Buprenorphine sublingual tablets: effects on IV heroin self-administration by humans

RATIONALE: Studies have shown that buprenorphine, a partial mu opioid agonist, effectively reduces heroin taking. While previous research with buprenorphine utilized a liquid formulation, a tablet formulation is proposed for clinical use. However, because recent research suggests that the liquid and tablet differ in bio-availability, it is unclear what dose of the buprenorphine tablet effectively antagonizes the reinforcing effects of heroin. OBJECTIVE: The present study was designed to compare the effects of two sublingual doses of buprenorphine maintenance on heroin self-administration. METHODS: Eight heroin-dependent men participated in a 6-week, double-blind, placebo-controlled inpatient study to evaluate the reinforcing effects of intravenous heroin (0, 6.25, 12.5, 25 mg) during maintenance on 8 or 16 mg sublingual buprenorphine. Participants first sampled the available dose of heroin, and then were allowed to respond under a progressive ratio schedule for either heroin or $20. For each heroin dose, one sample session and three choice sessions occurred. Two sessions per day were conducted. A sample session was followed by the first choice session on one day, and the second and third choice sessions occurred on the following day. These sessions were conducted while participants were maintained on daily doses of 8 or 16 mg buprenorphine (3 weeks each). RESULTS: Relative to placebo, 12.5 and 25 mg heroin produced significant increases in break point values under both maintenance dose conditions. The mean break point value for 12.5 mg heroin was significantly lower under 16 mg buprenorphine, compared to 8 mg. CONCLUSIONS: These results demonstrate that the reinforcing effects of heroin were not fully antagonized by these doses of the tablet formulation of buprenorphine, and that 16 mg buprenorphine reduced heroin self-administration relative to 8 mg.     

Effects of buprenorphine/naloxone in opioid-dependent humans

RATIONALE: Buprenorphine is a partial mu opioid agonist under development as a sublingual (SL) medication for opioid dependence treatment in the United States. Because buprenorphine may be abused, tablets combining buprenorphine with naloxone in a 4:1 ratio have been developed to reduce that risk. Low doses of injected buprenorphine/naloxone have been tested in opioid-dependent subjects, but higher doses (more than 2 mg of either medication) and direct comparisons to SL buprenorphine/naloxone have not been examined. OBJECTIVES: To assess and compare the effects of intramuscular (i.m.) versus SL buprenorphine/naloxone in opioid-dependent volunteers. METHODS: Opioid-dependent volunteers were maintained on 40 mg per day of oral hydromorphone while on a residential research ward. After safety testing in two pilot subjects, participants (n = 8) were tested with both i.m. and SL buprenorphine/naloxone (1/0.25, 2/0.5, 4/1, 8/2, 16/4 mg); i.m. hydromorphone (10 mg) and naloxone (0.25 mg); both i.m. and SL buprenorphine alone (8 mg); and placebo. Test sessions were twice per week; dosing was double-blind. RESULTS: Intramuscular buprenorphine/naloxone produced dose-related increases on indices of opioid antagonist effects. Effects were consistent with naloxone-precipitated withdrawal, and were short-lived. As withdrawal effects dissipated, euphoric opioid agonist effects from buprenorphine did not appear. Sublingual buprenorphine/naloxone produced neither opioid agonist nor antagonist effects. CONCLUSIONS: Intramuscular injection of buprenorphine/naloxone precipitates withdrawal in opioid dependent persons; therefore, the combination has a low abuse potential by the injection route in this population. Sublingual buprenorphine/naloxone by tablet is well tolerated in opioid dependent subjects, and shows neither adverse effects (i.e., precipitated withdrawal) nor a high abuse potential (i.e., opioid agonist effects).     

Effects of methadone and morphine maintenance on drug-seeking behavior in the dog

The effects of methadone and morphine maintenance on morphine self-administration were studied in the dog. Methadone was given passively for 2 weeks by continuous i.v. infusion. The amount of methadone administered daily was the same in mg/kg as the mean daily mg/kg of morphine the dogs had self-administered during the premaintenance control week. Morphine self-administration was markedly reduced initially but returned to normal levels within 2 weeks of methadone administration. Following the methadone maintenance period, morphine self-administration was increased over the premaintenance period for 2 weeks. A result similar to that with methadone was obtained in a second experiment when morphine was used as the maintenance drug in an amount that was three times the amount the dogs had been self-administering during the premaintenance control week.A division of the US Department of Health, Education and Welfare, Public Health Service, Alcohol, Drug Abuse and Mental Administration     

Effects of buprenorphine on candy and sweetened fluid self-administration by rhesus monkeys

Abstract Rationale. Previous studies have shown that buprenorphine differentially suppresses the reinforcing effects of different drugs (cocaine, alfentanil), drug versus nondrug reinforcers (food, drug), and the same reinforcer (food) maintained under different schedules of reinforcement. Objectives. The purpose of the present study was to determine whether buprenorphine (0.03, 0.1, 0.3 mg/kg) differentially affects candy versus sweetened fluid self-administration. The hypotheses were that (1) candy would maintain higher rates of responding and would be chosen on more occasions than sweetened fluid, and (2) buprenorphine would produce smaller disruptions in responding for the more-preferred reinforcer. Methods. During separate sessions, rhesus monkeys self-administered candy alone, sweetened fluid alone, or had the opportunity to choose between candy and sweetened fluid. Monkeys responded under a second order, two-chain schedule of reinforcement. Results. Candy was a more-preferred reinforcer than sweetened fluid. Buprenorphine significantly decreased rates of responding for fluid, but increased rates of responding for candy. Although buprenorphine significantly decreased both candy and fluid intake, it produced a more robust, and longer-lasting suppression of sweetened-fluid intake than candy. Choice to self-administer candy or fluid was not affected by buprenorphine. Conclusions. These results demonstrate that behavior maintained by a less-preferred reinforcer is more easily disrupted by buprenorphine than is behavior maintained by a more-preferred reinforcer. Electronic Publication     

Determinants of buprenorphine treatment for opioid dependence

This study assessed the social, demographic and clinical determinants of whether an opioid-dependent patient received buprenorphine versus an alternative therapy. A retrospective cohort analysis of opioid-dependent adults enrolled in Group Health Cooperative between January 1, 2006 and December 1, 2010 was performed. Increasing the number of physicians with DATA waivers in a region and living in a relatively-populated area increased the likelihood of being treated with buprenorphine, indicating that lack of access is a potential barrier. Comorbidity also appeared to be a factor in receipt of treatment, with the effect varying by diagnosis. Finally, patients with an insurance plan allowing health services to be sought from any provider, with increased cost sharing, were significantly more likely to receive buprenorphine, implying that patient demand is a factor. Programs integrating patient education, physician training, and support from addiction specialists would be likely facilitators of increasing access to this cost-effective treatment.     

Self-administration of remifentanil, an ultra-short acting opioid, under continuous and progressive-ratio schedules of reinforcement in rats

RATIONALE: Remifentanil is a mu-opioid agonist with an exceptionally short duration of action. Evaluating remifentanil's effects within the self-administration model of drug abuse may provide insight into the relationship between a drug's duration of action and its effectiveness as a reinforcer. OBJECTIVES: This study was conducted to establish a dose-effect function for intravenous remifentanil self-administration in rats and to assess the drug's ability to maintain responding under intermittent schedules of reinforcement. METHODS: Inter-infusion intervals were recorded under two continuous-reinforcement schedules of remifentanil self-administration. In the fixed-dose schedule, the unit dose (0.25-32 micrograms/kg) was held constant within sessions but varied across sessions. In the variable-dose schedule, four different doses were self-administered in random order within each session. For comparison, heroin (6.25-125 micrograms/kg) was studied with the variable-dose schedule. Remifentanil and heroin were also compared under a progressive-ratio schedule of reinforcement in which the response requirements increased exponentially with each successive infusion until responding ceased within each session. RESULTS: Under the continuous-reinforcement schedules, inter-infusion intervals for both drugs increased monotonically as a function of dose, with the remifentanil curve being considerably flatter. Under the progressive-ratio schedule, breaking points varied as an inverted-U shaped function, and the highest breaking points maintained by remifentanil and heroin were similar. At the doses that maintained the highest breaking points under the progressive-ratio schedule, post-infusion pauses under the continuous-reinforcement schedule were about three times shorter with remifentanil than with heroin. CONCLUSIONS: Although rates of self-administration are clearly influenced by a drug's duration of action, the ability to maintain responding under intermittent schedules of reinforcement may be independent of duration of action.     

Effects of buprenorphine versus buprenorphine/naloxone tablets in non-dependent opioid abusers

Rationale: Buprenorphine is an opioid agonist-antagonist under development in the United States as a sublingual medication for treatment of opioid dependence. Buprenorphine may be abused; therefore, tablets combining buprenorphine with naloxone have been developed with the intent of reducing the abuse risk in people physically dependent upon opioids. The characteristics and abuse potential of buprenorphine and buprenorphine/naloxone tablets in non-dependent opioid abusers have not been determined. Non-parenteral abuse of opioids such as buprenorphine may be more likely in people who have less severe substance abuse disorders (e.g., are not physically dependent upon opioids). Objectives: To assess the abuse potential of sublingual buprenorphine and buprenorphine/naloxone tablets in non-dependent opioid abusers. Methods: Subjects (n=7) were tested with sublingual buprenorphine (4, 8, 16 mg), sublingual buprenorphine/naloxone (1/0.25, 2/0.5, 4/1, 8/2, 16/4 mg), as well as intramuscular hydromorphone as an opioid agonist control (2, 4 mg) and placebo in laboratory sessions conducted twice per week. Dosing was double-blind and double-dummy. Results: The higher doses of both buprenorphine and buprenorphine/naloxone produced similar opioid agonist-like effects. The onset of these effects was slowed, consistent with the sublingual route of administration, and the magnitude of effects was moderate. There was no evidence to suggest the addition of naloxone attenuated buprenorphine’s opioid agonist effects in this population when buprenorphine was delivered by the sublingual route. Conclusions: These results suggest that sublingual buprenorphine and buprenorphine/naloxone may both be abused by opioid users who are not physically dependent upon opioids. Received: 15 April 1999 / Final version: 11 September 1999     

Predictors of attrition with buprenorphine/naloxone treatment in opioid dependent youth

Background

In opioid dependent youth there is substantial attrition from medication-assisted treatment. If youth at risk for attrition can be identified at treatment entry or early in treatment, they can be targeted for interventions to help retain them in treatment.

Methods

Opioid dependent adolescents and young adults (n = 152), aged 15–21, were randomized to 12 weeks (BUP, n = 74) or 2 weeks of detoxification (DETOX, n = 78) with buprenorphine/naloxone (Bup/Nal), both in combination with 12 weeks of psychosocial treatment. Baseline and early treatment related predictors of treatment attrition were identified in each group using bivariate and multivariate logistic regression.

Results

In the DETOX group 36% left between weeks 2 and 4, at the end of the dose taper, while in the BUP group only 8% left by week 4. In the BUP group, early adherence to Bup/Nal, early opioid negative urines, use of any medications in the month prior to treatment entry, and lifetime non-heroin opioid use were associated with retention while prior 30-day hallucinogen use was associated with attrition. In the DETOX group, only use of sleep medications was associated with retention although not an independent predictor. A broad range of other pre-treatment characteristics was unrelated to attrition.

Conclusions

Prompt attention to those with early non-adherence to medication or an early opioid positive urine, markers available in the first 2 weeks of treatment, may improve treatment retention. Extended Bup/Nal treatment appeared effective in improving treatment retention for youth with opioid dependence across a wide range of demographics, and pre-treatment clinical characteristics.     

Determination of buprenorphine in plasma by liquid chromatography: application to heroin-dependent subjects

A rapid, sensitive, precise and accurate HPLC assay with UV detection was developed for the determination of buprenorphine (BN) in human plasma. This method involved a two-step extraction in the presence of clothiapine as internal standard. The compounds were chromatographied on a reversed-phase Spherisorb® C8 column with a mobile phase consisting of 0.06 M KH₂PO₄/Na₂HPO₄ pH 6.4–acetonitrile–triethylamine–Pic B5® (520:480:0.5:15, v/v) and detected at 214 nm. The recovery of BN was greater than 94% with an intra-day relative standard deviation ≤4.8% and an inter-day relative standard deviation ≤14.6% at any studied level. Studies of drug stability during sample storage at −20°C and at +4°C did not show any significative degradation of BN. This method was successfully applied to explore the overdose state of heroin-dependent subjects treated by high-dose BN.     

Results of a pilot randomized controlled trial of buprenorphine for opioid dependent women in the criminal justice system

Aims

Recent studies have demonstrated the efficacy of both methadone and buprenorphine when used with opioid dependent men transitioning from prison to the community, but no studies have been conducted with women in the criminal justice (CJ) system. The aim of this study was to determine the efficacy of buprenorphine for relapse prevention among opioid dependent women in the CJ system transitioning back to the community.

Methods

36 women under CJ supervision were recruited from an inpatient drug treatment facility that treats CJ individuals returning back to the community. Nine were enrolled in an open label buprenorphine arm then 27 were randomized to buprenorphine (n = 15) or placebo (n = 12; double-blind). All women completed baseline measures and started study medication prior to release. Participants were followed weekly, provided urine drug screens (UDS), received study medication for 12 weeks, and returned for a 3-month follow-up. Intent-to-treat analyses were performed for all time points through 3 month follow-up.

Results

The majority of participants were Caucasian (88.9%), young (M ± SD = 31.8 ± 8.4 years), divorced/separated (59.2%) women with at least a high school/GED education (M ± SD = 12 ± 1.7 years). GEE analyses showed that buprenorphine was efficacious in maintaining abstinence across time compared to placebo. At end of treatment, 92% of placebo and 33% of active medication participants were positive for opiates on urine drug screen (Chi-Square = 10.9, df = 1; p < 0.001). However, by the three month follow-up point, no differences were found between the two groups, with 83% of participants at follow-up positive for opiates.

Conclusions

Women in the CJ system who received buprenorphine prior to release from a treatment facility had fewer opiate positive UDS through the 12 weeks of treatment compared to women receiving placebo. Initiating buprenorphine in a controlled environment prior to release appears to be a viable strategy to reduce opiate use when transitioning back to the community.     

丁丙诺啡舌下含片与美沙酮用于海洛因依赖门诊稽延期治疗的对照研究

目的观察丁丙诺啡舌下含片与美沙酮用于海洛因依赖者稽延期治疗的价值。方法对完成脱毒治疗患者，依先后次序交叉纳入观察组与对照组，分别给予丁丙诺啡舌下含片和美沙酮治疗6个月，观察操守时间，并于人组前后做焦虑量表评分。结果丁丙诺啡舌下含片组比美沙酮组的操守时间长（P〈0．01），焦虑评分低（P〈0．05）。结论丁丙诺啡舌下含片于海洛因依赖门诊稽延期治疗能更好地缓解焦虑情绪并延长操守时间。     

Effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on sublingual buprenorphine metabolism in heroin addicts: An improved PCR-RFLP assay for the detection of rs7662029 polymorphism

This study aimed to determine the effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on plasma buprenorphine (BUP) concentration and different treatment responses in a sample of 109 patients with opioid use disorder (OUD) treated with sublingual BUP/naloxone. Polymorphisms were analysed by PCR-RFLP. Plasma concentrations of BUP and its metabolite norbuprenorphine were detected by LC–MS/MS. Craving, withdrawal, depression and anxiety were measured by appropriate scales. OUD patients with rs7439366 CC or rs7662029 GG genotypes had significantly lower dose-normalized (BUP/D) and dose/kg-normalized BUP (BUP/D.kg^-1) levels than those who were CT or AA carriers. Significant associations between UGT2B7 rs7662029 and increased craving (p = 0.037) and withdrawal symptoms (p = 0.029) were detected. Our findings were pointing to an important role of UGT2B7 in the metabolism of sublingual BUP/naloxone in the heroin addicts for the first time. A novel PCR-RFLP assay was developed for the determination of UGT2B7 rs7662029 polymorphism, based on utilizing novel restriction enzyme.     

Buprenorphine/naloxone reduces the reinforcing and subjective effects of heroin in heroin-dependent volunteers

Rationale Although buprenorphine is effective in treating opioid dependence, optimal maintenance doses of buprenorphine or the buprenorphine/naloxone combination have not yet been established. Objective The present study was designed to evaluate the effects of buprenorphine/naloxone maintenance (2/0.5, 8/2, 32/8 mg sublingual) on the reinforcing and subjective effects of heroin (0, 12.5, 25, 50, and 100 mg intranasal) in heroin-dependent individuals. Methods During test weeks, participants (N=7) first sampled a dose of heroin and $20. During subsequent choice sessions, participants could choose to self-administer heroin and/or money. Participants responded under a modified progressive-ratio schedule (PR 50, ..., 2,800) during a ten-trial self-administration task. Results Heroin break point values and subjective responses were significantly lower under 8/2 and 32/8 mg buprenorphine/naloxone compared to 2/0.5 mg. The self-administration and subjective effects data for heroin in the presence of buprenorphine/naloxone were compared to a separate control group of recently detoxified participants (N=8) in order to obtain estimates for the apparent in vivo dissociation constant (K _A), the efficacy estimate (τ), and the estimated fraction of receptors remaining after buprenorphine/naloxone treatment (q). The apparent in vivo dissociation constant for heroin ranged from 50 to 126 mg (K _A) and the efficacy estimate ranged from 13 to 20 (τ). In addition, 2/0.5, 8/2, and 32/8 mg buprenorphine/naloxone dose-dependently reduced the receptor population by 74, 83, and 91%, respectively. Conclusions These data demonstrate that both 8/2 and 32/8 mg buprenorphine/naloxone were well tolerated and effective in reducing the reinforcing and subjective effects of heroin, relative to the 2/0.5-mg dose. The data also show for the first time in humans that it is possible to quantify the efficacy and affinity of heroin for mu opioid receptors, and that 80–90% of mu receptors need to be inactivated in order to obtain significant reductions in heroin-induced effects. These results have important implications for future studies in which it will be possible to obtain estimates of relative affinity and efficacy of different agonists at mu opioid receptors.     

Sublingual buprenorphine/naloxone precipitated withdrawal in subjects maintained on 100mg of daily methadone

RATIONALE: Acute doses of buprenorphine can precipitate withdrawal in opioid dependent persons. The likelihood of this withdrawal increases as a function of the level of physical dependence. OBJECTIVES: To test the acute effects of sublingual buprenorphine/naloxone tablets in volunteers with a higher level of physical dependence. The goal was to identify a dose that would precipitate withdrawal (Phase 1), then determine if withdrawal could be attenuated by splitting this dose (Phase 2). METHODS: Residential laboratory study; subjects (N=16) maintained on 100mg per day of methadone. Phase 1: randomized, double blind, triple dummy, within subject study. Conditions were sublingual buprenorphine/naloxone (4/1, 8/2, 16/4, 32mg/8mg), intramuscular naloxone (0.2mg), oral methadone (100mg), or placebo. Medication conditions were randomized, but buprenorphine/naloxone doses were ascending within the randomization. Phase 2: Conditions were methadone, placebo, naloxone, 100% of the buprenorphine/naloxone dose that precipitated withdrawal in Phase 1 (full dose), and 50% of this dose administered twice in a session (split dose). Analyses covaried by trough methadone serum levels. RESULTS: Six subjects did not complete the study. Of the 10 who completed, 3 tolerated up to 32mg/8mg of buprenorphine/naloxone without evidence of precipitated withdrawal. For the seven completing both phases, split doses generally produced less precipitated withdrawal compared to full doses. CONCLUSIONS: There is considerable between subject variability in sensitivity to buprenorphine's antagonist effects. Low, repeated doses of buprenorphine/naloxone (e.g., 2mg/0.5mg) may be an effective mechanism for safely dosing this medication in persons with higher levels of physical dependence.     

Quality of life under maintenance treatment with heroin versus methadone in patients with opioid dependence

Background

There is increasing evidence that health-related quality of life (HRQOL) is associated with a successful treatment and better outcome in opioid addiction. The aim of the present study was the longitudinal investigation of HRQOL in patients with severe opioid dependence, who were randomly assigned to four groups of medical and psychosocial treatment: heroin (diacetylmorphine) versus methadone and case management (CM) versus psychoeducation (PSE) respectively.

Methods

HRQOL (MSQoL) and physical health (OTI) were investigated in 938 subjects, who participated in the German multi-centre study examining the effects of heroin-assisted treatment in patients with severe opioid dependence. Data for the present analysis were taken from baseline and 12-month follow up.

Results

Under both forms of maintenance and psychosocial treatment HRQOL improved significantly during the observation period. HRQOL improvement under maintenance with heroin exceeded improvement under methadone, especially with regard to subjective physical health. HRQOL improvement was significantly associated with better expert-rated physical health. Further analyses showed significant better improvement of HRQOL in subjects treated with PSE compared with CM.

Conclusions

The advantage of heroin with regard to the improvement of HRQOL may be partially explained by a better improvement of physical health under maintenance with heroin compared with methadone, which highlights the importance of a comprehensive model of health care for patients with severe opioid dependence. Future studies need to investigate the benefits of PSE for patients in maintenance therapy.     

The effect of telephonic patient support on treatment for opioid dependence: outcomes at one year follow-up

Objective

The present study examined the impact of a telephonic patient support program known as HereToHelp™ (HTH) on compliance and treatment outcomes among opioid dependent (OD) patients new to buprenorphine treatment (BUP).

Method

A total of 1426 OD patients new to BUP were randomized to receive BUP alone (standard care) or BUP plus the HTH patient support program. All patients completed the Addiction Severity Index (ASI) at the time of enrollment, and at 12 months post-enrollment.

Results

Subjects randomized to the HTH support program who accepted at least 3 care coach intervention calls were more compliant with BUP than the standard care group at month 12 (64.4% vs. 56.1%, χ² = 5.09, p < .025). Compared to patients who were non-compliant with BUP, compliant patients reported significantly lower scores on all 7 of the ASI composite scores, indicating lower severity on addiction-related problems.

Conclusions

The HTH intervention seemed to improve patient treatment outcomes indirectly by improving compliance with BUP. Supplementing BUP with a structured, telephonic compliance-enhancement program is an effective way to improve compliance with medication which then improves patient outcomes.     

Retention on buprenorphine treatment reduces emergency department utilization,but not hospitalization,among treatment-seeking patients with opioid dependence

Drug users are marginalized from typical primary care, often resulting in emergency department (ED) usage and hospitalization due to late-stage disease. Though data suggest methadone decreases such fragmented healthcare utilization (HCU), the impact of buprenorphine maintenance treatment (BMT) on HCU is unknown. Chart review was conducted on opioid dependent patients seeking BMT, comparing individuals (n = 59) who left BMT ≤ 7 days with those retained on BMT (n = 150), for ED use and hospitalization. Using negative binomial regressions, including comparison of time before BMT induction, ED utilization and hospitalization were assessed. Overall, ED utilization was 0.93 events per person year and was significantly reduced by BMT, with increasing time (retention) on BMT. BMT had no significant effect on hospitalizations or average length of stay.     

Comparison of intravenous and intranasal heroin self-administration by morphine-maintained humans

Eight heroin-dependent individuals, maintained on divided daily doses of oral morphine, participated in a 2.5-week inpatient study comparing the effects of intranasal (IN) (placebo, 12.5, 25, 50, 100 mg) and intravenous (IV) (placebo, 6.25, 12.5, 25, 50 mg) heroin. Each morning, participants received $20 and a sample dose of heroin, and each afternoon they had the opportunity to self-administer all or part of the morning heroin dose or money amount. Participants responded under a modified progressive-ratio schedule (PR 50, 100, 200, 400, 800, 1200, 1600, 2000, 2400, 2800) during a ten-trial self-administration task. During each trial, participants could respond for 1/10th of the heroin dose or 1/10th of the money amount. The total amount of heroin and/or money chosen during the self-administration task was given at the end of the task. Thus, participants received drug and/or money twice each day: once during the morning sample session and once during the afternoon self-administration session. Participants received IV solution and IN powder simultaneously during each dosing; only one route contained active drug. Heroin produced dose-related increases in break point values by both routes of administration. Although IV heroin was approximately four-fold more potent than IN heroin, the maximal break point values for both routes were not significantly different. A similar difference in potency between the IV and IN routes was found for several ratings of subjective effects (e.g., “I feel a good drug effect,”“I feel high”), but maximal subjective ratings were lower for IN compared to IV heroin. These results suggest that the reinforcing efficacy of heroin is similar by the two routes of administration, but that IN heroin is less potent than IV heroin. The results also underscore the importance of evaluating drug self-administration in the evaluation of the abuse liability of drugs. Received: 20 May 1997/Final version: 13 November 1998     

Effects of ibogaine on responding maintained by food,cocaine and heroin reinforcement in rats

The effects of ibogaine (40 and 80 mg/kg, IP), an indole alkaloid proposed for the treatment of drug abuse, were determined in three different groups of rats responding under an FR10 schedule of food, cocaine or heroin reinforcement. Ibogaine (80 mg/kg, IP) given 60 min before the start of the session resulted in a 97% decrease in the number of ratios completed under the food reinforcement schedule and resulted in a decrease in responding the following day. Neither 40 mg/kg ibogaine given 60 min prior to the session nor 80 mg/kg given 24 h before the session suppressed responding maintained by cocaine infusions (0.33 mg/infusion). Pretreatment with 80 mg/kg ibogaine either 60 or 90 min prior to the session suppressed cocaine self-administration on the day it was administered and the longer pretreatment continued to suppress responding for 48 h. Responding maintained by heroin (18 µg/infusion) was the most sensitive to the effects of ibogaine. Both 40 and 80 mg/kg ibogaine resulted in an almost complete suppression of responding following a 60-min pretreatment period. Responding maintained by heroin returned to control levels the day following the administration of ibogaine.     

The effects of chronic buprenorphine on intake of heroin and cocaine in rats and its effects on nucleus accumbens dopamine levels during self-administration

Rationale Buprenorphine reduces both heroin and cocaine intake in opioid addicts, but the mechanisms remain unclear.Objectives To determine the effects of chronic buprenorphine treatment on intake of heroin and/or cocaine and measure nucleus accumbens (NAc) dopamine (DA) levels during self-administration.Methods In experiment 1, plasma levels of buprenorphine were determined in rats with buprenorphine osmotic minipumps (3.0 mg/kg/day) using an ELISA. In experiment 2, rats self-administered (FR1) one dose of heroin [(0.025, 0.05, or 0.1 mg/kg/infusion (inf)] and one dose of cocaine (0.25, 0.5, or 1.0 mg/kg/inf) before and under sham or chronic buprenorphine treatment (1.5 or 3.0 mg/kg/day). In experiment 3, the effect of sham or chronic buprenorphine treatment (3.0) on heroin (0.05 mg/kg/inf) or cocaine (0.5 mg/kg/inf) self-administration under FR5 and progressive ratio (PR) schedules was evaluated. In experiment 4, in vivo microdialysis sampling from the NAc was carried out during heroin (0.05 mg/kg/inf) or cocaine (0.5 mg/kg/inf) self-administration (FR1) under sham or buprenorphine treatment (3.0).Results Buprenorphine levels in plasma were stable over time. Buprenorphine treatment had no effect on total heroin intake at any dose or under any schedule, whereas it suppressed cocaine intake at all doses and under all schedules. Buprenorphine enhanced basal levels of DA, attenuated the NAc DA response to heroin, and enhanced the DA response to cocaine. It is interesting to note that buprenorphine increased the latency to respond to drug-associated cues at the start of self-administration sessions.Conclusions Chronic buprenorphine reduces cocaine, but not heroin, intake and possibly reduces drug seeking by reducing the salience of the drug-associated cues.