Naltrexone treatment of heroin addiction: one-year follow-up

Selective review and commentary on emerging pharmacotherapies for opioid addiction

Pharmacotherapies for opioid addiction under active development in the US include lofexidine (primarily for managing withdrawal symptoms) and Probuphine®, a distinctive mode of delivering buprenorphine for six months, thus relieving patients, clinicians, and regulatory personnel from most concerns about diversion, misuse, and unintended exposure in children. In addition, two recently approved formulations of previously proven medications are in early phases of implementation. The sublingual film form of buprenorphine + naloxone (Suboxone®) provides a less divertible, more quickly administered, more child-proof version than the buprenorphine + naloxone sublingual tablet. The injectable depot form of naltrexone (Vivitrol®) ensures consistent opioid receptor blockade for one month between administrations, removing concerns about medication compliance. The clinical implications of these developments have attracted increasing attention from clinicians and policymakers in the US and around the world, especially given that human immunodeficiency virus/acquired immunodeficiency syndrome and other infectious diseases are recognized as companions to opioid addiction, commanding more efforts to reduce opioid addiction. While research and practice improvement efforts continue, reluctance to adopt new medications and procedures can be expected, especially considerations in the regulatory process and in the course of implementation. Best practices and improved outcomes will ultimately emerge from continued development efforts that reflect input from many quarters.

Can the chronic administration of the combination of buprenorphine and naloxone block dopaminergic activity causing anti-reward and relapse potential?

Opiate addiction is associated with many adverse health and social harms, fatal overdose, infectious disease transmission, elevated health care costs, public disorder, and crime. Although community-based addiction treatment programs continue to reduce the harms of opiate addiction with narcotic substitution therapy such as methadone maintenance, there remains a need to find a substance that not only blocks opiate-type receptors (mu, delta, etc.) but also provides agonistic activity; hence, the impetus arose for the development of a combination of narcotic antagonism and mu receptor agonist therapy. After three decades of extensive research, the federal Drug Abuse Treatment Act 2000 (DATA) opened a window of opportunity for patients with addiction disorders by providing increased access to options for treatment. DATA allows physicians who complete a brief specialty-training course to become certified to prescribe buprenorphine and buprenorphine/naloxone (Subutex, Suboxone) for treatment of patients with opioid dependence. Clinical studies indicate that buprenorphine maintenance is as effective as methadone maintenance in retaining patients in substance abuse treatment and in reducing illicit opioid use. With that stated, we must consider the long-term benefits or potential toxicity attributed to Subutex or Suboxone. We describe a mechanism whereby chronic blockade of opiate receptors, in spite of only partial opiate agonist action, may ultimately block dopaminergic activity causing anti-reward and relapse potential. While the direct comparison is not as yet available, toxicity to buprenorphine can be found in the scientific literature. In considering our cautionary note in this commentary, we are cognizant that, to date, this is what we have available, and until such a time when the real magic bullet is discovered, we will have to endure. However, more than anything else this commentary should at least encourage the development of thoughtful new strategies to target the specific brain regions responsible for relapse prevention.

Oral naltrexone maintenance treatment for opioid dependence

BACKGROUND

Research on clinical application of oral naltrexone agrees on several things. From a pharmacological perspective, naltrexone works. From an applied perspective, the medication compliance and the retention rates are poor.

OBJECTIVES

To evaluate the effects of naltrexone maintenance treatment versus placebo or other treatments in preventing relapse in opioid addicts after detoxification.

SEARCH STRATEGY

We searched: Cochrane Central Register of Controlled Trials (CENTRAL - The Cochrane Library issue 6 2010), PubMed (1973- June 2010), CINAHL (1982- June 2010). We inspected reference lists of relevant articles and contacted pharmaceutical producers of naltrexone, authors and other Cochrane review groups.

SELECTION CRITERIA

All randomised controlled clinical trials which focus on the use of naltrexone maintenance treatment versus placebo, or other treatments to reach sustained abstinence from opiate drugs

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed studies for inclusion and extracted data. One reviewer carried out the qualitative assessments of the methodology of eligible studies using validated checklists.

MAIN RESULTS

Thirteen studies, 1158 participants, met the criteria for inclusion in this review.Comparing naltrexone versus placebo or no pharmacological treatments, no statistically significant difference were noted for all the primary outcomes considered. The only outcome statistically significant in favour of naltrexone is re incarceration, RR 0.47 (95%CI 0.26-0.84), but results come only from two studies. Considering only studies were patients were forced to adherence a statistical significant difference in favour of naltrexone was found for retention and abstinence, RR 2.93 (95%CI 1.66-5.18).Comparing naltrexone versus psychotherapy, in the two considered outcomes, no statistically significant difference was found in the single study considered.Naltrexone was not superior to benzodiazepines and to buprenorphine for retention and abstinence and side effects. Results come from single studies.

AUTHORS' CONCLUSIONS

The findings of this review suggest that oral naltrexone did not perform better than treatment with placebo or no pharmacological agent with respect to the number of participants re-incarcerated during the study period. If oral naltrexone is compared with other pharmacological treatments such as benzodiazepine and buprenorphine, no statistically significant difference was found. The percentage of people retained in treatment in the included studies is however low (28%). The conclusion of this review is that the studies conducted have not allowed an adequate evaluation of oral naltrexone treatment in the field of opioid dependence. Consequently, maintenance therapy with naltrexone cannot yet be considered a treatment which has been scientifically proved to be superior to other kinds of treatment.

Oral naltrexone maintenance treatment for opioid dependence

BACKGROUND

Research on the clinical application of oral naltrexone agrees on several things. From a pharmacological perspective, naltrexone works. From an applied perspective, however, the medication compliance and the retention rates are very poor.

OBJECTIVES

To evaluate the effects of naltrexone maintenance treatment versus placebo or other treatments in preventing relapse in opioid addicts after detoxification.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL - The Cochrane Library issue 6 2010), PubMed (1973- June 2010), CINAHL (1982- June 2010). We inspected reference lists of relevant articles and we contacted pharmaceutical producers of naltrexone, authors and other Cochrane review groups.

SELECTION CRITERIA

All randomised and controlled clinical trials which focus on the use of naltrexone maintenance treatment versus placebo, or other treatments to reach sustained abstinence from opiate drugs

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed studies for inclusion and extracted data. One reviewer carried out the qualitative assessments of the methodology of eligible studies using validated checklists.

MAIN RESULTS

Thirteen studies, 1158 participants, met the criteria for inclusion in this review.Comparing naltrexone versus placebo or no pharmacological treatments, no statistically significant difference were noted for all the primary outcomes considered. The only outcome statistically significant in favour of naltrexone is re incarceration, RR 0.47 (95%CI 0.26-0.84), but results come only from two studies.Comparing naltrexone versus psychotherapy, in the two considered outcomes, no statistically significant difference was found in the single study considered.Naltrexone was not superior to benzodiazepines and to buprenorphine for retention and abstinence and side effects. Results come from single studies.

AUTHORS' CONCLUSIONS

The findings of this review suggest that oral naltrexone did not perform better than treatment with placebo or no pharmacological agent with respect to the number of participants re-incarcerated during the study period. If oral naltrexone is compared with other pharmacological treatments such as benzodiazepine and buprenorphine, no statistically significant difference was found. The percentage of people retained in treatment in the included studies is however low (28%). The conclusion of this review is that the studies conducted have not allowed an adequate evaluation of oral naltrexone treatment in the field of opioid dependence. Consequently, maintenance therapy with naltrexone cannot yet be considered a treatment which has been scientifically proved to be superior to other kinds of treatment.

A randomized trial of oral naltrexone for treating opioid-dependent offenders

Offenders with a history of opioid dependence are a particularly difficult group to treat. A large proportion of offenders typically relapse shortly after release from prison, commit drug-related crimes, and then are arrested and eventually re-incarcerated. Previous research demonstrated that oral naltrexone was effective in reducing opioid use and preventing recidivism among offenders under federal supervision. The 111 opioid-dependent offenders in this study were under various levels of supervision that included county and federal probation/parole, a treatment court, an alternative disposition program, and an intermediate punishment program. Subjects were randomly assigned to receive 6 months of either 300 mg per week of oral naltrexone plus standard psychosocial treatment as usual (n = 56) or standard psychosocial treatment as usual (TAU) without naltrexone (n = 55). While the TAU subjects who remained in treatment used more opioids than the naltrexone subjects who remained, the high dropout rate for both groups made it difficult to assess the effectiveness of naltrexone. The study provides limited support for the use of oral naltrexone for offenders who are not closely monitored by the criminal justice system.

Pharmacological options for management of opioid dependence

Methadone is currently the only opioid available for the pharmacotherapy of opioid dependence. Cross-tolerance between methadone and other opioids constitutes the pharmacological basis for substitution and attenuating the effects of illicit opioid use. However, these principles limit the utility of methadone. Potential alternative opioids include long-acting partial agonists such as buprenorphine and pure antagonists such as naltrexone. Buprenorphine is an alternative to methadone with intermediate intrinsic efficacy. It has a large margin of safety, yet displays some agonist actions similar to methadone. It has greater potential than methadone to safely and effectively block the actions of illicit opioids. Naltrexone is a safe, convenient opioid-antagonist for use following detoxification from opioid agonists. Its main use is to block the actions of other opioids, thereby attenuating or eliminating illicit use during treatment. However, it is poorly accepted by many clients, limiting its application to a sub-group who are highly motivated to detoxify. The distinct pharmacological properties of these opioids can overcome some of the drawbacks of methadone, but other limitations may emerge. Non-opioid adjuncts such as alpha2-adrenoceptor agonists can also have a role during detoxification. These drugs might be of use for specific groups of opioid users, providing therapists with the flexibility to tailor pharmacotherapy to the individual needs of clients.

A 50-year-old woman addicted to heroin: review of treatment of heroin addiction

Heroin addiction is a complicated medical and psychiatric issue, with well-established as well as newer modes of treatment. The case of Ms W, a 50-year-old woman with a long history of opiate addiction who has been treated successfully with methadone for 9 years and who now would like to consider newer alternatives, illustrates the complex issues of heroin addiction. The treatment of heroin addiction as a chronic disease is reviewed, including social, medical, and cultural issues and pharmacologic treatment with methadone and the more experimental medication options of buprenorphine and naltrexone.

Opiate addiction in China: current situation and treatments

BACKGROUND

Historically, China has had extraordinarily high rates of opiate dependence. These rates declined drastically following the 1949 revolution; however, opiate abuse has re-emerged in the late 1980's and has spread quickly since then.

AIMS

To describe the current situation of opiate addiction and treatments in China and make some suggestions.

DESIGN

A descriptive study based on literature searched from Medline and the China National Knowledge Infrastructure database (1996 to 2004) and hand-picked references.

FINDINGS

The number of registered addicts in 2004 was 1.14 million (more than 75% of them heroin addicts), but the actual number is probably far higher. Opiate abuse contributes substantially to the spread of HIV/AIDS in China, with intravenous drug use the most prevalent route of transmission (51.2%). Currently, the main treatments for opiate dependence in China include short-term detoxification with opiate agonists or non-opiate agents, such as clonidine or lofexidine; Chinese herbal medicine and traditional non-medication treatments are also used. Methadone maintenance treatment (MMT) has not been officially approved by the Chinese government for widespread implementation, but some pilot studies are currently underway.

CONCLUSION

China faces substantial drug abuse problems that appear to be worsening with time. Opiate dependence is a major threat to the public health and social security of China because of its devastating medical effects, its impact on risk for HIV/AIDS and criminal behaviors, low rates of recovery and high rates of relapse. There is an urgent need to implement MMT and other modern treatments for opiate dependence more widely in China.

Oral naltrexone maintenance treatment for opioid dependence

BACKGROUND

Research on the clinical application of oral naltrexone agrees on several things. From a pharmacological perspective, naltrexone works. From an applied perspective, however, this medication is not used since the medication compliance and the retention rates are very poor.

OBJECTIVES

To evaluate the effects of naltrexone maintenance treatment versus placebo or other treatments in preventing relapse in opioid addicts after detoxification.

SEARCH STRATEGY

We searched the Cochrane Drugs and Alcohol Group Register of Trials (January 2005), Cochrane Central Register of Controlled Trials (CENTRAL - The Cochrane Library Issue 1, 2005), MEDLINE (1973-first year of naltrexone use in humans- January 2005), EMBASE (1974- January 2005), PsycINFO (OVID-January 1985 to January 2004). We inspected reference lists of relevant articles and we contacted pharmaceutical producers of naltrexone, authors and other Cochrane review groups.

SELECTION CRITERIA

All randomised and controlled clinical trials which focus on the use of naltrexone maintenance treatment versus placebo, or other treatments to reach sustained abstinence from opiate drugs

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed studies for inclusion and extracted data. One reviewer carried out the qualitative assessments of the methodology of eligible studies using validated checklists.

MAIN RESULTS

Ten studies, 696 participants, met the criteria for inclusion in this review. Only two studies described an adequate allocation concealment. The results show that naltrexone maintenance therapy alone or associated with psychosocial therapy is more efficacious that placebo alone or associated with psychosocial therapy in limiting the use of heroin during the treatment (RR 0,72 95% confidence interval 0.58 to 0.90). If we consider only the studies comparing naltrexone with placebo, the difference do not reach the statistical significancy, RR 0.79 (95%CI 0.59 to 1.06). With respect to the number of participants re incarcerated during the study period, the naltrexone associated with psychosocial therapy is more effective than the psychosocial treatment alone; RR 0.50 (95%CI 0.27 to 0.91). No statistically significant benefit was shown in terms of retention in treatment, side effects or relapse results at follow-up for any of the considered comparisons.

AUTHORS' CONCLUSIONS

Unfortunately the studies did not provide an objective evaluation of naltrexone treatment in the field of opioid dependence. The conclusions are also limited due to the heterogeneity of the trials both in the interventions and in the assessment of outcomes.

Plasma concentrations during naltrexone implant treatment of opiate-dependent patients

AIMS

To evaluate individual variations in plasma concentrations over time in patients with naltrexone implants.

METHODS

Ten opioid-dependent patients received up to four implants. Plasma samples were collected regularly for the analyses of naltrexone and the metabolite beta-naltrexol.

RESULTS

The median naltrexone C(max) was 12.3 (range 5.8-22.1) ng ml(-1), the median T(max) was 1 day (range 3 h to 35 days), and the median length of time that plasma concentrations were above 1 ng ml(-1) was 55 (range 30-80) days. Two patients reported heroin use without experiencing any effect. Tissue reactions were recorded in two patients after repeated implantation.

CONCLUSION

Marked individual and intraindividual variations in naltrexone concentrations were observed. Further studies should be performed to evaluate the need for therapeutic drug monitoring during naltrexone implant treatment.

The development and application of a rapid gas chromatography-mass spectrometry method to monitor buprenorphine withdrawal protocols

There are several drug therapies that can be used to treat opiate abuse. One such treatment that is currently gaining wide acceptance is the use of the combined agonist/antagonist drug buprenorphine. As with all long-term treatments, there is a potential for compliance issues to arise, which establishes the need for a technique to facilitate the monitoring of individuals prescribed buprenorphine. One such method has been developed and applied to the routine monitoring of buprenorphine and its primary metabolite in urine. The method was found to be sensitive (limits of detection of 1.0 ng/mL for both buprenorphine and norbuprenorphine), reproducible and linear up to 2000 ng/mL. This article describes the application of this method to the analysis of specimens collected from subjects prescribed a reducing low-dose buprenorphine regimen (10.0-0.4 mg per day) for acute opiate detoxification. A significant relationship between the daily dose and the mean creatinine-corrected concentration of buprenorphine in the urine was observed, together with a relatively stable relationship between the ratio of the urinary concentrations of norbuprenorphine to buprenorphine across the dose range studied.

Characteristics, retention and readmissions of opioid-dependent clients treated with oral naltrexone

The aims of this study were to examine the retention rates of opioid-dependent clients treated with oral naltrexone and identify factors that influence retention in treatment of 981 opioid-dependent clients at a public out-patient clinic in Perth, Western Australia. The average retention period for all clients was 9.0 weeks. The factors associated with longer retention were being employed and referral source. Clients who were employed stayed significantly longer in treatment than unemployed clients. Clients referred from a private clinic were retained in treatment significantly longer than those referred from other sources (X = 10.3 vs. 5.9 weeks). While the majority (80.8%) had one admission to naltrexone treatment, 19.2% presented for readmission, some on three or more occasions in the study period. The median period between the end of the first episode of treatment and commencement of the second was 15.6 weeks. The median period between the end of the second episode of treatment and commencement of the third was 11.4 weeks. Those employed had a higher probability of being retained longer in treatment than those who were unemployed in subsequent treatment episodes. Clinicians should expect that initial retention in naltrexone is likely to be relatively short, and that a substantial proportion of clients will represent for further treatment.

A systematic review on the efficacy of naltrexone maintenance treatment in opioid dependence

AIM

To evaluate the efficacy of naltrexone maintenance treatment in preventing relapse in opioid addicts after detoxification.

DESIGN

A systematic review according to the methodology developed by the Cochrane Collaboration based on either randomized controlled trials (RCTs) or controlled clinical trials (CCTs).

PARTICIPANTS

Seven hundred and seven heroin dependent in- and out-patients, or former heroin addicts dependent on methadone and participating in a naltrexone treatment programme; 89% were male.

INTERVENTION

Maintenance treatments on opiate dependent people after detoxification, comparing naltrexone with placebo, pharmacological or behavioural treatments.

MEASUREMENTS

The outcomes considered were successfully completed treatment, opioid use under treatment (re)-incarcerations during the study period, mean duration of treatment.

FINDINGS

The outcomes tended to be slightly although not significantly in favour of the naltrexone groups. Use of naltrexone in addition to behavioural treatment significantly decreased the probability of (re-)incarceration (OR=0.30; 95% CI 0.12, 0.76). The difficulties in producing a quantitative analysis were due mainly to the heterogeneity of the included studies.

CONCLUSIONS

From the available clinical trials performed up to this time, there is insufficient evidence to justify the use of naltrexone in maintenance treatment of opioid addicts.

Naltrexone maintenance treatment for opioid dependence

BACKGROUND

Despite widespread use of naltrexone maintenance in many countries for more than a decade, the evidence of its effects has not yet been systematically evaluated.

OBJECTIVES

To evaluate the effects of naltrexone maintenance treatment in preventing relapse in opioid addicts after detoxification.

SEARCH STRATEGY

We searched MEDLINE (1973-first year of naltrexone use in humans-July 2000), EMBASE (1974-July 2000), Cochrane Controlled Trials Register (Cochrane Library issue 2001.4) and handsearched the "Bolletino per le Farmacodipendenze e l'Alcolismo" (1978 to 1997) and reference lists of relevant articles. We contacted pharmaceutical producers of naltrexone, authors and other Cochrane review groups. Date of most recent searches: December 2001.

SELECTION CRITERIA

All controlled studies of naltrexone; treatment of heroin addicts after detoxification.

DATA COLLECTION AND ANALYSIS

Reviewers evaluated data independently and analysed outcome measures taking into consideration adherence to and success of the study intervention. Data were extracted and analysed stratifying for the three categories of study quality. Where possible, meta-analysis was performed.

MAIN RESULTS

Eleven studies met the criteria for inclusion in this review, even if not all of them were randomised. The methodological quality of the included studies varied, but was generally poor. Meta-analysis could be performed to a very low degree only, because the studies and their outcome measures were very heterogeneous. A statistically significant reduction of (re-)incarcerations was found for patients treated with naltrexone and behaviour therapy in respect to those treated with behaviour therapy only. The other outcomes considered in the meta-analysis did not yield any significant results. Final conclusions on whether naltrexone treatment may be considered effective in maintenance therapy cannot be drawn from the clinical trials available so far.

REVIEWER'S CONCLUSIONS

The available trials do not allow a final evaluation of naltrexone maintenance treatment yet. A trend in favour of treatment with naltrexone was observed for certain target groups (particularly people who are highly motivated), as has been previously described in the literature.

Naltrexone pharmacotherapy for opioid dependent federal probationers

Federal probationers or parolees with a history of opioid addiction were referred by themselves or their probation/parole officer for a naltrexone treatment study. Participation was voluntary and subjects could drop out of the study at any time without adverse consequences. Following orientation and informed consent, 51 volunteers were randomly assigned in a 2:1 ratio to a 6-month program of probation plus naltrexone and brief drug counseling, or probation plus counseling alone. Naltrexone subjects received medication and counseling twice a week; controls received counseling at similar intervals. All therapy and medication were administered in an office located adjacent to the federal probation department. Fifty-two percent of subjects in the naltrexone group continued for 6 months and 33% remained in the control group. Opioid use was significantly lower in the naltrexone group. The overall mean percent of opioid positive urine tests among the naltrexone subjects was 8%, versus 30% for control subjects (p < .05). Fifty-six percent of the controls and 26% of the naltrexone group (p < .05) had their probation status revoked within the 6-month study period and returned to prison. Treatment with naltrexone and brief drug counseling can be integrated into the Federal Probation/Parole system with favorable results on both opioid use and re-arrest rates.

Compliance to naltrexone treatment after ultra-rapid opiate detoxification: an open label naturalistic study

Studies have found that naltrexone, a long-acting opiate antagonist, owing to poor patient compliance, is of limited value in preventing relapse. The current study investigates compliance with a 9-month course of naltrexone (25-50 mg daily) given with counseling after ultra-rapid opiate detoxification which uses clonidine and naltrexone under general anesthesia. Eighty-three of 113 randomly selected patients (out of 640), who were detoxified more than 1 year prior (average 1.5 years), responded to phone interviews. Phone questionnaire asked about patients' compliance with naltrexone, counseling and drug use since detoxification. Similar interviews were also conducted with patients' significant other. Non-relapse patients (n = 47, 57%) took naltrexone an average of 2 months longer than did relapse patients (n = 36, 43%). About half of the non-relapse patients completed at least 5 months of naltrexone, 30% completed at least 7 months and about 20% completed 9 months. Fifty-five percent of the relapse patients stopped using naltrexone by the end of the 3rd month, and by the end of 7th month 10% continued to take it. After the first 2 months the decline in naltrexone compliance was about the same for relapse and non-relapse patients. These results are more encouraging about the use of naltrexone for relapse prevention than previous studies. This method of using naltrexone should be further tested in prospective random assignment controlled studies.

Pharmacologic interventions for the treatment of opioid dependence and withdrawal

This article discusses current pharmacologic methods in the treatment of heroin dependence and withdrawal. Methadone hydrochloride, the most commonly used opiate agonist, is used for both withdrawal and maintenance therapy. However, it produces dependence and withdrawal results upon abrupt discontinuation. Other opiate agonists including L-alpha acetyl methadyl (LAAM) and propoxyphene napsylate have been used for both withdrawal and maintenance therapy. LAAM is currently available only as an investigational agent and propoxyphene is easily accessible but has been associated with hallucinations and dysphoria at high doses. Alpha 2-adrenergic agonists decrease opiate withdrawal symptoms by decreasing the central adrenergic hyperarousal that is associated with withdrawal. Clonidine effectively attenuates but does not totally eliminate withdrawal symptoms. Other alpha 2-adrenergic agonists (e.g., lofexidine hydrochloride, guanfacine hydrochloride, and guanabenz) have undergone only preliminary investigations. Although alpha 2 agonists effectively decrease most withdrawal symptoms they often cause hypotension. Buprenorphine hydrochloride is a partial opiate agonist that shows some promise in the treatment of the heroin-dependent population. It attenuates opiate craving and causes only minimal withdrawal upon abrupt discontinuation. Because it is well accepted by the heroin-dependent population, however, it may ultimately become an abused substance. Naltrexone is a potent, orally acting opiate antagonist that blocks all opiate-agonist effects and causes no euphoria. Unfortunately, it has not been well accepted by the heroin-dependent population. Scant research has been conducted concerning the use of adjunctive medications during opioid withdrawal.

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

Naltrexone is a long acting competitive antagonist at opioid receptors which blocks the subjective and objective responses produced by intravenous opioid challenge. It is suitable for oral administration, and has been studied as an adjunct for use in opioid addiction management programmes. In non-comparative clinical trials involving detoxified patients, oral naltrexone reduced heroin craving and between 23 and 62% of patients remained in treatment after 3 to 4 weeks. However, in two studies 32 to 58% of patients who continued in treatment were opioid-free between 6 and 12 months after stopping naltrexone. As might be expected studies involving highly motivated patients have shown this type of patient group to achieve greater treatment success rates during naltrexone therapy, and remain opioid-free longer than other groups of apparently less motivated patients. In addition, when naltrexone is combined with family support, psychotherapy and counselling, patients are more likely to remain opioid-free. Naltrexone produces a low incidence of side effects, with gastrointestinal effects being the most commonly reported symptoms. Thus, despite the overall high attrition rates from trials, in selected patient groups and in combination with appropriate support mechanisms and psychotherapy, naltrexone represents a useful adjunct for the maintenance of abstinence in the detoxified opioid addict.

Chronic naltrexone supersensitizes the reinforcing and locomotor-activating effects of morphine

Rats were implanted for 10 days with a slow-release naltrexone pellet and then the pellet was removed. Sham-control animals were treated similarly, except no pellet was implanted. One day after pellet removal or sham treatment, animals were assessed for morphine-induced conditioned place preference (CPP) or locomotor activity. CPP was evident in sham animals following two conditioning trials using 5 mg/kg subcutaneous morphine (Experiment 1) and following one conditioning trial using 8 mg/kg intravenous morphine (Experiment 2). Animals conditioned while implanted with a naltrexone pellet showed no morphine-induced CPP. More important, one day after pellet removal, naltrexone-pretreated animals given one conditioning trial with 5 mg/kg intravenous morphine displayed a greater preference for morphine-associated cues relative to sham animals given morphine (Experiment 3 and 4). This single IV morphine dose was insufficient to produce CPP in sham animals, suggesting that naltrexone-induced supersensitization may only be evident at a morphine dose below the reinforcing threshold in control animals. Further, chronic naltrexone potentiated the locomotor-activating effect of 2 mg/kg subcutaneous morphine but not of either 1 or 5 mg/kg morphine (Experiment 5). Behavioral supersensitization assessed by morphine-induced locomotor activation was transient, as it was evident one day, but not either three or 10 days following pellet removal (Experiment 6). These results confirm the functional significance of opiate receptor up-regulation following chronic opioid blockade.

Endogenous opiates: 1984

This paper is the seventh in an annual series of reviews of research involving the endogenous opiate peptides, each installment being restricted to work published during the previous year. As in the past three years, the review this year is limited to non-analgesic and behavioral studies of the opiate peptides. The specific topics this year include: stress, tolerance and dependence, consummatory responses, gastric and renal activity, alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, seizures and neurological disorders, activity, and miscellaneous other topics.