dissemination of the results will help harm reduction organizations to ensure that FTS they use for drug checking are fit for the purpose.

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.

Bedside urine testing for fentanyl in self-reported heroin users in a tertiary Brisbane emergency department.

OBJECTIVE: To determine if patients presenting to our toxicology unit following self-reported heroin use had positive urine immunoassay testing for fentanyl or its analogues. METHODS: Urine samples from consenting patients were tested at the bedside for the presence of opiates or fentanyl and its analogues. RESULTS: Over a 30-month period, 58 patients were recruited. All samples tested positive for opiates, but none tested positive for fentanyl or its analogues. CONCLUSION: In patients presenting to our toxicology unit in Brisbane, we did not find any cases where the urine of patients self-reporting heroin exposure tested positive for fentanyl or its analogues.

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.

Understand the FDA-cleared fentanyl testing: A clinical evaluation of the SEFRIA fentanyl immunoassay.

BACKGROUND: Screening for fentanyl has been adopted by many clinical laboratories to detect illicit drug use and monitor medication adherence. However, compared to other urine drug testing, fentanyl screening assays are relatively new and therefore their clinical performances are largely unknown. This study extensively evaluated the clinical performance, positive cutoff, and interference profile of SEFRIA fentanyl immunoassay in real patient settings. METHODS: The FDA-cleared cutoff of 1.0 was verified with 21 urine samples with low or undetectable levels of fentanyl. After assay implementation, all screened-positive samples were confirmed by liquid chromatography-tandem mass spectrometry. A new cutoff was derived from the numeric values of the false positive (FP) screening results. The FP rates before and after implementing the new cutoff were compared. Interferences were identified by an untargeted drug analysis and confirmed by spiking experiments. RESULTS: A total of 3951 screening results were reviewed in the first two months of the assay utilization, 410 were screened-positive, and 157 (38 %) were FP. After a new cutoff of 1.3 was implemented, the FP rate was reduced to 17 % based on 11119 screening results. Trazodone, labetalol, and haloperidol were identified as major interferents, accounting for 56 % of the FP results using the cutoff of 1.3. CONCLUSION: By applying the new cutoff and including an interference comment to positive screening results, the FP rate was reduced from initial 38 % to 7.5 % (17 % times 56 %).

Rapid detection of furanyl fentanyl in complex matrices using Leidenfrost desorption-assisted low-temperature arc plasma ionization mass spectrometry.

The abuse of illicit drugs poses serious threats to the physical and mental health of users, as well as to the overall safety and welfare of society. In this work, we present a newly developed technique for drug detection based on mass spectrometry. This technique combines Leidenfrost desorption with low-temperature arc plasma ionization mass spectrometry. This method is applicable for detecting furanyl fentanyl in complex matrices. Key advantages of this technique include minimal sample fragmentation and high sensitivity for detection. The Leidenfrost desorption plays a pivotal role in this methodology, as it spontaneously concentrates analyte molecules during the gradual evaporation of the solvent. Eventually, these concentrated molecules are redistributed at their highest concentrations, resulting in exceptionally high sensitivity. In the course of our investigation, we achieved a remarkable detection limit of 10 pg mL-1 for furanyl fentanyl in pure water. Moreover, the characteristic ion peaks of furanyl fentanyl can be distinctly identified within complex matrices such as wine, beverages, urine, and lake water. This innovative drug detection technology offers several advantages, including a simple setup, cost-effectiveness, rapid detection, high sensitivity, and minimal sample pretreatment.

Evaluation of in-house drug evidence testing by King County Medical Examiner's Office in "real-time" fatal overdose surveillance.

With the escalating overdose epidemic, many surveillance efforts have appeared. In 2018, King County Medical Examiner's Office (KCMEO) initiated a fatal overdose surveillance project aimed at expediting death certification and disseminating timely information. In this project, KCMEO investigators collected items of evidence of drug use from overdose death scenes, which were tested by five in-house methods, four using handheld devices: TruNarc Raman spectrometer, with and without the manufacture's H-Kit, Rigaku ResQ Raman spectrometer, and MX908 mass spectrometer. The fifth in-house method used fentanyl-specific urine test strips. Results from in-house testing were compared with results from Washington State Patrol (WSP) Materials Analysis Laboratory. From 2019 to 2022, there were 4244 evidence items of drugs and paraphernalia collected from 1777 deaths scenes. A total of 7526 in-house tests were performed on collected specimens, and 2153 tests were performed by the WSP laboratory using standard analytical methods. The WSP results served as reference standards to calculate performance metrics of the in-house methods. Sensitivities, specificities, and predictive values ranged from good to poor depending on the method, drug, and evidence type. Certain drugs were often associated with specific evidence types. Acetaminophen was frequently found in combination with fentanyl. Fentanyl test strips gave good scores for detecting fentanyl; otherwise, in-house methods using handheld devices had poor performance scores with novel drugs and drugs diluted in mixtures. The results showed that in-house testing of drug evidence has value for medical examiner overdose surveillance, but it is resource intensive, and success depends on collaboration with forensic laboratories.

Advances in fentanyl testing.

Fentanyl is a synthetic opioid that was approved by the FDA in the late 1960s. In the decades since, non-prescription use of fentanyl, its analogs, and structurally unrelated novel synthetic opioids (NSO) has become a worsening public health crisis. There is a clear need for accessible testing for these substances in biological specimens and in apprehended drugs. Immunoassays for fentanyl in urine are available but their performance is restricted to facilities that hold moderate complexity laboratory licenses. Immunoassays for other matrices such as oral fluid (OF), blood, and meconium have been developed but are not widely available. Point of care tests (POCT), such as lateral flow immunoassays or fentanyl test strips (FTS), are widely available but not approved by the FDA for clinical use. All immunoassays are vulnerable to false positive and false negative results. Immunoassays may or may not be able to detect fentanyl analogs and NSOs. Mass spectrometry (MS) can accurately and reliably measure fentanyl and its major metabolite norfentanyl in urine and oral fluid. MS is available at reference laboratories and large hospitals. Liquid chromatography paired with tandem mass spectrometry (LC-MS/MS) is the most widely used method and has outstanding specificity and sensitivity for fentanyl and norfentanyl. When compared to immunoassays, MS is more expensive, requires more technical skill, and takes longer to result. Newer mass spectrometry methods can measure fentanyl analogs and NSO. Both mass spectrometry assays and immunoassays [in the form of fentanyl test strips (FTS)] have potential use in harm reduction programs.

Strong π-Metal Interaction Enables Liquid Interfacial Nanoarray-Molecule Co-assembly for Raman Sensing of Ultratrace Fentanyl Doped in Heroin, Ketamine, Morphine, and Real Urine.

Toward the challenge on reliable determination of trace fentanyl to avoid opioid overdose death in drug crisis, here we realize rapid and direct detection of trace fentanyl in real human urine without pretreatment by a portable surface enhanced Raman spectroscopy (SERS) strategy on liquid/liquid interfacial (LLI) plasmonic arrays. It was observed that fentanyl could interact with the gold nanoparticles (GNPs) surface, facilitate the LLI self-assembly, and consequently amplify the detection sensitivity with a limit of detection (LOD) as low as 1 ng/mL in aqueous solution and 50 ng/mL spiked in urine. Furthermore, we achieve multiplex blind sample recognition and classification of ultratrace fentanyl doped in other illegal drugs, which has extremely low LODs at mass concentrations of 0.02% (2 ng in 10 µg of heroin), 0.02% (2 ng in 10 µg of ketamine), and 0.1% (10 ng in 10 µg of morphine). A logic circuit of the AND gate was constructed for automatic recognition of illegal drugs with or without fentanyl doping. The data-driven analog soft independent modeling model could quickly distinguish fentanyl-doped samples from illegal drugs with 100% specificity. Molecular dynamics (MD) simulation elucidates the underlying molecular mechanism of nanoarray-molecule co-assembly through strong π-metal interactions and the differences in the SERS signal of various drug molecules. It paves a rapid identification, quantification, and classification strategy for trace fentanyl analysis, indicating broad application prospects in response to the opioid epidemic crisis.

Update: Correlation of Fentanyl Positive Drug Screens with other Medications in Patients from Pain, Rehabilitation and Behavioral Programs.

OBJECTIVE: To monitor fentanyl polydrug use over past six years. METHOD: Calculate percent of fentanyl and other drugs positive in urine drug tests. RESULTS: Percent of fentanyl positive drug tests remained unchanged, but increases in fentanyl/methamphetamine and fentanyl/marijuana were observed. CONCLUSIONS: Fentanyl laced illicit drugs remain a major substance abuse problem.

Bupivacaine Metabolite Can Interfere with Norfentanyl Measurement by LC-MS/MS.

BACKGROUND: Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard for the measurement of fentanyl and norfentanyl (NF) in urine and is favored over immunoassays due to its superior specificity. NF is the principal metabolite of fentanyl found in the urine and is typically present in higher abundance than fentanyl. Thus, the sensitivity and specificity of LC-MS/MS relies largely on the ability to identify and quantitate NF. METHODS: We analyzed urine specimens from women who had received bupivacaine and fentanyl for epidural analgesia during labor. We analyzed the contents of the epidural bag itself and purified bupivacaine metabolite N-desbutyl bupivacaine [or N-(2,6-dimethylphenyl)piperidine-2-carboxamide (NDB)] by LC-MS/MS. RESULTS: NDB interferes with the LC-MS/MS assay for NF. NDB passes through the Q1 mass selection filter because it is isobaric with the NF precursor ion (233 m/z). Further, it shares product ions with NF (84 m/z and 150 m/z), used as quantifier and qualifier ions, respectively, in our urine NF detection method. Baseline resolution of NDB and NF using these quantifier and qualifier ions could not be achieved. A unique product ion of NF (177 m/z) was useful for distinguishing NDB from NF. CONCLUSION: Bupivacaine is a commonly used drug. Recognition of this interference by laboratories is critical for preventing the misidentification of NF, which can have profound effects on patient care.

Polysubstance Use Among Patients Treated With Buprenorphine From a National Urine Drug Test Database.

Importance: Polysubstance use is a concern for patients treated for opioid use disorder (OUD). While buprenorphine can curtail harmful opioid use, co-occurring use of nonprescribed substances, such as cocaine, methamphetamine, and other opioids, may negatively affect treatment outcomes. Objective: To characterize factors associated with urine drug positivity for nonprescribed substances among patients prescribed buprenorphine. Design, Setting, and Participants: This cross-sectional study included patients who had been prescribed buprenorphine and who provided urine specimens for urine drug testing (UDT), as ordered by clinicians in primary care or behavioral health or at substance use disorder treatment centers, from 2013 to 2019. Specimens were analyzed by liquid chromatography-tandem mass spectrometry to assess positivity for several commonly used substances. Exposures: Buprenorphine prescription. Main Outcomes and Measures: Positivity for buprenorphine and several nonprescribed substances. Unadjusted trends in positivity for each nonprescribed substance were compared between specimens that did and did not test positive for buprenorphine. Multivariable logistic regression was used to examine factors associated with positivity; factors included patient age, sex, setting of care, payer, collection year, and census division. Results: The study included first UDT specimens from 150 000 patients, of whom 82 107 (54.74%) were men and 77 300 (51.53%) were aged 18 to 34 years. Across all specimens, 128 240 (85.49%) were positive for buprenorphine, and 71 373 (47.58%) were positive for 1 or more nonprescribed substances. From 2013 to 2019, positivity rates increased for most substances (eg, fentanyl: from 131 of 21 412 [0.61%] to 1464 of 13 597 [10.77%]). Factors associated with positivity varied widely by substance; for example, fentanyl positivity was highest for men (OR, 1.13; 95% CI, 1.06-1.21), patients aged 18 to 24 years (OR for patients ≥55 years, 0.46; 95% CI, 0.39-0.54), patients living in New England (OR, 1.19; 95% CI, 1.07-1.33), and patients with Medicaid (OR, 1.20; 95% CI, 1.11-1.31), whereas oxycodone positivity was greatest for women (OR for men, 0.84; 95% CI, 0.79-0.89), patients older than 55 years (OR, 1.42; 95% CI, 1.22-1.64), patients living in the South Atlantic (OR, 1.45, 95% CI, 1.33-1.58), and patients with private insurance (OR for Medicaid, 0.78; 95% CI, 0.73-0.84). Patients whose specimens were positive for buprenorphine were significantly less likely to be positive for other opioids (eg, fentanyl: OR for buprenorphine-negative samples, 6.71; 95% CI, 6.29-7.16; heroin: OR for buprenorphine-negative samples, 9.93; 95% CI, 9.31-10.59). Conclusions and Relevance: In this cross-sectional study, patterns of nonprescribed substance positivity among patients prescribed buprenorphine varied widely. This study highlights the utility of UDT in public health surveillance efforts related to patients treated with buprenorphine for OUD.

Untargeted Metabolomics in Forensic Toxicology: A New Approach for the Detection of Fentanyl Intake in Urine Samples.

The misuse of fentanyl, and novel synthetic opioids (NSO) in general, has become a public health emergency, especially in the United States. The detection of NSO is often challenged by the limited diagnostic time frame allowed by urine sampling and the wide range of chemically modified analogues, continuously introduced to the recreational drug market. In this study, an untargeted metabolomics approach was developed to obtain a comprehensive "fingerprint" of any anomalous and specific metabolic pattern potentially related to fentanyl exposure. In recent years, in vitro models of drug metabolism have emerged as important tools to overcome the limited access to positive urine samples and uncertainties related to the substances actually taken, the possible combined drug intake, and the ingested dose. In this study, an in vivo experiment was designed by incubating HepG2 cell lines with either fentanyl or common drugs of abuse, creating a cohort of 96 samples. These samples, together with 81 urine samples including negative controls and positive samples obtained from recent users of either fentanyl or "traditional" drugs, were subjected to untargeted analysis using both UHPLC reverse phase and HILIC chromatography combined with QTOF mass spectrometry. Data independent acquisition was performed by SWATH in order to obtain a comprehensive profile of the urinary metabolome. After extensive processing, the resulting datasets were initially subjected to unsupervised exploration by principal component analysis (PCA), yielding clear separation of the fentanyl positive samples with respect to both controls and samples positive to other drugs. The urine datasets were then systematically investigated by supervised classification models based on soft independent modeling by class analogy (SIMCA) algorithms, with the end goal of identifying fentanyl users. A final single-class SIMCA model based on an RP dataset and five PCs yielded 96% sensitivity and 74% specificity. The distinguishable metabolic patterns produced by fentanyl in comparison to other opioids opens up new perspectives in the interpretation of the biological activity of fentanyl.

Determination of nine new fentanyl analogues and metabolites in consumers' urine by ultra-high-performance liquid chromatography-tandem mass spectrometry.

OBJECTIVE: New fentanyl analogues have been constantly emerging into the illegal drug market as cheap substitutes of heroin posing a serious health threat for consumers because of their high toxicity. Analytical methods to disclose the presence of these compounds in biological fluids of intoxicated individuals need to be updated to keep up with the new trends. In this study, we updated an ultra-high-performance liquid chromatography-tandem mass spectrometry method previously developed, for detecting some new fentanyl analogues and metabolites (sufentanil and norsufentanil, cis-3-methylnorfentanyl, trans-3-methylnorfentanyl, metabolites of cis and transmethylfentanyl, beta-phenylfentanyl, phenylfentanyl, para-fluoro furanyl fentanyl, isobutyryl fentanyl and ocfentanil) in urine sample. MATERIALS AND METHODS: Urine samples were simply diluted before injection in the chromatograph equipped with a reversed phase microcolumn. Detection was achieved with a triple quadrupole mass spectrometer with an electrospray ionization source in positive ion mode and operated in multiple reaction monitoring. RESULTS: The chromatographic separation was short (5 min) and the method was fully validated with a high sensitivity being limits of quantifications from 0.003 to 0.006 µg/L urine for the analytes under investigation. CONCLUSIONS: The suitability of the method was tested with urine specimens from former heroin addicts, which resulted positive by immunological screening to the class of fentanyl analogues. This method represents a valid tool to document recent exposure to the above-reported compounds for clinical and forensic purposes.

Evidence of increased Fentanyl use during the COVID-19 pandemic among opioid agonist treatment patients in Ontario, Canada.

BACKGROUND: Amid the opioid crisis, the health care system is restructuring to prevent and treat COVID-19. Individuals in opioid agonist treatment (OAT) are uniquely challenged because of disruption to treatment, medication diversion, and isolation during the pandemic. METHODS: Between January and September 2020, we utilized the electronic medical record from a chain of 67 opioid agonist treatment clinics in Ontario, Canada, to examine routinely collected urine drug screen results of patients in opioid agonist treatment by Public Health Units. RESULTS: We present evidence of a 108% increase in the percentage of fentanyl positive urine drug screens from April to September (p< 0.001). During the same period, health regions in northern and southwestern Ontario, areas with a high concentration of rural communities, have seen the most notable increase in the percent of fentanyl positive urine drug screen results. CONCLUSION: The use of fentanyl increased by 108% among OAT patients in Ontario during the COVID 19 pandemic. We argue that the persistent increase of fentanyl exposure over time, specifically in the OAT population, suggests that reduced monitoring may decrease OAT's effectiveness and negatively impact patient outcomes.

Structure Elucidation of Urinary Metabolites of Fentanyl and Five Fentanyl Analogs using LC-QTOF-MS, Hepatocyte Incubations and Synthesized Reference Standards.

Fentanyl analogs constitute a particularly dangerous group of new psychoactive compounds responsible for many deaths around the world. Little is known about their metabolism, and studies utilizing liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis of hepatocyte incubations and/or authentic urine samples do not allow for determination of the exact metabolite structures, especially when it comes to hydroxylated metabolites. In this study, seven motifs (2-, 3-, 4- and ß-OH as well as 3,4-diOH, 4-OH-3-OMe and 3-OH-4-OMe) of fentanyl and five fentanyl analogs, acetylfentanyl, acrylfentanyl, cyclopropylfentanyl, isobutyrylfentanyl and 4F-isobutyrylfentanyl were synthesized. The reference standards were analyzed by LC-QTOF-MS, which enabled identification of the major metabolites formed in hepatocyte incubations of the studied fentanyls. By comparison with our previous data sets, major urinary metabolites could tentatively be identified. For all analogs, ß-OH, 4-OH and 4-OH-3-OMe were identified after hepatocyte incubation. ß-OH was the major hydroxylated metabolite for all studied fentanyls, except for acetylfentanyl where 4-OH was more abundant. However, the ratio 4-OH/ß-OH was higher in urine samples than in hepatocyte incubations for all studied fentanyls. Also, 3-OH-4-OMe was not detected in any hepatocyte samples, indicating a clear preference for the 4-OH-3-OMe, which was also found to be more abundant in urine compared to hepatocytes. The patterns appear to be consistent across all studied fentanyls and could serve as a starting point in the development of methods and synthesis of reference standards of novel fentanyl analogs where nothing is known about the metabolism.