The Effect of Opioid Agonist Treatment on Injection-Related Sequelae: A Population-Based Observational Study

Introduction Opioid agonist treatment (OAT) reduces drug-related poisonings and injection-related infections among people with opioid use disorder (OUD). Despite buprenorphine-naloxone (BNX) and methadone (MET) both being first-line OAT options in Canada, their comparative effectiveness in preventing recurrent injection-related infections and poisonings remains unclear. Objectives This study compared the effectiveness of buprenorphine-naloxone and methadone in reducing recurrent risks of injection-related bacterial infections and opioid-related poisoning among people on OAT. Methods We used administrative health data from Québec, Canada to create our cohort of adult patients (aged 18–65 years) on OAT maintenance between 2014 and 2019. We applied a time-dependent Cox proportional hazards model for our time-varying exposure definition to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the recurrent risks of injection-related bacterial infections and opioid-related poisoning, adjusting for age, sex, socio-demographic, and clinical factors. We also compared the effectiveness of buprenorphine-naloxone and methadone during the OAT induction phase (i.e., first 30 days of treatment). Results The study population included 2010 patients (mean age: 41.21 years, 67.41% male). Compared to methadone, buprenorphine-naloxone was associated with 45% lower recurrent risk of opioid-related poisoning (HR: 0.55; 95% CI 0.35–0.86). Overall, the association between buprenorphine-naloxone and recurrent risk of injection-related bacterial infections suggested a weak protective effect (HR: 0.80; 95% CI 0.59–1.09). During the induction phase, there was limited evidence of differences between buprenorphine-naloxone and methadone for the recurrent risks of injection-related bacterial infections (HR: 0.91; 95% CI 0.51–1.60) and opioid-related poisoning (HR: 1.07; 95% CI 0.51–2.24). Conclusion Among patients in OAT maintenance, buprenorphine-naloxone was associated with lower risk of recurrent opioid-related poisoning compared to methadone, but not for injection-related infections. This advantage was not observed during induction, suggesting the need for improved treatment retention early in OAT.