Maria Socias

Background: Canada is currently facing an overdose epidemic primarily attributed to prescription and synthetic opioids. Previous work has revealed that individuals with a history of non-fatal overdose (NFO) are at a higher risk of mortality, but little is known about treatment outcomes among this population. The aim of this thesis was to characterize opioid agonist treatment (OAT) seeking individuals with prescription-type opioid use disorder (POUD) and a history of NFO, as well as their treatment outcomes. Methods: Data were drawn from OPTIMA, a multi-site, 24-week, pragmatic, randomized control trial evaluating the relative effectiveness of buprenorphine/naloxone and methadone models of care for adults with POUD. Multivariable logistic regression was used to determine correlates of NFO and to explore treatment retention among participants with a history of NFO. Analysis of covariance (ANCOVA) was used to examine the mean difference in opioid use between treatment arms. Finally, descriptive statistics were produced to determine the prevalence of overdose during treatment and investigate patterns of opioid use before and after overdose.Results: Among the 272 randomized participants, 159 (58%) had a lifetime history of NFO. Homelessness, receiving income assistance and positive urine drug screens (UDS) for fentanyl and methamphetamine were all independently associated with a history of NFO. Among participants with a history of NFO, retention was 17% for the buprenorphine/naloxone group and 18% for the methadone group and was not statistically different between the treatment arms (p = 0.54). Across the study period, there was an 11.9% adjusted mean difference in opioid-free UDS, favouring the buprenorphine/naloxone arm (95% CI= 3.5 to 20.3; p=0.0057). A total of 24 overdoses were reported during the study period (6 participants randomized to buprenorphine/naloxone; 12 randomized to methadone). All participants that initiated treatment continued to use opioids after overdose. Conclusions: Findings from this research indicate that a considerable proportion of OAT-seeking individuals have a history of NFO. Low retention rates and high opioid use in treatment highlight the importance of an individualized, multidimensional approach to treatment for this population. Timely initiation of low-barrier treatment and interventions to address socio-structural barriers could potentially mitigate future overdose and improve treatment outcomes.

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