The partial opioid agonist, buprenorphine, protects against lethal effects of cocaine

Buprenorphine (0.3-3.0 mg/kg) produced dose-dependent protection against the lethal effects of cocaine in mice. The (+)-enantiomer of buprenorphine did not protect up to doses over 100 times greater than the lowest effective dose of its (-)-enantiomer. The protective effects were also produced by the opioid agonists morphine and methadone, but not by the opioid antagonist, naltrexone. Low doses of naltrexone (0.3-1.0 mg/kg) blocked the protective effects of buprenorphine. Protection conferred by buprenorphine was not observed in CXBK mice, a recombinant inbred strain relatively devoid of mu-opioid receptors. Thus, buprenorphine appears to protect against the lethal effects of cocaine by a process mediated by mu-opioid receptors. The present results should provide some additional safety assurance in future clinical trials with buprenorphine, especially in outpatient trials where cocaine abuse may continue along with treatment.