Research Article: Methadone maintenance treatment and mortality in people with criminal convictions: A population-based retrospective cohort study from Canada

Date Published: July 31, 2018

Publisher: Public Library of Science

Author(s): Angela Russolillo, Akm Moniruzzaman, Julian M. Somers, Wayne D. Hall

Abstract: BackgroundIndividuals with criminal histories have high rates of opioid dependence and mortality. Excess mortality is largely attributable to overdose deaths. Methadone maintenance treatment (MMT) is one of the best evidence-based opioid substitution treatments (OSTs), but there is uncertainty about whether methadone treatment reduces the risk of mortality among convicted offenders over extended follow-up periods. The objective of this study was to investigate the association between adherence to MMT and overdose fatality as well as other causes of mortality.Methods and findingsWe conducted a retrospective cohort study involving linked population-level administrative data among individuals in British Columbia (BC), Canada with a history of conviction and who filled a methadone prescription between January 1, 1998 and March 31, 2015. Participants were followed from the date of first-dispensed methadone prescription until censoring (date of death or March 31, 2015). Methadone was divided into medicated (methadone was dispensed) and nonmedicated (methadone was not dispensed) periods and analysed as a time-varying exposure. Hazard ratios (HRs) with 95% CIs were estimated using multivariable Cox regression to examine mortality during the study period. All-cause and cause-specific mortality rates were compared during medicated and nonmedicated methadone periods. Participants (n = 14,530) had a mean age of 34.5 years, were 71.4% male, and had a median follow-up of 6.9 years. A total of 1,275 participants died during the observation period. The overall all-cause mortality rate was 11.2 per 1,000 person-years (PYs). Participants were significantly less likely to die from both nonexternal (adjusted HR [AHR] 0.27 [95% CI 0.23–0.33]) and external (AHR 0.41 [95% CI 0.33–0.51]) causes during medicated periods, independent of sociodemographic, criminological, and health-related factors. Death due to infectious diseases was 5 times lower (AHR 0.20 [95% CI 0.13–0.30]), and accidental poisoning (overdose) deaths were nearly 3 times lower (AHR 0.39 [95% CI 0.30–0.50]) during medicated periods. A competing risk regression demonstrated a similar pattern of results. The use of a Canadian offender population may limit generalizability of results. Furthermore, our observation period represents community-based methadone prescribing and may omit prescriptions administered during hospital separations. Therefore, the magnitude of the protective effects of methadone from nonexternal causes of death should be interpreted with caution.ConclusionsAdherence to methadone was associated with significantly lower rates of death in a population-level cohort of Canadian convicted offenders. Achieving higher rates of adherence may reduce overdose deaths and other causes of mortality among offenders and similarly marginalized populations. Our findings warrant examination in other study centres in response to the crisis of opiate-involved deaths.

Partial Text: Overdoses and deaths caused by opioids have been declared a public health emergency in North America. The rising prevalence of opioid dependence [1], alongside the emergence of fentanyl in the illicit drug market [2], is contributing to premature mortality and sparking an urgent need to mobilize public health and public safety resources. Many of North America’s leading health organisations (American Medical Association, Health Canada, and Centers for Disease Control and Prevention) have set priorities in response to the escalating public health crisis [3]. Interventions emphasize prevention, education, and comprehensive care, including access to substitution treatment where indicated [4]. Particular attention has been directed toward high-risk populations, including offenders. Accidental poisoning is the most common cause of mortality among opioid-dependent individuals [5,6], with opioids present in the vast majority of drug-related deaths among ex-prisoners [7]. Several mortality-related risk factors are overrepresented among offenders (e.g., repeated incarceration, low socioeconomic status, and homelessness) [8,9], compounding the hazards associated with substance misuse. The prevalence of opioid dependence [10] and risk of death from illicit drugs [11,12], such as heroin, is higher among offenders and is acutely elevated in the weeks following prison release [13,14]. Despite evidence that prevention and treatment options (e.g., methadone) may reduce the risk of death among opioid-dependent individuals [15,16], there remain significant barriers [17,18] and underutilisation [19] of substitution treatment options for offenders. Factors such as stigma, insufficient pharmacotherapy knowledge, concerns related to medication diversion, and poor links between corrections and community-based care providers can restrict access to methadone maintenance treatment (MMT) and continuity of care for offenders with opioid dependence [20,21] whether they are sentenced to custody or community settings, as well as following the completion of sentencing.

The study cohort included 14,530 convicted offenders (mean [SD] age 34.5 [9.4] years; 71.4% male) followed from January 1, 1998 to March 31, 2015 for a total of 114,243.7 person-years (PYs). Table 1 shows baseline sociodemographic and criminological information as well as diagnostic and medical services details for the eligible sample. For methadone prescriptions, the median number of medicated and nonmedicated periods in years were 2.0 (IQR 0.5–4.9) and 3.2 (IQR 0.9–7.1), respectively, representing a total medicated time of 47,681.7 PYs and a nonmedicated time of 66,562.0 PYs.

In this longitudinal cohort study, dispensed methadone was associated with significantly lower risk of both all-cause and cause-specific mortality among patients diagnosed with opioid dependence and with prior convictions. To our knowledge, this is the first study to investigate the association between MMT and mortality in a large sample over an extended period (i.e., greater than 10 years) with adjustment for diverse covariates. The majority of our sample did not commit an offence in the year preceding methadone initiation (62%), and few received sentences that included time in custody (19%). Therefore, our observation period overwhelmingly corresponds to events occurring in community settings while participants were not under correctional supervision.

In a large cohort of Canadian convicted offenders, rates of mortality were significantly lower during periods when individuals were dispensed methadone compared with periods in which they were not dispensed methadone. Our findings strongly indicate that efforts to increase methadone adherence may reduce mortality in high-risk populations such as opioid-dependent offenders. Our findings warrant examination in other study centres in response to the crisis of opiate-involved deaths.



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