Assessment of buprenorphine in a drug discrimination procedure in humans

These studies indicate that buprenorphine shares stimulus effects with other opioid drugs and that in overall profile of effects buprenorphine is more similar to hydromorphone than are the other opioid mixed agonist-antagonists tested-pentazocine, butorphanol, and nalbuphine. This characterization is supported by the behavioral drug discrimination results and by the subjective effect self-report results. In the drug discrimination assessments buprenorphine showed a pattern of generalization that was different from that of the other opioid-mixed agonist-antagonists. It did not generalize completely to either pentazocine or butorphanol, but it did generalize to hydromorphone in two studies and partially in a third. Both nalbuphine and pentazocine showed at least partial generalization to butorphanol, but buprenorphine did not. Butorphanol showed little generalization to hydromorphone except in the two-choice hydromorphone vs. saline discrimination in which all the tested mixed agonist-antagonists generalized to hydromorphone. The subjective effect self-report data also revealed a pattern of response to buprenorphine that was different from that to the other mixed agonist-antagonists. In particular, buprenorphine's profile of acute subjective effects was similar to that of hydromorphone. There were dose-related increases on various scales reflecting positive subjective effects, with little evidence of the dysphoric effects that are characteristic of high doses of the other mixed agonist-antagonists. These data are compatible with the view that buprenorphine is a partial agonist at the mu-receptor. Although they do not demonstrate the ceiling on magnitude of pharmacological effects that would be characteristic of a partial agonist, they do demonstrate that buprenorphine's profile of activity--both stimulus effects and subjective effects--is similar to that of the pure mu-agonist hydromorphone.