The anomalous pharmacology of fentanyl

A study comparing brain wave patterns of fentanyl and ketamine in adult patients undergoing minimally invasive surgery

This study aimed to investigate and compare the neurophysiological impacts of two widely used anesthetic agents, Fentanyl and Ketamine, on EEG power spectra during different stages of anesthesia in adult patients undergoing minimally invasive surgery. EEG data were collected from patients undergoing anesthesia with either Fentanyl or Ketamine. The data were analyzed for relative power spectrum and fast-to-slow wave power ratios, alongside Spectral Edge Frequency 95% (SEF95), at 3 key stages: pre-anesthesia, during stable anesthesia, and post-anesthesia. EEG Relative Power Spectrum: Initially, both groups exhibited similar EEG spectral profiles, establishing a uniform baseline (P > .05). Upon anesthesia induction, the Fentanyl group showed a substantial increase in delta band power (P < .05), suggesting deeper anesthesia, while the Ketamine group maintained higher alpha and beta band activity (P < .05), indicative of a lighter sedative effect. Fast and Slow Wave Power Ratios: The Fentanyl group exhibited a marked reduction in the fast-to-slow wave power ratio during anesthesia (P < .05), persisting post-anesthesia (P < .05) and indicating a lingering effect on brain activity. Conversely, the Ketamine group demonstrated a more stable ratio (P > .05), conducive to settings requiring rapid cognitive recovery. Spectral Edge Frequency 95% (SEF95): Analysis showed a significant decrease in SEF95 values for the Fentanyl group during anesthesia (P < .05), reflecting a shift towards lower frequency power. The Ketamine group experienced a less pronounced decrease (P > .05), maintaining a higher SEF95 value that suggested a lighter level of sedation. The study highlighted the distinct impacts of Fentanyl and Ketamine on EEG power spectra, with Fentanyl inducing deeper anesthesia as evidenced by shifts towards lower frequency activity and a significant decrease in SEF95 values. In contrast, Ketamine's preservation of higher frequency activity and more stable SEF95 values suggests a lighter, more dissociative anesthetic state. These findings emphasize the importance of EEG monitoring in anesthesia for tailoring anesthetic protocols to individual patient needs and optimizing postoperative outcomes.

Sustained fentanyl exposure inhibits neuronal activity in dissociated striatal neuronal-glial cocultures through actions independent of opioid receptors

Besides having high potency and efficacy at the µ-opioid (MOR) and other opioid receptor types, fentanyl has some affinity for some adrenergic receptor types, which may underlie its unique pathophysiological differences from typical opioids. To better understand the unique actions of fentanyl, we assessed the extent to which fentanyl alters striatal medium spiny neuron (MSN) activity via opioid receptors or α1-adrenoceptors in dopamine type 1 or type 2 receptor (D1 or D2)-expressing MSNs. In neuronal and mixed-glial cocultures from the striatum, acute fentanyl (100 nM) exposure decreased the frequency of spontaneous action potentials. Overnight exposure of cocultures to 100 nM fentanyl severely reduced the proportion of MSNs with spontaneous action potentials, which was unaffected by coexposure to the opioid receptor antagonist naloxone (10 µM) but fully negated by coadministering the pan-α1-adrenoceptor inverse agonist prazosin (100 nM) and partially reversed by the selective α1A-adrenoceptor antagonist RS 100329 (300 nM). Acute fentanyl (100 nM) exposure modestly reduced the frequency of action potentials and caused firing rate adaptations in D2, but not D1, MSNs. Prolonged (2-5 h) fentanyl (100 nM) application dramatically attenuated firing rates in both D1 and D2 MSNs. To identify possible cellular sites of α1-adrenoceptor action, α1-adrenoceptors were localized in subpopulations of striatal astroglia and neurons by immunocytochemistry and Adra1a mRNA by in situ hybridization in astrocytes. Thus, sustained fentanyl exposure can inhibit striatal MSN activity via a nonopioid receptor-dependent pathway, which may be modulated via complex actions in α1-adrenoceptor-expressing striatal neurons and/or glia.NEW & NOTEWORTHY Acute fentanyl exposure attenuated the activity of striatal medium spiny neurons (MSNs) in vitro and in dopamine D2, but not D1, receptor-expressing MSNs in ex vivo slices. By contrast, sustained fentanyl exposure suppressed the spontaneous activity of MSNs cocultured with glia through a nonopioid receptor-dependent mechanism modulated, in part, by α1-adrenoceptors. Fentanyl exposure can affect striatal function via a nonopioid receptor mechanism of action that appears mediated by α1-adrenoreceptor-expressing striatal neurons and/or astroglia.

Xylazine Exacerbates Fentanyl-Induced Respiratory Depression and Bradycardia

Fatal opioid overdoses in the United States have nearly tripled during the past decade, with greater than 92% involving a synthetic opioid like fentanyl. Fentanyl potently activates the μ-opioid receptor to induce both analgesia and respiratory depression. The danger of illicit fentanyl has recently been exacerbated by adulteration with xylazine, an α2-adrenergic receptor agonist typically used as a veterinary anesthetic. In 2023, over a 1,000% increase in xylazine-positive overdoses was reported in some regions of the U.S. Xylazine has been shown to potentiate the lethality of fentanyl in mice, yet a mechanistic underpinning for this effect has not been defined. Herein, we evaluate fentanyl, xylazine, and their combination in whole-body plethysmography (to measure respiration) and pulse oximetry (to measure blood oxygen saturation and heart rate) in male and female CD-1 mice. We show that xylazine decreases breathing rate more than fentanyl by increasing the expiration time. In contrast, fentanyl primarily reduces breathing by inhibiting inspiration, and xylazine exacerbates these effects. Fentanyl but not xylazine decreased blood oxygen saturation, and when combined, xylazine did not change the maximum level of fentanyl-induced hypoxia. Xylazine also reduced heart rate more than fentanyl. Finally, loss in blood oxygen saturation correlated with the frequency of fentanyl-induced apneas, but not breathing rate. Together, these findings provide insight into how the addition of xylazine to illicit fentanyl may increase the risk of overdose.

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

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

Addressing the Opioids Lipophilicity Challenge via a Straightforward and Simultaneous 1H NMR-Based logP/D Determination, Both Separately and in Mixtures

A systematic study of trends in the lipophilicity of prominent representatives of the opioid family, including natural, semisynthetic, synthetic, and endogenous neuropeptide opioids, is described. This was enabled by a straightforward 1H NMR-based logP/D determination method developed for compounds holding at least one aromatic hydrogen atom. Moreover, the new method enables a direct simultaneous logD determination of opioid mixtures, overcoming the high sensitivity of this family to the measurement conditions, which is critical when a determination of the exact ΔlogD values of matched pairs is required. Interpretation of the experimental ΔlogD7.4 values of selected matched pairs, focusing inter alia on the 3-OMe and 14-OMe motifs in morphinan opioids, is suggested with the aid of DFT calculations and may be useful for the discovery of new opioid therapeutics.

A Review of the Literature on Episodes of Acute Fentanyl Intoxication in Pediatric Age and Toxicological Applications

Fentanyl is an opioid with powerful analgesic effects and a high speed of action. Due to its pharmacological properties, this molecule has therapeutic application as an anesthetic in surgery or as palliative therapy for cancer patients. Unfortunately, in recent years, the easy availability of this substance, the low cost and the illegal online market have favored the large-scale diffusion of fentanyl. Fentanyl is available in different forms, including nasal spray, oral patches, soluble capsules, aerosol or the new version of fentanyl mixed with other drugs, making its use very widespread. Subjects of various ages are involved in fentanyl consumption, including minors that have not yet reached adolescence. In this work, we performed a literature review using the search engines PubMed NCBI and SCOPUS regarding episodes of acute fentanyl intoxication occurring in those of a pediatric age using the Mesh Terms "fentanyl" AND "overdose" AND "children". The inclusion criteria were English papers published in the last 10 years regarding the cases of children under the age of 10. We evaluated the most frequent methods of intake and the circumstances of such episodes. In cases of death, we analyzed the autopsy, the toxicological findings and the investigations carried out. The review results show that in this age group (under < 10 y.o. s), it is possible to identify the risk factors for fentanyl intake, such as the presence of this molecule within the family unit due to drug addiction or medical therapy. The results also demonstrate a significant risk of underestimation of this phenomenon, since the molecule is often not investigated through adequate toxicological analysis. These results, therefore, suggest always carrying out toxicological investigations in the case of suspected fentanyl intoxication, both on patients or cadavers. The investigations must always include a urinary screening for opiates, and the request for a second level analysis with molecule dosage in cases of positivity or in cases of strong suspicion for assumption. In cases of intoxication in a family context of drug addiction, it is necessary to investigate the chronicity of the intake through hair analysis and evaluate the possible co-administration of other drugs. In conclusion, we suggest a protocol, applicable both on patients or cadavers, which can be useful for physicians and forensic pathologists in order to promptly identify these cases and allow for the reporting of them to the judicial authorities with the adoption of strict prevention and control measures.

Nalbuphine Potentiates Reversal of Fentanyl Overdose by Naloxone

Developing an effective antidote for fentanyl-induced overdose to achieve timely reversal is an unmet public health need. Previously, we found that naloxone derivative NX90 with mild κ-opioid agonistic properties was three-fold more effective than the parent naloxone in reversing a fentanyl overdose in rats. To investigate whether κ-agonistic properties could indeed augment the robustness of overdose reversal, we evaluated a κ-agonist/µ-antagonist nalbuphine (NB) as well as its combinations with naloxone (NX) in a fentanyl overdose model in rodents. An administration of either NB or NX as single agents at 0.1 mg/kg doses produced a full recovery in 90 ± 9.9 min and 11.4 ± 2.7 min, respectively. A higher dose of NX at 0.2 mg/kg reversed an overdose within 4.8 ± 1.0 min. In contrast to that, the coadministration of NB and NX at 0.1 mg/kg each produced a synergistic effect, with overdose reversal in 3.4 ± 0.2 min. The coadministration of NX and NB at sub-therapeutic doses of 0.05 mg/kg each was also 1.2-fold more effective than NX at 0.2 mg/kg. We further found that co-administration of NB at different doses (0.025, 0.05, 0.1 mg/kg) and ratios (1:4 and 1:1) with NX had differential effects on overdose reversal, cardiorespiratory liabilities, and analgesia.

Perioperative analgesic efficacy and adverse events of fentanyl in dentistry: A systematic review

OBJECTIVES

To assess the efficacy and adverse events linked to the utilization of fentanyl for perioperative pain management in dentistry.

METHODS

This systematic review of randomized clinical trials (RCTs) adhered to the PRISMA guidelines and incorporated various databases.

RESULTS

Eleven RCTs studying 674 patients were analyzed. Perioperative pain was predominantly evaluated in patients undergoing surgery for impacted molars, although some studies also included patients with other conditions such as oral submucous fibrosis, maxillary cancer, bony temporomandibular joint ankylosis, irreversible pulpitis, among others. Combined with dexmedetomidine, fentanyl produced enhanced analgesic effects. It demonstrated comparable efficacy when compared to nefopam and nalbuphine. Both intranasal and intravenous administration routes proved equally effective. In four RCTs, the transdermal fentanyl patch outperformed the control group, except in the clinical trial where it was compared to ropivacaine. The main adverse events associated with the use of fentanyl included nausea, vomiting, drowsiness, delirium, and respiratory depression; however, they were like those reported in the comparison groups.

CONCLUSIONS

While fentanyl demonstrated satisfactory perioperative analgesic efficacy, there were other alternatives that displayed better or comparable outcomes. Due to the risks and potential for misuse of fentanyl, these alternatives must be considered although adverse events were also reported.

Reversal of Opioid-Induced Respiratory Depression in Healthy Volunteers: Comparison of Intranasal Nalmefene and Intranasal Naloxone

An open-label, randomized, crossover study in healthy volunteers compared the reversal of remifentanil-induced respiratory depression by intranasal (IN) naloxone hydrochloride (4 mg) to IN nalmefene (2.7 mg) (NCT04828005). Subjects were administered a hypercapnic gas mixture which produces an elevation in minute ventilation (MV), a result of the ventilatory response to hypercapnia. Subjects breathed a hypercapnic gas mixture through a tight-fitting mask for an initial period of 46 min prior to a series of mask "holidays" introduced to reduce subject discomfort and encourage study completion. Ten minutes after initiating the hypercapnic gas mixture, a remifentanil bolus was administered, and an infusion continued for the study duration. Subjects were administered either naloxone or nalmefene 15 min after initiating the remifentanil infusion and MV monitored for 21 min followed by a mask holiday. Both nalmefene and naloxone produced a time-dependent reversal of remifentanil-induced reductions in MV measured 2.5-20 min post administration. At the primary endpoint (5 min post administration), nalmefene increases in MV (5.75 L/min) were nearly twice that produced by naloxone (3.01 L/min) (P < .0009); the point estimate favors nalmefene, demonstrating non-inferiority and superiority. In this model of opioid-induced respiratory depression, nalmefene has a more rapid onset of action than naloxone, which required 20 min to achieve a comparable reversal of respiratory depression. Both nalmefene and naloxone were well tolerated by healthy volunteers. This rapid onset of action may prove particularly valuable in an era when over 90% of fatalities are linked to synthetic opioid overdose.

Methyl methacrylate-modified polystyrene microspheres: an effective strategy to enhance the fluorescence of Eu-complexes

The in vitro detection applications of europium complex-doped microspheres mainly rely on strong fluorescence intensity and a well-defined morphology. In this work, using methyl methacrylate-modified polystyrene microspheres has been proven an effective strategy to enhance the fluorescence and morphology of Eu-complexes. The experimental results showed that the modification resulted in the formation of a porous structure within the polystyrene microspheres, enhancing the doping uniformity and facilitating a more significant accumulation of fluorescent molecules. Furthermore, because of their encapsulation ability, microspheres efficiently confine the fluorescent molecules within them. In addition, the nano-scale porous structure endowed the microspheres with enhanced properties without compromising solvent swelling capability, thereby significantly boosting the fluorescence performance of porous PSMMA. In lateral flow immunoassays (LFIAs), PSMMA-Eu microspheres were effectively utilized to detect fentanyl with exceptional sensitivity by capitalizing on these benefits, capable of detecting concentrations as low as 0.10 ng mL-1. This technology has significant potential for rapid point-of-care screening and clinical applications.

Fentanyl and xylazine crisis: Crafting coherent strategies for opioid overdose prevention

The United States is in the throes of a severe opioid overdose epidemic, primarily fueled by the pervasive use of fentanyl and the emerging threat of xylazine, a veterinary sedative often mixed with fentanyl. The high potency and long duration of fentanyl is compounded by the added risks from xylazine, heightening the lethal danger faced by opioid users. Measures such as enhanced surveillance, public awareness campaigns, and the distribution of fentanyl-xylazine test kits, and naloxone have been undertaken to mitigate this crisis. Fentanyl-related overdose deaths persist despite these efforts, partly due to inconsistent policies across states and resistance towards adopting harm reduction strategies. A multifaceted approach is imperative in effectively combating the opioid overdose epidemic. This approach should include expansion of treatment access, broadening the availability of medications for opioid use disorder, implementation of harm reduction strategies, and enaction of legislative reforms and diminishing stigma associated with opioid use disorder.

Comparison of intranasal naloxone and intranasal nalmefene in a translational model assessing the impact of synthetic opioid overdose on respiratory depression and cardiac arrest

Introduction

Using a validated translational model that quantitatively predicts opioid-induced respiratory depression and cardiac arrest, we compared cardiac arrest events caused by synthetic opioids (fentanyl, carfentanil) following rescue by intranasal (IN) administration of the μ-opioid receptor antagonists naloxone and nalmefene.

Methods

This translational model was originally developed by Mann et al. (Clin Pharmacol Ther 2022) to evaluate the effectiveness of intramuscular (IM) naloxone. We initially implemented this model using published codes, reproducing the effects reported by Mann et al. on the incidence of cardiac arrest events following intravenous doses of fentanyl and carfentanil as well as the reduction in cardiac arrest events following a standard 2 mg IM dose of naloxone. We then expanded the model in terms of pharmacokinetic and µ-opioid receptor binding parameters to simulate effects of 4 mg naloxone hydrochloride IN and 3 mg nalmefene hydrochloride IN, both FDA-approved for the treatment of opioid overdose. Model simulations were conducted to quantify the percentage of cardiac arrest in 2000 virtual patients in both the presence and absence of IN antagonist treatment.

Results

Following simulated overdoses with both fentanyl and carfentanil in chronic opioid users, IN nalmefene produced a substantially greater reduction in the incidence of cardiac arrest compared to IN naloxone. For example, following a dose of fentanyl (1.63 mg) producing cardiac arrest in 52.1% (95% confidence interval, 47.3-56.8) of simulated patients, IN nalmefene reduced this rate to 2.2% (1.0-3.8) compared to 19.2% (15.5-23.3) for IN naloxone. Nalmefene also produced large and clinically meaningful reductions in the incidence of cardiac arrests in opioid naïve subjects. Across dosing scenarios, simultaneous administration of four doses of IN naloxone were needed to reduce the percentage of cardiac arrest events to levels that approached those produced by a single dose of IN nalmefene.

Conclusion

Simulations using this validated translational model of opioid overdose demonstrate that a single dose of IN nalmefene produces clinically meaningful reductions in the incidence of cardiac arrest compared to IN naloxone following a synthetic opioid overdose. These findings are especially impactful in an era when >90% of all opioid overdose deaths are linked to synthetic opioids such as fentanyl.

High-Dose Buprenorphine Initiation in the Management of Opioid Use Disorder in Pregnancy

Buprenorphine is commonly used as a treatment for opioid use disorder (OUD). Transition to buprenorphine traditionally has been done using a low-dose initiation regimen due to concerns surrounding precipitated withdrawal. There are increasing data supporting use of a high-dose initiation regimen in the nonpregnant population. This retrospective case series describes six individuals with OUD who underwent high-dose buprenorphine initiation in pregnancy. There were no instances of sedation, respiratory depression, supplemental oxygen use, or death. All individuals were successfully transitioned to buprenorphine. These findings provide support for high-dose buprenorphine initiation in pregnancy, but future large studies are needed.

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

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

Clinical Pharmacokinetics and Pharmacodynamics of Naloxone

Naloxone is a World Health Organization (WHO)-listed essential medicine and is the first choice for treating the respiratory depression of opioids, also by lay-people witnessing an opioid overdose. Naloxone acts by competitive displacement of opioid agonists at the μ-opioid receptor (MOR). Its effect depends on pharmacological characteristics of the opioid agonist, such as dissociation rate from the MOR receptor and constitution of the victim. Aim of treatment is a balancing act between restoration of respiration (not consciousness) and avoidance of withdrawal, achieved by titration to response after initial doses of 0.4-2 mg. Naloxone is rapidly eliminated [half-life (t1/2) 60-120 min] due to high clearance. Metabolites are inactive. Major routes for administration are intravenous, intramuscular, and intranasal, the latter primarily for take-home naloxone. Nasal bioavailability is about 50%. Nasal uptake [mean time to maximum concentration (Tmax) 15-30 min] is likely slower than intramuscular, as reversal of respiration lag behind intramuscular naloxone in overdose victims. The intraindividual, interindividual and between-study variability in pharmacokinetics in volunteers are large. Variability in the target population is unknown. The duration of action of 1 mg intravenous (IV) is 2 h, possibly longer by intramuscular and intranasal administration. Initial parenteral doses of 0.4-0.8 mg are usually sufficient to restore breathing after heroin overdose. Fentanyl overdoses likely require higher doses of naloxone. Controlled clinical trials are feasible in opioid overdose but are absent in cohorts with synthetic opioids. Modeling studies provide valuable insight in pharmacotherapy but cannot replace clinical trials. Laypeople should always have access to at least two dose kits for their interim intervention.

Systematic review on intentional non-medical fentanyl use among people who use drugs

Objectives

Fentanyl is a highly potent opioid and has, until recently, been considered an unwanted contaminant in the street drug supply among people who use drugs (PWUD). However, it has become a drug of choice for an increasing number of individuals. This systematic review evaluated intentional non-medical fentanyl use among PWUD, specifically by summarizing demographic variance, reasons for use, and resulting patterns of use.

Methods

The search strategy was developed with a combination of free text keywords and MeSH and non-MeSH keywords, and adapted with database-specific filters to Ovid MEDLINE, Embase, Web of Science, and PsychINFO. Studies included were human studies with intentional use of non-medical fentanyl or analogues in individuals older than 13. Only peer-reviewed original articles available in English were included.

Results

The search resulted in 4437 studies after de-duplication, of which 132 were selected for full-text review. Out of 41 papers included, it was found that individuals who use fentanyl intentionally were more likely to be young, male, and White. They were also more likely to have experienced overdoses, and report injection drug use. There is evidence that fentanyl seeking behaviours are motivated by greater potency, delay of withdrawal, lower cost, and greater availability.

Conclusions

Among PWUD, individuals who intentionally use fentanyl have severe substance use patterns, precarious living situations, and extensive overdose history. In response to the increasing number of individuals who use fentanyl, alternative treatment approaches need to be developed for more effective management of withdrawal and opioid use disorder.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42021272111.

Fentanyl dysregulates neuroinflammation and disrupts blood-brain barrier integrity in HIV-1 Tat transgenic mice

Opioid overdose deaths have dramatically increased by 781% from 1999 to 2021. In the setting of HIV, opioid drug abuse exacerbates neurotoxic effects of HIV in the brain, as opioids enhance viral replication, promote neuronal dysfunction and injury, and dysregulate an already compromised inflammatory response. Despite the rise in fentanyl abuse and the close association between opioid abuse and HIV infection, the interactive comorbidity between fentanyl abuse and HIV has yet to be examined in vivo. The HIV-1 Tat-transgenic mouse model was used to understand the interactive effects between fentanyl and HIV. Tat is an essential protein produced during HIV that drives the transcription of new virions and exerts neurotoxic effects within the brain. The Tat-transgenic mouse model uses a glial fibrillary acidic protein (GFAP)-driven tetracycline promoter which limits Tat production to the brain and this model is well used for examining mechanisms related to neuroHIV. After 7 days of fentanyl exposure, brains were harvested. Tight junction proteins, the vascular cell adhesion molecule, and platelet-derived growth factor receptor-β were measured to examine the integrity of the blood brain barrier. The immune response was assessed using a mouse-specific multiplex chemokine assay. For the first time in vivo, we demonstrate that fentanyl by itself can severely disrupt the blood-brain barrier and dysregulate the immune response. In addition, we reveal associations between inflammatory markers and tight junction proteins at the blood-brain barrier.

Pharmacokinetic Properties of an FDA-approved Intranasal Nalmefene Formulation for the Treatment of Opioid Overdose

Nalmefene is a high-affinity, long-duration opioid antagonist that was approved in 1995 as an injection for the treatment of opiate overdose, but subsequently withdrawn (2008) for reasons other than safety or effectiveness. The dramatic rise in opioid overdose deaths over the past 7-8 years catalyzed the development of an intranasal (IN) formulation of nalmefene for the emergency treatment of opioid overdose. The studies described here compare the pharmacokinetic properties and safety profiles of an IN formulation containing nalmefene (2.7 mg in 0.1 mL) to an approved 1 mg intramuscular (IM) dose. IN nalmefene produced maximum plasma concentrations that were significantly higher than observed following the IM dose (12.2 and 1.77 ng/mL, respectively). The time to reach maximum plasma concentrations was also faster following IN administration (0.25 and 0.33 hours, respectively) with significant differences in plasma concentrations manifested as early as 2.5 minutes after administration (NCT04759768). The plasma half-life of nalmefene was similar following IM and IN administration (10.6-11.4 hours). Furthermore, dose-normalized nalmefene exposure was similar for both 1 spray in each nostril and 2 sprays in the same nostril compared to a single spray in each nostril (NCT05219669). There were no sex differences in the pharmacokinetic properties of either IN or IM nalmefene. In an era when almost 90% of opioid overdose deaths have been linked to high-potency synthetic opioids, the ability to rapidly deliver high concentrations of nalmefene could represent an important tool for reducing both morbidity and mortality.

Investigation of monoclonal antibody CSX-1004 for fentanyl overdose

The opioid crisis in the United States is primarily driven by the highly potent synthetic opioid fentanyl leading to >70,000 overdose deaths annually; thus, new therapies for fentanyl overdose are urgently needed. Here, we present the first clinic-ready, fully human monoclonal antibody CSX-1004 with picomolar affinity for fentanyl and related analogs. In mice CSX-1004 reverses fentanyl antinociception and the intractable respiratory depression caused by the ultrapotent opioid carfentanil. Moreover, toxicokinetic evaluation in a repeat-dose rat study and human tissue cross-reactivity study reveals a favorable pharmacokinetic profile of CSX-1004 with no safety-related issues. Using a highly translational non-human primate (NHP) model of respiratory depression, we demonstrate CSX-1004-mediated protection from repeated fentanyl challenges for 3-4 weeks. Furthermore, treatment with CSX-1004 produces up to a 15-fold potency reduction of fentanyl in NHP respiration, antinociception and operant responding assays without affecting non-fentanyl opioids like oxycodone. Taken together, our data establish the feasibility of CSX-1004 as a promising candidate medication for preventing and reversing fentanyl-induced overdose.

Xylazine potentiates the lethal but not the rewarding effects of fentanyl in mice

BACKGROUND

Fentanyl is commonly laced with xylazine. People who use this combination report heightened effects, but it also increases death risk. Although no medication has been approved to counteract overdoses produced by fentanyl and xylazine, naloxone is frequently used. This paper studies the preclinical rewarding and lethal effects of fentanyl combined with xylazine and the efficacy of yohimbine or naloxone to prevent death.

METHODS

Male Swiss Webster mice were treated with (in mg/kg, i.p.) xylazine (0.3, 1, 3, or 5.6), fentanyl (0.01, 0.3, or 0.1), or 1 xylazine plus 0.01 (non-effective) or 0.1 (effective) fentanyl doses during the conditioned-place preference (CPP) test. In addition, independent groups received (in mg/kg, i.p.): xylazine (31.6, 60, 74.2, or 100), fentanyl (3.1 or 10), or both substances at two doses: 31.6 xylazine + 3.1 fentanyl, or 60 xylazine + 10 fentanyl to analyze lethal effects. We determined whether yohimbine or naloxone (each medication tested at 10 or 30mg/kg) could prevent the lethality produced by fentanyl/xylazine combinations. Female mice were also tested in key experiments.

RESULTS

Xylazine neither induced CPP nor altered fentanyl's rewarding effects. In contrast, lethality was potentiated when fentanyl was combined with xylazine. Naloxone, but not yohimbine, effectively prevented the lethality of the fentanyl/xylazine combinations.

CONCLUSIONS

At the doses tested, xylazine does not increase the rewarding effect of fentanyl on the CPP in male mice but potentiates the risk of fatal overdose in male and female mice. A high naloxone dose prevents death induced by coadministration of fentanyl and xylazine in both sexes.

Comparison of the effects of fentanyls and other μ opioid receptor agonists on the electrical activity of respiratory muscles in the rat

Introduction: Deaths due to overdose of fentanyls result primarily from depression of respiration. These potent opioids can also produce muscle rigidity in the diaphragm and the chest muscles, a phenomenon known as Wooden Chest Syndrome, which further limits ventilation. Methods: We have compared the depression of ventilation by fentanyl and morphine by directly measuring their ability to induce muscle rigidity using EMG recording from diaphragm and external and internal intercostal muscles, in the rat working heart-brainstem preparation. Results: At equipotent bradypnea-inducing concentrations fentanyl produced a greater increase in expiratory EMG amplitude than morphine in all three muscles examined. In order to understand whether this effect of fentanyl was a unique property of the phenylpiperidine chemical structure, or due to fentanyl's high agonist intrinsic efficacy or its lipophilicity, we compared a variety of agonists with different properties at concentrations that were equipotent at producing bradypnea. We compared carfentanil and alfentanil (phenylpiperidines with relatively high efficacy and high to medium lipophilicity, respectively), norbuprenorphine (orvinolmorphinan with high efficacy and lipophilicity) and levorphanol (morphinan with relatively low efficacy and high lipophilicity). Discussion: We observed that, agonists with higher intrinsic efficacy were more likely to increase expiratory EMG amplitude (i.e., produce chest rigidity) than agonists with lower efficacy. Whereas lipophilicity and chemical structure did not appear to correlate with the ability to induce chest rigidity.

IUPHAR themed review: Opioid efficacy, bias, and selectivity

Drugs acting at the opioid receptor family are clinically used to treat chronic and acute pain, though they represent the second line of treatment behind GABA analogs, antidepressants and SSRI's. Within the opioid family mu and kappa opioid receptor are commonly targeted. However, activation of the mu opioid receptor has side effects of constipation, tolerance, dependence, euphoria, and respiratory depression; activation of the kappa opioid receptor leads to dysphoria and sedation. The side effects of mu opioid receptor activation have led to mu receptor drugs being widely abused with great overdose risk. For these reasons, newer safer opioid analgesics are in high demand. For many years a focus within the opioid field was finding drugs that activated the G protein pathway at mu opioid receptor, without activating the β-arrestin pathway, known as biased agonism. Recent advances have shown that this may not be the way forward to develop safer analgesics at mu opioid receptor, though there is still some promise at the kappa opioid receptor. Here we discuss recent novel approaches to develop safer opioid drugs including efficacy vs bias and fine-tuning receptor activation by targeting sub-pockets in the orthosteric site, we explore recent works on the structural basis of bias, and we put forward the suggestion that Gα subtype selectivity may be an exciting new area of interest.

Identify the influences of systemic lupus erythematosus on acquired ADAMTS13-deficient thrombotic thrombocytopenic purpura using comprehensive bioinformatics analysis

BACKGROUND

The association between acquired ADAMTS13-deficient thrombotic thrombocytopenic purpura (aTTP) and systemic lupus erythematosus (SLE) has been studied; however, the underlying molecular causes remain poorly understood. This research aimed to employ bioinformatics approaches to elucidate potential molecular mechanisms contributing to the pathogenesis of SLE and aTTP.

MATERIAL AND METHODS

The Gene Expression Omnibus (GEO) database yielded GSE121239 and GSE36418 to get mutual different expression genes (DEGs). Subsequently, DEGs were subjected to process Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Then, the DEGs were used for protein-protein interaction (PPI) analysis and screened for hub genes and drugs by the DGIDB drug database.

RESULTS

A total of 87 DEGs between the SLE and TTP datasets were identified. In the GO and KEGG analyses, DEGs were mainly enriched in the "regulation of transcription by RNA polymerase II" and "signaling pathways regulating pluripotency of stem cells." After a PPI analysis, three hub genes (BMPR2, SMAD5, and ATF2) were identified. Finally, two drugs targeted to ATF2 were predicted by the DGIDB drug database.

CONCLUSIONS

Three core genes were linked to the molecular pathogenesis of SLE and aTTP, and two drugs may be viable treatments for both diseases.

Self-Adjuvanting TLR7/8 Agonist and Fentanyl Hapten Co-Conjugate Achieves Enhanced Protection against Fentanyl Challenge

Currently approved pharmacotherapies for opioid use disorders (OUDs) and overdose reversal agents are insufficient to slow the spread of OUDs due to the proliferation of fentanyl. This is evident in the 31% rise in drug overdose deaths from 2019 to 2022, with rates increasing from 21.6 to 28.3 overdoses per 100,000 deaths. Vaccines are a potential alternative or adjunct therapy for the treatment of several substance use disorders (nicotine, cocaine) but have shown limited clinical success due to suboptimal antibody titers. In this study, we demonstrate that coconjugation of a Toll-like receptor 7/8 (TLR7/8) agonist (UM-3006) alongside a fentanyl-based hapten (F1) on the surface of the carrier protein cross-reactive material 197 (CRM) significantly increased generation of high-affinity fentanyl-specific antibodies. This demonstrated enhanced protection against fentanyl challenges relative to an unconjugated (admix) adjuvant control in mice. Inclusion of aluminum hydroxide (alum) adjuvant further increased titers and enhanced protection, as determined by analysis of fentanyl concentration in serum and brain tissue. Collectively, our findings present a promising approach to enhance the efficacy of antiopioid vaccines, underscoring the need for extensive exploration of TLR7/8 agonist conjugates as a compelling strategy to combat opioid use disorders.

Overdose mortality rates for opioids and stimulant drugs are substantially higher in men than in women: state-level analysis

Drug overdoses from opioids and stimulants are a major cause of mortality in the United States. It is unclear if there are stable sex differences in overdose mortality for these drugs across states, whether these differ across the lifespan, and if so, whether they can be accounted for by different levels of drug misuse. This was a state-level analysis of epidemiological data on overdose mortality, across 10-year age bins (age range: 15-74), using the CDC WONDER platform for decedents in the United States in 2020-1. The outcome measure was rate of overdose death (per 100,000) for: synthetic opioids (e.g., fentanyl), heroin, psychostimulants with potential for misuse (e.g., methamphetamine), and cocaine. Multiple linear regressions controlled for ethnic-cultural background, household net worth, and sex-specific rate of misuse (from NSDUH, 2018-9). For all these drug categories, males had greater overall overdose mortality than females, after controlling for rates of drug misuse. The mean male/female sex ratio of mortality rate was relatively stable across jurisdictions: synthetic opioids (2.5 [95% CI, 2.4-7]), heroin, (2.9 [95% CI, 2.7-3.1], psychostimulants (2.4 [95% CI, 2.3-5]), and cocaine (2.8 [95% CI, 2.6-9]). With data stratified in 10-year age bins, the sex difference generally survived adjustment (especially in the 25-64 age range). Results indicate that males are significantly more vulnerable than females to overdose deaths caused by opioid and stimulant drugs, taking into account differing state-level environmental conditions and drug misuse levels. These results call for research into diverse biological, behavioral, and social factors that underlie sex differences in human vulnerability to drug overdose.

Systematic assessment of non-medical use of prescription drugs using doctor-shopping indicators: A nation-wide, repeated cross-sectional study

AIMS

The aim of this study was to present the first nation-wide, systematic, repeated assessment of doctor-shopping (i.e. visiting multiple physicians to be prescribed the same drug) during 10 years for more than 200 psychoactive prescription drugs in the 67 million inhabitants in France.

DESIGN

This was a nation-wide, repeated cross-sectional study.

SETTING AND PARTICIPANTS

Data are from the French National Health Data System in 2010, 2015 and 2019 for 214 psychoactive prescription drugs (i.e. anaesthetics, analgesics, antiepileptics, anti-Parkinson drugs, psycholeptics, psychoanaleptics, other nervous system drugs and antihistamines for systemic use).

MEASUREMENTS

The detection and quantification of doctor-shopping relied upon an algorithm that detects overlapping prescriptions from repeated visits to different physicians. We used two doctor-shopping indicators aggregated at population level for each drug dispensed to more than 5000 patients: (i) the quantity doctor-shopped, expressed in defined daily doses (DDD), which measures the total quantity doctor-shopped by the study population for a given drug; and (ii) the proportion doctor-shopped, expressed as a percentage, which standardizes the quantity doctor-shopped according to the use level of the drug.

FINDINGS

The analyses included approximately 200 million dispensings to approximately 30 million patients each year. Opioids (e.g. buprenorphine, methadone, morphine, oxycodone and fentanyl), benzodiazepines and non-benzodiazepine hypnotics (Z-drugs) (e.g. diazepam, oxazepam, zolpidem and clonazepam) had the highest proportions doctor-shopped during the study period. In most cases, the proportion and the quantity doctor-shopped increased for opioids and decreased for benzodiazepines and Z-drugs. Pregabalin had the sharpest increase in the proportion doctor-shopped (from 0.28 to 1.40%), in parallel with a sharp increase in the quantity doctor-shopped (+843%, from 0.7 to 6.6 DDD/100 000 inhabitants/day). Oxycodone had the sharpest increase in the quantity doctor-shopped (+1000%, from 0.1 to 1.1 DDD/100 000 inhabitants/day), in parallel with a sharp increase in the proportion doctor-shopped (from 0.71 to 1.41%). Detailed results for all drugs during the study period can be explored interactively at: https://soeiro.gitlab.io/megadose/.

CONCLUSIONS

In France, doctor-shopping occurs for many drugs from many pharmacological classes, and mainly involves opioid maintenance drugs, some opioids analgesics, some benzodiazepines and Z-drugs and pregabalin.

Focus on fentanyl in females: Sex and gender differences in the physiological and behavioral effects of fentanyl

The prevalence of opioid use disorder and overdose continues to harm the U.S. population and is further exacerbated by the use of the synthetic opioid, fentanyl, and its analogs. Gender differences in the effects of fentanyl are not well understood. The present article reviews evidence for gender and sex differences in the physiological and behavioral effects of fentanyl in humans and animals. Biological sex seems to be a foundational driver in addiction vulnerability and affects mechanisms related to opioid use including fentanyl. Fentanyl has distinct pharmacodynamics and enhanced efficacy relative to other opioids that highlights the need to investigate how females may be uniquely altered by its use. Behavioral and physiological responses to fentanyl are found to differ by sex and gender in many cases, including outputs like affective symptoms, analgesia, tolerance, and withdrawal emphasizing the need for further research about the role of biological sex on fentanyl use.

Carfentanil is a β-arrestin-biased agonist at the μ opioid receptor

BACKGROUND AND PURPOSE

The illicit use of fentanyl-like drugs (fentanyls), which are μ opioid receptor agonists, and the many overdose deaths that result, has become a major problem. Fentanyls are very potent in vivo, leading to respiratory depression and death. However, the efficacy and possible signalling bias of different fentanyls is not clearly known. Here, we compared the relative efficacy and bias of a series of fentanyls.

EXPERIMENTAL APPROACH

For agonist signalling bias and efficacy measurements, Bioluminescence Resonance Energy Transfer experiments were undertaken in HEK293T cells transiently transfected with μ opioid receptors, to assess Gi protein activation and β-arrestin 2 recruitment. Agonist-induced cell surface receptor loss was assessed using an enzyme-linked immunosorbent assay, whilst agonist-induced G protein-coupled inwardly rectifying potassium channel current activation was measured electrophysiologically from rat locus coeruleus slices. Ligand poses in the μ opioid receptor were determined in silico using molecular dynamics simulations.

KEY RESULTS

Relative to the reference ligand DAMGO, carfentanil was β-arrestin-biased, whereas fentanyl, sufentanil and alfentanil did not display bias. Carfentanil induced potent and extensive cell surface receptor loss, whilst the marked desensitisation of G protein-coupled inwardly rectifying potassium channel currents in the continued presence of carfentanil in neurones was prevented by a GRK2/3 inhibitor. Molecular dynamics simulations suggested unique interactions of carfentanil with the orthosteric site of the receptor that could underlie the bias.

CONCLUSIONS AND IMPLICATIONS

Carfentanil is a β-arrestin-biased opioid drug at the μ receptor. It is uncertain how such bias influences in vivo effects of carfentanil relative to other fentanyls.

Revolutionizing Precision Medicine: Exploring Wearable Sensors for Therapeutic Drug Monitoring and Personalized Therapy

Precision medicine, particularly therapeutic drug monitoring (TDM), is essential for optimizing drug dosage and minimizing toxicity. However, current TDM methods have limitations, including the need for skilled operators, patient discomfort, and the inability to monitor dynamic drug level changes. In recent years, wearable sensors have emerged as a promising solution for drug monitoring. These sensors offer real-time and continuous measurement of drug concentrations in biofluids, enabling personalized medicine and reducing the risk of toxicity. This review provides an overview of drugs detectable by wearable sensors and explores biosensing technologies that can enable drug monitoring in the future. It presents a comparative analysis of multiple biosensing technologies and evaluates their strengths and limitations for integration into wearable detection systems. The promising capabilities of wearable sensors for real-time and continuous drug monitoring offer revolutionary advancements in diagnostic tools, supporting personalized medicine and optimal therapeutic effects. Wearable sensors are poised to become essential components of healthcare systems, catering to the diverse needs of patients and reducing healthcare costs.

Opioid research in the time of the opioid crisis

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Overdose mortality rates for opioids or stimulants are higher in males than females, controlling for rates of drug misuse: State-level data

Importance

Drug overdoses from opioids like fentanyl and heroin and stimulant drugs such as methamphetamine and cocaine are a major cause of mortality in the United States, with potential sex differences across the lifespan.

Objective

To determine overdose mortality for specific drug categories across the lifespan of males and females, using a nationally representative state-level sample.

Design

State-level analyses of nationally representative epidemiological data on overdose mortality for specific drug categories, across 10-year age bins (age range: 15-74).

Setting

Population-based study of Multiple Cause of Death 2020-2021 data from the Centers of Disease Control and Prevention (CDC WONDER platform).

Participants

Decedents in the United States in 2020-2021.

Main outcome measures

The main outcome measure was sex-specific rates of overdose death (per 100,000) for: synthetic opioids excluding methadone (ICD-10 code: T40.4; predominantly fentanyl), heroin (T40.1), psychostimulants with potential for misuse, excluding cocaine (T43.6, predominantly methamphetamine; labeled "psychostimulants" hereafter), and cocaine (T40.5). Multiple regression analyses were used to control for ethnic-cultural background, household net worth, and sex-specific rate of misuse of the relevant substances (from the National Survey on Drug Use and Health, 2018-2019).

Results

For each of the drug categories assessed, males had greater overall overdose mortality than females, after controlling for rates of drug misuse. The mean male/female sex ratio of mortality rate for the separate drug categories was relatively stable across jurisdictions: synthetic opioids (2.5 [95%CI, 2.4-2.7]), heroin, (2.9 [95%CI, 2.7-3.1], psychostimulants (2.4 [95%CI, 2.3-2.5]), and cocaine (2.8 [95%CI, 2.6-2.9]). With data stratified in 10-year age bins, the sex difference generally survived adjustment for state-level ethnic-cultural and economic variables, and for sex-specific misuse of each drug type (especially for bins in the 25-64 age range). For synthetic opioids, the sex difference survived adjustment across the lifespan (i.e., 10-year age bins ranging from 15-74), including adolescence, adulthood and late adulthood.

Conclusions and Relevance

The robustly greater overdose mortality in males versus females for synthetic opioids (predominantly fentanyl), heroin, and stimulant drugs including methamphetamine and cocaine indicate that males who misuse these drugs are significantly more vulnerable to overdose deaths. These results call for research into diverse biological, behavioral, and social factors that underlie sex differences in human vulnerability to drug overdose.

Biased Agonism: Lessons from Studies of Opioid Receptor Agonists

In ligand bias different agonist drugs are thought to produce distinct signaling outputs when activating the same receptor. If these signaling outputs mediate therapeutic versus adverse drug effects, then agonists that selectively activate the therapeutic signaling pathway would be extremely beneficial. It has long been thought that μ-opioid receptor agonists that selectively activate G protein- over β-arrestin-dependent signaling pathways would produce effective analgesia without the adverse effects such as respiratory depression. However, more recent data indicate that most of the therapeutic and adverse effects of agonist-induced activation of the μ-opioid receptor are actually mediated by the G protein-dependent signaling pathway, and that a number of drugs described as G protein biased in fact may not be biased, but instead may be low-intrinsic-efficacy agonists. In this review we discuss the current state of the field of bias at the μ-opioid receptor and other opioid receptor subtypes.

Molecular recognition of morphine and fentanyl by the human μ-opioid receptor

Morphine and fentanyl are among the most used opioid drugs that confer analgesia and unwanted side effects through both G protein and arrestin signaling pathways of μ-opioid receptor (μOR). Here, we report structures of the human μOR-G protein complexes bound to morphine and fentanyl, which uncover key differences in how they bind the receptor. We also report structures of μOR bound to TRV130, PZM21, and SR17018, which reveal preferential interactions of these agonists with TM3 side of the ligand-binding pocket rather than TM6/7 side. In contrast, morphine and fentanyl form dual interactions with both TM3 and TM6/7 regions. Mutations at the TM6/7 interface abolish arrestin recruitment of μOR promoted by morphine and fentanyl. Ligands designed to reduce TM6/7 interactions display preferential G protein signaling. Our results provide crucial insights into fentanyl recognition and signaling of μOR, which may facilitate rational design of next-generation analgesics.

The PharmNet Harm Reduction Intervention for Community Pharmacies: Protocol for a Pilot Randomized Controlled Trial

Background

The overdose epidemic in the United States has continued to worsen despite substantial efforts to mitigate its harms. The opioid antagonist naloxone has been identified as a key means of reducing the prevalence of fatal overdoses. An important evidence-based approach to optimizing naloxone’s impact is to seed it throughout the community, because bystanders are often able to reverse overdoses more quickly than first responders and sometimes are the only possible means of overdose reversal. As part of a multipronged approach to distributing naloxone nationwide, community pharmacies have been identified as ideal venues for naloxone dispensing, especially under standing orders. However, dispensing rates remain surprisingly low, and there is a need to understand how best to engage community pharmacies in naloxone-based harm reduction services.

Objective

The objective of this trial is to determine whether a tailored, pragmatic pharmacy intervention (PharmNet) results in greater naloxone dispensing relative to baseline (the prior 3 months) compared to a control condition. This pilot trial is intended to determine whether it is appropriate to invest the substantial resources that would be required to conduct a full-scale, randomized controlled study of PharmNet.

Methods

We will conduct a 3-month randomized controlled pilot trial consisting of 2 parallel groups with a 4:3 allocation ratio. A group of 7 independent pharmacies from rural areas in Indiana will be randomly assigned to either the PharmNet intervention arm (n=4) or the control arm (n=3). The primary outcome will be overall naloxone dispensing (both at cost and free), and secondary outcomes will include the distribution of referral cards and multiple variables at the level of individual staff members. Dispensing data will be collected for the 3 months prior to the intervention and the 3 months of the intervention, and all other data will be collected using a pretest-posttest design. The primary analysis will be a generalized linear mixed model with a Poisson distribution with fixed effects for group, time, and their interaction and a random effect for pharmacy ID to account for repeated measures within pharmacies.

Results

This study was approved by the Indiana University institutional review board in 2 phases (August 2, 2021, and April 26, 2022) and was funded by the Indiana University Grand Challenge: Responding to the Addictions Crisis.

Conclusions

If this study produces evidence that the PharmNet intervention results in increased naloxone dispensing relative to control pharmacies, it will be both appropriate and important to study it in a large, full-scale randomized controlled trial.

International Registered Report Identifier (IRRID)

PRR1-10.2196/42373

A role for the circadian transcription factor NPAS2 in the progressive loss of non-rapid eye movement sleep and increased arousal during fentanyl withdrawal in male mice

RATIONALE

Synthetic opioids like fentanyl are contributing to the rise in rates of opioid use disorder and drug overdose deaths. Sleep dysfunction and circadian rhythm disruption may worsen during opioid withdrawal and persist during abstinence. Severe and persistent sleep and circadian alterations are putative factors in opioid craving and relapse. However, very little is known about the impact of fentanyl on sleep architecture and sleep-wake cycles, particularly opioid withdrawal. Further, circadian rhythms regulate sleep-wake cycles, and the circadian transcription factor, neuronal PAS domain 2 (NPAS2) is involved in the modulation of sleep architecture and drug reward. Here, we investigate the role of NPAS2 in fentanyl-induced sleep alterations.

OBJECTIVES

To determine the effect of fentanyl administration and withdrawal on sleep architecture, and the role of NPAS2 as a factor in fentanyl-induced sleep changes.

METHODS

Electroencephalography (EEG) and electromyography (EMG) was used to measure non-rapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS) at baseline and following acute and chronic fentanyl administration in wild-type and NPAS2-deficient male mice.

RESULTS

Acute and chronic administration of fentanyl led to increased wake and arousal in both wild-type and NPAS2-deficient mice, an effect that was more pronounced in NPAS2-deficient mice. Chronic fentanyl administration led to decreased NREMS, which persisted during withdrawal, progressively decreasing from day 1 to 4 of withdrawal. The impact of fentanyl on NREMS and arousal was more pronounced in NPAS2-deficient mice.

CONCLUSIONS

Chronic fentanyl disrupts NREMS, leading to a progressive loss of NREMS during subsequent days of withdrawal. Loss of NPAS2 exacerbates the impact of fentanyl on sleep and wake, revealing a potential role for the circadian transcription factor in opioid-induced sleep changes.

Efficacy and Selectivity of Monovalent and Bivalent Vaccination Strategies to Protect against Exposure to Carfentanil, Fentanyl, and Their Mixtures in Rats

Drug-related fatal overdoses have significantly increased in the past decade due to the widespread availability of illicit fentanyl and other potent synthetic opioids such as carfentanil. Deliberate or accidental consumption or exposure to carfentanil, fentanyl, and their mixture induces respiratory depression and bradycardia that can be difficult to reverse with the opioid receptor antagonist naloxone. Vaccines offer a promising strategy to reduce the incidence of fatalities associated with fentanyl-related substances, as well as treatment for opioid use disorder (OUD). This study reports monovalent and bivalent vaccination strategies that elicit polyclonal antibody responses effective in protecting against the pharmacological actions of carfentanil, fentanyl, or carfentanil/fentanyl mixtures. Rats were prophylactically immunized with individual conjugate vaccines containing either carfentanil- or fentanyl-based haptens, or their combination in bivalent vaccine formulations, and then challenged with carfentanil, fentanyl, or their mixture. First, these studies identified a lead vaccine protective against carfentanil-induced antinociception, respiratory depression, and bradycardia. Then, efficacy against both carfentanil and fentanyl was achieved through bivalent vaccination strategies that combined lead anti-carfentanil and anti-fentanyl vaccines via either heterologous prime/boost or co-administration immunization regimens. These preclinical data support the development of vaccines as a viable strategy to prevent toxicity from exposure to excessive doses of carfentanil, fentanyl, or their mixtures.

A comprehensive evaluation of the potential binding poses of fentanyl and its analogs at the µ-opioid receptor

Fentanyl and its analogs are selective agonists of the µ-opioid receptor (MOR). Among novel synthetic opioids (NSOs), they dominate the recreational drug market and are the main culprits for the opioid crisis, which has been exacerbated by the COVID-19 pandemic. By taking advantage of the crystal structures of the MOR, several groups have investigated the binding mechanism of fentanyl, but have not reached a consensus, in terms of both the binding orientation and the fentanyl conformation. Thus, the binding mechanism of fentanyl at the MOR remains an unsolved and challenging question. Here, we carried out a systematic computational study to investigate the preferred fentanyl conformations, and how these conformations are being accommodated in the MOR binding pocket. We characterized the free energy landscape of fentanyl conformations with metadynamics simulations, and compared and evaluated several possible fentanyl binding conditions in the MOR with long-timescale molecular dynamics simulations. Our results indicate that the most preferred binding pose in the MOR binding pocket corresponds well with the global minimum on the energy landscape of fentanyl in the absence of the receptor, while the energy landscape can be reconfigured by modifying the fentanyl scaffold. The interactions with the receptor may stabilize a slightly unfavored fentanyl conformation in an alternative binding pose. By extending similar investigations to fentanyl analogs, our findings establish a structure–activity relationship of fentanyl binding at the MOR. In addition to providing a structural basis to understand the potential toxicity of the emerging NSOs, such insights will contribute to developing new, safer analgesics.

Interaction With the Lipid Membrane Influences Fentanyl Pharmacology

Overdose deaths from fentanyl have reached epidemic proportions in the USA and are increasing worldwide. Fentanyl is a potent opioid agonist that is less well reversed by naloxone than morphine. Due to fentanyl’s high lipophilicity and elongated structure we hypothesised that its unusual pharmacology may be explained by its interactions with the lipid membrane on route to binding to the μ-opioid receptor (MOPr). Through coarse-grained molecular dynamics simulations, electrophysiological recordings and cell signalling assays, we determined how fentanyl and morphine access the orthosteric pocket of MOPr. Morphine accesses MOPr via the aqueous pathway; first binding to an extracellular vestibule, then diffusing into the orthosteric pocket. In contrast, fentanyl may take a novel route; first partitioning into the membrane, before accessing the orthosteric site by diffusing through a ligand-induced gap between the transmembrane helices. In electrophysiological recordings fentanyl-induced currents returned after washout, suggesting fentanyl deposits in the lipid membrane. However, mutation of residues forming the potential MOPr transmembrane access site did not alter fentanyl’s pharmacological profile in vitro. A high local concentration of fentanyl in the lipid membrane, possibly in combination with a novel lipophilic binding route, may explain the high potency and lower susceptibility of fentanyl to reversal by naloxone.

Pharmacokinetic considerations for community-based dosing of nasal naloxone in opioid overdose in adults

INTRODUCTION

The administration of the opioid antagonist naloxone in the community is a measure to prevent death from opioid overdose. Approved nasal naloxone sprays deliver initial doses of 0.9 to 8 mg. The level of the initial community dose is controversial, as the scientific base is weak.In this review knowledge of the pharmacokinetics of nasal, both approved and improvised nasal sprays, and intramuscular naloxone will be utilized to evaluate dose-effect relationships in previous studies of opioid overdose outcomes.

AREAS COVERED

The aim was to present scientifically based considerations on the initial nasal naloxone doses currently available, which reasonably balances the effect and adverse outcomes, given that at least two doses are at hand. Also included in these considerations is the challenge by illicitly manufactured fentanyl and analogs.This paper is based on both peer-reviewed and grey literature identified by several searches, of such as naloxone pharmacokinetics/formulations/outcomes/emergency medical services, in PubMed and Embase.

EXPERT OPINION

There is little scientific evidence that supports the use of initial systemic dosing that exceeds 0.8 mg in the community. Higher doses increase the risk of withdrawal symptoms feared in people who use opioids. Many obstacles may reduce the potential of community-administered naloxone.

Long-term antagonism and allosteric regulation of mu opioid receptors by the novel ligand, methocinnamox

Opioid overdose is a leading cause of death in the United States. The only treatment available currently is the competitive antagonist, naloxone (Narcan® ). Although naloxone is very effective and has saved many lives, as a competitive antagonist it has limitations. Due to the short half-life of naloxone, renarcotization can occur if the ingested opioid agonist remains in the body longer. Moreover, because antagonism by naloxone is surmountable, renarcotization can also occur in the presence of naloxone if a relatively larger dose of opioid agonist is taken. In such circumstances, a long-lasting, non-surmountable antagonist would offer an improvement in overdose treatment. Methocinnamox (MCAM) has been reported to have a long duration of antagonist action at mu opioid receptors in vivo. In HEK cells expressing the human mu opioid receptor, MCAM antagonism of mu agonist-inhibition of cAMP production was time-dependent, non-surmountable and non-reversible, consistent with (pseudo)-irreversible binding. In vivo, MCAM injected locally into the rat hindpaw antagonized mu agonist-mediated inhibition of thermal allodynia for up to 96 h. By contrast, antagonism by MCAM of delta or kappa agonists in HEK cells and in vivo was consistent with simple competitive antagonism. Surprisingly, MCAM also shifted the concentration-response curves of mu agonists in HEK cells in the absence of receptor reserve in a ligand-dependent manner. The shift in the [D-Ala2 ,N-MePhe4 ,Gly-ol5 ]-enkephalin (DAMGO) concentration-response curve by MCAM was insensitive to naloxone, suggesting that in addition to (pseudo)-irreversible orthosteric antagonism, MCAM acts allosterically to alter the affinity and/or intrinsic efficacy of mu agonists.

Treatment of overdose in the synthetic opioid era

Overdose deaths are often viewed as the leading edge of the opioid epidemic which has gripped the United States over the past two decades (Skolnick, 2018a). This emphasis is perhaps unsurprising because opioid overdose is both the number-one cause of death for individuals between 25 and 64 years old (Dezfulian et al., 2021) and a significant contributor to the decline in average lifespan (Dowell et al., 2017). Exacerbated by the COVID 19 pandemic, it was estimated there were 93,400 drug overdose deaths in the United States during the 12 months ending December 2020, with more than 69,000 (that is, >74%) of these fatalities attributed to opioid overdose (Ahmad et al., 2021). However, the focus on mortality statistics (Ahmad et al., 2021; Shover et al., 2020) tends to obscure the broader medical impact of nonfatal opioid overdose. Analyses of multiple databases indicate that for each opioid-induced fatality, there are between 6.4 and 8.4 non-fatal overdoses, exacting a significant burden on both the individual and society. Over the past 7-8 years, there has been an alarming increase in the misuse of synthetic opioids ("synthetics"), primarily fentanyl and related piperidine-based analogs. Within the past 2-3 years, a structurally unrelated class of high potency synthetics, benzimidazoles exemplified by etonitazene and isotonitazene ("iso"), have also appeared in illicit drug markets (Thompson, 2020; Ujvary et al. 2021). In 2020, it was estimated that over 80% of fatal opioid overdoses in the United States now involve synthetics (Ahmad et al., 2021). The unique physicochemical and pharmacological properties of synthetics described in this review are responsible for both the morbidity and mortality associated with their misuse as well as their widespread availability. This dramatic increase in the misuse of synthetics is often referred to as the "3rd wave" (Pardo et al., 2019; Volkow and Blanco, 2020) of the opioid epidemic. Among the consequences resulting from misuse of these potent opioids is the need for higher doses of the competitive antagonist, naloxone, to reverse an overdose. The development of more effective reversal agents such as those described in this review is an essential component of a tripartite strategy (Volkow and Collins, 2017) to reduce the biopsychosocial impact of opioid misuse in the "synthetic era".

Predicting the Membrane Permeability of Fentanyl and Its Analogues by Molecular Dynamics Simulations

The lipid membrane is considered a crucial component of opioid general anesthesia. The main drug used for the induction and maintenance of opioid anesthesia is fentanyl and its various analogues. However, these drugs have different clinical effects, and detailed atomic-level insight into the drug–membrane interactions could lead to a better understanding how these drugs exert their anesthetic properties. In this study, we have used extensive umbrella sampling molecular dynamics simulations to study the permeation process of fentanyl and three of its analogues into a variety of simple phospholipid membrane models. Our simulations show that we can accurately predict the permeability coefficients of these drug molecules, which is an important process in understanding how pharmaceuticals reach their molecular targets. We were also able to show that one phospholipid provides more accurate predictions than other lipids commonly used in these types of permeation studies, which will aid future studies of these types of processes.