Associations between fentanyl use and initiation, persistence, and retention on medications for opioid use disorder among people living with uncontrolled HIV disease.

BACKGROUND: Associations between fentanyl use and initiation and retention on medications for opioid use disorder (MOUD) are poorly understood. METHODS: Data were from a multisite clinical trial comparing extended-release naltrexone (XR-NTX) with treatment as usual (TAU; buprenorphine or methadone) to achieve HIV viral suppression among people with OUD and uncontrolled HIV disease. The exposure of interest was fentanyl use, as measured by urine drug screening. Outcomes were time to MOUD initiation, defined as date of first injection of XR-NTX, buprenorphine prescription, or methadone administration; MOUD persistence, the total number of injections, prescriptions, or administrations received over 24 weeks; and MOUD retention, having an injection, prescription, or administration during weeks 20-24. RESULTS: Participants (N = 111) averaged 47 years old and 62% were male. Just over half (57%) were Black and 13% were Hispanic. Sixty-four percent of participants tested positive for fentanyl at baseline. Participants with baseline fentanyl positivity were 11 times less likely to initiate XR-NTX than those negative for fentanyl (aHR = 0.09, 95% CI 0.03-0.24, p < .001), but there was no evidence that fentanyl use impacted the likelihood of TAU initiation (aHR = 1.50, 0.67-3.36, p = .323). Baseline fentanyl use was not associated with persistence or retention on any MOUD. CONCLUSIONS: Fentanyl use was a substantial barrier to XR-NTX initiation for the treatment of OUD in persons with uncontrolled HIV infection. There was no evidence that fentanyl use impacted partial/full agonist initiation and, once initiated, retention on any MOUD.

Fentanyl causes naloxone-resistant vocal cord closure: A platform for testing opioid overdose treatments.

BACKGROUND: High doses of the synthetic opioid fentanyl cause rapid and sustained vocal cord closure (VCC) leading to airway obstruction that prevents overdose victims from breathing. This airway effect is not caused by morphine-derived opiates (e.g. heroin), is distinct from respiratory depression, resistant to naloxone, and can be lethal. However, VCC has not been previously included in animal models of opioid overdose. METHODS: Video laryngoscopy was used to monitor vocal cord movement in anesthetized Sprague-Dawley rats. Rats were administered saline, fentanyl (5, 25, or 50 µg/kg) or morphine (5 mg/kg) in an intravenous (IV) bolus delivered over a 10 s period. The mu opioid receptor (MOR) antagonist naloxone was administered as a pre-treatment (1 mg/kg, IV) 5 min prior to fentanyl (25 µg/kg) or a post-treatment (1 and 2 mg/kg) 1 min after fentanyl (25 µg/kg). RESULTS: Fentanyl (25 and 50 µg/kg) caused sustained and lethal VCC within 10 s. Morphine (5 mg/kg) and fentanyl (5 µg/kg) caused only brief laryngospasm with full recovery. Pre-treatment with naloxone (1 mg/kg) prevented fentanyl-induced VCC, but naloxone (1 and 2 mg/kg) was unable to reverse VCC when administered after fentanyl. CONCLUSIONS: These results indicate sustained VCC is a lethal physiological reaction, specific to fentanyl and resistant to naloxone treatment. While pre-treatment with naloxone prevented fentanyl-induced VCC, naloxone was unable to reverse the effect, suggesting a non-opioid receptor-mediated mechanism. These findings demonstrate the necessity of VCC inclusion in animal models of synthetic opioid overdose and the urgent need for more effective treatments for fentanyl-related overdoses.

Long-acting buprenorphine vs. naltrexone opioid treatments in CJS-involved adults (EXIT-CJS).

The EXIT-CJS (N = 1005) multisite open-label randomized controlled trial will compare retention and effectiveness of extended-release buprenorphine (XR-B) vs. extended-release naltrexone (XR-NTX) to treat opioid use disorder (OUD) among criminal justice system (CJS)-involved adults in six U.S. locales (New Jersey, New York City, Delaware, Oregon, Connecticut, and New Hampshire). With a pragmatic, noninferiority design, this study hypothesizes that XR-B (n = 335) will be noninferior to XR-NTX (n = 335) in retention-in-study-medication treatment (the primary outcome), self-reported opioid use, opioid-positive urine samples, opioid overdose events, and CJS recidivism. In addition, persons with OUD not eligible or interested in the RCT will be recruited into an enhanced treatment as usual arm (n = 335) to examine usual care outcomes in a quasi-experimental observational cohort.

Affinity, potency, efficacy, selectivity, and molecular modeling of substituted fentanyls at opioid receptors.

Substituted fentanyls are abused and cause rapid fatal overdose. As their pharmacology is not well characterized, we examined in vitro pharmacology and structure-activity relationships of 22 substituted fentanyls with modifications of the fentanyl propyl group, and conducted in silico receptor/ligand modeling. Affinities for mu, kappa, and delta opioid receptors (MOR, KOR, and DOR, respectively) heterologously expressed in mammalian cells were assessed in agonist radioligand binding assays. At MOR, furanyl fentanyl had higher affinity than fentanyl, while acryl, isobutyryl and cyclopropyl fentanyls had similar affinities. Comparing affinities, thiophene and methoxyacetyl fentanyls had highest selectivity for MOR (2520- and 2730-fold compared to KOR and DOR, respectively). Functional activities were assessed using [35S]GTPγS binding assays. At MOR, furanyl fentanyl had higher potency and 11 substituted fentanyls had similar high potencies compared to fentanyl. Eight compounds were full agonists of MOR and twelve compounds were partial agonists, with efficacies from 8.8% (phenyl fentanyl) to 60.2% (butyryl fentanyl). All efficacious compounds had selective functional potency for MOR. The predicted binding poses of flexible fentanyl and rigid morphine against MOR show partially overlapping binding pockets, with fentanyl maintaining additional interaction with the transmembrane (TM) 2 helix. Subsequent molecular dynamics simulations revealed a predominant fentanyl binding pose involving various TM interactions. The piperidine nitrogen of substituted fentanyls establishes a salt-bridge with the conserved D-1473.32 residue and the propanamide carbonyl group establishes a hydrogen bond with the indole side-chain (-NH) of W-3187.35. The simulation suggests theN-linked phenethyl group may regulate the rotameric switch of W-2936.48. The predicted binding pose, in conjunction with in vitro binding affinity, clarified the molecular basis of the binding/selectivity profile of furanyl fentanyl and other derivatives at the sequence level. In summary, substituted fentanyls with high MOR potencies, selectivities, and efficacies are likely to have abuse and overdose potential. The work presented here is a prototype to investigate fentanyl derivatives and their abuse potential.

Fentanyl but not Morphine Interacts with Nonopioid Recombinant Human Neurotransmitter Receptors and Transporters.

Synthetic opioids, including fentanyl and its analogs, have therapeutic efficacy in analgesia and anesthesia. However, their illicit use in the United States has increased and contributed to the number one cause of death for adults 18-50 years old. Fentanyl and the heroin metabolite morphine induce respiratory depression that can be treated with the µ opioid receptor (MOR) antagonist naloxone. With higher or more rapid dosing, fentanyl, more than morphine, causes chest wall rigidity and can also induce rapid onset laryngospasm. Because non-MORs could mediate differing clinical manifestations, we examined the interactions of fentanyl and morphine at recombinant human neurotransmitter transporters, G protein-coupled receptors, and the N-methyl-D-aspartate glutamate receptor. Both drugs were agonists at MOR, κ, and δ opioid receptors. Morphine had little or no affinity at other human receptors and transporters (K i or IC50 value >100 µM). However, fentanyl had K i values of 1407 and 1100 nM at α 1A and α 1B adrenoceptor subtypes, respectively, and K i values of 1049 and 1670 nM at dopamine D4.4 and D1 receptor subtypes, respectively; it also blocked [3H]neurotransmitter uptake by the vesicular monoamine transporter 2 (IC50 = 911 nM). Pharmacokinetic models indicate that these Ki and IC50 values are pharmacologically relevant. Fentanyl had little affinity for other receptors or transporters. Thus, noradrenergic disposition at specific receptor subtypes in relevant organs may play a role in respiratory and cardiothoracic effects of fentanyl. Data suggest that less selective fentanyl receptor pharmacology could play a role in the different clinical effects of morphine compared with fentanyl, including fentanyl-induced deaths after illicit use. SIGNIFICANCE STATEMENT: The synthetic opioid fentanyl induces different clinical effects, including rapid onset muscular rigidity, vocal cord closure, and rapid death, than the heroin metabolite morphine. Our data indicate for the first time that the two drugs have very different effects at recombinant human neurotransmitter receptors and transporters that might explain those clinical differences.

Noradrenergic Mechanisms in Fentanyl-Mediated Rapid Death Explain Failure of Naloxone in the Opioid Crisis.

In December 2018, the Centers for Disease Control declared fentanyl the deadliest drug in America. Opioid overdose is the single greatest cause of death in the United States adult population (ages 18-50), and fentanyl and its analogs [fentanyl/fentanyl analogs (F/FAs)] are currently involved in >50% of these deaths. Anesthesiologists in the United States were introduced to fentanyl in the early 1970s when it revolutionized surgical anesthesia by combining profound analgesia with hemodynamic stability. However, they quickly had to master its unique side effect. F/FAs can produce profound rigidity in the diaphragm, chest wall and upper airway within an extremely narrow dosing range. This clinical effect was called wooden chest syndrome (WCS) by anesthesiologists and is not commonly known outside of anesthesiology or to clinicians or researchers in addiction research/medicine. WCS is almost routinely fatal without expert airway management. This review provides relevant clinical human pharmacology and animal data demonstrating that the significant increase in the number of F/FA-induced deaths may involve α-adrenergic and cholinergic receptor-mediated mechanical failure of the respiratory and cardiovascular systems with rapid development of rigidity and airway closure. Although morphine and its prodrug, heroin, can cause mild rigidity in abdominal muscles at high doses, neither presents with the distinct and rapid respiratory failure seen with F/FA-induced WCS, separating F/FA overdose from the slower onset of respiratory depression caused by morphine-derived alkaloids. This distinction has significant consequences for the design and implementation of new pharmacologic strategies to effectively prevent F/FA-induced death. SIGNIFICANCE STATEMENT: Deaths from fentanyl and F/FAs are increasing in spite of availability and awareness of the opioid reversal drug naloxone. This article reviews literature suggesting that naloxone may be ineffective against centrally mediated noradrenergic and cholinergic effects of F/FAs, which clinically manifest as severe muscle rigidity and airway compromise (e.g., wooden chest syndrome) that is rapid and distinct from respiratory depression seen with morphine-derived alkaloids. A physiologic model is proposed and implications for new drug development and treatment are discussed.