Aim: To compare overdose mortality associated with methadone and buprenorphine treatment for opioid dependence.
Methods: Data linkage study. Since 1 April 2006, the Division of Analytic Laboratories (DAL) has routinely tested all New South Wales (NSW) coronial post-mortem samples for both methadone and buprenorphine. Names of all methadone or buprenorphine-positive cases between April and December 2006 inclusive were linked to the National Coroners Information System (NCIS) database, which provided information on cause of death, autopsy findings and circumstances of death. Names were linked to the Pharmaceutical Services Branch Drugs of Addiction System (PHDAS) database to identify whether people were in treatment, and in decedents not registered in treatment, the source of methadone or buprenorphine was presumed to be diversion from treatment programs. Mean number in treatment during 2006 for methadone and buprenorphine were derived from the PHDAS database. Rate of opioid overdose per thousand people in treatment were calculated for methadone and buprenorphine.
Results: In the 9-month period there were 13,718 in methadone treatment and 2716 people in buprenorphine. There were 60 sudden deaths positive for methadone (32 in-treatment) and 7 buprenorphine-positive decedents (none in treatment). Most out-of-treatment deaths occurred in people with known histories of drug misuse. Forty-three methadone positive cases - 19/32 in treatment, and 24/28 out-of-treatment - and 2 of the 7 buprenorphine-positive deaths were due to overdose. The risk of overdose death per thousand people in treatment was lower for buprenorphine than for methadone (RR 4.25 [1.03, 17.54]).
Conclusion: In this short-term study, buprenorphine was associated with lower overdose risk than methadone.