Sustained-release naltrexone: novel treatment for opioid dependence

Comparing outcomes of extended-release naltrexone in adolescents and young adults with opioid use disorder

INTRODUCTION

Opioid use among youth is a public health concern in the United States, with >3300 overdose deaths occurring nationally each year. Unfortunately, youth in the United States are still prescribed medication for opioid use disorder (OUD) at a lower rate than their adult counterparts.

METHODS

From 10/2013 to 01/2018, adolescents (ages 15-17; n = 25) and young adults (ages 18-21; n = 263) with moderate to severe OUD enrolled in the parent trial of extended-release naltrexone (XR-NTX; n = 82) versus treatment-as-usual (TAU; either buprenorphine maintenance [n = 94] or counseling without buprenorphine maintenance [n = 112]). The study assessed opioid use outcomes for adolescents vs. young adults using timeline follow-back self-report procedures at baseline and 3-/6-month follow-up assessments. Mixed-effects longitudinal and clustered panel regression models compared treatment effects over time of XR-NTX and TAU on opioid use outcomes in this secondary analysis.

RESULTS

Though adolescent participants reported significantly less opioid use at baseline relative to their young adult counterparts (p < 0.05), the two age groups reported similar rates of opioid use throughout the intervention period. Additionally, both adolescents and young adults receiving XR-NTX evidenced lower rates of opioid use than those receiving TAU at all time points, and adolescents on XR-NTX were the only group who reduced their opioid use at all time points. Mixed-effects models indicated adolescents receiving XR-NTX demonstrated a 48 % lower rate of opioid use days [Incidence Rate Ratio (IRR) = 0.52; p = 0.020], while young adults receiving XR-NTX reported an estimated 26 % lower rate (IRR = 0.74; p = 0.009).

CONCLUSIONS

Results indicate that adolescents respond favorably to XR-NTX relative to TAU for treatment of OUD, demonstrating similar outcomes to young adults.

Insights into the mechanisms underlying opioid use disorder and potential treatment strategies

Opioid use disorder is a worldwide societal problem and public health burden. Strategies for treating opioid use disorder can be divided into those that target the opioid receptor system and those that target non-opioid receptor systems, including the dopamine and glutamate receptor systems. Currently, the clinical drugs used to treat opioid use disorder include the opioid receptor agonists methadone and buprenorphine, which are limited by their abuse liability, and the opioid receptor antagonist naltrexone, which is limited by poor compliance. Therefore, the development of effective medications with lower abuse liability and better potential for compliance is urgently needed. Based on recent advances in the understanding of the neurobiological mechanisms underlying opioid use disorder, potential treatment strategies and targets have emerged. This review focuses on the progress made in identifying potential targets and developing medications to treat opioid use disorder, including progress made by our laboratory, and provides insights for future medication development. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Sustained drug delivery strategies for treatment of common substance use disorders: Promises and challenges

Substance use disorders (SUDs) are a leading cause of death and other ill health effects in the United States and other countries in the world. Several approaches ranging from detoxification, behavioral therapy, and the use of antagonists or drugs with counter effects are currently being applied for its management. Amongst these, drug therapy is the mainstay for some drug abuse incidences, as is in place specifically for opioid abuse or alcohol dependence. The severity of the havocs observed with the SUDs has triggered constant interest in the discovery and development of novel medications as well as suitable or most appropriate methods for the delivery of these agents. The chronic need of such drugs in users warrants the need for their prolonged or sustained systemic availability. Further, the need to improve patient tolerance to medication, limit invasive drug use and overall treatment outcome are pertinent considerations for embracing sustained release designs for medications used in managing SUDs. This review aims to provide an overview on up-to-date advances made with regards to sustained delivery systems for the drugs for treatment of different types of SUDs such as opioid, alcohol, tobacco, cocaine, and cannabis use disorders. The clinical relevance, promises and the limitations of deployed sustained release approaches along with future opportunities are discussed.

Nanoparticle delivery systems for substance use disorder

Innovative breakthroughs in nanotechnology are having a substantial impact in healthcare, especially for brain diseases where effective therapeutic delivery systems are desperately needed. Nanoparticle delivery systems offer an unmatched ability of not only conveying a diverse array of diagnostic and therapeutic agents across complex biological barriers, but also possess the ability to transport payloads to targeted cell types over a sustained period. In substance use disorder (SUD), many therapeutic targets have been identified in preclinical studies, yet few of these findings have been translated to effective clinical treatments. The lack of success is, in part, due to the significant challenge of delivering novel therapies to the brain and specific brain cells. In this review, we evaluate the potential approaches and limitations of nanotherapeutic brain delivery systems. We also highlight the examples of promising strategies and future directions of nanocarrier-based treatments for SUD.

Naltrexone Implant for Opioid Use Disorder

The continued rise in the availability of illicit opioids and opioid-related deaths in the United States has left physicians, researchers, and lawmakers desperate for solutions to this ongoing epidemic. The research into therapeutic options for the treatment of opioid use disorder (OUD) began with the introduction of methadone in the 1960s. The approval of oral naltrexone initially showed much promise, as the drug was observed to be highly potent in antagonizing the effects of opioids while producing no opioid agonist effects of its own and having a favorable side effect profile. Patients that routinely take their naltrexone reported fewer days of heroin use and had more negative drug tests than those without treatment. Poor outcomes in OUD patients treated with naltrexone have been directly tied to short treatment time. Studies have shown that naltrexone given orally vs. as an implant at the 6-month interval showed a higher non-compliance rate among those who used oral medications at the 6-month mark and a slower return to use rate. There were concerns that naltrexone could possibly worsen negative symptoms seen in opiate use disorder related to blockade of endogenous opioids that are important for pleasurable stimuli. Studies have shown that naltrexone demonstrated no increase in levels of anxiety, depression and anhedonia in participants and another study found that those treated with naltrexone had a significant reduction in mental health-related hospitalizations. The latter study also concluded that there was no increased risk for mental health-related incidents in patients taking naltrexone via a long-acting implant. Although not yet FDA approved in the United States, naltrexone implant has shown promising results in Europe and Australia and may provide a novel treatment option for opioid addiction.

Comparison of lipid liquid crystal formulation and Vivitrol® for sustained release of Naltrexone: In vitro evaluation and pharmacokinetics in rats

Camurus' FluidCrystal® injection depot is a lipid liquid crystal (LLC) phase formation-based method, comprising of glycerol dioleate (GDO) and soy phosphatidylcholine (SPC), together with minute quantities of N-methyl-2-pyrrolidone solvent (NMP). The present study aimed to develop a method for LLC using sorbitan monooleate (LLC-SMO) instead of GDO to prepare a one-month sustained-release formulation of naltrexone (NTX) that is applied for the treatment of autism and treating alcohol dependence. The optical characteristics of the LLC were assessed by polarizing light microscopy (PLM) to reveal the presence of lamellar, hexagonal, and cubic mesophases. Furthermore, in vitro release of NTX and NMP, degradation, pharmacokinetics, and histopathology of LLC-GDO and LLC-SMO in rats were evaluated and compared to those of Vivitrol®. The PLM images revealed that the structure of LLC-SMO is hexagonal, similar to LLC-GDO. The in vitro release of NTX and its pharmacokinetic results in rats indicted that the LLC-SMO system is more uniform than LLC-GDO and Vivitrol® during 35 days. Histopathological results of LLC-GDO and LLC-SMO confirmed the biocompatibility of our LLC delivery systems. Taken together these data demonstrate that the LLC-SMO-based method, was efficient enough to sustain the release of NTX in vitro and in vivo, confirming the biocompatible nature of this delivery system.

Medications Development for Treatment of Opioid Use Disorder

This review describes methods for preclinical evaluation of candidate medications to treat opioid use disorder (OUD). The review is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effectiveness, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and effects of candidate medications. Effects of opioid medications and vaccines on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications (e.g., G-protein-biased μ-opioid agonists), and (2) continued development of nonopioid medications (e.g., clonidine) that might serve as adjunctive agents to current opioid medications.

Clinically established biodegradable long acting injectables: An industry perspective

Long acting injectable formulations have been developed to sustain the action of drugs in the body over desired periods of time. These delivery platforms have been utilized for both systemic and local drug delivery applications. This review gives an overview of long acting injectable systems that are currently in clinical use. These products are categorized in three different groups: biodegradable polymeric systems, including microparticles and implants; micro and nanocrystal suspensions and oil-based formulations. Furthermore, the applications of these drug delivery platforms for the management of various chronic diseases are summarized. Finally, this review addresses industrial challenges regarding the development of long acting injectable formulations.

Bivalent Ligand Aiming Putative Mu Opioid Receptor and Chemokine Receptor CXCR4 Dimers in Opioid Enhanced HIV-1 Entry

A bivalent compound 1a featuring both a mu opioid receptor (MOR) and a CXCR4 antagonist pharmacophore (naltrexone and IT1t) was designed and synthesized. Further binding and functional studies demonstrated 1a acting as a MOR and a CXCR4 dual antagonist with reasonable binding affinities at both receptors. Furthermore, compound 1a seemed more effective than a combination of IT1t and naltrexone in inhibiting HIV entry at the presence of morphine. Additional molecular modeling results suggested that 1a may bind with the putative MOR-CXCR4 heterodimer to induce its anti-HIV activity. Collectively, bivalent ligand 1a may serve as a promising lead to develop chemical probes targeting the putative MOR-CXCR4 heterodimer in comprehending opioid exacerbated HIV-1 invasion.

Extended-release naltrexone versus standard oral naltrexone versus placebo for opioid use disorder: the NEAT three-arm RCT

BACKGROUND

People recovering from heroin addiction need better treatments than are currently offered. The chronic relapsing nature of drug dependence means that helping a patient to achieve abstinence is often difficult. Naltrexone blocks the effects of ingested heroin; however, evidence is conflicting regarding the best delivery method.

OBJECTIVES

The primary purpose of the trial was to evaluate the clinical effectiveness and cost-effectiveness of extended-release naltrexone versus standard oral naltrexone versus relapse prevention therapy without medication for opioid use disorder (OUD).

DESIGN

This was a 3-year, definitive, three-centre, three-arm, parallel group, placebo-controlled, double-blind, double-dummy, randomised controlled trial.

SETTING

Two specialist NHS outpatient addiction clinics: one in London and one in Birmingham.

PARTICIPANTS

Planned study sample - 300 adult patients with OUD who had completed detoxification.

INTERVENTIONS

One iGen/Atral-Cipan Extended Release Naltrexone device (iGen/Atral-Cipan, Castanheira do Ribatejo, Portugal) (765 mg naltrexone or placebo) at day 0 of study week 1. Three weekly directly observed active or placebo oral naltrexone tablets (2 × 50 mg, Monday and Wednesday; 3 × 50 mg, Friday) at day 0 of study week 1 (for 4 weeks) and then an 8-week regimen of patient-administered dosing at the same dosing level.

MAIN OUTCOME MEASURE

The primary outcome measure was the proportion of heroin-negative urine drug screen (UDS) results at the end of the 12-week post-randomisation time point.

RESULTS

Six patients were recruited and randomised to receive study interventions. Two patients had no positive UDS samples for heroin during the 12-week treatment period, one patient had only one positive UDS sample and the remaining patients had two, six and eight positive UDS results for heroin. All patients had at least one missed clinic visit (range 1-14).

CONCLUSIONS

Considerable problems were encountered with (1) the stipulated requirement of a validated 'detoxified' status prior to the initiation of the study naltrexone, (2) the requirement for a consent cooling-off period and (3) delays awaiting the surgical implant procedure. Major upheaval to the organisation and delivery of NHS community treatment services across England led to extremely poor levels of actual entry of patients into the trial. Research-vital clinical and procedural requirements were, therefore, more challenging to implement. The potential therapeutic value of the opioid antagonist naltrexone still needs clear investigation, including comparison of the established oral form with the new ultra-long-acting depot implant formulations (for which no licensed products exist in Europe). Despite the small number of study participants, some tentative conclusions can be reached, relevant to potential future work. The blinding of the active/placebo medications appeared to be good. Self-report was not sufficient to detect instances of heroin use. Self-report plus UDS information provided a fuller picture. Instances of lapsed heroin use were not necessarily followed by full relapse, and future work should consider the lapse-relapse relationship. The prison release setting also warrants special consideration. In future, investigators should consider seeking ethics approval for studies in which clinical procedures to accelerate the treatment process are permitted, even if outside orthodox clinical practice, if they address a clinical need at the time of challenge and clinical risk. In addition, it may be appropriate to seek exemption from the ordinary requirement of a cooling-off period after securing consent because it is often essential to initiate treatment promptly.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN95809946.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 23, No. 3. See the NIHR Journals Library website for further project information.

Design and synthesis of a bivalent probe targeting the putative mu opioid receptor and chemokine receptor CXCR4 heterodimer

The first bivalent ligand targeting the putative heterodimer of the mu opioid receptor and the chemokine receptor CXCR4.

Opioid abuse and HIV/AIDS have been defined as synergistic epidemics. Opioids can accelerate HIV replication in the immune system by up-regulating the expression of HIV co-receptor CXCR4. Several hypotheses have been suggested as the mechanism of CXCR4 modulation by opioids through their activation on the mu opioid receptor (MOR). One hypothesis is the putative heterodimerization of the MOR and CXCR4 as a mechanism of cross-talk and subsequent exacerbation of HIV replication. Bivalent chemical probes can be powerful molecular tools to characterize protein–protein interactions, and modulate the function related to such interactions. Herein we report the design and synthesis of a novel bivalent probe to explore the putative MOR–CXCR4 dimerization and its potential pharmacological role in enhancing HIV progression. The developed bivalent probe was designed with two distinct pharmacophores linked through a spacer. One pharmacophore (naltrexone) will interact with the MOR and the other (IT1t) with the CXCR4. The overall synthetic routes to prepare the bivalent probe and its corresponding monovalent controls were comprised of 18–22 steps with acceptable yields. Preliminary biological evaluation showed that the bivalent probe preserved binding affinity and functional activity at both respective receptors, supporting the initial molecular design.

Treating opioid dependence with extended-release naltrexone (XR-NTX) in Ukraine: Feasibility and three-month outcomes

BACKGROUND

Although opioid agonist treatments (OAT) with methadone or buprenorphine are available to treat opioid use disorders (OUD) in Ukraine, OAT acceptability and coverage remains low. Extended-release naltrexone (XR-NTX) that recently became available as another treatment option provides new opportunities for treating OUDs in this region and we aimed to test its feasibility.

METHODS

Patients with OUD (N=135) and interested in treatment with XR-NTX were initiated on monthly XR-NTX injections and monitored for three months. Correlates of 3-month retention on XR-NTX and drug use at each time-point using self-reports and urine drug testing (UDT) were assessed.

RESULTS

Of the 134 participants initiated XR-NTX, 101 (75%) completed three months, defined as 4 consecutive XR-NTX injections. Independent factors negatively associated with retention in XR-NTX treatment included previous maintenance with OAT (aOR=0.3; 95%CI=0.1-0.9) and extrinsic help-seeking treatment motivation (aOR=0.7; 95%CI=0.5-0.9). Of these 101 participants completing three months of treatment, opioid use markedly reduced using self-report (67%% to 22%; p>0.001) and UDT (77% to 24%; p<0.001) outcomes over time. Alcohol, marijuana and stimulant use, however, remained unchanged. Craving for opioids and symptoms of depression also significantly decreased, while health-related quality of life scores improved over time. No adverse side effects were reported during the period of observation.

CONCLUSION

The first introduction of XR-NTX in Ukraine among persons with OUD resulted in high levels of retention, marked reductions in opioid use and improved quality of life. These descriptive results suggest that XR-NTX treatment is feasible and well-tolerated over a 3-month period in Ukraine.

Implants and depot injections for treating opioid dependence: Qualitative study of people who use or have used heroin

BACKGROUND

Long-acting opioid pharmacotherapy (OPT) is presumed to offer benefits over more conventional OPT formulations. This paper analyzes the views and experiences of people who use or have used heroin in order to explore two novel systems for delivering long-acting OPT: implants and depot injections. New materialism theorizing is used to interpret and frame the findings.

METHODS

Qualitative data were generated via seven focus groups conducted during 2017 in London, UK. Participants (n = 44; 28 men and 16 women; ages 33-66 years) had all received OPT. Focus group discussions covered real and potential OPT delivery systems. All participant data relating to implants and depot injections were coded using MAXQDA software and analysed inductively via Iterative Categorisation.

FINDINGS

Participants discussed implants and depot injections in terms of interacting physical, psychological and social factors: dose stability; OPT administration; stopping treatment; co-presence of an antagonist; breaking rituals and habits; reduced choice and control; feeling normal; information needs; getting on with everyday life; and social interaction. Participants identified both benefits and concerns, and variable needs and preferences, with respect to each delivery system.

CONCLUSIONS

Implants and depot injections are not 'fixed' medications that can be administered to people to achieve pre-determined treatment aims. Rather, they are complex 'assemblages' with uncertain outcomes. Furthermore, they are themselves part of wider interactive 'assemblages'. Drug developers and treatment providers need to understand this complexity in order to target long-acting OPT at people most likely to benefit from it, and to reduce any unintended negative consequences.

Safety and efficacy of an oxycodone vaccine: Addressing some of the unique considerations posed by opioid abuse

Among vaccines aimed at treating substance use disorders, those targeting opioids present several unique medication development challenges. 1) Opioid overdose is a common complication of abuse, so it is desirable for an opioid vaccine to block the toxic as well as the addictive effects of opioids. 2) It is important that an opioid vaccine not interfere with the action of opioid antagonists used to reverse opioid overdose or treat addiction. 3) Some opioids are immunosuppressive and chronic ongoing opioid use could interfere with vaccine immunogenicity. 4) Although antibody-bound oxycodone is unable to enter the brain because of its size, it might still be able to activate peripheral opioid receptors. To assess vaccine impact on opioid toxicity, rats vaccinated with oxycodone conjugated to keyhole limpet hemocyanin subunit dimer (OXY-dKLH) adsorbed to alum or controls vaccinated with dKLH were compared with regard to oxycodone-induced hotplate analgesia and oxycodone-induced respiratory depression and bradycardia. Vaccination shifted the dose-response curves to the right, representing protection, for each of these endpoints. Naloxone was equally effective in both OXY-dKLH and control groups, providing complete and rapid reversal of respiratory depression. The administration of a long-acting naltrexone formulation during vaccination did not impair vaccine immunogenicity in mice. Similarly, serum anti-oxycodone antibody titers were not altered by continuous morphine infusion during vaccination compared to opioid-naïve controls. Competitive ELISA assay showed negligible or low affinity of immune antiserum for endogenous opioids or opioid antagonists. In vitro receptor binding assays showed that antibody-bound oxycodone does not activate mu opioid receptors. These data support further study of OXY-dKLH as a potential treatment for oxycodone abuse and suggest that vaccination might also reduce the severity of oxycodone overdose.

Utility of preclinical drug versus food choice procedures to evaluate candidate medications for methamphetamine use disorder

Substance use disorders are diagnosed as a manifestation of inappropriate behavioral allocation toward abused drugs and away from other behaviors maintained by more adaptive nondrug reinforcers (e.g., money and social relationships). Substance use disorder treatment goals include not only decreasing drug-maintained behavior but also promoting behavioral reallocation toward these socially adaptive alternative reinforcers. Preclinical drug self-administration procedures that offer concurrent access to both drug and nondrug reinforcers provide a translationally relevant dependent measure of behavioral allocation that may be useful for candidate medication evaluation. In contrast to other abused drugs, such as heroin or cocaine, preclinical methamphetamine versus food choice procedures have been a more recent development. We hypothesize that preclinical to clinical translatability would be improved by the evaluation of repeated pharmacological treatment effects on methamphetamine self-administration under a methamphetamine versus food choice procedure. In support of this hypothesis, a literature review suggests strong concordance between preclinical pharmacological treatment effects on methamphetamine versus food choice in nonhuman primates and clinical medication treatment effects on methamphetamine self-administration in human laboratory studies or methamphetamine abuse metrics in clinical trials. In conclusion, this literature suggests preclinical methamphetamine versus food choice procedures may be useful in developing innovative pharmacotherapies for methamphetamine use disorder.

Use of Preclinical Drug vs. Food Choice Procedures to Evaluate Candidate Medications for Cocaine Addiction

Drug addiction is a disease that manifests as an inappropriate allocation of behavior towards the procurement and use of the abused substance and away from other behaviors that produce more adaptive reinforcers (e.g. exercise, work, family and social relationships). The goal of treating drug addiction is not only to decrease drug-maintained behaviors, but also to promote a reallocation of behavior towards alternative, nondrug reinforcers. Experimental procedures that offer concurrent access to both a drug reinforcer and an alternative, nondrug reinforcer provide a research tool for assessment of medication effects on drug choice and behavioral allocation. Choice procedures are currently the standard in human laboratory research on medications development. Preclinical choice procedures have been utilized in biomedical research since the early 1940's, and during the last 10-15 years, their use for evaluation of medications to treat drug addiction has increased. We propose here that parallel use of choice procedures in preclinical and clinical studies will facilitate translational research on development of medications to treat cocaine addiction. In support of this proposition, a review of the literature suggests strong concordance between preclinical effectiveness of candidate medications to modify cocaine choice in nonhuman primates and rodents and clinical effectiveness of these medications to modify either cocaine choice in human laboratory studies or metrics of cocaine abuse in patients with cocaine use disorder. The strongest evidence for medication effectiveness in preclinical choice studies has been obtained with maintenance on the monoamine releaser d-amphetamine, a candidate agonist medication for cocaine use analogous to use of methadone to treat heroin abuse or nicotine formulations to treat tobacco dependence.

Factors associated with willingness to take extended release naltrexone among injection drug users

BACKGROUND

Although opioid-agonist therapy with methadone or buprenorphine/naloxone is currently the mainstay of medical treatment for opioid use disorder, these medications often are not well accepted or tolerated by patients. Recently, extended release naltrexone (XR-NTX), an opioid antagonist, has been advanced as an alternative treatment. The willingness of opioid-addicted patients to take XR-NTX has not been well described.

METHODS

Opioid-using persons enrolled in a community-recruited cohort in Vancouver, Canada, were asked whether or not they would be willing to take XR-NTX. Logistic regression was used to independently identify factors associated with willingness to take the medication.

RESULTS

Among the 657 participants surveyed between June 1, 2013, and November 30, 2013, 342 (52.1%) were willing to take XR-NTX. One factor positively associated with willingness was daily heroin injection (adjusted odds ratio [AOR] = 1.53; 95% confidence interval [CI] = 1.02-2.31), whereas Caucasian ethnicity was negatively associated (AOR = 0.59; 95% CI = 0.43-0.82). Satisfaction with agonist therapy (13.4%) and unwillingness to stop opioids being used for pain (26.9%) were the most common reasons for being unwilling to take XR-NTX.

CONCLUSIONS

A high level of willingness to take XR-NTX was observed in this setting. Interestingly, daily injection heroin use was positively associated with willingness, whereas Caucasian participants were less willing to take XR-NTX. Although explanations for unwillingness were described in this study, further research is needed to investigate real-world acceptability of XR-NTX as an additional option for the treatment of opioid use disorder.

Animal models for opioid addiction drug discovery

INTRODUCTION

Since ancient times, the opium poppy has been used in a variety of settings, including pain management. Natural and synthetic derivatives of opium are commonly used in medicine today and include drugs, such as morphine, codeine, hydromorphone and oxycodone. Although excellent at inhibiting pain, these narcotics often produce a state of euphoria leading to misuse and abuse by the general population, particularly in young adults. The misuse of prescription opiates has continually increased over the past 10 years despite associated negative outcomes, resulting in opiate psychological dependence, withdrawal and relapse.

AREAS COVERED

This paper briefly refers to the history of opiate use and the modern challenges associated with chronic exposure. The authors present the prevalence of addiction and misuse of prescription opiates and discuss some of the opiate-associated effects. This includes activation of reward circuitry and compensatory receptor mechanisms. Finally, the authors provide a review on neuroadaptive changes that manifest during opiate dependence, withdrawal and relapse in animal models.

EXPERT OPINION

In spite of the various methods available to treat opiate addiction, there is still a huge unmet need for its management, including the creative design of novel, non-addictive pain medications. The authors believe that multifunctional compounds or combinations of compounds that inhibit pain pathways, whereas not activating the reward pathways, will begin to subdue the opiate addiction endemic.

Naltrexone implant treatment for buprenorphine dependence--Mauritian case series

Although substitution therapy with opiate agonist treatments such as methadone and buprenorphine has resulted in a reduction of illicit drug use related harm, such treatment has also resulted in severe problems in some countries where opioid-dependent individuals now inject illicitly sold buprenorphine or buprenorphine-naloxone instead of heroin. There is no approved treatment for buprenorphine dependence. Naltrexone is an opioid antagonist which has been used for the treatment of both alcohol and opioid dependencies. Although both buprenorphine and heroin resemble each other concerning their effects, buprenorphine has a higher affinity to opioid receptors than heroin. Therefore, it is not known if naltrexone can block the psychoactive effects of buprenorphine as it does for heroin. This paper presents observational case series data on the use of a sustained-release naltrexone implant for the treatment of buprenorphine dependence. To the authors' knowledge this is the first use of sustained-release naltrexone for this indication.

Naltrexone: a review of existing sustained drug delivery systems and emerging nano-based systems

Narcotic antagonists such as naltrexone (NTX) have shown some efficiency in the treatment of both opiate addiction and alcohol dependence. A few review articles have focused on clinical findings and pharmacogenetics of NTX, advantages and limitations of sustained release systems as well as pharmacological studies of NTX depot formulations for the treatment of alcohol and opioid dependency. To date, three NTX implant systems have been developed and tested in humans. In this review, we summarize the latest clinical data on commercially available injectable and implantable NTX-sustained release systems and discuss their safety and tolerability aspects. Emphasis is also laid on recent developments in the area of nanodrug delivery such as NTX-loaded micelles and nanogels as well as related research avenues. Due to their ability to increase the therapeutic index and to improve the selectivity of drugs (targeted delivery), nanodrug delivery systems are considered as promising sustainable drug carriers for NTX in addressing opiate and alcohol dependence.

Novel Pharmacologic Approaches to Treating Cannabis Use Disorder

With large and increasing numbers of people using cannabis, the development of cannabis use disorder (CUD) is a growing public health concern. Despite the success of evidence-based psychosocial therapies, low rates of initial abstinence and high rates of relapse during and following treatment for CUD suggest a need for adjunct pharmacotherapies. Here we review the literature on medication development for the treatment of CUD, with a particular focus on studies published within the last three years (2010-2013). Studies in both the human laboratory and in the clinic have tested medications with a wide variety of mechanisms. In the laboratory, the following medication strategies have been shown to decrease cannabis withdrawal and self-administration following a period of abstinence (a model of relapse): the cannabinoid receptor agonist, nabilone, and the adrenergic agonist, lofexidine, alone and in combination with dronabinol (synthetic THC), supporting clinical testing of these medication strategies. Antidepressant, anxiolytic and antipsychotic drugs targeting monoamines (norepinephrine, dopamine, and serotonin) have generally failed to decrease withdrawal symptoms or laboratory measures of relapse. In terms of clinical trials, dronabinol and multiple antidepressants (fluoxetine, venlafaxine and buspirone) have failed to decrease cannabis use. Preliminary results from controlled clinical trials with gabapentin and N-acetylcysteine (NAC) support further research on these medication strategies. Data from open label and laboratory studies suggest lithium and oxytocin also warrant further testing. Overall, it is likely that different medications will be needed to target distinct aspects of problematic cannabis use: craving, ongoing use, withdrawal and relapse. Continued research is needed in preclinical, laboratory and clinical settings.

A placebo-controlled trial of memantine as an adjunct to injectable extended-release naltrexone for opioid dependence

There is preclinical support for using NMDA receptor glutamatergic antagonists to aid in naltrexone-based treatment of opioid dependence. We hypothesized that adding memantine will improve efficacy of extended-release (XR) naltrexone to prevent relapse. In this double blind study opioid-dependent participants (N=82) underwent inpatient detoxification and naltrexone induction. During naltrexone initiation participants were randomized to receive memantine 40 mg or placebo and continued treatment for 12-weeks with XR naltrexone and relapse-prevention therapy. Sixty eight percent of participants completed detoxification and received the first dose of XR naltrexone. Rates of trial completion were significantly greater in participants receiving placebo than memantine (70% vs. 43%, p<0.05). Severity of opioid withdrawal symptoms during the first 3 weeks of the trial appeared to be lower in the group receiving memantine (p=0.07). Adding memantine does not appear to increase the effectiveness of injectable XR naltrexone as a relapse prevention strategy in opioid dependence and may lead to an increase in treatment drop-out.

DSM IV axis II traits can influence compliance to treatment with oral naltrexone: a preliminary study on 30 opiate dependent patients

For many decades, health specialists have successfully used their clinical ingenuity to increase the efficiency of opiate detoxification protocols. However, even if drop-out rate has decreased significantly in today's protocols, relapse after opiate detoxification remains a major problem. Therefore, naltrexone hydrochloride, an opiate antagonist, has been considered by many as a potential tool to support abstinence in what has been called "antagonist-assisted abstinence" (AAA). Nevertheless, while naltrexone implants are becoming more accessible, a large majority of centers still use oral naltrexone and adherence to treatment remains a major obstacle to AAA's efficiency. As the personality profile could give an insight into compliance, we investigated the relationship between personality profiles and naltrexone adherence in a cohort of 30 patients. The results indicate that the Axis II profile influences the likely pattern of oral naltrexone compliance. As clinicians need to identify opiate dependent patients who are most likely to benefit from oral naltrexone treatment, it therefore carries important implications and could lead to a better adjustment of therapeutic strategies for opiate dependent patients.

Improving clinical outcomes for naltrexone as a management of problem alcohol use

Despite being a relatively effective and safe treatment, the clinical management of alcohol abuse/dependence by oral naltrexone can be compromised due to the patient's non-compliance with daily use of this medication. Over the past decade an increasing body of research has suggested that the use of sustained release depot naltrexone preparations can overcome this issue and deliver improved clinical outcomes. However, at the same time, research findings from diverse areas of pharmacogenetics, neurobiology and behavioural psychology have also been converging to identify variables including genetic markers, patient psychosocial characteristics and drug use history differences, or clusters of these variables that play a major role in mediating the response of alcohol abuse/dependent persons to treatment by naltrexone. While this article does not attempt to review all available data pertaining to an individual alcohol dependent patient's response to treatment by naltrexone, it does identify relevant research areas and highlights the importance of data arising from them. The characterization of clinical markers, to identify those patients who are most likely to benefit from naltrexone and to tailor a more individual naltrexone treatment, will ultimately provide significant benefit to both patients and clinicians by optimizing treatment outcome.

A novel bivalent HIV-1 entry inhibitor reveals fundamental differences in CCR5-μ-opioid receptor interactions between human astroglia and microglia

OBJECTIVE

We explored whether the opiate, morphine, affects the actions of maraviroc, as well as a recently synthesized bivalent derivative of maraviroc linked to an opioid antagonist, naltrexone, on HIV-1 entry in primary human glia.

METHODS

HIV-1 entry was monitored in glia transiently transfected with an LTR construct containing a luciferase reporter gene under control of a promoter for the HIV-1 transactivator protein Tat. The effect of maraviroc and the bivalent ligand with or without morphine on CCR5 surface expression and cytokine release was also explored.

RESULTS

Maraviroc inhibits HIV-1 entry into glial cells, whereas morphine negates the effects of maraviroc leading to a significant increase in viral entry. We also demonstrate that the maraviroc-containing bivalent ligand better inhibits R5-tropic viral entry in astrocytes than microglia compared to maraviroc when coadministered with morphine. Importantly, the inhibitory effects of the bivalent compound in astrocytes were not compromised by morphine. Exposure to maraviroc decreased the release of pro-inflammatory cytokines and restricted HIV-1-dependent increases in CCR5 expression in both astrocytes and microglia, whereas exposure to the bivalent had a similar effect in astrocytes but not in microglia. The CCR5-μ-opioid receptor (MOR) stoichiometric ratio varied among the two cell types with CCR5 expressed at much higher levels than MOR in microglia, which could explain the effectiveness of the bivalent ligand in astrocytes compared to microglia.

CONCLUSION

A novel bivalent compound reveals fundamental differences in CCR5-MOR interactions and HIV-1 infectivity among glia, and has unique therapeutic potential in opiate abuse-HIV interactive comorbidity.

Naltrexone in the treatment of opioid-dependent pregnant women: the case for a considered and measured approach to research

The present paper considers naltrexone to treat opioid dependence during pregnancy. The public health problem of opioid dependence and its treatment during pregnancy is reviewed first. Next, the naltrexone and opioid dependence treatment literature is summarized, with overviews of the pre-clinical and clinical research on prenatal naltrexone exposure. Finally, considerations and recommendations for future medication research for the treatment of opioid dependence in pregnant women are provided. The efficacy of long-acting injectable naltrexone relative to placebo, its blockade of opioid agonist euphoric effects, its lack of abuse and tolerance development and its modest adverse effect profile make it a potential medication for opioid-dependent pregnant women. However, it is not without seriously concerning potential drawbacks, including the difficulty surrounding medication induction that may lead to vulnerability with regard to relapse, physical dependence re-establishment, increased risk behaviors, treatment dropout and resulting opioid overdose. Before embarking on future research with this medication, the benefits and risks for the mother-embryo/fetus/child dyad should be weighed carefully. Should future research be conducted, a multi-level commitment to proactive ethical research is needed to reach the ultimate goal of improving the lives of women and children affected by opioid dependence.

Employment-based reinforcement of adherence to oral naltrexone treatment in unemployed injection drug users

Oral naltrexone has high potential for use as a relapse prevention pharmacotherapy for opiate dependence yet suffers from notoriously poor adherence. This study evaluated whether entry to a therapeutic workplace could reinforce adherence with oral naltrexone. Opiate-dependent and cocaine-using injection drug users were detoxified, inducted onto oral naltrexone, and randomly assigned to a contingency (n = 35) or prescription (n = 32) group for a 26-week period. Contingency participants were required to ingest naltrexone under staff observation to gain access to the therapeutic workplace. Prescription participants received a take-home supply of naltrexone and could access the workplace independent of naltrexone ingestion. Primary outcome measures were percent of urine samples positive for naltrexone at 30-day assessments and negative for opiates and cocaine at 30-day assessments. Contingency participants provided significantly more urine samples that were positive for naltrexone compared with prescription participants (72% vs. 21%, p < .01); however, no effect of experimental group was observed on percent opiate-negative (71% vs. 60%, p = .19.) or cocaine-negative (56% vs. 53%, p = .82) samples in the contingency and prescription groups, respectively. Opiate-positive samples were significantly more likely to occur in conjunction with cocaine (p < .001) and when not protected by naltrexone (p < .02), independent of experimental group. Overall, these results show that contingent access to a therapeutic workplace significantly promoted adherence to oral naltrexone, and that the majority of opiate use occurred in conjunction with cocaine use, suggesting that untreated cocaine use may limit the effectiveness of oral naltrexone in promoting opiate abstinence.

Long-acting Preparations in Substance Abuse Management: A Review and Update

Many pharmacological approaches have been used in managing substance use disorders. Conventional pharmacological agents have relatively short durations of action which make them vulnerable to non-adherence and relapse to substance use disorder. To overcome this problem, long-acting preparations have been developed with the aim of reducing the frequency of use and hence improving adherence. This review takes a broad overview of the long-acting preparations available for the management of substance use disorders. The pharmacology, advantages and disadvantages of these preparations are discussed. Many of these preparations hold promise for improving patient outcomes.

Medications development for opioid abuse

Here we describe methods for preclinical evaluation of candidate medications to treat opioid abuse and dependence. Our perspective is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effects, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) the states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and the effects of candidate medications. Effects of opioid medications on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications, and (2) continued development of nonopioids such as inhibitors of endocannabinoid catabolic enzymes or inhibitors of opioid-induced glial activation.

Assessing the usefulness of health data linkage in obtaining adverse event data in a randomised controlled trial of oral and implant naltrexone in the treatment of heroin dependence

Background

The completeness of self-reported serious adverse events (SAEs) in clinical trials can be reduced by inaccuracies in subject reporting and lost to follow-up.

Purpose

This study assesses the usefulness of a health data linkage system in obtaining SAE data in a randomised controlled study of oral and implant naltrexone.

Methods

SAEs were collected from 68 heroin-dependent subjects during a randomised controlled trial of oral and implant naltrexone with follow-up to 26 weeks. Patient self-report data were cross-matched against hospital and emergency department (ED) attendances for the same period using a health data linkage system.

Results

A total of 29 hospital admissions and 74 ED attendances were identified using health data linkage. Of these, 12 (41.4%) hospital admissions and 50 (67.7%) of ED attendances had not been reported as SAE in the randomised controlled trial. In subjects participating in the trial at the time of the event, there was a 1.25-fold increase in the number of hospital admissions and a 2.25-fold increase in the number of ED attendances recorded using data linkage. Overall (including withdrawn subjects or those lost to follow-up), there was a 1.71-fold increase in hospital admission and a 3.09-fold increase in ED attendance recorded.

Limitations

The use of data linkage should not be used as a replacement for thorough follow-up, as the datasets can take substantial periods to update, making them a poor substitute for real-time follow-up. Additionally, some SAEs such as life-threatening events that do not involve ED or hospital attendance may be overlooked as would SAEs that occurred outside the dataset’s range, for example, interstate or overseas.

Conclusions

Health data linkage can be used to effectively reduce the extent of missing health data in a clinical trial.

Maintenance of reinforcement to address the chronic nature of drug addiction

BACKGROUND

Drug addiction can be a chronic problem. Abstinence reinforcement can initiate drug abstinence, but as with other treatments many patients relapse after the intervention ends. Abstinence reinforcement can be maintained to promote long-term drug abstinence, but practical means of implementing long-term abstinence reinforcement are needed.

METHODS

We reviewed 8 clinical trials conducted in Baltimore, MD from 1996 through 2010 that evaluated the therapeutic workplace as a vehicle for maintaining reinforcement for the treatment of drug addiction. The therapeutic workplace uses employment-based reinforcement in which employees must provide objective evidence of drug abstinence or medication adherence to work and earn wages.

RESULTS

Employment-based reinforcement can initiate (3 of 4 studies) and maintain (2 studies) cocaine abstinence in methadone patients, although relapse can occur even after long-term exposure to abstinence reinforcement (1 study). Employment-based reinforcement can also promote abstinence from alcohol in homeless alcohol dependent adults (1 study), and maintain adherence to extended-release naltrexone in opioid dependent adults (2 studies).

CONCLUSION

Treatments should seek to promote life-long effects in patients. Therapeutic reinforcement may need to be maintained indefinitely to prevent relapse. Workplaces could be effective vehicles for the maintenance of therapeutic reinforcement contingencies for drug abstinence and adherence to addiction medications.

The use of incentives to reinforce medication adherence

OBJECTIVE

Poor medication adherence is a longstanding problem, and is especially pertinent for individuals with chronic conditions or diseases. Adherence to medications can improve patient outcomes and greatly reduce the cost of care. The purpose of the present review is to describe the literature on the use of incentives as applied to the problem of medication adherence.

METHODS

We conducted a systematic review of peer-reviewed empirical evaluations of incentives provided to patients contingent upon medication adherence.

RESULTS

This review suggests that incentive-based medication adherence interventions can be very effective, but there are few controlled studies. The studies on incentive-based medication adherence interventions most commonly feature patients taking medication for drug or alcohol dependence, HIV, or latent tuberculosis. Across studies that reported percent adherence comparisons, incentives increased adherence by a mean of 20 percentage points, but effects varied widely. Cross-study comparisons indicate a positive relationship between the value of the incentive and the impact of the intervention. Post-intervention evaluations were rare, but tended to find that adherence effects diminish after the interventions are discontinued.

CONCLUSIONS

Incentive-based medication adherence interventions are promising but understudied. A significant challenge for research in this area is the development of sustainable and cost-effective long-term interventions.

Examination of mortality rates in a retrospective cohort of patients treated with oral or implant naltrexone for problematic opiate use

AIMS

To examine and compare mortality rates in patients treated with oral and implant naltrexone.

DESIGN

A retrospective cohort study.

SETTING

A community not-for-profit drug treatment clinic.

PARTICIPANTS

Patients treated with oral naltrexone (n = 2155, 17 207 patient-years) and implant naltrexone (n = 2389, 11 678 patient-years) for problematic opiate use between August 1997 and December 2009.

MEASUREMENTS

Crude gender, age, treatment period and cause-specific mortality rates were calculated using data obtained from the National Death Index.

FINDINGS

Crude mortality rates for patients treated with oral naltrexone [8.78 deaths per 1000 patient-years (ptpy), 95% confidence interval (CI): 7.38-10.17] were significantly different to those treated with implant naltrexone (6.59 ptpy, 95% CI: 5.13-8.06) (P = 0.0339). During the first 4 months following treatment, differences in the two groups were particularly apparent, with a mortality rate of 26.28 ptpy in patients treated with oral naltrexone compared to 7.34 ptpy in patients treated with implant naltrexone (P = 0.0003). Differences in initial mortality rates following treatment were associated predominantly with high rates of opiate overdoses in oral naltrexone patients during the first 4 months following treatment (17.22 ptpy compared with 0.67 ptpy in implant naltrexone patients) (P < 0.0001).

CONCLUSIONS

The use of implant naltrexone can reduce all-cause mortality and opiate overdose during the first 4 months following treatment compared with patients treated with oral naltrexone.

Opioid detoxification and naltrexone induction strategies: recommendations for clinical practice

BACKGROUND

Opioid dependence is a significant public health problem associated with high risk for relapse if treatment is not ongoing. While maintenance on opioid agonists (i.e., methadone, buprenorphine) often produces favorable outcomes, detoxification followed by treatment with the μ-opioid receptor antagonist naltrexone may offer a potentially useful alternative to agonist maintenance for some patients.

METHOD

Treatment approaches for making this transition are described here based on a literature review and solicitation of opinions from several expert clinicians and scientists regarding patient selection, level of care, and detoxification strategies.

CONCLUSION

Among the current detoxification regimens, the available clinical and scientific data suggest that the best approach may be using an initial 2-4 mg dose of buprenorphine combined with clonidine, other ancillary medications, and progressively increasing doses of oral naltrexone over 3-5 days up to the target dose of naltrexone. However, more research is needed to empirically validate the best approach for making this transition.

Naltrexone decreases D-amphetamine and ethanol self-administration in rhesus monkeys

Amphetamines are the second most highly abused illicit drugs worldwide, yet there is no pharmacological treatment for amphetamine abuse and dependence. Preclinical studies and, more recently, human studies, suggest that the opioid receptor antagonist, naltrexone, might be useful in the treatment of amphetamine abuse. Naltrexone, an opioid receptor antagonist, is currently used for the treatment of alcohol dependence. The aim of this study was to explore the ability of naltrexone to modify self-administration of amphetamine or ethanol in rhesus monkeys. Monkeys were trained to respond to intravenous injections of either D-amphetamine (0.003 mg/kg/injection) or ethanol (0.05 g/kg/injection) on a fixed ratio 30 schedule. Naltrexone (0.01-1 mg/kg) was administered intramuscularly 30 min before the start of treatment test sessions. Naltrexone dose-dependently decreased both amphetamine and ethanol self-administration. These findings support the potential use of naltrexone as therapy for amphetamine and polydrug abuse.

African American patients seeking treatment in the public sector: characteristics of buprenorphine vs. methadone patients

BACKGROUND

To expand its public-sector treatment capacity, Baltimore City made buprenorphine treatment accessible to low-income, largely African American residents. This study compares the characteristics of patients entering methadone treatment vs. buprenorphine treatment to determine whether BT was attracting different types of patients.

METHODS

Participants consisted of two samples of adult heroin-dependent African Americans. The first sample was newly admitted to a health center or a mental health center providing buprenorphine (N=200), and the second sample was newly admitted to one of two hospital-based methadone programs (N=178). The Addiction Severity Index (ASI) and the Friends Supplemental Questionnaire were administered at treatment entry and data were analyzed with logistic regression.

RESULTS

BT participants were more likely to be female (p=.017) and less likely to inject (p=.001). Participants with only prior buprenorphine treatment experience were nearly five time more likely to enter buprenorphine than methadone treatment (p<.001). Those with experience with both treatments were more than twice as likely to enter BT (OR=2.7, 95% CI=1.11-6.62; p=.028). In the 30 days prior to treatment entry, BT participants reported more days of medical problems (p=.002) and depression (p=.044), and were more likely to endorse a lifetime history of depression (p<.001).

CONCLUSION

Methadone and buprenorphine treatment provided in the public sector may attract different patient subpopulations. Providing buprenorphine treatment through drug treatment programs co-located with a health and mental health center may have accounted for their higher rates of medical and psychiatric problems and appears to be useful in attracting a diverse group of patients into public-sector funded treatment.

Design and synthesis of a bivalent ligand to explore the putative heterodimerization of the mu opioid receptor and the chemokine receptor CCR5

The bivalent ligand approach has been utilized not only to study the underlying mechanism of G protein-coupled receptors dimerization and/or oligomerization, but also to enhance ligand affinity and/or selectivity for potential treatment of a variety of diseases by targeting this process. Substance abuse and addiction have made both the prevention and the treatment of human immunodeficiency virus (HIV) infection more difficult to tackle. Morphine, a mu opioid receptor (MOR) agonist, can accelerate HIV infection through up-regulating the expression of the chemokine receptor CCR5, a well-known co-receptor for HIV invasion to the host cells and this has been extensively studied. Meanwhile, two research groups have described the putative MOR-CCR5 heterodimers in their independent studies. The purpose of this paper is to report the design and synthesis of a bivalent ligand to explore the biological and pharmacological process of the putative MOR-CCR5 dimerization phenomenon. The developed bivalent ligand thus contains two distinct pharmacophores linked through a spacer; ideally one of which will interact with the MOR and the other with the CCR5. Naltrexone and Maraviroc were selected as the pharmacophores to generate such a bivalent probe. The overall reaction route to prepare this bivalent ligand was convergent and efficient, and involved sixteen steps with moderate to good yields. The preliminary biological characterization showed that the bivalent compound 1 retained the pharmacological characteristics of both pharmacophores towards the MOR and the CCR5 respectively with relatively lower binding affinity, which tentatively validated our original molecular design.

Employment-based reinforcement of adherence to an FDA approved extended release formulation of naltrexone in opioid-dependent adults: a randomized controlled trial

BACKGROUND

Naltrexone provides excellent opioid blockade, but its clinical utility is limited because opioid-dependent patients typically refuse it. An injectable suspension of naltrexone for extended release (XR-NTX) was recently approved by the FDA for treatment of opioid dependence. XR-NTX treatment may require concurrent behavioral intervention to maximize adherence and effectiveness, thus we sought to evaluate employment-based reinforcement as a method of improving adherence to XR-NTX in opiate dependent adults.

METHODS

Opioid-dependent adults (n=38) were detoxified and inducted onto oral naltrexone, then randomly assigned to contingency or prescription conditions. Participants received up to six doses of XR-NTX at four-week intervals. All participants could earn vouchers for attendance and performance at a therapeutic workplace. Contingency participants were required to accept XR-NTX injections to access the workplace and earn vouchers. Prescription participants could earn vouchers independent of their acceptance of XR-NTX injections.

RESULTS

Contingency participants accepted significantly more naltrexone injections than prescription participants (87% versus 52%, p=.002), and were more likely to accept all injections (74% versus 26%, p=.004). Participants in the two conditions provided similar percentages of samples negative for opiates (72% versus 65%) and for cocaine (58% versus 54%). Opiate positivity was significantly more likely when samples were also cocaine positive, independent of naltrexone blockade (p=.002).

CONCLUSIONS

Long-term adherence to XR-NTX in unemployed opiate dependent adults is low under usual care conditions. Employment-based reinforcement can maintain adherence to XR-NTX. Ongoing cocaine use appears to interfere with the clinical effectiveness of XR-NTX on opiate use.

Epidemiologic and Molecular Pathophysiology of Chronic Opioid Dependence and the Place of Naltrexone Extended-Release Formulations in its Clinical Management

Naltrexone implants and depot injections (NI) are a novel form of treatment for opiate dependence (OD). Major questions relate to their absolute and relative efficacy and safety. Opportunely, six recent clinical trial data from several continents have uniformly provided dramatic evidence of the potent, dose-related and highly significant efficacy of NI, with minimal or manageable accompanying toxicity and safety concerns. The opiate-free lifestyle is attained significantly more often with NI adjusted O.R. = 6.00 (95% C.I. 3.86–9.50), P < 10⁻¹⁰. Other drug use and drug craving are also rapidly reduced. The optimum manner in which to commence NI remains to be established. Of particular relevance is the relative safety of NI compared to the chronic opiate agonists (COA) usually employed, as the long-term toxicity of COA is only just being elucidated. Large population-based studies have found elevated rates of cardiovascular disease, six cancers, liver and respiratory disease, and all-cause mortality in COA. Whilst opiates have been shown to trigger numerous molecular pathways, the most interesting is the demonstration that the opiate morphinan’s nucleus binds to the endotoxin groove of the TLR4-MD2 heterodimer. This has the effect of triggering a low grade endotoxaemic-like state, which over time may account for these protean clinical findings, an effect which is reversed by opiate antagonists. This emerging evidence suggests an exciting new treatment paradigm for OD and a corresponding increase in the role of NI in treatment.

Naltrexone extended-release injection: an option for the management of opioid abuse

The United States Food and Drug Administration (FDA) approved naltrexone, a synthetic competitive antagonist at opioid receptors, in oral form in 1984 for use in the management of opioid abuse and addiction. Because naltrexone and its major metabolite, 6-β-naltrexone, are both competitive antagonists at opioid receptors - and thereby inhibit opioid agonist-induced effects including those desired by abusers - it was hypothesized that once maintained on naltrex-one, opioid-induced desirable effects would be diminished to the point that relapse to illicit use would decline because it was no longer rewarding. However, good medication compliance is a requisite for such a strategy to be effective and a systematic review of oral naltrexone concluded that this method of treatment was not superior for any outcomes measured (ie, retention, abstinence, or side effects) to placebo, psychotherapy, benzodiazepines, or buprenorphine treatment. In addition, the retention rate on oral naltrexone was very low (less than 30%). Recently, the FDA approved an extended-release formulation (intramuscular depot injection) of naltrexone for prevention of relapse to opioid dependence following opioid detoxification and to be used along with counseling and social support. Since it needs to be administered only monthly, as opposed to the daily administration required for the oral formulation, naltrexone injection has the potential for increasing adherence and retention rates. Concerns include liver damage at high doses (oral formulation) and possible opioid overdose if an attempt is made to surmount receptor antagonism by taking higher doses of an opioid agonist or if opioid receptors become "sensitized" under long-term antagonism. The focus of the present review is the current information regarding the safety and efficacy of naltrexone extended-release therapy.

Structure selectivity relationship studies of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan derivatives toward the development of the mu opioid receptor antagonists

Mu opioid receptor antagonists have been applied to target a variety of diseases clinically. The current study is designed to explore the structure selectivity relationship (SSR) of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan (NAP), a lead compound identified as a selective mu opioid receptor antagonist based on the previous study. Among a series of NAP derivatives synthesized, compounds 6 (NMP) and 9 (NGP) maintained comparable binding affinity, selectivity and efficacy to the lead compound. Particularly, the mu opioid receptor selectivity over kappa opioid receptor of NGP was considerably enhanced compared to that of NAP. Overall, the preliminary SSR supported our original hypothesis that an alternate 'address' domain may exist in the mu opioid receptor, which favors the ligands carrying a hydrogen bond acceptor and an aromatic system to selectively recognize the mu opioid receptor.

Patterns in admission delays to outpatient methadone treatment in the United States

Waiting lists for methadone treatment have existed in many U.S. communities, but little is known nationally about what patient and service system factors are related to admission delays that stem from program capacity shortfalls. Using a combination of national data sources, this study examined patterns in capacity-related admission delays to outpatient methadone treatment in 40 U.S. metropolitan areas (N = 28,920). Patient characteristics associated with admission delays included racial/ethnic minority status, lower education, criminal justice referral, prior treatment experience, secondary cocaine or alcohol use, and co-occurring psychiatric problems. Injection drug users experienced fewer delays, as did self-pay patients and referrals from health care and addiction treatment providers. Higher community-level utilization of methadone treatment was associated with delay, whereas delays were less common in communities with higher utilization of alternative modalities. These findings highlight potential disparities in timely admission to outpatient methadone treatment. Implications for improving treatment access and service system monitoring are discussed.

Employment-based reinforcement of adherence to depot naltrexone in unemployed opioid-dependent adults: a randomized controlled trial

AIMS

Naltrexone can be used to treat opioid dependence, but patients refuse to take it. Extended-release depot formulations may improve adherence, but long-term adherence rates to depot naltrexone are not known. This study determined long-term rates of adherence to depot naltrexone and whether employment-based reinforcement can improve adherence.

DESIGN

Participants who were inducted onto oral naltrexone were assigned randomly to contingency (n = 18) or prescription (n = 17) groups. Participants were offered six depot naltrexone injections and invited to work at the therapeutic workplace on week days for 26 weeks, where they earned stipends for participating in job skills training. Contingency participants were required to accept naltrexone injections to maintain workplace access and to maintain maximum pay. Prescription participants could work independently of whether they accepted injections.

SETTING

The therapeutic workplace, a model employment-based intervention for drug addiction and unemployment.

PARTICIPANTS

Opioid-dependent unemployed adults.

MEASUREMENTS

Depot naltrexone injections accepted and opiate-negative urine samples.

FINDINGS

Contingency participants accepted significantly more naltrexone injections than prescription participants (81% versus 42%), and were more likely to accept all injections (66% versus 35%). At monthly assessments (with missing urine samples imputed as positive), the groups provided similar percentages of samples negative for opiates (74% versus 62%) and for cocaine (56% versus 54%). Opiate-positive samples were more likely when samples were also positive for cocaine.

CONCLUSIONS

Employment-based reinforcement can maintain adherence to depot naltrexone. Future research should determine whether persistent cocaine use compromises naltrexone's effect on opiate use. Workplaces may be useful for promoting sustained adherence to depot naltrexone.

Favorable mortality profile of naltrexone implants for opiate addiction

Several reports express concern at the mortality associated with the use of oral naltrexone for opiate dependency. Registry controlled follow-up of patients treated with naltrexone implant and buprenorphine was performed. In the study, 255 naltrexone implant patients were followed for a mean (+/- standard deviation) of 5.22 +/- 1.87 years and 2,518 buprenorphine patients were followed for a mean (+/- standard deviation) of 3.19 +/- 1.61 years, accruing 1,332.22 and 8,030.02 patient-years of follow-up, respectively. The crude mortality rates were 3.00 and 5.35 per 1,000 patient-years, respectively, and the age standardized mortality rate ratio for naltrexone compared to buprenorphine was 0.676 (95% confidence interval = 0.014 to 1.338). Most sex, treatment group, and age comparisons significantly favored the naltrexone implant group. Mortality rates were shown to be comparable to, and intermediate between, published mortality rates of an age-standardized methadone treated cohort and the Australian population. These data suggest that the mortality rate from naltrexone implant is comparable to that of buprenorphine, methadone, and the Australian population.

Clinical safety of 1500 mg oral naltrexone overdose

This case represents a clinical overdose of the largest known dose of oral naltrexone, equivalent to the taking of a whole bottle of the oral naltrexone preparation. The patient's intention was to control craving for alcohol and opiates. The patient quickly settled with expectant management. As such it demonstrates that earlier concerns that have been voiced in this area, particularly relating to naltrexone-related hepatotoxicity and depression, may have been overstated, at least in the experience of this patient. This patient's course was marked only by gastric irritation, of which she had some history. As such the present profile provides case report evidence consistent with more robust views of the patient safety of naltrexone itself, and opposing more cautious views. Her polydrug craving was suppressed for a period of 2 weeks, which raises the important question of the mechanism of action of naltrexone's generalised suppression of refractory hedonic consumptive addictive behaviours.

Challenges to antagonist blockade during sustained-release naltrexone treatment

AIMS

Naltrexone is a competitive opioid antagonist that effectively blocks the action of heroin and other opioid agonists. Sustained-release naltrexone formulations are now available that provide long-acting opioid blockade. This study investigates the use of heroin and other opioids among opioid-dependent patients receiving treatment with long-acting naltrexone implants, their subjective experience of drug 'high' after opioid use, and factors associated with opioid use.

METHODS

Participants (n = 60) were opioid-dependent patients receiving treatment with naltrexone implants. Outcome data on substance use, drug 'high', depression and criminal activity were collected over a 6-month period. Blood samples were taken to monitor naltrexone plasma levels, and hair samples to verify self-reported opioid use.

FINDINGS

More than half [n = 34 or 56%; 95% confidence interval (CI) 44-68%)] the patients challenged the blockade with illicit opioids during the 6-month treatment period; 44% (n = 26; 95% CI 32-56%) were abstinent from opioids. Mean opioid use was reduced from 18 [standard deviation (SD)13] days during the month preceding treatment to 6 days (SD 11) after 6 months. Of the respondents questioned on opioid 'high' (n = 31), nine patients (30%; 95% CI 16-47%) reported partial drug 'high' following illicit opioid use, and three (12%; 95% CI 3-26%) reported full 'high'. Opioid use was associated with use of non-opioid drugs and criminal behaviour.

CONCLUSIONS

Challenging naltrexone blockade with heroin on at least one occasion is common among sustained-release naltrexone patients, but only a minority of patients use opioids regularly. Challenges represent a warning sign for poor outcomes and often occur in the context of polydrug use and social adjustment problems.

Risk factors for craving and relapse in heroin users treated with oral or implant naltrexone

BACKGROUND

Oral naltrexone effectively antagonizes heroin, but patient noncompliance limits its utility; sustained-release preparations may overcome this. Few data are available on optimal blood naltrexone levels for preventing craving and/or return to heroin use. This study assesses various risk factors, including blood naltrexone level, for heroin craving and relapse to illicit opioids.

METHODS

Heroin-dependent persons from a randomized controlled trial of oral versus implant naltrexone were followed up for 6 months. Thirty-four participants received 50 mg oral naltrexone daily, plus placebo implant; thirty-five participants received a single dose of 2.3 g naltrexone implant, plus daily oral placebo tablets.

RESULTS

Compared to oral naltrexone patients, implant naltrexone patients were significantly less likely to use any opioids and had one-fifth the risk of using heroin > or = weekly. Risk of > or = weekly heroin use increased by 2.5 times at blood naltrexone concentration < .5 ng/mL compared with > or = .5 ng/mL, with 3 ng/mL associated with very low risk of use. Craving remained near "floor" levels for implant patients but rebounded to higher levels among oral patients. Lower craving scores (< or = 20/70) predicted lower relapse risk. Noncompliance with daily oral formula, higher baseline craving, longer history of use, and being younger predicted higher craving at follow-up.

CONCLUSIONS

Implant naltrexone was better associated with reduced heroin craving and relapse than oral naltrexone. Effective treatment was achieved at blood naltrexone levels of 1 ng/mL to 3 ng/mL, with higher levels associated with greater efficacy. Craving assessment may be valuable in predicting relapse risk allowing timely intervention.