Naltrexone. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic efficacy in the management of opioid dependence

Alcohol use disorder in the perioperative period: a summary and recommendations for anesthesiologists and pain physicians

Excessive alcohol consumption and alcohol use disorder (AUD) increase the risk of perioperative morbidity and mortality. Aspiration, malnutrition, coagulopathies, seizures, and hemodynamic alterations are only a few of the major concerns related to acute alcohol intoxication and AUD. There are also numerous physiological effects, changes in medication metabolism and pharmacology, and adverse events related to chronic alcohol consumption. These are all important considerations for the anesthesiologist in the perioperative management of a patient with AUD. Pain perception and thresholds are altered in patients with acute and chronic alcohol use. Medications used to manage AUD symptoms, particularly naltrexone, can have significant perioperative implications. Patients on naltrexone who continue or stop this medication in the perioperative period are at an increased risk for undertreated pain or substance use relapse. This review highlights key considerations for the anesthesiologist and pain physician in the perioperative management of patients with active AUD (or those in recovery). It discusses the effects of acute and chronic alcohol use on pain perception and thresholds, provides guidance on the perioperative management of naltrexone and low-dose naltrexone, and reviews a multimodal approach to pain management.

Reversal of subtype-selectivity and function by the introduction of a para-benzamidyl substituent to N-cyclopropylmethyl nornepenthone

The discovery and development of novel μ-opioid receptor (MOR) antagonists is a significant area to combat Opioid Use Disorder (OUD). In this work, a series of para-substituted N-cyclopropylmethyl-nornepenthone derivatives were designed and synthesized and pharmacologically assayed. Compound 6a was identified as a selective MOR antagonist both in vitro and in vivo. Its molecular basis was elucidated using molecular docking and MD simulations. A subpocket on the extracellular side of the TM2 domain of MOR, in particular the residue Y^2.64, was proposed to be responsible for the reversal of subtype selectivity and functional reversal of this compound.

Treatment of Acute Pain in Patients on Naltrexone: A Narrative Review

PURPOSE OF REVIEW

The tissue damage and trauma associated with surgery almost always result in acute postoperative pain. The intensity of postoperative pain can range from mild to severe. Naltrexone is suitable for patients who do not wish to be on an agonist treatment such as methadone or buprenorphine. However, naltrexone has been shown to complicate postoperative pain management.

RECENT FINDINGS

Multiple studies have found that the use of naltrexone can increase the opioid requirement for postoperative pain control. Other modalities exist that can help outside of opioids such as ketamine, lidocaine/bupivacaine, duloxetine, and non-pharmacological management can help manage pain. Multimodal pain regiments should also be employed in patients. In addition to traditional methods for postoperative pain management, other methods of acute pain control exist that can help mitigate opioid dependence and help control pain in patients who use naltrexone for their substance use disorders.

Naltrexone-bupropion combinations do not affect cocaine self-administration in humans

The FDA has not yet approved a pharmacotherapy for cocaine use disorder despite nearly four decades of research. This study determined the initial efficacy, safety, and tolerability of naltrexone-bupropion combinations as a putative pharmacotherapy for cocaine use disorder. Thirty-one (31) non-treatment seeking participants with cocaine use disorder completed a mixed-design human laboratory study. Participants were randomly assigned to the naltrexone conditions (i.e., 0, 50 mg/day; between-subject factor) and maintained on escalating doses of bupropion (i.e., 0, 100, 200, 400 mg/day; within-subject factor) for at least four days prior to the conduct of experimental sessions. Cocaine self-administration (IN, 0, 40, 80 mg) was then determined using a modified progressive ratio and relapse procedure. Subjective and cardiovascular effects were also measured. Cocaine produced prototypical dose-related increases in self-administration, subjective outcomes (e.g., "Like Drug"), and cardiovascular indices (e.g., heart rate, blood pressure) during placebo maintenance. Naltrexone and bupropion alone, or in combination, did not significantly decrease self-administration on either procedure. Low doses of bupropion (i.e., 100 mg) blunted the effects of the cocaine on subjective measures of "Like Drug" and "Stimulated". No unexpected adverse effects were observed with naltrexone and bupropion, alone and combined, in conjunction with cocaine. Together, these results do not support the use of these bupropion-naltrexone combinations for the treatment of cocaine use disorder. Future research should determine if novel drug combinations may decrease cocaine self-administration.

The role of opioid transmission in music-induced pleasure

Studies conducted in rodents indicate a crucial role of the opioid circuit in mediating objective hedonic reactions to primary rewards. However, it remains unclear whether opioid transmission is also essential to experience pleasure with more abstract rewards, such as music. We addressed this question using a double-blind within-subject pharmacological design in which opioid levels were up- and downregulated by administering an opioid agonist (oxycodone) and antagonist (naltrexone), respectively, before healthy participants (n = 21) listened to music. Participants also performed a monetary incentive delay (MID) task to control for the effectiveness of the treatment and the specificity of the effects. Our results revealed that the pharmacological intervention did not modulate subjective reports of pleasure, nor the occurrence of chills. On the contrary, psychophysiological (objective) measures of emotional arousal, such as skin conductance responses (SCRs), were bidirectionally modulated in both the music and MID tasks. This modulation specifically occurred during reward consumption, with greater pleasure-related SCR following oxycodone than naltrexone. These findings indicate that opioid transmission does not modulate subjective evaluations but rather affects objective reward-related psychophysiological responses. These findings raise new caveats about the role of the opioidergic system in the modulation of pleasure for more abstract or cognitive forms of rewarding experiences, such as music.

Naltrexone Transport by a Proton-Coupled Organic Cation Antiporter in hCMEC/D3 Cells, an in Vitro Human Blood-Brain Barrier Model

Naltrexone is a mu-opioid receptor antagonist used in the treatment of opioid and alcohol dependence. The blood-brain barrier (BBB) transport characteristics of naltrexone was investigated by means of hCMEC/D3 cells, a human immortalized brain capillary endothelial cell line. In hCMEC/D3 cells, naltrexone is taken up in a concentration-dependent manner. Furthermore, naltrexone uptake significantly decreased in the presence of H⁺/organic cation (OC) antiporter substrates, during the little alteration exhibited by substrates of well-identified OC transporters classified into SLC22A family. Although naltrexone uptake by hCMEC/D3 cells was partially affected by changes of ionic conditions, it was markedly decreased in the presence of the metabolic inhibitor sodium azide. Furthermore, when treated by ammonium chloride, naltrexone uptake by hCMEC/D3 cells was altered by intracellular acidification and alkalization, suggesting the involvement of oppositely directed proton gradient in naltrexone transport across the BBB. The results obtained in the present in vitro study suggest the active transport of naltrexone from blood to the brain across the BBB by the H⁺/OC antiporter.

Is there a therapeutic potential in combining bupropion and naltrexone in schizophrenia?

INTRODUCTION

A sustained-release tablet composed of a combination of the dopamine and norepinephrine reuptake inhibitor bupropion (BUP) and the µ-opioid receptor antagonist naltrexone (NAT) is marketed under the brand name Contrave by Orexigen Therapeutics for appetite control. Minimal literature is available regarding the use of combination bupropion and naltrexone (BUPNAT) in individuals with schizophrenia.

AREAS COVERED

In this review, we propose a theoretical model where BUPNAT may have a therapeutic effect in the treatment of schizophrenia. We explore the pathways targeted by the constituent drugs BUP and NAT and summarize the literature on their efficacy and possible adverse effects. We then look at the potential use of BUPNAT in schizophrenia.

EXPERT OPINION

Research has hinted that BUP's dopaminergic properties affect the same striatal pathways involved in schizophrenia. NAT, via opioid receptor antagonism, indirectly increases striatal dopamine release by disinhibiting nicotinic acetylcholine receptors. As such, we hypothesize that BUPNAT can have a therapeutic effect in schizophrenia, particularly on negative symptoms. We also suggest that it may ameliorate comorbidities frequently seen in this group of patients, including obesity, smoking, and substance use. Further research and clinical data are needed to elucidate the potential clinical benefits of BUPNAT in the treatment of schizophrenia.

Naltrexone a potential therapeutic candidate for COVID-19

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the cause of Coronavirus Disease (COVID-19) that has resulted in a global pandemic. At the time of writing, approximately 16.06 million cases have been reported worldwide. Like other coronaviruses, SARS-CoV-2 relies on the surface Spike glycoprotein to access the host cells, mainly through the interaction of its Receptor Binding Domain (RBD) with the host receptor Angiotensin-Converting Enzyme2 (ACE2). SARS-CoV-2 infection induces a profound downstream pro-inflammatory cytokine storm. This release of the pro-inflammatory cytokines is underpinning lung tissue damage, respiratory failure, and eventually multiple organ failure in COVID-19 patients. The phosphorylation status of ERK1/2 is positively correlated with virus load and ERK1/2 inhibition suppressed viral replication and viral infectivity. Therefore, molecular entities able to interfere with binding of the SARS-CoV-2 Spike protein to ACE2, or damping hyperinflammatory cytokines storm, blocking ERK1/2 phosphorylation have a great potential to inhibit viral entry along with viral infectivity. Herein, we report that the FDA-approved non-peptide opioid antagonist drug, naltrexone suppresses high fat/LPS induced pro-inflammatory cytokine release both from macrophage cells and Adipose Tissue Macrophage. Moreover, Low Dose Naltrexone (LDN) also showed its activity as an ERK1/2 inhibitor. Notably, virtual docking and simulation data also suggest LDN may disrupt the interaction of ACE2 with RBD. LDN may be considered as a target as the treatment and (or) adjuvant therapy for coronavirus infection. Clinical toxicity measurements may not be required for LDN since naltrexone was previously tested and is an approved drug by the FDA.Communicated by Ramaswamy H. Sarma.

Naltrexone moderates the association of alcohol use and affect among adolescent drinkers in daily life

BACKGROUND

Naltrexone is an efficacious medication for the treatment of alcohol use disorder in adults. As an opioid receptor antagonist, naltrexone blocks activation of the endogenous opioid system, which is involved in the affectively reinforcing properties of substance use. Few studies, however, have examined the moderating effect of naltrexone on the association between affect and alcohol use. Additionally, most existing research on naltrexone has been with adults in the human laboratory.

METHOD

We conducted a secondary analysis of ecological momentary assessment data from a randomized, double-blinded, placebo-controlled cross-over study that compared naltrexone (50 mg/daily) and placebo in 26 adolescents (15 to 19 years old) who exhibited problematic drinking patterns. Multilevel models tested whether naltrexone moderated associations of alcohol use with both positive and negative affect (PA, NA).

RESULTS

Results indicated that, during naltrexone treatment, greater estimated blood alcohol concentration (eBAC) levels were associated with greater NA further into drinking episodes. In turn, greater NA after the first drink of an episode was associated with reduced subsequent eBAC values during naltrexone treatment. Low PA was also associated with lower subsequent eBAC levels in the naltrexone condition after the first drink.

CONCLUSIONS

These findings support the idea that naltrexone can disrupt the association between affect and alcohol use, effects that emerge later in drinking episodes. Greater attention to the effects of naltrexone on affect and reinforcement may help to tailor psychotherapy to maximize the benefits of naltrexone. However, in the present study, as most drink reports were in the first 2 h of the drinking episode and participants reported affect only at the first three end-drink reports of a drinking episode (limiting the number of drinks reported), we had reduced power to detect effects in the continuation phase. Thus, replication of the findings is needed using a design that assesses the impact of naltrexone across the entire episode.

Endogenous opioids contribute to the feeling of pain relief in humans

Endogenous opioids mediate the pleasurable responses to positively reinforcing stimuli such as palatable food. Yet, the reduction or omission of a negative experience can also be rewarding (negative reinforcement). As such, pain relief leads to negative reinforcement and evokes a pleasant feeling in humans. Although it has been shown that the feeling of pleasure associated with positive reinforcement is at least partly mediated through endogenous opioids, it is currently unknown whether similar neurochemical mechanisms are involved in the pleasant feeling evoked by pain relief. In this study, 27 healthy participants completed 2 identical experimental sessions, 1 with placebo and 1 with naltrexone, an endogenous opioid antagonist. Pain relief was induced by superficial cooling after heat stimulation of capsaicin-sensitized skin. Participants rated the relief and pleasantness in response to the cooling. Endogenous opioid blockade by naltrexone decreased relief and pleasantness ratings compared with placebo (P = 0.0027). This study provides evidence that endogenous opioids play a role in mediating the pleasant feeling of pain relief in humans. Clinically, the rewarding nature of pain relief and its underlying mechanisms require consideration because of their potential reinforcing effects on behaviors that might be beneficial short-term but maladaptive long-term.

Risk of Relapse Among Opioid-Dependent Patients Treated With Extended-Release Naltrexone or Buprenorphine-Naloxone: A Randomized Clinical Trial

BACKGROUND AND OBJECTIVES

Compare the risk of relapse to heroin and other illicit opioids among opioid-dependent patients receiving treatment with extended-release naltrexone (XR-NTX) or buprenorphine-naloxone (BP-NLX).

METHODS

Re-analyzed data from a 12-week multicenter, open-label, randomized treatment study with a subsequent 36-week open-label follow-up study. All patients, N = 143, had completed detoxification and received at least one dose of study medication.

RESULTS

Of 143 patients (72% men), mean age 36 years, 71 received XR-NTX and 72 BP-NLX. The risk of first relapse and the risk of any relapse to heroin and other illicit opioids were both significantly lower in the XR-NTX group compared with the BP-NLX group (hazard ratio [HR], 0.46; 95% confidence interval [CI], 0.28-0.76; P = .002, and HR, 0.11; 95% CI, 0.04-0.29; P < .001, respectively) and (HR, 0.15; 95% CI, 0.09-0.27; P < .001 and HR, 0.05; 95% CI, 0.03-0.09; P < .001, respectively). There was a stable low risk of relapse among participants receiving XR-NTX in the follow-up.

DISCUSSION AND CONCLUSIONS

Compared to BP-NLX, patients on XR-NTX had a substantially reduced risk of relapse to illicit opioids and showed a stable low risk of relapse over time in longer-term treatment.

SCIENTIFIC SIGNIFICANCE

Our data support XR-NTX as a first-line treatment option for patients with opioid addiction both in short and longer-term treatment. This is the first European study showing that XR-NTX significantly reduces the risk of first and any relapse to heroin use in opioid-dependent patients compared to BP-NLX. Our data contradict previous data from the X:BOT study, showing no significant difference in relapse risk between the groups in a 6-month randomised controlled trial. (© 2021 Authors. The American Journal on Addictions published by Wiley Periodicals LLC on behalf of The American Academy of Addiction Psychiatry). (Am J Addict 2021;30:451-458).

Gas Chromatography-Mass Spectrometry Analysis of Synthetic Opioids Belonging to the Fentanyl Class: A Review

The rising number of deaths caused by fentanyl overdosing in the US due to the overwhelming illicit use of this synthetic opioid has started a global campaign to develop efficient ways to control its production and distribution as well as discovering efficient antidotes to mitigate its lethal effects. Another important vein of focused research established by various agencies lies in the development of efficient and practical protocols for the detection of this opioid and analogs thereof in various matrices, whether environmental or biological in nature, particularly in the field of gas chromatography-mass spectrometry (GC-MS). The following review will cover the literature dealing with the detection and identification of synthetic opioids belonging to the fentanyl class by GC-MS means and hyphenated versions of the technique. Detailed descriptions will be given for the GC-MS methods employed for the analysis of the opioid, starting with the nature of the extraction protocol employed prior to analysis to the actual findings presented by the cited reports. Great effort has gone into describing the methods involved in each paper in a detailed manner and these have been compiled by year in tables at the end of each section for the reader's convenience. Lastly, the review will end with concluding remarks about the state of GC-MS analysis with regards to these powerful opioids and what lies ahead for this analytical field.

Naltrexone for cholestatic itch: a systematic review

BACKGROUND

Cholestatic itch is caused by intrahepatic liver diseases, such as primary biliary cirrhosis and extrahepatic obstruction of the biliary tree, often caused by tumours. The pathophysiology of cholestatic itch is complex and no single treatment has proved definitive. Naltrexone is an opioid receptor antagonist, which reduces central opioidergic tone, believed to be raised in patients with cholestatic pruritus.

AIM

To review and assess the efficacy of oral naltrexone for the treatment of cholestatic itch.

METHODS

Search of electronic databases, grey literature, clinical trials registries and handsearching for studies including naltrexone for cholestatic itch. Full papers were obtained if relevant and studies graded.

RESULTS

Thirteen papers were included in the analysis, including three randomised controlled trials, one controlled clinical trial, one open-label pilot study, seven case reports and one retrospective notes review. All studies found naltrexone to be effective in relieving pruritus. In all five studies performing statistical analysis, naltrexone significantly reduced pruritus compared with baseline. 37% of patients reported side effects, notably opioid withdrawal-type reactions and recurrence of previous pain, from all pathologies.

CONCLUSIONS

Oral naltrexone therapy helps relieve cholestatic itch and although it should be used with caution in patients using exogenous opioids for analgesia, it should be considered when treating refractory pruritus in patients with end-stage liver disease.

Naltrexone-induced drug eruption

Treatment of alcohol dependence with oral naltrexone may elicit an urticarial rash and angioedema. Acute spontaneous urticaria and an allergic reaction to an excipient represent important differential diagnoses.

Blocking mu-opioid receptors inhibits social bonding in rituals

Religious rituals are universal human practices that play a seminal role in community bonding. In two experiments, we tested the role of mu-opioids as the active factor fostering social bonding. We used a mu-opioid blocker (naltrexone) in two double-blind studies of rituals from different religious traditions. We found the same effect across both studies, with naltrexone leading to significantly lower social bonding compared with placebo. These studies suggest that mu-opioids play a significant role in experiences of social bonding within ritual contexts.

Intranasal Low-Dose Naltrexone Against Opioid Side Effects: A Preclinical Study

Opioids are broad spectrum analgesics that are an integral part of the therapeutic armamentarium to combat pain in the clinical practice. Unfortunately, together with analgesia, a number of adverse effects can occur such as nausea, vomiting, constipation, gastrointestinal alterations and cognitive impairments. Naltrexone is a competitive antagonist of opioid receptors commonly used to treat opioid addiction; its oral use against agonists side effects is limited by the decrease of opioids-therapeutic efficacy and own adverse effects. The intranasal delivery of naltrexone could offer a quick and effective achievement of CNS based on extracellular mechanisms including perineural and perivascular transport. The aim of the study was to test the efficacy of intranasal low-dose naltrexone in reducing intraperitoneal morphine and oxycodone side effects in rodents. In mice, 1 μg naltrexone intranasally administered 30 min before opioids reduced cognitive impairments and motor alteration induced by 10 mg kg^-1 morphine and 60 mg kg^-1 oxycodone in the Passive avoidance and Rota rod tests, respectively. Moreover, naltrexone rebalanced opioid-induced reduction of the intestinal transit and latency of feces expulsion as well as food intake inhibition. Importantly, 1 μg naltrexone instillation did not block analgesia as demonstrated by the Hot plate test. In rats, intranasal naltrexone counteracted the opioid-induced pica phenomenon related to emesis and increased water and palatable food intake. The effects were comparable to that achieved by metoclopramide used as reference drug. Treatments did not influence body weight. Lastly, the safety of the intranasal delivery has been checked by hematoxylin-eosin staining that did not show histological alterations of the nasal cavity. In conclusion, intranasal low-dose naltrexone counteracted morphine and oxycodone induced gastrointestinal and CNS side effects without impairing opioid analgesia. It is a candidate to be a valid clinical strategy deserving deep analysis.

Retention rates in two naltrexone programmes for heroin addicts in Vitoria, Spain

The main finding of a former Spanish multicenter study (SMS) on the effectiveness of naltrexone maintenance in heroin addicts, was the high retention rate achieved at 24 weeks of follow-up since naltrexone induction (40%). The authors claimed this rate was one of the highest ever reported in the literature for a non-selected sample of opiate addicts and discussed the possible relevance of a set of variables — like motivations and expectations due to a new treatment — on the findings. To assess the possible effects of these variables, we have compared the retention rates in two similar naltrexone programmes. The first programme (hospital sample) included 56 individuals who were also included in the SMS where they accounted for 37% of the total sample. That programme was developed formerly to the naltrexone marketing. The second sample (ambulatory sample) included 67 individuals who were recruited at least a year apart since naltrexone marketing was approved by the Spanish Health Boards. The time-lag between the beginnig of both studies was in the range of 15 to 25 months.

The subjects in both programmes had similar distributions regarding age (p = 0.27), sex (p = 0.79), weeks on treatment after naltrexone induction (p = 0.20), and program compliance (p = 0.78). The retention rates evaluated over a period of 24 weeks were also similar (p = 0.45). The only difference appeared at 12 weeks of follow-up, showing in higher retention the hospital sample than the ambulatory sample (+23%; p < 0.05). The results are discussed according to other studies and it is concluded that findings reported in the former SMS and in this study are not unusual but compatible with recent research. Also underlined is the potential importance of naltrexone as a concomitant treatment for extinguishing high risk behaviours and the conditional stimuli associated with treatment relapse in heroin addicts.

Modulation of experimental facial pain via somatosensory stimuli targeting sensations of different valence

BACKGROUND

Knowledge of pain modulation from oro-facial somatosensory stimuli with different valence (pleasant-unpleasant) is limited.

OBJECTIVES

To investigate (a) the modulatory effects of painful, pleasant and unpleasant somatosensory stimuli on two models of experimental facial pain, (b) whether modulation could be changed by blocking peripheral nerves via application of a local anaesthetic, EMLA, or blocking endogenous opioid receptors via naltrexone and (c) whether pain ratings were significantly correlated with participant psychological profiles.

METHODS

Thirty-eight healthy women received experimental facial skin burning pain or jaw myalgia for four randomised sessions on different days. The painful region was stimulated with mechanical or thermal painful, pleasant, unpleasant and control stimuli, with ratings recorded before and during stimulation. Sessions differed in pre-treatment: EMLA/naltrexone/placebo tablet/cream.

RESULTS

Significant effects of thermal or mechanical stimuli (P < .017), but not session (P > .102), were found on pain ratings for both models. In myalgia, painful cold resulted in a greater reduction in pain ratings than unpleasant cold, pleasant cold, control and pleasant warmth (P < .004). Decreases in pain ratings from painful, unpleasant and pleasant mechanical stimuli were greater than control (P < .002). In burning pain, painful cold resulted in a greater reduction in pain ratings than all but one of the other thermal stimuli (P < .033). The pleasant mechanical stimulus reduced pain ratings more than all other mechanical stimuli (P ≤ .003). There were no significant correlations between pain and psychometrics.

CONCLUSION

Valence-targeted thermal and mechanical stimuli modulated experimental myalgia and skin burning pain (P < .017). Partially blocking peripheral afferents or opioid receptors did not affect modulation.

Opioids: A Review of Pharmacokinetics and Pharmacodynamics in Neonates, Infants, and Children

Pain management in the pediatric population is complex for many reasons. Mild pain is usually managed quite well with oral acetaminophen or ibuprofen. Situations involving more severe pain often require the use of an opioid, which may be administered by many different routes, depending on clinical necessity. Acute and chronic disease states, as well as the constantly changing maturational process, produce unique challenges at every level of pediatrics in dosing and management of all medications, especially with regard to high-risk opioids. Although there has been significant progress in the understanding of opioid pharmacokinetics and pharmacodynamics in neonates, infants, children, and adolescents, somewhat limited data exist from which necessary information, concerning the safe and effective use of these agents, may be drawn. The evidence here provided is intended to be helpful in directing the practitioner to patient-specific reasons for preferring one opioid over another. As our knowledge of opioids and their effects has grown, it has become clear that older medications like codeine and meperidine (pethidine) have very limited use in pediatrics. This review provides pharmacokinetic and pharmacodynamic evidence on the currently available opioids: morphine, fentanyl (and derivatives), codeine, meperidine, oxycodone, hydrocodone, hydromorphone, methadone, buprenorphine, butorphanol, nalbuphine, pentazocin, ketobemidone, tramadol, piritramide, naloxone and naltrexone. Morphine, being the most studied opioid analgesic, is the standard against which all others are compared. Pharmacokinetic parameters of morphine that have been found in neonates, i.e., higher volume of distribution, immature metabolic processes that develop at various rates, elimination that is variable based on age and weight, as well as treated and untreated disease processes, are an example of all opioids in the population discussed in this review. Outside the premature and neonatal population, the use of opioids in infants, children, and adolescents quickly begins to resemble the established values found in adults. As such, the concerns (risks) of these medications become comparable to those seen in adults.

Opioid Withdrawal Precipitated by Long-Acting Antagonists

BACKGROUND

Precipitated opioid withdrawal (POW) after opioid antagonist administration can be challenging to manage in the emergency department (ED), particularly if caused by a long-acting opioid antagonist such as naltrexone. There are no evidence-based guidelines to assist in safely and efficiently managing patients with this syndrome.

OBJECTIVE OF REVIEW

To review current practice on the treatment of long-acting antagonist POW and make recommendations on the treatment of this complex disease process.

METHODS

A literature search of opioid withdrawal cases precipitated by naltrexone was done using PubMed. One of the authors screened all the results of this search by title and abstract, leading to a final count of 27 articles that were reviewed in full by all authors. English language cases that involved precipitated opioid withdrawal from a long-acting opioid antagonist were included. Data were extracted, including the precipitant involved and dose, severity of opioid withdrawal, treatments rendered, and response to treatment. In all cases where symptoms and signs were described, a Clinical Opiate Withdrawal Scale score was calculated based on the information available.

RESULTS

Twenty-seven papers were included. Naltrexone alone was the primary antagonist reported in 19 of the papers, extended-release naltrexone in two, naltrexone-morphine combination in two, and nalmefene in four. Treatment most commonly included fluid replacement, benzodiazepines, antiemetics, and clonidine. Full opioid agonist treatment, although often suggested, was poorly described. Buprenorphine successfully reduced the severity and duration of withdrawal in several cases. No standardized response scale was used, and response to treatment ranged from 3 to 48 h prior to resolution of clinical effects.

CONCLUSIONS

Management of POW from long-acting antagonists is a complex problem with little formal evaluation of treatment options. There is not currently a sufficiently robust body of literature to support an evidence-based guideline. However, use of intravenous fluids, antiemetics, and benzodiazepines is commonly reported as successful and seems to be a reasonable approach until this process is better studied. A treatment strategy using partial agonists such as buprenorphine is emerging and may represent a safe and effective treatment pathway for these patients.

Exploring the new horizons of drug repurposing: A vital tool for turning hard work into smart work

Drug discovery and development are long and financially taxing processes. On an average it takes 12-15 years and costs 1.2 billion USD for successful drug discovery and approval for clinical use. Many lead molecules are not developed further and their potential is not tapped to the fullest due to lack of resources or time constraints. In order for a drug to be approved by FDA for clinical use, it must have excellent therapeutic potential in the desired area of target with minimal toxicities as supported by both pre-clinical and clinical studies. The targeted clinical evaluations fail to explore other potential therapeutic applications of the candidate drug. Drug repurposing or repositioning is a fast and relatively cheap alternative to the lengthy and expensive de novo drug discovery and development. Drug repositioning utilizes the already available clinical trials data for toxicity and adverse effects, at the same time explores the drug's therapeutic potential for a different disease. This review addresses recent developments and future scope of drug repositioning strategy.

Evidence for a dynorphin-mediated inner ear immune/inflammatory response and glutamate-induced neural excitotoxicity: an updated analysis

Acoustic overstimulation (AOS) is defined as the stressful overexposure to high-intensity sounds. AOS is a precipitating factor that leads to a glutamate (GLU)-induced Type I auditory neural excitotoxicity and an activation of an immune/inflammatory/oxidative stress response within the inner ear, often resulting in cochlear hearing loss. The dendrites of the Type I auditory neural neurons that innervate the inner hair cells (IHCs), and respond to the IHC release of the excitatory neurotransmitter GLU, are themselves directly innervated by the dynorphin (DYN)-bearing axon terminals of the descending brain stem lateral olivocochlear (LOC) system. DYNs are known to increase GLU availability, potentiate GLU excitotoxicity, and induce superoxide production. DYNs also increase the production of proinflammatory cytokines by modulating immune/inflammatory signal transduction pathways. Evidence is provided supporting the possibility that the GLU-mediated Type I auditory neural dendritic swelling, inflammation, excitotoxicity, and cochlear hearing loss that follow AOS may be part of a brain stem-activated, DYN-mediated cascade of inflammatory events subsequent to a LOC release of DYNs into the cochlea. In support of a DYN-mediated cascade of events are established investigations linking DYNs to the immune/inflammatory/excitotoxic response in other neural systems.

The Role of Dynorphin and the Kappa Opioid Receptor in the Symptomatology of Schizophrenia: A Review of the Evidence

Schizophrenia is a debilitating mental illness that affects approximately 1% of the world's population. Despite much research in its neurobiology to aid in developing new treatments, little progress has been made. One system that has not received adequate attention is the kappa opioid system and its potential role in the emergence of symptoms, as well as its therapeutic potential. Here we present an overview of the kappa system and review various lines of evidence derived from clinical studies for dynorphin and kappa opioid receptor involvement in the pathology of both the positive and negative symptoms of schizophrenia. This overview includes evidence for the psychotomimetic effects of kappa opioid receptor agonists in healthy volunteers and their reversal by the pan-opioid antagonists naloxone and naltrexone and evidence for a therapeutic benefit in schizophrenia for 4 pan-opioid antagonists. We describe the interactions between kappa opioid receptors and the dopaminergic pathways that are disrupted in schizophrenia and the histologic evidence suggesting abnormal kappa opioid receptor signaling in schizophrenia. We conclude by discussing future directions.

Characterization of the Pharmacokinetics of Samidorphan in Healthy Volunteers: Absolute Bioavailability and the Effect of Food and Age

BACKGROUND AND OBJECTIVES

Samidorphan (SAM) is a novel μ-opioid receptor antagonist. We report clinical pharmacokinetic (PK) properties of SAM following different routes of administration, and the effects of food and age on the PK of SAM following oral administration in healthy volunteers.

METHODS

An open-label, fixed-sequence study (study 1, N = 10) examined the PK parameters following intravenous, sublingual, and oral exposure to SAM to determine absolute bioavailability. A double-blind, placebo-controlled study (study 2, N = 45) compared the PK in participants aged 18-40 years (cohort 1, n = 30) and ≥ 65 years (cohort 2, n = 15) who received a single oral dose of SAM 10 mg under fed (cohort 1 only) or fasted conditions.

RESULTS

In study 1, intravenous SAM had a plasma clearance of 33.7 L/h, volume of distribution of 341 L, and elimination half-life of 7-8 h. SAM was well-absorbed following sublingual or oral administration and reached peak concentrations (C_max) within 2 h, with absolute bioavailability of 71% (sublingual) and 69% (oral). In study 2, concentration-time profiles were similar under fed and fasted conditions (cohort 1) and for young and elderly participants from both cohorts; 90% confidence intervals for the geometric least squares mean ratios for C_max and area under the concentration-time curve from time zero extrapolated to infinity indicated equivalence.

CONCLUSIONS

SAM has high bioavailability that is comparable following sublingual and oral administration and is not subject to extensive first-pass metabolism. The PK of orally administered SAM are not affected by food or age.

Naltrexone Treatment for Pregnant Women With Opioid Use Disorder Compared With Matched Buprenorphine Control Subjects

PURPOSE

The use of the opioid antagonist naltrexone (NTX) for pregnant women with opioid use disorder (OUD) remains understudied. The purpose of this pilot study was to examine pregnancy and neonatal outcomes in a cohort of NTX-treated women.

METHODS

This single-center, retrospective cohort study included 6 mother-infant dyads taking NTX compared with 13 taking buprenorphine (BUP) between 2017 and 2019. Maternal demographic characteristics, any unprescribed or illicit opioid use per urine toxicology or provider report during the pregnancy or 6 months' postdelivery, delivery outcomes, gestational age, birth weight, Apgar scores, neonatal intensive care unit admission, and neonatal abstinence syndrome (NAS) outcomes (NAS diagnosis, pharmacologic treatment, and total hospital length of stay) were compared.

FINDINGS

Maternal and infant demographic characteristics were similar between the 2 groups, with the exception of cigarette smoking in the BUP group being more common (92% vs 33%; P = 0.02). None of the women on NTX versus 23% of the women on BUP had documented opioid misuse (P = 0.52). No infants in the NTX group had a NAS diagnosis versus 92% in the BUP group (P < 0.001). Forty-six percent of the BUP-exposed infants were treated for NAS versus 0% in the NTX group (P < 0.001). NTX-exposed infants had a shorter length of stay (mean [SD], 3.2 [1.6] vs 10.9 [8.2] days; P = 0.008).

IMPLICATIONS

Maintaining women on NTX during pregnancy was associated with favorable outcomes. These results support the need for larger multicenter studies sufficiently powered to detect possible differences between the medications on long-term maternal and child safety and efficacy outcomes.

Severe Uncontrolled Pain in Buttock in a Patient on Naltrexone: A Diagnostic Challenge

A 26-year-old woman with a history of intravenous drug use was admitted to hospital with worsening pain in the right buttock radiating to the lateral part of the thigh and to the calf with no suspicion of cauda equina compression. Eventually, a diagnosis of sacroiliitis was made and appropriate antibiotics were administered. Provision of analgesia for this patient was difficult. On admission her medications included naltrexone, venlafaxine and tramadol. Initially naltrexone was continued and analgesia provided by epidural local anaesthetic and clonidine, intravenous ketamine and oral agents. After several days, naltrexone was ceased and opioids were used in addition to the other analgesics. The epidural analgesia was only partially effective, perhaps because of inadequate blockade of the L4-S1 nerve roots, which carry sensation from the sacroiliac joint.

Naltrexone is a long-acting opioid antagonist. If opioid analgesia is planned, it is necessary to cease naltrexone for 24 to 72 hours. In an emergency, if non-opioid techniques prove ineffective, short-acting opioids can be titrated to effect in a monitored environment.

New solvates of the drug naltrexone: protonation, conformation and interplay of synthons

Naltrexone [systematic name: (4R,4aS,7aR,12bS)-3-cyclopropylmethyl-4a,9-dihydroxy-2,4,5,6,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-one] is an important morphine-related drug used for combating alcoholism and opioid dependence. Of the eight crystal forms of naltrexone known thus far, only one exists in the neutral form and it crystallizes as a monohydrate. We have isolated the naltrexone free base as two new solvate forms, i.e. the ethyl acetate 0.33-solvate, C₂₀H₂₃NO₄·0.33C₄H₈O₂, (I), and the diethyl ether hemisolvate, C₂₀H₂₃NO₄·0.5C₄H₁₀O, (II). While just one solvent molecule is present in the asymmetric unit of each solvate, there are three drug molecules (Z' = 3) in ethyl acetate solvate (I) and two (Z' = 2) in diethyl ether solvate (II). In (I), one of the three crystallographically independent drug molecules is present with its cyclopropyl group disordered over two sets of positions, as is the whole diethyl ether solvent molecule in (II). In all known forms, including the title forms, the naltrexone molecule exhibits the same conformation of the fused rings. The only conformational variability of naltrexone is in the cyclopropylmethyl group. Two conformations can be found around the bond connecting this group to the N-heterocycle, which is directly related to drug protonation. We have calculated, at the B3LYP/6-31G** level of theory, the minimum energy conformations of protonated and neutral naltrexone molecules for a chosen torsion angle about this bond. The lowest energy conformers depend on the protonation state and are in agreement with those found in the solid state. Within the cyclopropylmethyl group, the bond joining the methylene C atom to the cyclopropyl fragment also evidences conformational variability. In the literature, there are two well defined conformations around this bond. A third cyclopropyl conformation around this second bond is observed in the title solvates. Concerning the supramolecular features of the previously reported crystal structures, only one classical hydrogen bond between naltrexone molecules and one C(8) homosynthon is known, pointing to the robustness of this synthon and the difficulty in disrupting it. New R₂²(7) and C₂²(10) homosynthons are found in both (I) and (II), suggesting that their occurrence derives from crystallization of the neutral drug from nonpolar solvents.

Effect of combined opioid receptor and α2-adrenoceptor blockade on anxiety and electrically evoked startle responses

The R3 component of the electrically evoked blink reflex may form part of a startle reaction. Acoustic startle responses are augmented by yohimbine, an α₂-adrenoceptor antagonist that blocks α₂-autoreceptors, and are potentiated by opioid receptor blockade. To investigate these influences on electrically evoked startle responses, 16 mg yohimbine, with (16 participants) or without 50 mg naltrexone (23 participants), was administered in separate double-blind placebo-controlled cross-over experiments. In each experiment, R3 (a probable component of the startle response) was examined before and after high-frequency electrical stimulation of the forearm, a procedure that initiates inhibitory pain controls. Anxiety and somatic symptoms were greater after yohimbine than placebo, and were potentiated by naltrexone. Pain ratings for the electrically evoked startle stimuli decreased after high-frequency electrical stimulation in the placebo session but remained stable after drug administration. Yohimbine with naltrexone, but not yohimbine alone, also blocked an inhibitory effect of high-frequency electrical stimulation on electrically evoked sharp sensations and R3. Together, the findings suggest that adding naltrexone to yohimbine potentiated anxiety and blocked inhibitory influences of high-frequency electrical stimulation on electrically evoked sensations and startle responses. Thus, opioid peptides could reduce activity in nociceptive and startle-reflex pathways, or inhibit crosstalk between these pathways. Failure of this inhibitory opioid influence might be important in chronically painful conditions that are aggravated by startle stimuli.

Evaluation of the counter-regulatory responses to hypoglycaemia in patients with type 1 diabetes during opiate receptor blockade with naltrexone

AIMS

Hypoglycaemia is the major limiting factor in achieving optimal glycaemic control in people with type 1 diabetes (T1DM), especially intensively treated patients with impaired glucose counter-regulation during hypoglycaemia. Naloxone, an opiate receptor blocker, has been reported to enhance the acute counter-regulatory response to hypoglycaemia when administered intravenously in humans. The current study was undertaken to investigate the oral formulation of the long-acting opiate antagonist, naltrexone, and determine if it could have a similar effect, and thus might be useful therapeutically in treatment of T1DM patients with a high risk of hypoglycaemia.

MATERIALS AND METHODS

We performed a randomized, placebo-controlled, double-blinded, cross-over study in which 9 intensively treated subjects with T1DM underwent a 2-step euglycaemic-hypoglycaemic-hyperinsulinaemic clamp on 2 separate occasions. At 12 hours and at 1 hour before the clamp study, participants received 100 mg of naltrexone or placebo orally. Counter-regulatory hormonal responses were assessed at baseline and during each step of the hyperinsulinaemic-clamp.

RESULTS

Glucose and insulin levels did not differ significantly between the naltrexone and placebo visits; nor did the glucose infusion rates required to keep glucose levels at target. During hypoglycaemia, naltrexone, in comparison with the placebo group, induced an increase in epinephrine levels ( P  = .05). However, no statistically significant differences in glucagon, cortisol and growth hormone responses were observed.

CONCLUSION

In contrast to the intravenous opiate receptor blocker naloxone, overnight administration of the oral long-acting opiate receptor blocker, naltrexone, at a clinically used dose, had a limited effect on the counter-regulatory response to hypoglycaemia in intensively treated subjects with T1DM.

Opioid-receptor antagonism increases pain and decreases pleasure in obese and non-obese individuals

RATIONALE

Endogenous opioids inhibit nociceptive processing and promote the experience of pleasure. It has been proposed that pain and pleasure lie at opposite ends of an affective spectrum, but the relationship between pain and pleasure and the role of opioids in mediating this relationship has not been tested.

OBJECTIVES

Here, we used obese individuals as a model of a dysfunctional opioid system to assess the role of the endogenous opioid peptide, beta-endorphin, on pain and pleasure sensitivity.

METHODS

Obese (10M/10F) and age- and gender-matched non-obese (10M/10F) controls were included in the study. Pain sensitivity using threshold, tolerance, and subjective rating assessments and perceived sweet pleasantness using sucrose solutions were assessed in two testing sessions with placebo or the opioid antagonist, naltrexone (0.7 mg/kg body weight). Beta-endorphin levels were assessed in both sessions.

RESULTS AND CONCLUSIONS

Despite having higher levels of baseline beta-endorphin and altered beta-endorphin-reactivity to naltrexone, obese individuals reported a similar increase in pain and decrease in pleasantness following naltrexone compared to non-obese individuals. Beta-endorphin levels did not correlate with pain or pleasantness in either group, but naltrexone-induced changes in pain and pleasantness were mildly correlated. Moreover, naltrexone-induced changes in pain were related to depression scores, while naltrexone-induced changes in sweet pleasantness were related to anxiety scores, indicating that pain and pleasantness are related, but influenced by different processes.

Research Note — Review of Corrections-Based Therapy for Opiate-Dependent Patients: Implications for Buprenorphine Treatment among Correctional Populations

Inmates with a history of opiate dependence represent a substantial proportion of the correctional population in the United States. Opiate use has negative consequences for both the inmate and society, including increased recidivism rates, increased infectious disease prevalence, avoidable emergency room use, decreased access to primary care services, and overdose. While there have been great successes in community-based treatment of opiate dependence, these successes have not yet been achieved in correctional settings. This paper reviews the pharmacological treatment options for opiate-dependent inmates, along with potential application for community-to-correctional approaches. The recent approval by the Food and Drug Administration (FDA) of physician-prescribed buprenorphine and the new opportunities it presents to corrections-based treatment are also explored in depth. Successful implementation of such strategies is likely to result in desirable health and social outcomes for both the inmate and the community at large.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

Pharmacokinetic and pharmacodynamic evaluation of oxycodone and naltrexone for the treatment of chronic lower back pain

INTRODUCTION

Chronic low back pain (CLBP) is a common and difficult illness to manage. Some individuals with CLBP have pain processing disorders and are also at risk for opioid abuse, misuse; addiction and diversion. Guidelines have been published to guide management; neuromodulation, exercise, mindfulness-based stress reduction and cognitive behavior therapies among other non-pharmacological reduce the pain of CLBP with minimal toxicity. Pharmacological management includes acetaminophen, NSAIDs and antidepressants, mainly duloxetine. Abuse-deterrent opioids have been developed which have been shown to reduce pain and opioid abuse risk. ALO-02 is a tamper-resistant sustained release opioid consisting of extended release oxycodone and sequestered naltrexone. Pivotal studies of ALO-02 have centered on patients with CLBP.

AREAS COVERED

This manuscript will review CLBP, the pivotal analgesic and clinical abuse potential studies of ALO-02. The opinion will cover whether opioids should be used for CLBP, when they should be used and opioid choices.

EXPERT OPINION

ALO-02 is one of several opioids which can be considered in the management of CLBP. The outcome to a trial of opioids should be function rather than analgesia. Most analgesic trials for CLBP have had analgesia as the primary outcome and function has not been vigorously studied as an outcome. Opioids should be considered as a trial only when other non-opioid analgesics have failed to improve analgesia and function. Universal precautions should be routinely part of phase III analgesic trial particularly for chronic non-malignant pain.

Evaluation of N-substituent structural variations in opioid receptor profile of LP1

The benzomorphan scaffold has great potential as lead structure and the nature of the N-substituent is able to influence affinity, potency, and efficacy at all three opioid receptors. Building upon these considerations, we synthesized a new series of LP1 analogues by introducing naphthyl or heteroaromatic rings in propanamide side chain of its N-substituent (9-15). In vitro competition-binding assays in HEK293 cells stably expressing MOR, DOR or KOR showed that in compound 9 the 1-naphthyl ring led to the retention of MOR affinity (Ki(MOR)=38±4nM) displaying good selectivity versus DOR and KOR. In the electrically stimulated GPI, compound 9 was inactive as agonist but produced an antagonist potency value (pA2) of 8.6 in presence of MOR agonist DAMGO. Moreover, subcutaneously administered it antagonized the antinociceptive effects of morphine with an AD50=2.0mg/kg in mouse-tail flick test. Modeling studies on MOR revealed that compound 9 fit very well in the binding pocket but in a different way in respect to the agonist LP1. Probably the replacement of its N-substituent on the III, IV and V TM domains reflects an antagonist behavior. Therefore, compound 9 could represent a potential lead to further develop antagonists as valid therapeutic agents and useful pharmacological tools to study opioid receptor function.

Lipophilic nalmefene prodrugs to achieve a one-month sustained release

Nalmefene is an opioid antagonist which as a once-a-day tablet formulation has recently been approved for reducing ethanol intake in alcoholic subjects. In order to address the compliance issue in this patient population, a number of potential nalmefene prodrugs were synthesized with the aim of providing a formulation that could provide plasma drug concentrations in the region of 0.5-1.0ng/mL for a one-month period when dosed intramuscular to dogs or minipigs. In an initial series of studies, three different lipophilic nalmefene derivatives were evaluated: the palmitate (C16), the octadecyl glutarate diester (C18-C5) and the decyl carbamate (CB10). They were administered intramuscularly to dogs in a sesame oil solution at a dose of 1mg-eq. nalmefene/kg. The decyl carbamate was released relatively quickly from the oil depot and its carbamate bond was too stable to be used as a prodrug. The other two derivatives delivered a fairly constant level of 0.2-0.3ng nalmefene/mL plasma for one month and since there was no significant difference between these two, the less complex palmitate monoester was chosen to demonstrate that dog plasma nalmefene concentrations were dose-dependent at 1, 5 and 20mg-eq. nalmefene/kg. In a second set of experiments, the effect of the chain length of the fatty acid monoester promoieties was examined. The increasingly lipophilic octanoate (C8), decanoate (C10) and dodecanoate (C12) derivatives were evaluated in dogs and in minipigs, at a dose of 5mg-eq. nalmefene/kg and plasma nalmefene concentrations were measured over a four-week period. The pharmacokinetic profiles were very similar in both species with Cmax decreasing and Tmax increasing with increasing fatty acid chain length and the target plasma concentrations (0.5-1.0ng/mL over a month-long period) were achieved with the dodecanoate (C12) prodrug. These data therefore demonstrate that sustained plasma nalmefene concentrations can be achieved in both dog and minipig using nalmefene prodrugs and that the pharmacokinetic profile of nalmefene can be tuned by varying the length of the alkyl group.

Opioid antagonists in broadly defined behavioral addictions: a narrative review

INTRODUCTION

Naltrexone (NTX), a mu-opioid receptor antagonist, has been approved for the treatment of alcoholism and opioid dependence. More recently, however, NTX and a related drug, nalmefene (NMF), have also shown positive results for the treatment of gambling disorders.

AREAS COVERED

In this study, we reviewed the trials testing the effect of opioid antagonists (OA) in gambling disorders and in other broadly defined behavioral addictions, including selected DSM-5 disruptive, impulse-control, and conduct disorders, obsessive-compulsive and related disorders, eating disorders, and other conditions not currently recognized by official classification schemes. We found six randomized controlled trials (RCTs) of OA in gambling disorder, two RCTs of OA in trichotillomania (hair pulling disorder), two RCTs of OA in binge eating disorder, and one RCT of OA for kleptomania. We also reviewed case reports on hypersexual disorder, compulsive buying and skin picking disorders.

EXPERT OPINION

The reviewed data supported the use of OA, namely NTX and NMF, in gambling disorder (both) and kleptomania (NTX). We did not find enough evidence to support the use of NTX or NMF in trichotillomania (hair pulling disorder), excoriation (skin-picking) disorder, compulsive buying disorder, hypersexual disorder, or binge eating disorder.

Endogenous opioid antagonism in physiological experimental pain models: a systematic review

Opioid antagonists are pharmacological tools applied as an indirect measure to detect activation of the endogenous opioid system (EOS) in experimental pain models. The objective of this systematic review was to examine the effect of mu-opioid-receptor (MOR) antagonists in placebo-controlled, double-blind studies using ʻinhibitoryʼ or ʻsensitizingʼ, physiological test paradigms in healthy human subjects. The databases PubMed and Embase were searched according to predefined criteria. Out of a total of 2,142 records, 63 studies (1,477 subjects [male/female ratio = 1.5]) were considered relevant. Twenty-five studies utilized ʻinhibitoryʼ test paradigms (ITP) and 38 studies utilized ʻsensitizingʼ test paradigms (STP). The ITP-studies were characterized as conditioning modulation models (22 studies) and repetitive transcranial magnetic stimulation models (rTMS; 3 studies), and, the STP-studies as secondary hyperalgesia models (6 studies), ʻpainʼ models (25 studies), summation models (2 studies), nociceptive reflex models (3 studies) and miscellaneous models (2 studies). A consistent reversal of analgesia by a MOR-antagonist was demonstrated in 10 of the 25 ITP-studies, including stress-induced analgesia and rTMS. In the remaining 14 conditioning modulation studies either absence of effects or ambiguous effects by MOR-antagonists, were observed. In the STP-studies, no effect of the opioid-blockade could be demonstrated in 5 out of 6 secondary hyperalgesia studies. The direction of MOR-antagonist dependent effects upon pain ratings, threshold assessments and somatosensory evoked potentials (SSEP), did not appear consistent in 28 out of 32 ʻpainʼ model studies. In conclusion, only in 2 experimental human pain models, i.e., stress-induced analgesia and rTMS, administration of MOR-antagonist demonstrated a consistent effect, presumably mediated by an EOS-dependent mechanisms of analgesia and hyperalgesia.

Subchronic administration of short-acting naltrexone has no effect on striatal dopamine transporter availability, food intake or body weight gain in rats

The opioid receptor antagonist naltrexone is successfully used in the treatment of opioid and alcohol dependence. However, questions have been raised about possible anhedonic side effects, because the opioid system is directly involved in hedonic responses to natural rewarding activities, possibly due to its indirect effects on the striatal dopamine transporter (DAT). In order to test this hypothesis, 30 rats were randomized to either a 10-day treatment with 3 mg/kg short-acting naltrexone or vehicle. No significant differences between the groups were found in striatal DAT availability, cumulative food intake (for 48 or 72 h), body weight gain and abdominal fatpad weight. Thus, the results of this study suggest that (sub)chronic treatment with short-acting naltrexone does not induce possible anhedonic effects. However, it cannot be ruled out the anhedonic effect of naltrexone is only short-lived and thus not detected in the current study. Therefore, future studies are needed to study possible acute anhedonic effects at several time points shortly after short-acting naltrexone administration and to directly compare the possible anhedonic effects of long-acting with those of short-acting opioid antagonists.

Pharmacological means of reducing human drug dependence: a selective and narrative review of the clinical literature

Substance abuse or addictive disorder is a global problem. A greater understanding of the associated changes in brain pathophysiology supports the notion that pharmacological treatments are part of the necessary treatment options. Craving is a core symptom of addictive disorder. It refers to a strong desire to use drugs again either to re-experience positive effects or to diminish negative experiences. Currently there are a number of medicines that are effective in the treatment of addictive disorders. These medications can either be for substitution (same pharmacological effect as the abused substance) or anticraving (decrease the craving of the abused substance). In this MEDLNE based review, specific compounds (naltrexone, acamprosate, topiramate, disulfiram, baclofen, N-acetylcysteine and bupropion) were selected that are known to diminish desire to use (anticraving effect) and that have been trialled for a number of different substance addictive disorders. Their therapeutic potential in clinical practice is discussed in light of their efficacy.

Effects of naltrexone on adolescent alcohol cue reactivity and sensitivity: an initial randomized trial

Adolescent alcohol use is associated with myriad adverse consequences and contributes to the leading causes of mortality among youth. Despite the magnitude of this public health problem, evidenced-based treatment initiatives for alcohol use disorders in youth remain inadequate. Identifying promising pharmacological approaches may improve treatment options. Naltrexone is an opiate receptor antagonist that is efficacious for reducing drinking in adults by attenuating craving and the rewarding effects of alcohol. Implications of these findings for adolescents are unclear; however, given that randomized trials of naltrexone with youth are non-existent. We conducted a randomized, double-blinded, placebo-controlled cross-over study, comparing naltrexone (50 mg/daily) and placebo in 22 adolescent problem drinkers aged 15-19 years (M = 18.36, standard deviation = 0.95; 12 women). The primary outcome measures were alcohol use, subjective responses to alcohol consumption, and alcohol-cue-elicited craving assessed in the natural environment using ecological momentary assessment methods, and craving and physiological reactivity assessed using standard alcohol cue reactivity procedures. Results showed that naltrexone reduced the likelihood of drinking and heavy drinking (P's ≤ 0.03), blunted craving in the laboratory and in the natural environment (P's ≤ 0.04), and altered subjective responses to alcohol consumption (P's ≤ 0.01). Naltrexone was generally well tolerated by participants. This study provides the first experimentally controlled evidence that naltrexone reduces drinking and craving, and alters subjective responses to alcohol in a sample of adolescent problem drinkers, and suggests larger clinical trials with long-term follow-ups are warranted.

Behavioral and cellular pharmacology characterization of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(isoquinoline-3'-carboxamido)morphinan (NAQ) as a mu opioid receptor selective ligand

Mu opioid receptor (MOR) selective antagonists and partial agonists have been used for the treatment of opioid abuse and addiction. Our recent efforts on the identification of MOR antagonists have provided several novel leads displaying interesting pharmacological profiles. Among them, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-[(3'-isoquinolyl)acetamido]morphinan (NAQ) showed sub-nanomolar binding affinity to the MOR with significant selectivity over the delta opioid receptor (DOR) and the kappa opioid receptor (KOR). Its central nervous system penetration capacity together with marginal agonism in the MOR-GTPγS binding assay made it a very interesting molecule for developing novel opioid abuse and addiction therapeutic agents. Therefore, further pharmacological characterization was conducted to fully understand its biological profile. At the molecular and cellular level, NAQ not only induced no translocation of β-arrestin2 to the MOR, but also efficaciously antagonized the effect of DAMGO in MOR-βarr2eGFP-U2OS cells in the β-arrestin2 recruitment assay. At the in vivo level, NAQ displayed a potent inhibition of the analgesic effect of morphine in the tail-flick assay (ID50=1.19 mg/kg). NAQ (10 mg/kg) also significantly decreased the hyper-locomotion induced by acute morphine without inducing any vertical jumps. Meanwhile NAQ precipitated lesser withdrawal symptoms in morphine dependent mice than naloxone. In conclusion, NAQ may represent a new chemical entity for opioid abuse and addiction treatment.

Sulfation of opioid drugs by human cytosolic sulfotransferases: metabolic labeling study and enzymatic analysis

The current study was designed to examine the sulfation of eight opioid drugs, morphine, hydromorphone, oxymorphone, butorphanol, nalbuphine, levorphanol, nalorphine, and naltrexone, in HepG2 human hepatoma cells and human organ samples (lung, liver, kidney, and small intestine) and to identify the human SULT(s) responsible for their sulfation. Analysis of the spent media of HepG2 cells, metabolically labeled with [35S]sulfate in the presence of each of the eight opioid drugs, showed the generation and release of corresponding [35S]sulfated derivatives. Five of the eight opioid drugs, hydromorphone, oxymorphone, butorphanol, nalorphine, and naltrexone, appeared to be more strongly sulfated in HepG2 cells than were the other three, morphine, nalbuphine, and levorphanol. Differential sulfating activities toward the opioid drugs were detected in cytosol or S9 fractions of human lung, liver, small intestine, and kidney, with the highest activities being found for the liver sample. A systematic analysis using eleven known human SULTs and kinetic experiment revealed SULT1A1 as the major responsible SULTs for the sulfation of oxymorphone, nalbuphine, nalorphine, and naltrexone, SULT1A3 for the sulfation of morphine and hydromorphone, and SULT2A1 for the sulfation of butorphanol and levorphanol. Collectively, the results obtained imply that sulfation may play a significant role in the metabolism of the tested opioid drugs in vivo.

Ex vivo studies for the passive transdermal delivery of low-dose naltrexone from a cream; detection of naltrexone and its active metabolite, 6β-naltrexol, using a novel LC Q-ToF MS assay

Naltrexone (NTX) is a long-acting opiate antagonist. Low-dose naltrexone (LDN) therapy has shown promising results in the treatment of several autoimmune disorders. Our aim was to formulate NTX into a cream for the delivery of LDN and develop an analytical technique for the quantification of NTX and its active metabolite 6-β-naltrexol (NTXol) during transdermal diffusion cell permeation studies. A 1% w/w NTX cream was formulated and drug permeation was examined over 24 h using static Franz diffusion cells mounted with pig skin. A Liquid Chromatography Quadrupole-Time of Flight Mass Spectrometry (LC-MS Q-ToF) method was developed for the detection of NTX and NTXol in the receptor solution, skin membrane and residual cream on the donor chamber after completion of the diffusion studies. The cream formulation exhibited steady state release of NTX over 24 h after an initial lag time of 2.74 h. The bioconversion of NTX to NTXol in the skin membrane was 1.1%. It was concluded that the cream may be an effective formulation for the sustained transdermal delivery of LDN. The novel LC Q-ToF MS method allowed the accurate measurement of NTX and NTXol levels across the diffusion cell assemblies and the quantification of NTX metabolism in the skin.

Extended release naltrexone injection is performed in the majority of opioid dependent patients receiving outpatient induction: a very low dose naltrexone and buprenorphine open label trial

BACKGROUND

The approval of extended release injectable naltrexone (XR-NTX; Vivitrol(®)) has introduced a new option for treating opioid addiction, but studies are needed to identify its place within the spectrum of available therapies. The absence of physiological opioid dependence is a necessary and challenging first step for starting XR-NTX. Outpatient detoxification gives poor results and inpatient detoxification is either unavailable or too brief for the physiological effects of opioids to resolve. Here we present findings from an open label study that tested whether the transition from opioid addiction to XR-NTX can be safely and effectively performed in an outpatient setting using very low dose naltrexone and buprenorphine.

METHODS

Twenty treatment seeking opioid addicted individuals were given increasing doses of naltrexone starting at 0.25mg with decreasing doses of buprenorphine starting at 4 mg during a 7-day outpatient XR-NTX induction procedure. Withdrawal discomfort, craving, drug use, and adverse events were assessed daily until the XR-NTX injection, then weekly over the next month.

RESULTS

Fourteen of the 20 participants received XR-NTX and 13 completed weekly assessments. Withdrawal, craving, and opioid or other drug use were significantly lower during induction and after XR-NTX administration compared with baseline, and no serious adverse events were recorded.

CONCLUSIONS

Outpatient transition to XR-NTX combining upward titration of very low dose naltrexone with downward titration of low dose buprenorphine was safe, well tolerated, and completed by most participants. Further studies with larger numbers of subjects are needed to see if this approach is useful for naltrexone induction.