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.