Overdoses due to fentanyl and its analogues (F/FAs) push naloxone to the limit

Withdrawal during outpatient low dose buprenorphine initiation in people who use fentanyl: a retrospective cohort study

BACKGROUND

Buprenorphine is an effective treatment for opioid use disorder (OUD); however, buprenorphine initiation can be complicated by withdrawal symptoms including precipitated withdrawal. There has been increasing interest in using low dose initiation (LDI) strategies to reduce this withdrawal risk. As there are limited data on withdrawal symptoms during LDI, we characterize withdrawal symptoms in people with daily fentanyl use who underwent initiation using these strategies as outpatients.

METHODS

We conducted a retrospective chart review of patients with OUD using daily fentanyl who were prescribed 7-day or 4-day LDI at 2 substance use disorder treatment clinics in San Francisco. Two addiction medicine experts assessed extracted chart documentation for withdrawal severity and precipitated withdrawal, defined as acute worsening of withdrawal symptoms immediately after taking buprenorphine. A third expert adjudicated disagreements. Data were analyzed using descriptive statistics.

RESULTS

There were 175 initiations in 126 patients. The mean age was 37 (SD 10 years). 71% were men, 26% women, and 2% non-binary. 21% identified as Black, 16% Latine, and 52% white. 60% were unstably housed and 75% had Medicaid insurance. Substance co-use included 74% who used amphetamines, 29% cocaine, 22% benzodiazepines, and 19% alcohol. Follow up was available for 118 (67%) initiations. There was deviation from protocol instructions in 22% of these initiations with follow up. 31% had any withdrawal, including 21% with mild symptoms, 8% moderate and 2% severe. Precipitated withdrawal occurred in 10 cases, or 8% of initiations with follow up. Of these, 7 had deviation from protocol instructions; thus, there were 3 cases with follow up (3%) in which precipitated withdrawal occurred without protocol deviation.

CONCLUSIONS

Withdrawal was relatively common in our cohort but was mostly mild, and precipitated withdrawal was rare. Deviation from instructions, structural barriers, and varying fentanyl use characteristics may contribute to withdrawal. Clinicians should counsel patients who use fentanyl that mild withdrawal symptoms are likely during LDI, and there is still a low risk for precipitated withdrawal. Future studies should compare withdrawal across initiation types, seek ways to support patients in initiating buprenorphine, and qualitatively elicit patients' withdrawal experiences.

Fact vs. fiction: naloxone in the treatment of opioid-induced respiratory depression in the current era of synthetic opioids

Opioid-induced respiratory depression (OIRD) deaths are ~80,000 a year in the US and are a major public health issue. Approximately 90% of fatal opioid-related deaths are due to synthetic opioids such as fentanyl, most of which is illicitly manufactured and distributed either on its own or as an adulterant to other drugs of abuse such as cocaine or methamphetamine. Other potent opioids such as nitazenes are also increasingly present in the illicit drug supply, and xylazine, a veterinary tranquilizer, is a prevalent additive to opioids and other drugs of abuse. Naloxone is the main treatment used to reverse OIRD and is available as nasal sprays, prefilled naloxone injection devices, and generic naloxone for injection. An overdose needs to be treated as soon as possible to avoid death, and synthetic opioids such as fentanyl are up to 50 times more potent than heroin, so the availability of new, higher-dose, 5-mg prefilled injection or 8-mg intranasal spray naloxone preparations are important additions for emergency treatment of OIRDs, especially by lay people in the community. Higher naloxone doses are expected to reverse a synthetic overdose more rapidly and the current formulations are ideal for use by untrained lay people in the community. There are potential concerns about severe withdrawal symptoms, or pulmonary edema from treatment with high-dose naloxone. However, from the perspective of first responders, the balance of risks would point to administration of naloxone at the dose required to combat the overdose where the risk of death is very high. The presence of xylazines as an adulterant complicates the treatment of OIRDs, as naloxone is probably ineffective, although it will reverse the respiratory depression due to the opioid. For these patients, hospitalization is particularly vital. Education about the benefits of naloxone remains important not only in informing people about how to treat emergency OIRDs but also how to obtain naloxone. A call to emergency services is also essential after administering naloxone because, although the patient may revive, they may overdose again later because of the short half-life of naloxone and the long-lasting potency of fentanyl and its analogs.

Examination of naloxone dosing patterns for opioid overdose by emergency medical services in Kentucky during increased fentanyl use from 2018 to 2021

BACKGROUND

Fatal overdoses involving fentanyl/fentanyl analogs (F/FA) have increased in the US, raising questions about naloxone doses for F/FA overdose reversal. Emergency medical services (EMS) data provide an opportunity to examine naloxone administration changes as fentanyl increases in the illicit opioid supply.

METHODS

Administered naloxone intranasal-equivalent total dose (INTD) in milligrams (mg) was calculated for Kentucky EMS suspected opioid overdose (SOO) encounters (n=33,846), 2018-2021, and patterns of administration were examined. County-level F/FA availability was measured as 1) proportion of fatal drug overdoses involving F/FA, and 2) F/FA police seizures. Linear mixed models estimated changes in INTD in relation to local F/FA availability accounting for patient characteristics.

RESULTS

From 2018-2021, SOOs increased by 44% (6853 to 9888) with an average INTD increase from 4.5mg to 4.7mg, with more than 99% of encounters resulting in successful reversal each year. For SOO encounters examined by outcome at the scene (i.e., non-fatal fatal vs fatal), average INTD for non-fatal were 4.6mg compared to 5.9mg for fatal overdoses. Mixed modeling found no significant relationship between INTD and the two measures for local F/FA availability.

CONCLUSION

As F/FA-involved overdose risk increased, we observed a modest increase in INTD administered in SOO EMS encounters - just slightly higher than the 4mg standard dose. The lack of significant relationship between F/FA and naloxone dose suggests that naloxone utilization in SOO with EMS involvement remains effective for overdose reversal, and that EMS naloxone dosing patterns have not changed substantially.

"Tranq-dope" overdose and mortality: lethality induced by fentanyl and xylazine

Introduction: The recreational use of fentanyl in combination with xylazine (i.e., "tranq-dope") represents a rapidly emerging public health threat characterized by significant toxicity and mortality. This study quantified the interactions between these drugs on lethality and examined the effectiveness of potential rescue medications to prevent a lethal overdose. Methods: Male and female mice were administered acute doses of fentanyl, xylazine, or their combination via intraperitoneal injection, and lethality was determined 0.5, 1.0, 1.5, 2.0, and 24 h after administration. Both fentanyl and xylazine produced dose-dependent increases in lethality when administered alone. Results: A nonlethal dose of fentanyl (56 mg/kg) produced an approximately 5-fold decrease in the estimated LD50 for xylazine (i.e., the dose estimated to produce lethality in 50% of the population). Notably, a nonlethal dose of xylazine (100 mg/kg) produced an approximately 100-fold decrease in the estimated LD50 for fentanyl. Both drug combinations produced a synergistic interaction as determined via isobolographic analysis. The opioid receptor antagonist, naloxone (3 mg/kg), but not the alpha-2 adrenergic receptor antagonist, yohimbine (3 mg/kg), significantly decreased the lethality of a fentanyl-xylazine combination. Lethality was rapid, with death occurring within 10 min after a high dose combination and generally within 30 min at lower dose combinations. Males were more sensitive to the lethal effects of fentanyl-xylazine combinations under some conditions suggesting biologically relevant sex differences in sensitivity to fentanyl-xylazine lethality. Discussion: These data provide the first quantification of the lethal effects of "tranq-dope" and suggest that rapid administration of naloxone may be effective at preventing death following overdose.

"Tranq-Dope" Overdose and Mortality: Lethality Induced by Fentanyl and Xylazine

The recreational use of fentanyl in combination with xylazine (i.e., "tranq-dope") represents a rapidly emerging public health threat characterized by significant toxicity and mortality. This study quantified the interactions between these drugs on lethality and examined the effectiveness of potential rescue medications to prevent a lethal overdose. Male and female mice were administered acute doses of fentanyl, xylazine, or their combination via intraperitoneal injection, and lethality was determined 30, 60, 90, 120, and 1440 min (24 hr) after administration. Both fentanyl and xylazine produced dose-dependent increases in lethality when administered alone. A nonlethal dose of fentanyl (56 mg/kg) produced an approximately 5-fold decrease in the estimated LD50 for xylazine (i.e., the dose estimated to produce lethality in 50% of the population). Notably, a nonlethal dose of xylazine (100 mg/kg) produced an approximately 100-fold decrease in the estimated LD50 for fentanyl. The opioid receptor antagonist, naloxone (3 mg/kg), but not the alpha-2 adrenergic receptor antagonist, yohimbine (3 mg/kg), significantly decreased the lethality of a fentanyl-xylazine combination. Lethality was rapid, with death occurring within 10 min after a high dose combination and generally within 30 min at lower dose combinations. Males were more sensitive to the lethal effects of fentanyl-xylazine combinations under some conditions, suggesting biologically relevant sex differences in sensitivity to fentanyl-xylazine lethality. These data provide the first quantification of the lethal effects of "tranq-dope" and suggest that rapid administration of naloxone may be effective at preventing death following overdose.

Catalytic Antibody Blunts Carfentanil-Induced Respiratory Depression

Carfentanil, the most potent of the fentanyl analogues, is at the forefront of synthetic opioid-related deaths, second to fentanyl. Moreover, the administration of the opioid receptor antagonist naloxone has proven inadequate for an increasing number of opioid-related conditions, often requiring higher/additional doses to be effective, as such interest in alternative strategies to combat more potent synthetic opioids has intensified. Increasing drug metabolism would be one strategy to detoxify carfentanil; however, carfentanil's major metabolic pathways involve N-dealkylation or monohydroxylation, which do not lend themselves readily to exogenous enzyme addition. Herein, we report, to our knowledge, the first demonstration that carfentanil's methyl ester when hydrolyzed to its acid was found to be 40,000 times less potent than carfentanil in activating the μ-opioid receptor. Physiological consequences of carfentanil and its acid were also examined through plethysmography, and carfentanil's acid was found to be incapable of inducing respiratory depression. Based upon this information, a hapten was chemically synthesized and immunized, allowing the generation of antibodies that were screened for carfentanil ester hydrolysis. From the screening campaign, three antibodies were found to accelerate the hydrolysis of carfentanil's methyl ester. From this series of catalytic antibodies, the most active underwent extensive kinetic analysis, allowing us to postulate its mechanism of hydrolysis against this synthetic opioid. In the context of potential clinical applications, the antibody, when passively administered, was able to reduce respiratory depression induced by carfentanil. The data presented supports further development of antibody catalysis as a biologic strategy to complement carfentanil overdose reversal.

βγ G-proteins, but not regulators of G-protein signaling 4, modulate opioid-induced respiratory rate depression

Opioid medications are the mainstay of pain management but present substantial side-effects such as respiratory depression which can be lethal with overdose. Most opioid drugs, such as fentanyl, act on opioid receptors such as the G-protein-coupled µ-opioid receptors (MOR). G-protein-coupled receptors activate pertussis toxin-sensitive G-proteins to inhibit neuronal activity. Binding of opioid ligands to MOR and subsequent activation G proteins βγ is modulated by regulator of G-protein signaling (RGS). The roles of G-proteins βγ and RGS in MOR-mediated inhibition of the respiratory network are not known. Using rodent models to pharmacologically modulate G-protein signaling, we aim to determine the roles of βγ G-proteins and RGS4. We showed that inhibition of βγ G-proteins using gallein perfused in the brainstem circuits regulating respiratory depression by opioid drugs results in complete reversal of respiratory depression. Blocking of RGS4 using CCG55014 did not change the respiratory depression induced by MOR activation despite co-expression of RGS4 and MORs in the brainstem. Our results suggest that neuronal inhibition by opioid drugs is mediated by G-proteins, but not by RGS4, which supports the concept that βγ G-proteins could be molecular targets to develop opioid overdose antidotes without the risks of re-narcotization often found with highly potent opioid drugs. On the other hand, RGS4 mediates opioid analgesia, but not respiratory depression, and RGS4 may be molecular targets to develop pain therapies without respiratory liability.

Molecular Docking and Dynamics Simulation Studies Predict Potential Anti-ADAR2 Inhibitors: Implications for the Treatment of Cancer, Neurological, Immunological and Infectious Diseases

Altered RNA editing has been linked to several neurodevelopmental disorders, including autism spectrum disorder (ASD) and intellectual disability, in addition to depression, schizophrenia, some cancers, viral infections and autoimmune disorders. The human ADAR2 is a potential therapeutic target for managing these various disorders due to its crucial role in adenosine to inosine editing. This study applied consensus scoring to rank potential ADAR2 inhibitors after performing molecular docking with AutoDock Vina and Glide (Maestro), using a library of 35,161 compounds obtained from traditional Chinese medicine. A total of 47 compounds were predicted to be good binders of the human ADAR2 and had insignificant toxicity concerns. Molecular dynamics (MD) simulations, including the molecular mechanics Poisson–Boltzmann surface area (MM/PBSA) procedure, also emphasized the binding of the shortlisted compounds. The potential compounds had plausible binding free energies ranging from −81.304 to −1068.26 kJ/mol from the MM/PBSA calculations. ZINC000085511995, a naphthoquinone had more negative binding free energy (−1068.26 kJ/mol) than inositol hexakisphosphate (IHP) [−873.873 kJ/mol], an agonist and a strong binder of ADAR2. The potential displacement of IHP by ZINC000085511995 in the IHP binding site of ADAR2 could be explored for possible deactivation of ADAR2. Bayesian-based biological activity prediction corroborates the neuropharmacological, antineoplastic and antiviral activity of the potential lead compounds. All the potential lead compounds, except ZINC000014612330 and ZINC000013462928, were predicted to be inhibitors of various deaminases. The potential lead compounds also had probability of activity (Pa) > 0.442 and probability of inactivity (Pi) < 0.116 values for treating acute neurologic disorders, except for ZINC000085996580 and ZINC000013462928. Pursuing these compounds for their anti-ADAR2 activities holds a promising future, especially against neurological disorders, some cancers and viral infections caused by RNA viruses. Molecular interaction, hydrogen bond and per-residue decomposition analyses predicted Arg400, Arg401, Lys519, Trp687, Glu689, and Lys690 as hot-spot residues in the ADAR2 IHP binding site. Most of the top compounds were observed to have naphthoquinone, indole, furanocoumarin or benzofuran moieties. Serotonin and tryptophan, which are beneficial in digestive regulation, improving sleep cycle and mood, are indole derivatives. These chemical series may have the potential to treat neurological disorders, prion diseases, some cancers, specific viral infections, metabolic disorders and eating disorders through the disruption of ADAR2 pathways. A total of nine potential lead compounds were shortlisted as plausible modulators of ADAR2.

Advancing humanized monoclonal antibody for counteracting fentanyl toxicity towards clinical development

Innovative therapies to complement current treatments are needed to curb the growing incidence of fatal overdoses related to synthetic opioids. Murine and chimeric monoclonal antibodies (mAb) specific for fentanyl and its analogs have demonstrated pre-clinical efficacy in preventing and reversing drug-induced toxicity in rodent models. However, mAb-based therapeutics require extensive engineering as well as in vitro and in vivo characterization to advance to first-in-human clinical trials. Here, novel murine anti-fentanyl mAbs were selected for development based on affinity for fentanyl, and efficacy in counteracting the pharmacological effects of fentanyl in mice. Humanization and evaluation of mutations designed to eliminate predicted post-translational modifications resulted in two humanized mAbs that were effective at preventing fentanyl-induced pharmacological effects in rats. These humanized mAbs showed favorable biophysical properties with respect to aggregation and hydrophobicity by chromatography-based assays, and thermostability by dynamic scanning fluorimetry. These results collectively support that the humanized anti-fentanyl mAbs developed herein warrant further clinical development for treatment of fentanyl toxicity.

Pharmacological Profiling of Antifentanyl Monoclonal Antibodies in Combination with Naloxone in Pre- and Postexposure Models of Fentanyl Toxicity

The incidence of fatal drug overdoses in the United States is an alarming public health threat that has been exacerbated by the COVID-19 pandemic, resulting in over 100,000 deaths between April 2020 and April 2021. A significant portion of this is attributable to widespread access to fentanyl and other synthetic opioids, alone or in combination with heroin or psychostimulants, such as cocaine or methamphetamine. Monoclonal antibodies (mAb) offer prophylactic and therapeutic interventions against opioid overdose by binding opioids in serum, reducing distribution of drug to the brain and other organs. Here, we investigated the efficacy of a leading antifentanyl mAb, clone HY6-F9, in reversal and prevention of fentanyl-induced toxicity compared with the opioid receptor antagonist naloxone (NLX) in rats. In postexposure models, rats were challenged with fentanyl, followed by HY6-F9, NLX, or both. HY6-F9 reversed fentanyl-induced antinociception, respiratory depression, and bradycardia, and rats retained protection against additional challenges for at least 1 week. Although intravenous NLX reversed fentanyl-induced respiratory depression more rapidly than mAb alone, kinetics of reversal by intravenous mAb were similar to subcutaneous NLX. Coadministration of mAb and NLX provided greater protection than individual treatments against high doses of fentanyl. Prophylactic administration of mAb reduced the ED50 of NLX approximately twofold against 2.25 mg/kg of fentanyl. Finally, mAb sequestered fentanyl and its metabolite norfentanyl in serum and reduced brain concentrations of fentanyl. These results support the translation of mAb as medical interventions alone or in combination with NLX to prevent and reverse fentanyl-related overdose. SIGNIFICANCE STATEMENT: Fentanyl-related overdoses have increased dramatically in the US and worldwide. Currently, approved pharmacotherapies for treatment of opioid use disorder and reversal of overdose are not sufficient to curb the incidence of opioid-related deaths. Additionally, fentanyl and its potent analogs present a potential risk from use in deliberate poisoning or chemical attacks. This study demonstrates the use of monoclonal antibodies as a countermeasure to fentanyl-induced toxicity in pre- and postexposure scenarios, supporting their use in combination with the opioid antagonist naloxone.

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".