Intravenous buprenorphine self-administration by detoxified heroin abusers

Patterns of use and adverse events reported among persons who regularly inject buprenorphine: a systematic review

BACKGROUND AND AIMS

Given the ongoing opioid crisis, novel interventions to treat severe opioid use disorder (OUD) are urgently needed. Injectable opioid agonist therapy (iOAT) with diacetylmorphine or hydromorphone is effective for the treatment of severe, treatment-refractory OUD, however barriers to implementation persist. Intravenous buprenorphine for the treatment of OUD (BUP iOAT) has several possible advantages over traditional iOAT, including a safety profile that might enable take-home dosing. We aimed to characterize injecting practices among real-world populations of persons who regularly inject buprenorphine, as well as associated adverse events reported in order to inform a possible future BUP iOAT intervention.

METHODS

We conducted a systematic review. We searched MEDLINE, EMBASE, and PsycINFO from inception through July 2020 and used backwards citation screening to search for publications reporting on dose, frequency among persons who regularly inject the drug, or adverse events associated with intravenous use of buprenorphine. The review was limited to English language publications and there was no limitation on study type. Study quality and risk of bias was assessed using the Mixed Methods Appraisal Tool. Narrative synthesis was used in reporting the results.

RESULTS

Eighty-eight studies were included in our review. Regular injection of buprenorphine was identified across diverse settings world-wide. Daily dose of oral buprenorphine injected was < 1-12 mg. Frequency of injection was 0-10 times daily. Adverse events could be characterized as known side effects of opioids/buprenorphine or injection-related complications. Most studies were deemed to be of low quality.

CONCLUSIONS

Extramedical, intravenous use of buprenorphine, continues to be documented. BUP iOAT may be feasible and results may inform the development of a study to test the efficacy and safety of such an intervention. Future work should also examine acceptability among people with severe OUD in North America. Our review was limited by the quality of included studies.

Buprenorphine as a Treatment for Major Depression and Opioid Use Disorder

Rates of major depressive disorder (MDD) are disproportionally high in subjects with opioid use disorder (OUD) relative to the general population. MDD is often more severe in OUD patients, leading to compliance issues with maintenance therapies and poor outcomes. A growing body of literature suggests that endogenous opioid system dysregulation may play a role in the emergence of MDD. Buprenorphine, a mixed opioid receptor agonist/antagonist approved for the treatment of OUD and chronic pain, may have potential as a novel therapeutic for MDD, especially for patients with a dual diagnosis of MDD and OUD. This paper presents a comprehensive review of papers relevant to the assessment of buprenorphine as a treatment for MDD, OUD, and/or suicide compiled using electronic databases per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The principal goal of this literature review was to compile the clinical studies that have interrogated the antidepressant activity of buprenorphine in opioid naïve MDD patients and OUD patients with comorbid MDD. Evidence supporting buprenorphine's superiority over methadone for treating comorbid OUD and MDD was also considered. Finally, recent evidence for the ability of buprenorphine to alleviate suicidal ideation in both opioid-naïve patients and opioid-experienced patients was evaluated. Synthesizing all of this information, buprenorphine emerges as a potentially effective therapeutic for the dual purposes of treating MDD and OUD.

Concomitant drugs with buprenorphine user deaths

BACKGROUND

Buprenorphine is abused in several countries notwithstanding its benefits as an analgesic and as an opioid agonist treatment medication. Benzodiazepines and alcohol have previously been associated with buprenorphine toxicity. This study elucidates the role of emerging concomitant drugs in different groups of buprenorphine user deaths.

METHODS

All cases in the Finnish national post-mortem toxicology database from 2016-2019 in which buprenorphine or norbuprenorphine was a laboratory finding in any post-mortem specimen and age at death of 15-64 years were investigated for cause and manner of death, concurrent drug and alcohol findings, age, and gender.

RESULTS

There were 792 deaths with a buprenorphine finding, of which buprenorphine was implicated in poisoning without other opioids in 271 cases (34 %). In this group of buprenorphine poisoning deaths, concomitant benzodiazepines were found in 94 % (clonazepam 53 %), illicit drugs in 63 %, gabapentinoids in 50 % (pregabalin 41 %), alcohol in 41 %, antidepressants in 32 %, and antipsychotics in 28 % of cases; only three deaths showed no benzodiazepines, alcohol, or gabapentinoids. Polydrug use was common regardless of the cause of death. In the age group 15 to 24 years, concomitant use of benzodiazepines and illicit drugs, and buprenorphine poisoning were more prevalent than in the age group 25-64 years.

CONCLUSIONS

The unprecedentedly high concomitant use of benzodiazepines in buprenorphine user deaths obscures other possible pharmacological risk factors for buprenorphine poisoning that could be relevant for prevention. Higher mortality in the younger age group suggests particularly unsafe drug use patterns that should be addressed.

Buprenorphine: prospective novel therapy for depression and PTSD

BACKGROUND

Depression and post-traumatic stress disorder (PTSD) are leading causes of disability and loss of life by suicide. Currently, there are less than satisfactory medical solutions to treat these mental disorders. Here, we explore recent preclinical and clinical studies demonstrating the potential of using buprenorphine to treat major depressive disorder, treatment-resistant depression, and PTSD.

METHOD

Bibliographic databases were searched to include preclinical and clinical studies demonstrating the therapeutic potential of buprenorphine and the involvement of the kappa opioid receptor (KOR) in mediating these effects.

RESULTS

Original clinical studies examining the effectiveness of buprenorphine to treat depression were mixed. The majority of participants in the PTSD studies were males and suffer from chronic pain and/or substance use disorders. Nonetheless, these recent studies and analyses established proof of concept warranting farther investigations. Additionally, KOR likely mediates the antidepressant and some of the anxiolytic effects of buprenorphine. Still, it appears that the full spectrum of buprenorphine's beneficial effects might be due to activity at other opioid receptors as well.

CONCLUSIONS

Pharmaceuticals' abilities to treat medical conditions directly relates to their ability to act upon the endogenous biological systems related to the conditions. Thus, these recent findings are likely a reflection of the central role that the endogenous opioid system has in these mental illnesses. Further studies are necessary to study the involvement of endogenous opioid systems, and specifically KOR, in mediating buprenorphine's beneficial effects and the ability to treat these medical conditions while minimizing risks for misuse and diversion.

Progress in agonist therapy for substance use disorders: Lessons learned from methadone and buprenorphine

Substance use disorders (SUD) are serious public health problems worldwide. Although significant progress has been made in understanding the neurobiology of drug reward and the transition to addiction, effective pharmacotherapies for SUD remain limited and a majority of drug users relapse even after a period of treatment. The United States Food and Drug Administration (FDA) has approved several medications for opioid, nicotine, and alcohol use disorders, whereas none are approved for the treatment of cocaine or other psychostimulant use disorders. The medications approved by the FDA for the treatment of SUD can be divided into two major classes - agonist replacement therapies, such as methadone and buprenorphine for opioid use disorders (OUD), nicotine replacement therapy (NRT) and varenicline for nicotine use disorders (NUD), and antagonist therapies, such as naloxone for opioid overdose and naltrexone for promoting abstinence. In the present review, we primarily focus on the pharmacological rationale of agonist replacement strategies in treatment of opioid dependence, and the potential translation of this rationale to new therapies for cocaine use disorders. We begin by describing the neural mechanisms underlying opioid reward, followed by preclinical and clinical findings supporting the utility of agonist therapies in the treatment of OUD. We then discuss recent progress of agonist therapies for cocaine use disorders based on lessons learned from methadone and buprenorphine. We contend that future studies should identify agonist pharmacotherapies that can facilitate abstinence in patients who are motivated to quit their illicit drug use. Focusing on those that are able to achieve abstinence from cocaine will provide a platform to broaden the effectiveness of medication and psychosocial treatment strategies for this underserved population. This article is part of the Special Issue entitled 'New Vistas in Opioid Pharmacology'.

Buprenorphine in the United States: Motives for abuse, misuse, and diversion

Opioid use disorder (OUD) and its consequences are a major public health concern. The partial agonist buprenorphine is a safe and effective treatment for OUD, but concerns about abuse, misuse, and diversion of buprenorphine have been raised. This narrative review examined the rates and motives for use of illicit buprenorphine in the United States. Findings from the 17 included studies suggest the majority of study participants using illicit buprenorphine do so for reasons related to misuse (to manage opioid withdrawal symptoms or achieve or maintain abstinence from other opioids). A smaller percentage of study respondents reported using buprenorphine for reasons related to abuse (to get high). There appears to be a gap between need for buprenorphine and access to adequate treatment. Attenuation of policy-related barriers and adoption of appropriate buprenorphine use by the treatment community are critical tools in the continued effort to reduce the burdens associated with OUD.

Why is buprenorphine coformulated with naloxone?

Combination buprenorphine-naloxone is a cornerstone of outpatient treatment for substance use disorder, and is more widely accessible in primary care. Because oral buprenorphine has been diverted and abused for its euphoric properties, a combination formulation was developed and will trigger withdrawal symptoms if injected IV.

Clinical models of decision making in addiction

As research on decision making in addiction accumulates, it is increasingly clear that decision-making processes are dysfunctional in addiction and that this dysfunction may be fundamental to the initiation and maintenance of addictive behavior. How drug-dependent individuals value and choose among drug and nondrug rewards is consistently different from non-dependent individuals. The present review focuses on the assessment of decision-making in addiction. We cover the common behavioral tasks that have shown to be fruitful in decision-making research and highlight analytical and graphical considerations, when available, to facilitate comparisons within and among studies. Delay discounting tasks, drug demand tasks, drug choice tasks, the Iowa Gambling Task, and the Balloon Analogue Risk Task are included.

The Abuse Potential of Prescription Opioids in Humans-Closing in on the First Century of Research

While opioids are very effective analgesics for treating acute pain, humans have struggled with opiate addiction for millenia. An opium abuse epidemic in the early 1900's led the US government to develop a systematic research infrastructure and scientific plan to produce new compounds with analgesic properties but without abuse liability. This review describes the techniques that were developed for testing in the human laboratory, including empirically derived outcome measures and required elements for human abuse potential assessment. The evaluation and characterization of semi-synthetic and synthetic opioids, including full mu opioid agonists, partial agonists and mixed agonist-antagonists, are described across several decades of research. Finally, the prescription opioid epidemic beginning in the 1990's in the US led to a resurgence in abuse potential evaluations, and the application of these methods to the study of novel abuse-deterrent formulations is discussed.

Buprenorphine Prescribing: To Expand or Not to Expand

As a result of the prescription opioid epidemic in the United States, there has been an increasing need for effective treatment interventions, both pharmacological and nonpharmacological. Buprenorphine has emerged as a critical component of the treatment of opioid use disorder, yet its adoption has not been without some concerns. This article first reviews the pharmacology, clinical use, and US legislative action related to buprenorphine, followed by a discussion of the misuse and diversion of buprenorphine in the United States as well as internationally. We then explore the impact of buprenorphine abuse as well as discussing strategies for its reduction, including changes in policy, prescription and pharmacy monitoring, and continuing medical education for guiding and improving clinical practice.

Buprenorphine and buprenorphine/naloxone diversion, misuse, and illicit use: an international review

The diversion, misuse, and non-medically supervised use of buprenorphine and buprenorphine/naloxone by opioid users are reviewed. Buprenorphine and buprenorphine/naloxone are used globally as opioid analgesics and in the treatment of opioid dependency. Diversion of buprenorphine and buprenorphine/naloxone represents a complex medical and social issue, and has been widely documented in various geographical regions throughout the world. We first discuss the clinical properties of buprenorphine and its abuse potential. Second, we discuss its diversion and illicit use on an international level, as well as motivations for those activities. Third, we examine the medical risks and benefits of buprenorphine's non-medically supervised use and misuse. These risks and benefits include the effect of buprenorphine's use on HIV risk and the risk of its concomitant use with other medications and drugs of abuse. Finally, we discuss the implications of diversion, misuse, and non-medically supervised use (including potential measures to address issues of diversion); and potential areas for further research.

Controversies in translational research: drug self-administration

RATIONALE

Laboratory animal and human models of drug self-administration are used to evaluate potential pharmacotherapies for drug abuse, yet the utility of these models in predicting clinically useful medications is variable.

OBJECTIVE

The objective of this study was to track how antagonist, agonist, and partial agonist medication approaches influence heroin and cocaine self-administration by rodents, non-human primates, and humans and to compare these results to clinical outcomes.

RESULTS

Across species, heroin self-administration was decreased by all three medication approaches, paralleling their demonstrated clinical utility. The heroin data emphasize the importance of assessing a medication's abuse liability preclinically to predict medication abuse and compliance and of considering subject characteristics (e.g., opioid dependence) when interpreting medication effects. For cocaine, the effects of ecopipam, modafinil, and aripiprazole were consistent in the laboratory and clinic, provided that the medications were administered repeatedly before self-administration sessions. Modafinil attenuated cocaine's reinforcing effects in the human laboratory and improved treatment outcome, while ecopipam and aripiprazole increased the reinforcing effects of cocaine and do not appear promising in the clinic.

CONCLUSIONS

The self-administration model has reliably identified medications to treat opioid dependence, and the recent data with modafinil suggest that the human laboratory model also identifies medications to treat cocaine dependence. There have been numerous false positives when subjective effects are the primary outcome measure, but not when self-administration is the outcome. Factors relevant to the predictive validity of self-administration procedures include medication maintenance and the concurrent assessment of a range of behaviors to determine abuse liability and the specificity of effect.

The role of human drug self-administration procedures in the development of medications

The purpose of this review is to illustrate the utility and value of employing human self-administration procedures in medication development, including abuse liability assessments of novel medications and evaluation of potential pharmacotherapies for substance use disorders. Traditionally, human abuse liability testing has relied primarily on subjective reports describing drug action by use of questionnaires; similarly, drug interactions between putative treatment agents and the drugs of abuse have relied on these measures. Subjective reports are highly valued because they provide qualitative and quantitative information about the characteristics of central and peripheral pharmacodynamic effects as well as safety and tolerability. However, self-administration procedures directly examine the behavior of interest-that is, drug taking. The present paper (1) reviews the most commonly used human self-administration procedures, (2) discusses the concordance of subjective reports and self-administration within the context of medications development for substance use disorders, focusing primarily on illustrative examples from development efforts with opioid and cocaine dependence, and (3) explores the utility of applying self-administration procedures to assess the abuse liability of novel compounds, including "abuse-deterrent" formulations (ADFs). The review will focus on opioid and cocaine dependence because a rich database from both clinical laboratory and clinical trial research exists for these two drug classes. The data reviewed suggest that drug-induced changes in self-administration and subjective effects are not always concordant. Therefore, assessment of self-administration in combination with subjective effects provides a more comprehensive picture that may have improved predictive validity for translating to the clinical setting.

Pharmacologic treatments for opioid dependence: detoxification and maintenance options

While opioid dependence has more treatment agents available than other abused drugs, none are curative. They can, however, markedly diminish withdrawal symptoms and craving, and block opioid effects due to lapses.

The most effective withdrawal method is substituting and tapering methadone or buprenorphine, α-2 Adrenergic agents can ameliorate untreated symptoms or substitute for agonists if not available. Shortening withdrawal by precipitating it with narcotic antagonists has been studied, but the methods are plagued by safety issues or persisting symptoms. Neither the withdrawal agents nor the methods are associated with better long-term outcome, which appears mostly related to post-detoxification treatment.

Excluding those with short-term habits, the best outcome occurs with long-term maintenance on methadone or buprenorphine accompanied by appropriate psychosocial interventions. Those with strong external motivation may do well on the antagonist naltrexone. Currently, optimum duration of maintenance on either is unclear. Better agents are needed to impact the brain changes related to addiction.

Abuse liability of prescription opioids compared to heroin in morphine-maintained heroin abusers

Abuse of prescription opioid medications has increased dramatically in the United States during the past decade, as indicated by a variety of epidemiological sources. However, few studies have systematically examined the relative reinforcing effects of commonly abused opioid medications. The current double-blind, placebo-controlled in-patient study was designed to compare the effects of intravenously delivered fentanyl (0, 0.0625, 0.125, 0.187, and 0.250 mg/70 kg), oxycodone (0, 6.25, 12.5, 25, and 50 mg/70 kg), morphine (0, 6.25, 12.5, 25, and 50 mg/70 kg), buprenorphine (0, 0.125, 0.5, 2, and 8 mg/70 kg), and heroin (0, 3.125, 6.25, 12.5, and 25 mg/70 kg) in morphine-maintained heroin abusers (N=8 completers maintained on 120 mg per day oral morphine in divided doses (30 mg q.i.d.)). All of the participants received all of the drugs tested; drugs and doses were administered in non-systematic order. All of the drugs produced statistically significant, dose-related increases in positive subjective ratings, such as 'I feel a good drug effect' and 'I like the drug.' In general, the order of potency in producing these effects, from most to least potent, was fentanyl>buprenorphine>or=heroin >morphine=oxycodone. In contrast, buprenorphine was the only drug that produced statistically significant increases in ratings of 'I feel a bad drug effect' and it was the only drug that was not self-administered above placebo levels at any dose tested. These data suggest that the abuse liability of buprenorphine in heroin-dependent individuals may be low, despite the fact that it produces increases in positive subjective ratings. The abuse liabilities of fentanyl, morphine, oxycodone, and heroin, however, appear to be similar under these experimental conditions.

Does high-dose buprenorphine cause respiratory depression?: possible mechanisms and therapeutic consequences

Buprenorphine is an opioid agonist-antagonist with a 'ceiling effect' for respiratory depression. Compared with methadone, its unique pharmacology offers practical advantages and enhanced safety when prescribed as recommended and supervised by a physician. Buprenorphine has been approved in several countries as an efficient and safe maintenance therapy for heroin addiction. Its use resulted in a salutary effect with a reduction in heroin overdose-related deaths in countries that implemented office-based buprenorphine maintenance. In France, however, where high-dose buprenorphine has been marketed since 1996, several cases of asphyxic deaths were reported among addicts treated with buprenorphine. Death resulted from buprenorphine intravenous misuse or concomitant sedative drug ingestion, such as benzodiazepines. In these situations of abuse, misuse, or in association with elevated doses of psychotropic drugs, buprenorphine may cause severe respiratory depression. Unlike other opiates, the respiratory effects from buprenorphine are not responsive to naloxone. However, the exact mechanism of buprenorphine-induced effects on ventilation is still unknown. The role of norbuprenorphine, the main N-dealkylated buprenorphine metabolite with potent respiratory depressor activity, also remains unclear. Experimental studies investigating the respiratory effects of combinations of high doses of buprenorphine and benzodiazepines suggested that this drug-drug interaction may result from a pharmacodynamic interaction. A pharmacokinetic interaction between buprenorphine and flunitrazepam is also considered. As there are many questions regarding the possible dangers of death or respiratory depression associated with buprenorphine use, we aimed to present a comprehensive critical review of the published clinical and experimental studies on buprenorphine respiratory effects.

Unlimited access to heroin self-administration: independent motivational markers of opiate dependence

The goal of the present study was to develop and validate an animal model of unlimited access to intravenous heroin self-administration combined with responding for food and water to characterize the transition to drug dependence. Male Wistar rats were allowed to lever press for heroin (60 microg/kg/0.1 ml infusion/s; fixed ratio 1; 20-s time out) and nosepoke for food and water in consecutive, daily 23-h sessions. Daily heroin intake increased over days, reaching significance by Day 14. Drug-taking increased across the circadian cycle, reflected as increases in both the nocturnal peak and diurnal nadir of heroin intake. Changes in the circadian pattern of food intake and meal patterning preceded and paralleled the changes in heroin intake. By Day 7, the circadian amplitude of feeding was blunted. Nocturnal intake decreased because rats consumed smaller and briefer meals. Diurnal intake increased due to increased meal frequency, whereas total daily food intake decreased. To control for time or experience in the self-administration boxes as a possible confound, rats with saline (no drug) tethers were tested and did not display significant changes in food intake pattern. Body weight gain slowed slightly in heroin rats relative to saline controls. Separate groups of rats revealed that significant physical dependence as measured by physical signs of opiate withdrawal following a naloxone injection (1.0 mg/kg, subcutaneous (s.c.)) was reached by Day 14. Significant increases in heroin intake could be produced using low doses of naloxone (0.003-0.03 mg/kg, s.c.) on days 28-31 of heroin access. After 6 weeks of heroin self-administration, rats injected with buprenorphine (0, 0.01, 0.04, and 0.2 mg/kg, s.c.) showed a dose-dependent reduction in heroin intake. Changes in the pattern of drug and food intake in the present unlimited heroin access model may serve as independent motivational markers for the transition to a drug-dependent state.

Critical assessment of how to study addiction and its treatment: human and non-human animal models

Laboratory models, both animal and human, have made enormous contributions to our understanding of addiction. For addictive disorders, animal models have the great advantage of possessing both face validity and a significant degree of predictive validity, already demonstrated. Another important advantage to this field is the ability of reciprocal interplay between preclinical and clinical experiments. These models have made important contributions to the development of medications to treat addictive disorders and will likely result in even more advances in the future. Human laboratory models have gone beyond data obtained from patient histories and enabled investigators to make direct observations of human drug self-administration and test the effects of putative medications on this behavior. This review examines in detail some animal and human models that have led not only to important theories of addiction mechanisms but also to medications shown to be effective in the clinic.

Comparison of intravenous buprenorphine and methadone self-administration by recently detoxified heroin-dependent individuals

Although buprenorphine is used worldwide as a safe and effective maintenance medication for opioid dependence, some countries have reported a growing incidence of abuse of this medication. Buprenorphine is considered to have lower abuse potential because of its partial agonist profile, but no studies have directly compared the reinforcing effects of buprenorphine with those of full mu opioid agonists in humans. The present double-blind, placebo-controlled inpatient study compared the reinforcing and subjective effects of intravenously administered buprenorphine (0.5, 2, and 8 mg) and methadone (5, 10, and 20 mg). Participants (n = 6) were detoxified from heroin during the first 1 to 2 weeks after admission. During subsequent weeks, participants received a sample drug dose and $20 on Monday, and they could self-administer either the sampled dose or $20 during one choice session per day on Thursday and Friday. Participants responded under a modified progressive ratio schedule during each choice session. All active doses maintained higher progressive ratio break points (largest completed ratio) than placebo. There were no significant differences in break point values between buprenorphine and methadone or among the different doses of drug. However, several subjective ratings, including "good drug effect", "high", and "liking" dose-dependently increased after administration of buprenorphine and methadone. The peak ratings for these effects did not significantly differ for the two drugs. These results demonstrate that under these experimental conditions, buprenorphine and methadone were equally effective in producing reinforcing and subjective effects.

Bringing buprenorphine-naloxone detoxification to community treatment providers: the NIDA Clinical Trials Network field experience

In October 2002, the U.S. Food and Drug Administration approved buprenorphine-naloxone (Suboxone) sublingual tablets as an opioid dependence treatment available for use outside traditionally licensed opioid treatment programs. The NIDA Center for Clinical Trials Network (CTN) sponsored two clinical trials assessing buprenorphine-naloxone for short-term opioid detoxification. These trials provided an unprecedented field test of its use in twelve diverse community-based treatment programs. Opioid-dependent men and women were randomized to a thirteen-day buprenorphine-naloxone taper regimen for short-term opioid detoxification. The 234 buprenorphine-naloxone patients averaged 37 years old and used mostly intravenous heroin. Direct and rapid induction onto buprenorphine-naloxone was safe and well tolerated. Most patients (83%) received 8 mg buprenorphine-2 mg naloxone on the first day and 90% successfully completed induction and reached a target dose of 16 mg buprenorphine-4 mg naloxone in three days. Medication compliance and treatment engagement was high. An average of 81% of available doses was ingested, and 68% of patients completed the detoxification. Most (80.3%) patients received some ancillary medications with an average of 2.3 withdrawal symptoms treated. The safety profile of buprenorphine-naloxone was excellent. Of eighteen serious adverse events reported, only one was possibly related to buprenorphine-naloxone. All providers successfully integrated buprenorphine-naloxone into their existing treatment milieus. Overall, data from the CTN field experience suggest that buprenorphine-naloxone is practical and safe for use in diverse community treatment settings, including those with minimal experience providing opioid-based pharmacotherapy and/or medical detoxification for opioid dependence.

Buprenorphine antinociception is abolished, but naloxone-sensitive reward is retained, in mu-opioid receptor knockout mice

Buprenorphine is a relatively nonselective opioid receptor partial agonist that is used in the management of both pain and addiction. To improve understanding of the opioid receptor subtypes important for buprenorphine effects, we now report the results of our investigation on the roles of mu-, delta-, and kappa-opioid receptors in antinociceptive responses and place preferences induced by buprenorphine. Buprenorphine antinociception, assessed by hot-plate and tail-flick tests, was significantly reduced in heterozygous mu-opioid receptor knockout (MOR-KO) mice and abolished in homozygous MOR-KO mice. In contrast, buprenorphine retained its ability to establish a conditioned place preference (CPP) in homozygous MOR-KO, although the magnitude of place preference was reduced as the number of copies of wild-type mu-opioid receptor genes was reduced. The remaining CPP of buprenorphine was abolished by pretreatment with the nonselective opioid antagonist naloxone, but only partially blocked by pretreatment with either the delta-selective opioid antagonist naltrindole or the kappa-selective opioid antagonist norbinaltorphimine. These data, and biochemical confirmation of buprenorphine actions as a partial delta-, mu-, and kappa-agonist, support the ideas that mu-opioid receptors mediate most of analgesic properties of buprenorphine, but that mu- and delta- and/or kappa-opioid receptors are each involved in the rewarding effects of this drug.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Office-based treatment of opiate addiction with a sublingual-tablet formulation of buprenorphine and naloxone

BACKGROUND

Office-based treatment of opiate addiction with a sublingual-tablet formulation of buprenorphine and naloxone has been proposed, but its efficacy and safety have not been well studied.

METHODS

We conducted a multicenter, randomized, placebo-controlled trial involving 326 opiate-addicted persons who were assigned to office-based treatment with sublingual tablets consisting of buprenorphine (16 mg) in combination with naloxone (4 mg), buprenorphine alone (16 mg), or placebo given daily for four weeks. The primary outcome measures were the percentage of urine samples negative for opiates and the subjects' self-reported craving for opiates. Safety data were obtained on 461 opiate-addicted persons who participated in an open-label study of buprenorphine and naloxone (at daily doses of up to 24 mg and 6 mg, respectively) and another 11 persons who received this combination only during the trial.

RESULTS

The double-blind trial was terminated early because buprenorphine and naloxone in combination and buprenorphine alone were found to have greater efficacy than placebo. The proportion of urine samples that were negative for opiates was greater in the combined-treatment and buprenorphine groups (17.8 percent and 20.7 percent, respectively) than in the placebo group (5.8 percent, P<0.001 for both comparisons); the active-treatment groups also reported less opiate craving (P<0.001 for both comparisons with placebo). Rates of adverse events were similar in the active-treatment and placebo groups. During the open-label phase, the percentage of urine samples negative for opiates ranged from 35.2 percent to 67.4 percent. Results from the open-label follow-up study indicated that the combined treatment was safe and well tolerated.

CONCLUSIONS

Buprenorphine and naloxone in combination and buprenorphine alone are safe and reduce the use of opiates and the craving for opiates among opiate-addicted persons who receive these medications in an office-based setting.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Self-administration of intravenous buprenorphine and the buprenorphine/naloxone combination by recently detoxified heroin abusers

Buprenorphine is a partial mu-opioid agonist and kappa-opioid antagonist currently under development as a maintenance medication for heroin dependence. Because of concerns about illicit diversion of buprenorphine, a combination tablet containing buprenorphine and naloxone has been developed. The present study evaluated the reinforcing effects of intravenously administered placebo, buprenorphine alone (BUP; 2 and 8 mg), and the buprenorphine/naloxone combination (BUP/NX; 2 mg of buprenorphine plus 0.5 mg of naloxone, and 8 mg of buprenorphine plus 2 mg of naloxone) in recently detoxified heroin abusers during a 6-week inpatient study. Participants (n = 6) were detoxified from heroin over approximately 1 week immediately after admission. During the next 5 weeks, the reinforcing effects of placebo, BUP, and BUP/NX were evaluated. Participants first received a dose of drug and $20 and then were given the opportunity to self-administer either the dose or $20 during choice sessions. Progressive ratio break point values were significantly higher after active drug, compared with placebo, but they did not significantly differ as a function of dose or drug. In contrast, positive subjective ratings were higher after administration of BUP compared with BUP/NX, and these ratings increased in a dose-dependent manner. BUP and the combination had few effects on performance. Relative to placebo, both BUP and BUP/NX decreased pupil diameter, but there were no significant differences in pupil diameter as a function of drug or dose. These results demonstrate that both BUP and BUP/NX served as reinforcers under these conditions and that they may have similar abuse liability in recently detoxified individuals who abuse heroin.