Fentanyl Analogs Exert Antinociceptive Effects via Sodium Channel Blockade in Mice.

The formalin test is one approach to studying acute pain in rodents. Similar to formalin, injection with glutamate and veratrine can also produce a nociceptive response. This study investigated whether opioid-related compounds could suppress glutamate- and veratrine-induced nociceptive responses in mice at the same dose. The administration of morphine (3 mg/kg), hydromorphone (0.4 mg/kg), or fentanyl (0.03 mg/kg) suppressed glutamate-induced nociceptive response, but not veratrine-induced nociceptive response at the same doses. However, high doses of morphine (10 mg/kg), hydromorphone (2 mg/kg), or fentanyl (0.1 mg/kg) produced a significant reduction in the veratrine-induced nociceptive response. These results indicate that high doses are required when using morphine, hydromorphone, or fentanyl for sodium channel-related neuropathic pain, such as ectopic activity. As a result, concerns have arisen about overdose and abuse if the dose of opioids is steadily increased to relieve pain. In contrast, trimebutine (100 mg/kg) and fentanyl analog isobutyrylfentanyl (iBF; 0.1 mg/kg) suppressed both glutamate- and veratrine-induced nociceptive response. Furthermore, nor-isobutyrylfentanyl (nor-iBF; 1 mg/kg), which is a metabolite of iBF, suppressed veratrine-induced nociceptive response. Besides, the optimal antinociceptive dose of iBF, unlike fentanyl, only slightly increased locomotor activity and did not slow gastrointestinal transit. Cancer pain is a complex condition driven by inflammatory, neuropathic, and cancer-specific mechanisms. Thus, iBF may have the potential to be a superior analgesic than fentanyl.

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.

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.

Not Carfentanil-A Case of Unexpected Xylazine Detection.

Historically, xylazine has been utilized in veterinary medicine for decades as an anesthetic and analgesic sedative to facilitate safe handling, diagnostic testing, and surgical procedures in large animals. Currently, xylazine is an emerging threat to human health. It has been detected in the illicit drug supply chain, often as an adulterant. It has been more commonly added to illicit substances, most notably fentanyl, by drugmakers to enhance drug effect. End users are often unaware of its presence. This is alarming given the large number of xylazine-involved overdose deaths while laboratory detections are deficient and reversal agents are absent. Herein, we present the first documented case of xylazine identified via gas chromatography-tandem mass spectrometry at University of California Davis Health despite a peculiarly mild clinical presentation. We hope to increase awareness of this potentially fatal adulterant that is often missed in evaluation and engender further opportunities to study this ongoing issue.

Validation of a LC-MS/MS method to simultaneously quantify thiafentanil and naltrexone in plasma for pharmacokinetic studies in wildlife.

Thiafentanil is a popular opioid agonist that is fully reversed by administering naltrexone. This agonist-antagonist combination is administered to a wide variety of wildlife species for chemical immobilisation, however plasma concentrations for thiafentanil remain unreported. This report describes a method that was developed and validated using human plasma and cross-validated for the analysis of goat plasma. Samples were extracted using a simple protein precipitation and analysed using LC-MS/MS. The assay was validated over the calibration range 4.38 - 1120 ng/mL for thiafentanil and 15.63 - 4000 ng/mL for naltrexone. The mean inter-day accuracies for QCs prepared in human plasma (n = 18) ranged from 94.8 - 103.8 % for thiafentanil and 94.8 - 95.9 % for naltrexone with corresponding precisions of 3.4 - 7.9 % and 2.8 - 11.4 %, respectively. The mean accuracies for QCs prepared in goat plasma (n = 6) ranged from 89.0 - 100.5 % for thiafentanil and 89.0 - 98.0 % for naltrexone with the associated precisions ranging from 7.1 - 11.6 % and 4.8 - 12.3 %, respectively. Both analytes were stable on bench for six hours and for three freeze-thaw cycles. The impact of heat-inactivation, necessary for the inactivation of potential foot-and-mouth disease, on analyte stability, matrix effect and recovery were evaluated, and a correction factor was established to determine the original analyte concentrations. The method was applied to pharmacokinetic samples collected from goats. The use of goats as a model species provides the first insight into the plasma concentrations of thiafentanil.

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.

Structure-based design of bitopic ligands for the µ-opioid receptor.

Mu-opioid receptor (µOR) agonists such as fentanyl have long been used for pain management, but are considered a major public health concern owing to their adverse side effects, including lethal overdose1. Here, in an effort to design safer therapeutic agents, we report an approach targeting a conserved sodium ion-binding site2 found in µOR3 and many other class A G-protein-coupled receptors with bitopic fentanyl derivatives that are functionalized via a linker with a positively charged guanidino group. Cryo-electron microscopy structures of the most potent bitopic ligands in complex with µOR highlight the key interactions between the guanidine of the ligands and the key Asp2.50 residue in the Na+ site. Two bitopics (C5 and C6 guano) maintain nanomolar potency and high efficacy at Gi subtypes and show strongly reduced arrestin recruitment-one (C6 guano) also shows the lowest Gz efficacy among the panel of µOR agonists, including partial and biased morphinan and fentanyl analogues. In mice, C6 guano displayed µOR-dependent antinociception with attenuated adverse effects, supporting the µOR sodium ion-binding site as a potential target for the design of safer analgesics. In general, our study suggests that bitopic ligands that engage the sodium ion-binding pocket in class A G-protein-coupled receptors can be designed to control their efficacy and functional selectivity profiles for Gi, Go and Gz subtypes and arrestins, thus modulating their in vivo pharmacology.

Use of fentanyl, butyrfentanyl and furanylfentanyl as discussed on Polish online forums devoted to 'designer drugs'. / Uzywanie fentanylu, butyrylofentanylu i furanylofentanylu w opinii uzytkowników polskich forów internetowych poswieconych "dopalaczom".

OBJECTIVES: The study was aimed to analyze information posted by users of synthetic opioids on Polish online drug discussion forums. Special emphasis was given to sources of drugs and their availability, routes of administration, dosages, expected and toxic effects. METHODS: 6,143 reports related to synthetic opioids, posted between 2005 and mid 2019 on three widely available popular Polish online forums devoted to psychoactive substances, i.e., hyperreal.info/talk, dopek.info and forum.dopalamy, were collected and analyzed. The article presents data on three most popular opioids, i.e., fentanyl, butyrfentanyl and furanylfentanyl. RESULTS: Fentanyl was the most widely used and relatively easily accessible synthetic opioid in Poland. Butyrfentanyl and furanylfentanyl were far less popular. The main source of fentanyl was diversion of medicines, notably transdermal patches. Fentanyl, butyrfentanyl and furanylfentanyl are administered orally, buccally, sublingually, intranasally, by inhalation and intravenously. Concomitant use of fentanyl and its derivatives with other psychoactive compounds increases the risk of severe adverse effects. CONCLUSIONS: Our study contributed to amore comprehensive understanding of problems related to abuse of fentanyl, butyrfentanyl and furanylfentanyl in Poland. In the light of the relatively high popularity of pharmaceutical fentanyl used for non-medical purposes, there is an urgent need for more strict control over illegal sales of fentanyl transdermal preparations via the Internet, as well as disposal of used patches. Furthermore, patients using fentanyl should be warned that giving it to another person is against the law, and may lead to development of addiction and other serious health consequences. It is important to educate the society in order to increase awareness of the problem of opioid use, especially by young people, and to pay attention to signals which may indicate addiction among family members.

Metabolism of the active carfentanil metabolite, 4-Piperidinecarboxylic acid, 1-(2-hydroxy-2-phenylethyl)-4-[(1-oxopropyl)phenylamino]-, methyl ester in vitro.

Carfentanil, a µ-opioid receptor (MOR) agonist with an analgesic potency 10,000 times that of morphine, is extensively metabolized to norcarfentanil (M1), 4-Piperidinecarboxylic acid, 1-(2-hydroxy-2-phenylethyl)-4-[(1-oxopropyl)phenylamino]-, methyl ester (M0 in this article), and other low abundant metabolites in human hepatocytes and liver/lung microsomes. M0 possessed comparable MOR activity to carfentanil, and accounted for approximately 12 % of the total carfentanil metabolite formation in human liver microsomes (HLMs). Little is known about the subsequent elimination of M0. This study investigated its metabolic pathway in HLMs, separation and preliminary identification of metabolites by liquid chromatography-tandem mass spectrometry, and possible involvement of cytochrome P450 enzymes in M0 metabolism with kinetic analysis. M0 produced 9 metabolites via N-dealkylation (M1), oxidation (M3, M6-9), N-dealkylation followed by oxidation (M2 and M4), and glucuronidation (M5). Formation of the major metabolite M1 fitted typical Michaelis-Menten kinetics. Recombinant human CYP3A5 showed the highest activity toward M1 formation followed by CYP3A4 and CYP2C8, while M8 was primarily formed by CYP3A4 followed by CYP2C19 and CYP2C8. These findings reveal the main involvement of CYP3A5 and 3A4 in human hepatic elimination of M0 with a kinetic profile similar to carfentanil which may inform development of treatment protocols for carfentanil exposure.

Determination of fentanyl and norfentanyl in cerumen in the setting of postmortem investigation.

Cerumen is an emerging alternative biological matrix in the field of forensic toxicology. An ultra-high-pressure liquid chromatography-mass spectrometry/mass spectrometry [UHPLC-MS/MS] method for the determination of fentanyl and norfentanyl in cerumen was developed and applied in a mixed drug toxicity fatal case. The method was found to be selective and sensitive (LOQ: 0.05 ng/mg for fentanyl and 0.02 ng/mg for norfentanyl), while validation included recovery, carryover, short-term stability, matrix effect, accuracy, and precision (RSD%). Accuracy ranged from 83.1% to 103.5%, while intra- and inter-day precision ranged from 8.6% to 13.1% and from 8.3% to 15.8%, respectively. Matrix effect experiments showed that matrix did not significantly affect signal intensity (82.3%-96.8%). Short-term stability concerning sample extracts was found satisfactory. Fentanyl and norfentanyl were detected in cerumen at a concentration of 1.17 and 0.36 ng/mg respectively. The findings in cerumen corroborate the cause of death and suggest that cerumen is a potential specimen for detecting drugs of abuse in forensic cases.

Carfentanil Blood Concentrations in Impaired Driving Investigations in Ontario, Canada.

Carfentanil is a potent opioid with no medical use in humans; it presents a serious threat to public health and road safety due to its presence in the illicit drug supply, the potency of the drug and instances of use prior to the operation of a motor vehicle. The identification and quantitation of carfentanil using liquid chromatography with tandem mass spectrometry was performed in blood samples obtained through impaired driving-related investigations from 2017 to 2019. In a series of 66 cases submitted to the Centre of Forensic Sciences in Ontario, Canada, blood concentrations of carfentanil ranged from <0.04 to 2.1 ng/mL in the population studied. Driving behaviors frequently came to the attention of concerned citizens, decreased levels of consciousness were commonly reported and a variety of medical interventions were required, in some cases, to preserve life due to apparent opioid toxicity.

Naloxone's dose-dependent displacement of [11C]carfentanil and duration of receptor occupancy in the rat brain.

The continuous rise in opioid overdoses in the United States is predominantly driven by very potent synthetic opioids, mostly fentanyl and its derivatives (fentanyls). Although naloxone (NLX) has been shown to effectively reverse overdoses by conventional opioids, there may be a need for higher or repeated doses of NLX to revert overdoses from highly potent fentanyls. Here, we used positron emission tomography (PET) to assess NLX's dose-dependence on both its rate of displacement of [11C]carfentanil ([11C]CFN) binding and its duration of mu opioid receptor (MOR) occupancy in the male rat brain. We showed that clinically relevant doses of intravenously (IV) administered NLX (0.035 mg/kg, Human Equivalent Dose (HED) 0.4 mg; 0.17 mg/kg, HED 2 mg) rapidly displaced the specific binding of [11C]CFN in the thalamus in a dose-dependent manner. Brain MOR occupancy by IV NLX was greater than 90% at 5 min after NLX administration for both doses, but at 27.3 min after 0.035 mg/kg dose and at 85 min after 0.17 mg/kg NLX, only 50% occupancy remained. This indicates that the duration of NLX occupancy at MORs is short-lived. Overall, these results show that clinically relevant doses of IV NLX can promptly displace fentanyls at brain MORs, but repeated or higher NLX doses may be required to prevent re-narcotization following overdoses with long-acting fentanyls.

Cardiopulmonary responses of free-ranging African elephant (Loxodonta africana) bulls immobilized with a thiafentanil-azaperone combination.

OBJECTIVE: To determine the time course and certain cardiopulmonary effects of trunk-breathing elephants immobilized with thiafentanil-azaperone. STUDY DESIGN: Prospective descriptive study. ANIMALS: A convenience sample of 10 free-ranging African elephant bulls (estimated weight range: 3000-6000 kg). METHODS: Elephants were immobilized using thiafentanil (15-18 mg) and azaperone (75-90 mg) administered by dart. Once recumbent, the respiratory rate, minute ventilation (V˙e), end-tidal carbon dioxide (Pe'CO2), arterial blood pressure and heart rate were recorded immediately after instrumentation and at 5 minute intervals until 20 minutes. Arterial blood gases were analysed at the time of initial instrumentation and at 20 minutes. On completion of data collection, thiafentanil was antagonized using naltrexone (10 mg mg-1 thiafentanil; administered intravenously). A stopwatch was used to record time to recumbency (dart placement to recumbency) and time to recovery (administration of antagonist to standing). Data were compared using a one-way anova. Data are presented as mean ± standard deviation. RESULTS: All elephants were successfully immobilized, and there were no significant changes in cardiopulmonary variables over the monitoring period. Average time to recumbency was 12.5 (± 3.9) minutes. The measured V˙e was 103 (± 30) L minute-1. The average heart and respiratory rates over the 20 minute immobilization were steady at 49 (± 6) beats minute-1 and 5 (± 1) breaths minute-1, respectively. The mean arterial blood pressure was 153 (± 31) mmHg. The elephants were acidaemic (pH: 7.18 ± 0.06), mildly hypoxaemic (PaO2: 68 ± 15 mmHg; 9.1 ± 2.0 kPa) and hypercapnic (PaCO2: 52 ± 7 mmHg; 6.9 ± 0.9 kPa). Average time to recovery was 2.2 ± 0.5 minutes. CONCLUSION AND CLINICAL RELEVANCE: African elephant bulls can be successfully immobilized using thiafentanil-azaperone. Recumbency was rapid, the cardiopulmonary variables were stable over time, and recovery was rapid and complete. Mild hypoxaemia and hypercapnia were evident.

In vitro and in vivo pharmaco-dynamic study of the novel fentanyl derivatives: Acrylfentanyl, Ocfentanyl and Furanylfentanyl.

Fentanyl derivatives (FENS) belongs to the class of Novel Synthetic Opioids that emerged in the illegal drug market of New Psychoactive Substances (NPS). These substances have been implicated in many cases of intoxication and death with overdose worldwide. Therefore, the aim of this study is to investigate the pharmaco-dynamic profiles of three fentanyl (FENT) analogues: Acrylfentanyl (ACRYLF), Ocfentanyl (OCF) and Furanylfentanyl (FUF). In vitro, we measured FENS opioid receptor efficacy, potency, and selectivity in calcium mobilization studies performed in cells coexpressing opioid receptors and chimeric G proteins and their capability to promote the interaction of the mu receptor with G protein and ß-arrestin 2 in bioluminescence resonance energy transfer (BRET) studies. In vivo, we investigated the acute effects of the systemic administration of ACRYLF, OCF and FUF (0.01-15 mg/kg i.p.) on mechanical and thermal analgesia, motor impairment, grip strength and cardiorespiratory changes in CD-1 male mice. Opioid receptor specificity was investigated in vivo using naloxone (NLX; 6 mg/kg i.p) pre-treatment. In vitro, the three FENS were able to activate the mu opioid receptor in a concentration dependent manner with following rank order potency: FUF > FENT=OCF > ACRYLF. All compounds were able to elicit maximal effects similar to that of dermorphin, with the exception of FUF which displayed lower maximal effects thus behaving as a partial agonist. In the BRET G-protein assay, all compounds behaved as partial agonists for the ß-arrestin 2 pathway in comparison with dermorphin, whereas FUF did not promote ß-arrestin 2 recruitment, behaving as an antagonist. In vivo, all the compounds increased mechanical and thermal analgesia with following rank order potency ACRYLF = FENT > FUF > OCF and impaired motor and cardiorespiratory parameters. Among the substances tested, FUF showed lower potency for cardiorespiratory and motor effects. These findings reveal the risks associated with the use of FENS and the importance of studying the pharmaco-dynamic properties of these drugs to better understand possible therapeutic interventions in the case of toxicity.

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.

Proton Affinity Values of Fentanyl and Fentanyl Analogues Pertinent to Ambient Ionization and Detection.

Proton affinity is a major factor in the atmospheric pressure chemical ionization of illicit drugs. The detection of illicit drugs by mass spectrometry and ion mobility spectrometry relies on the analytes having greater proton affinities than background species. Evaluating proton affinities for fentanyl and its analogues is informative for predicting the likelihood of ionization in different environments and for optimizing the compounds' ionization and detection, such as through the addition of dopant chemicals. Herein, density functional theory was used to computationally determine the proton affinity and gas-phase basicity of 15 fentanyl compounds and several relevant molecules as a reference point. The range of proton affinities for the fentanyl compounds was from 1018 to 1078 kJ/mol. Fentanyl compounds with the higher proton affinity values appeared to form a bridge between the oxygen on the amide and the protonated nitrogen on the piperidine ring based on models and calculated bond distances. Experiments with fragmentation of proton-bound clusters using atmospheric flow tube-mass spectrometry (AFT-MS) provided estimates of relative proton affinities and showed proton affinity values of fentanyl compounds >1000 kJ/mol, which were consistent with the computational results. The high proton affinities of fentanyl compounds facilitate their detection by ambient ionization techniques in complex environments. The detection limits of the fentanyl compounds with AFT-MS are in the low femtogram range, which demonstrates the feasibility of trace vapor drug detection.

Computational analyses of the vibrational spectra of fentanyl, carfentanil and remifentanil.

The infrared (IR) spectra of fentanyl, carfentanil and remifentanil, and protonated salts, are computed using quantum chemistry methods. New experimental FTIR spectra are also reported and compared to the calculations. The accuracy of two density functional theory methods, B3LYP and M06-2X, are tested against higher level theories (MP2) and the experimental data. Gas phase IR spectra are calculated for both the neutral and protonated molecules in order to compare with the experimental data measured for various salts of fentanyl and its analogues. Key vibrational modes are selected and studied in detail using a vibrational mode locality calculation. The main contributing atomic movements in these vibrational modes are identified.

Respiratory depressant effects of fentanyl analogs are opioid receptor-mediated.

Opioid-related fatalities involving synthetic opioids have reached unprecedented levels. This study evaluated the respiratory depressant effects of seven fentanyl analogs that have either emerged in the illicit drug supply or been identified in toxicological analyses following fatal or non-fatal intoxications. Adult male Swiss Webster mice were administered fentanyl analogs (isobutyrylfentanyl, crotonylfentanyl, para-methoxyfentanyl, para-methoxybutyrylfentanyl, 3-furanylfentanyl, thiophenefentanyl, and benzodioxolefentanyl) and their effects on minute volume as compared to mu-opioid receptor (MOR) agonist standards (fentanyl, morphine, and buprenorphine) were measured using whole body plethysmography (WBP). All drugs elicited significant (p ≤ 0.05) hypoventilation relative to vehicle for at least one dose tested: morphine (1, 3.2, 10, 32 mg/kg), buprenorphine, (0.032, 0.1, 0.32, 1, 3.2 mg/kg), fentanyl (0.0032, 0.01, 0.032, 0.1, 1, 32 mg/kg), isobutyrylfentanyl (0.1, 0.32, 1, 3.2, 10 mg/kg), crotonylfentanyl (0.1, 0.32, 1, 3.2, 10 mg/kg), para-methoxyfentanyl (0.1, 0.32, 1, 3.2, 10 mg/kg), para-methoxybutyrylfentanyl (0.32, 1, 3.2, 10 mg/kg), 3-furanylfentanyl (0.1, 0.32, 1, 3.2, 10 mg/kg), thiophenefentanyl (1, 3.2, 10, 32, 100 mg/kg), and benzodioxolefentanyl (3.2, 10, 32, 100 mg/kg). The ED50 values for hypoventilation showed a rank order of potency as follows: fentanyl (ED50 = 0.96 mg/kg) > 3-furanylfentanyl (ED50 = 2.60 mg/kg) > crotonylfentanyl (ED50 = 2.72 mg/kg) > para-methoxyfentanyl (ED50 = 3.31 mg/kg) > buprenorphine (ED50 = 10.8 mg/kg) > isobutyrylfentanyl (ED50 = 13.5 mg/kg) > para-methoxybutyrylfentanyl (ED50 = 16.1 mg/kg) > thiophenefentanyl (ED50 = 18.0 mg/kg) > morphine (ED50 = 55.3 mg/kg) > benzodioxolefentanyl (ED50 = 10,168 mg/kg). A naloxone pretreatment (10 mg/kg) attenuated the hypoventilatory effects of all drugs. These results establish that the respiratory depressant effects of these fentanyl analogs are at least in part mediated by the MOR.

Determination of Fentanyl, Alpha-Methylfentanyl, Beta-Hydroxyfentanyl and the Metabolite Norfentanyl in Rat Urine by LC-MS-MS.

Fentanyl and its analogs are potent synthetic opioids with a high potential for abuse and dependence. They have become major contributors to opioid deaths. This study aimed to determine whether the metabolites of fentanyl, alpha-methylfentanyl and beta-hydroxyfentanyl, excreted in the urine, can demonstrate historical drug exposure. Fentanyl is primarily metabolized via CYP3A4 into norfentanyl, although there is little research on its metabolization into alpha-methylfentanyl and beta-hydroxyfentanyl. We conducted in vitro experiments with human liver microsomes (HLMs) and rat liver microsomes (RLMs) to elucidate the major metabolic pathways of alpha-methylfentanyl and beta-hydroxyfentanyl using ultra-high-performance liquid chromatography coupled with mass spectrometry. The results showed that both alpha-methylfentanyl and beta-hydroxyfentanyl were predominantly metabolized into norfentanyl in HLM and RLM. Urine samples were collected at different intervals from 0 h to 72 h after intravenous administration of alpha-methylfentanyl and beta-hydroxyfentanyl (20 µg/kg) to Sprague-Dawley rats. We prepared the samples by liquid-liquid extraction, and the internal standard (IS) was cariprazine. A sensitive, rapid liquid chromatography-tandem mass spectrometry method was developed and validated to determine four analytes in the urine. The lower limit of qualification in urine was 2 pg/mL for fentanyl, 5 pg/mL for alpha-methylfentanyl, 10 pg/mL for beta-hydroxyfentanyl and 40 pg/mL for norfentanyl. The analytical range was 0.002-2 ng/mL for fentanyl, 0.005-5 ng/mL for alpha-methylfentanyl, 0.01-10 ng/mL for beta-hydroxyfentanyl and 0.04-40 ng/mL for norfentanyl. All analytes demonstrated good linearity (R2 > 0.99). The extraction recoveries were in the 67.8%-92.1% range, and the IS-normalized matrix effects were between 55.5% and 74.0% (coefficient of variance < 15%). Our data indicated that norfentanyl has a higher concentration in rat urine and was detectable for at least 3 days after exposure to these compounds. This developed method may be useful in various fields, including forensic analysis, workplace drug testing and monitoring drug abuse.

In Vitro and In Vivo Analysis of Fentanyl and Fentalog Metabolites using Hyphenated Chromatographic Techniques: A Review.

Fentanyl and fentanyl analogues (also called fentalogs) are used as medical prescriptions to treat pain for a long time. Apart from their pharmaceutical applications, they are misused immensely, causing the opioid crisis. Fentanyl and its analogues are produced in clandestine laboratories and sold over dark Web markets to different parts of the world, leading to a rise in the death rate due to drug overdose. This is because the users are unaware of the lethal effects of the newer forms of fentalogs. Unlike other drugs, these fentalogs cannot be detected easily, as very little data are available, and this is one of the major reasons for the risk of life-threatening poisoning or deaths. Hence, rigorous studies of these drugs and their possible metabolites are required. It is also necessary to develop techniques for the detection of minute traces of metabolites in biological fluids. This Review provides an overview of the application of hyphenated chromatographic techniques used to analyze multiple novel fentalogs, using in vivo and in vitro methods. The article focuses on the metabolites formed in phase I and phase II processes in biological specimens obtained in recent cases of drug abuse and overdose deaths that could be useful for the detection and differentiation of multiple fentalogs.