Buprenorphine to reverse respiratory depression from methadone overdose in opioid-dependent patients: a prospective randomized trial

Respiratory Depression Associated with Opioids: A Narrative Review

OPINION

All opioids have a risk of causing respiratory depression and reduced cerebral circulation. Fentanyl has the greatest risk of causing both. This is particularly a concern when combined with illicit opioids such as diamorphine (also known as heroin). Fentanyl should not be used as a frontline potent opioid due its significant risks. Buprenorphine, a schedule III opioid, morphine, or hydromorphone is preferred, followed by oxycodone, which has a significant risk of abuse relative to buprenorphine and morphine. Although all opioids were equally effective in producing analgesia, the relative safety of each opioid is no longer a secondary concern when prescribing. In the face of an international opioid epidemic, clinicians need to choose opioid analgesics safely, wisely, and carefully.

The cell-permeant antioxidant D-thiol ester D-cysteine ethyl ester overcomes physical dependence to morphine in male Sprague Dawley rats

The ability of morphine to decrease cysteine transport into neurons by inhibition of excitatory amino acid transporter 3 (EAA3) may be a key molecular mechanism underlying the acquisition of physical and psychological dependence to morphine. This study examined whether co-administration of the cell-penetrant antioxidant D-thiol ester, D-cysteine ethyl ester (D-CYSee), with morphine, would diminish the development of physical dependence to morphine in male Sprague Dawley rats. Systemic administration of the opioid receptor antagonist, naloxone (NLX), elicited pronounced withdrawal signs (e.g., wet-dog shakes, jumps, rears, circling) in rats that received a subcutaneous depot of morphine (150 mg/kg, SC) for 36 h and continuous intravenous infusion of vehicle (20 μL/h, IV). The NLX-precipitated withdrawal signs were reduced in rats that received an infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) for the full 36 h. NLX elicited pronounced withdrawal signs in rats treated for 48 h with morphine (150 mg/kg, SC), plus continuous infusion of vehicle (20 μL/h, IV) that began at the 36 h timepoint of morphine treatment. The NLX-precipitated withdrawal signs were reduced in rats that received a 12 h infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) that began at the 36 h timepoint of morphine treatment. These findings suggest that D-CYSee may attenuate the development of physical dependence to morphine and reverse established dependence to the opioid in male Sprague Dawley rats. Alternatively, D-CYSee may simply suppress the processes responsible for NLX-precipitated withdrawal. Nonetheless, D-CYSee and analogues may be novel therapeutics for the treatment of opioid use disorders.

Orally dissolving buprenorphine for opioid use disorder linked to caries

BACKGROUND

Buprenorphine is under scrutiny because of the development of xerostomia and caries. The purpose of this article was to inform dental care professionals about the oral effects of buprenorphine and to increase knowledge and awareness of medication-assisted treatment in the management of opioid use disorder (OUD).

CASE DESCRIPTION

In 2022, the US Food and Drug Administration issued a warning about xerostomia and caries associated with the use of transmucosal (sublingual and buccal formulations) buprenorphine. Dental health care professionals should instruct patients taking buprenorphine on how to prevent these dental issues by means of rinsing with water and swallowing once the drug has been completely dissolved, followed by toothbrushing at least 1 hour after taking the drug. In addition, a fluoride supplement should be prescribed.

PRACTICAL IMPLICATIONS

It is imperative for dentists to recognize buprenorphine as medication-assisted treatment and to recognize a patient as having an OUD. While taking buprenorphine, the patient should have more frequent oral health care appointments, including home care instructions and caries risk assessment to monitor for caries and xerostomia so that treatment, if indicated, could be initiated as soon as possible. In addition, the dentist's role in OUD is to make sure patients follow the treatment recommendations and use the buprenorphine and to not have them discontinue because of potential caries risk.

Lipophilic analogues of D-cysteine prevent and reverse physical dependence to fentanyl in male rats

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 μg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) was markedly reduced in rats that received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl.

Considerations and limitations of buprenorphine prescribing for opioid use disorder in the intensive care unit setting: A narrative review

PURPOSE

The purpose of this review is to discuss important considerations when prescribing buprenorphine for opioid use disorder (OUD) in the intensive care unit (ICU) setting, recognizing the challenges of providing detailed recommendations in the setting of limited available evidence.

SUMMARY

Buprenorphine is a partial mu-opioid receptor agonist that is likely to be increasingly prescribed for OUD in the ICU setting due to the relaxation of prescribing regulations. The pharmacology and pharmacokinetics of buprenorphine are complicated by the availability of several formulations that can be given by different administration routes. There is no single optimal dosing strategy for buprenorphine induction, with regimens ranging from very low-dose to high dose regimens. Faster induction with higher doses of buprenorphine has been studied and is frequently utilized in the emergency department. In patients admitted to the ICU who were receiving opioids either medically or illicitly, analgesia will not occur until their baseline opioid requirements are covered when their preadmission opioid is either reversed or interrupted. For patients in the ICU who are not on buprenorphine at the time of admission but have possible OUD, there are no validated tools to diagnose OUD or the severity of opioid withdrawal in critically ill patients unable to provide the subjective components of instruments validated in outpatient settings. When prescribing buprenorphine in the ICU, important issues to consider include dosing, monitoring, pain management, use of adjunctive medications, and considerations to transition to outpatient therapy. Ideally, addiction and pain management specialists would be available when buprenorphine is prescribed for critically ill patients.

CONCLUSION

There are unique challenges when prescribing buprenorphine for OUD in critically ill patients, regardless of whether they were receiving buprenorphine when admitted to the ICU setting for OUD or are under consideration for buprenorphine initiation. There is a critical need for more research in this area.

Quantifying a potential protective effect of buprenorphine on fatality risk during acute fentanyl exposures

INTRODUCTION

Buprenorphine is an important therapy for opioid use disorder and may also reduce the risk of fatal overdoses in fentanyl exposures. However, the role of buprenorphine in reducing this risk has not been quantified. This cross-sectional study examined the association between buprenorphine presence, decedent characteristics, and other factors with the predicted fentanyl concentrations in overdose deaths.

METHODS

The study identified unintentional fentanyl overdose decedents (n = 3036) from the West Virginia Forensic Drug Database, 2011 through mid-2020. The main outcome was fentanyl concentrations in overdose deaths in the presence and absence of buprenorphine. A multiple linear regression model examined the association of fentanyl concentrations with buprenorphine presence based on the concentrations of the parent drug buprenorphine (B) and its metabolite norbuprenorphine (N), adjusting for demographics, toxicological characteristics (presence of multiple opioids, benzodiazepines, stimulants, marijuana, and alcohol), and comorbidities. We used a B/N concentration ratio < 1 as an indirect indicator of longer-term buprenorphine exposure prior to drug overdose death.

RESULTS

The median fentanyl concentration was 65 % higher when buprenorphine was present (N = 168) vs. absent (N = 2868) (0.028 vs. 0.017 μg/mL, p < 0.001). In the multivariable model, statistically significant associations occurred between buprenorphine presence and increased fentanyl concentrations (+28.7 %) with a B/N ratio < 1. Obesity, male sex, alcohol presence, and comorbid cardiovascular diseases were statistically significantly associated with lower (-11.3 % to -20.7 %) fentanyl concentrations, whereas marijuana presence and a history of substance use disorder were associated with statistically significant higher fentanyl concentrations (+8.8 % to +31.3 %).

CONCLUSIONS

These findings suggest that sustained or longer-term buprenorphine intake might exert some protective effect on fatalities resulting from fentanyl exposure as documented by the association of higher fentanyl blood concentrations with buprenorphine presence among fatal drug overdoses. As fentanyl availability and overdose rates increase nationally, buprenorphine is a vital tool for effective opioid use disorder treatment that might also reduce the risk of fatality in an acute fentanyl exposure.

L-cysteine ethyl ester prevents and reverses acquired physical dependence on morphine in male Sprague Dawley rats

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the co-administration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150 mg/kg) for 36 h and were receiving a continuous infusion of saline (20 μL/h, IV) via osmotic minipumps for the same 36 h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8 μmol/kg/h, IV) for 36 h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150 mg/kg) for 48 h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150 mg/kg for 48 h)-treated rats that began receiving an infusion of L-CYSee (20.8 μmol/kg/h, IV) at 36 h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8 μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of L-CYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans.

Long-acting opioids and cardiovascular diseases: Help or hindrance!

Opioids are widely being used for chronic pain management, cough and diarrhea suppressants, anesthetic agents, and opioid de-addiction therapy. Opioid receptors, present in the central nervous system and peripheral tissues, are documented to regulate several cardiac functions through different signaling pathways. Long-acting opioids (LAO) have been successfully evaluated for their beneficial effects in various cardiovascular diseases viz. myocardial infarction, ischemic reperfusion injuries, atherosclerosis etc. However, on the other hand, several research studies pointed towards the harmful effects of LAOs which are mainly associated with QTc prolongation, torsade de pointes, ventricular arrhythmias, and cardiac arrest. This review shall familiarize readers with the benefits as well as the harmful effects of long-acting opioids in cardiovascular diseases. We have also provided an overview of cardiac opioid receptors, endogenous cardiac opioid peptides, and regulation of cardiovascular functions by central and cardiac opioid receptors.

Endogenous opiates and behavior: 2020

This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Treatment of opioid overdose: current approaches and recent advances

BACKGROUND

The USA has recently entered the third decade of the opioid epidemic. Opioid overdose deaths reached a new record of over 74,000 in a 12-month period ending April 2021. Naloxone is the primary opioid overdose reversal agent, but concern has been raised that naloxone is not efficacious against the pervasive illicit high potency opioids (i.e., fentanyl and fentanyl analogs).

METHODS

This narrative review provides a brief overview of naloxone, including its history and pharmacology, and the evidence regarding naloxone efficacy against fentanyl and fentanyl analogs. We also highlight current advances in overdose treatments and technologies that have been tested in humans.

RESULTS AND CONCLUSIONS

The argument that naloxone is not efficacious against fentanyl and fentanyl analogs rests on case studies, retrospective analyses of community outbreaks, pharmacokinetics, and pharmacodynamics. No well-controlled studies have been conducted to test this argument, and the current literature provides limited evidence to suggest that naloxone is ineffective against fentanyl or fentanyl analog overdose. Rather a central concern for treating fentanyl/fentanyl analog overdose is the rapidity of overdose onset and the narrow window for treatment. It is also difficult to determine if other non-opioid substances are contributing to a drug overdose, for which naloxone is not an effective treatment. Alternative pharmacological approaches that are currently being studied in humans include other opioid receptor antagonists (e.g., nalmefene), respiratory stimulants, and buprenorphine. None of these approaches target polysubstance overdose and only one novel approach (a wearable naloxone delivery device) would address the narrow treatment window.

Advances in Reversal Strategies of Opioid-induced Respiratory Toxicity

Opioids may produce life-threatening respiratory depression and death from their actions at the opioid receptors within the brainstem respiratory neuronal network. Since there is an increasing number of conditions where the administration of the opioid receptor antagonist naloxone is inadequate or undesired, there is an increased interest in the development of novel reversal and prevention strategies aimed at providing efficacy close to that of the opioid receptor antagonist naloxone but with fewer of its drawbacks such as its short duration of action and lesser ability to reverse high-affinity opioids, such as carfentanil, or drug combinations. To give an overview of this highly relevant topic, the authors systematically discuss predominantly experimental pharmacotherapies, published in the last 5 yr, aimed at reversal of opioid-induced respiratory depression as alternatives to naloxone. The respiratory stimulants are discussed based on their characteristics and mechanism of action: nonopioid controlled substances (e.g., amphetamine, cannabinoids, ketamine), hormones (thyrotropin releasing hormone, oxytocin), nicotinic acetylcholine receptor agonists, ampakines, serotonin receptor agonists, antioxidants, miscellaneous peptides, potassium channel blockers acting at the carotid bodies (doxapram, ENA001), sequestration techniques (scrubber molecules, immunopharmacotherapy), and opioids (partial agonists/antagonists). The authors argue that none of these often still experimental therapies are sufficiently tested with respect to efficacy and safety, and many of the agents presented have a lesser efficacy at deeper levels of respiratory depression, i.e., inability to overcome apnea, or have ample side effects. The authors suggest development of reversal strategies that combine respiratory stimulants with naloxone. Furthermore, they encourage collaborations between research groups to expedite development of viable reversal strategies of potent synthetic opioid-induced respiratory depression.

Sublingual Buprenorphine/Naloxone and Multi-Modal Management for High-Risk Chronic Pain Patients

Patients with chronic pain managed with opioid medications are at high risk for opioid overuse or misuse. West Virginia University (WVU) established a High-Risk Pain Clinic to use sublingual buprenorphine/naloxone (bup/nal) plus a multimodal approach to help chronic pain patients with history of Substance Use Disorder (SUD) or aberrant drug-related behavior. The objective of this study was to report overall retention rates and indicators of efficacy in pain control from approximately six years of High-Risk Pain Clinic data. A retrospective chart review was conducted for a total of 78 patients who enrolled in the High-Risk Pain Clinic between 2014 and 2020. Data gathered include psychiatric diagnoses, prescribed medications, pain score, buprenorphine/naloxone dosing, time in clinic, and reason for dismissal. A linear mixed effects model was used to assess the pain score from the Defense and Veterans Pain Rating Scale (DVPRS) and daily bup/nal dose across time. The overall retention of the High-Risk Pain Clinic was 41%. The mean pain score demonstrated a significant downward trend across treatment time (p < 0.001), while the opposite trend was seen with buprenorphine dose (p < 0.001). With the benefit of six years of observation, this study supports buprenorphine/naloxone as a safe and efficacious component of comprehensive chronic pain treatment in patients with SUD or high-risk of opioid overuse or misuse.