Treatment outcomes after initiating buprenorphine/naloxone or methadone for opioid use disorder among First Nation Peoples in Ontario, Canada.

BACKGROUND: The Canadian opioid toxicity crisis has disproportionately harmed First Nation Peoples. We compared opioid agonist treatment (OAT) outcomes within this population. METHODS: Our population-based cohort included First Nation Peoples in Ontario, Canada, who initiated buprenorphine/naloxone or methadone between October 1st, 2016 and March 31st, 2021. The primary outcome was fatal/non-fatal opioid toxicity in the first year of treatment. Secondary outcomes were OAT discontinuation, receipt of a 7-day take-home supply, and OUD-related physician visits. We used inverse probability of treatment-weighted Cox proportional hazards and Poisson regression models to compare outcomes between buprenorphine/naloxone and methadone, overall and stratifying by sex and residence within/outside of First Nation communities. RESULTS: We included 3270 and 2186 First Nation individuals initiating buprenorphine/naloxone and methadone, respectively. Compared with methadone, buprenorphine/naloxone was associated with a lower risk of opioid toxicity (wHR, 0.65; 95% CI, 0.45-0.93), higher receipt of take-home doses (wHR, 1.17; 95% CI, 1.09-1.26), higher risk of OAT discontinuation (wHR, 1.11; 95% CI, 1.06-1.17), and a lower rate of physician visits (wRR, 0.63; 95% CI, 0.61-0.65). Findings were consistent when stratified by residence and sex. Females initiating buprenorphine/naloxone had a lower risk of opioid toxicity (wHR 0.35; 95% CI, 0.19-0.66), a difference not observed among males (wHR 0.95; 95% CI, 0.60-1.50; interaction term p-value=0.01). CONCLUSIONS: The safety and accessibility of buprenorphine/naloxone supports First Nation-led efforts expanding its availability in rural and remote regions of Ontario. Higher methadone retention rates underscore the need for equitable access to OAT options for First Nation Peoples, regardless of where they live.