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.