A national cohort study published online in Heroin Addiction and Related Clinical Problems aimed to describe characteristics of methadone-related overdose deaths in Ireland and to compare deaths occurring among those registered for opioid agonist treatment (OAT) with deaths among those not registered.1 OAT involves the use of drugs such as methadone or buprenorphine to reduce cravings and withdrawal symptoms among those addicted to opioids such as heroin.

It is well established that OAT, including methadone substitution therapy, can reduce deaths among problem opiate users. However, OAT is also associated with a risk of accidental overdose, as patients can experience lowered tolerance for opioids following a period of abstinence. Individuals completing detoxification, leaving prison, or exiting OAT may therefore be especially vulnerable to accidental death by overdose. Previous research in Ireland found that people treated with methadone were nearly four times more likely to die in periods off treatment than in periods on treatment.2

Methodology

The current study drew on the Irish National Drug-Related Deaths Index (NDRDI) to identify persons who had died of a drug overdose involving methadone between 2012 and 2013. The NDRDI is an epidemiological database that draws on four sources — the Coroner Service, the Hospital Inpatients Enquiry Scheme, the Central Treatment List (CTL), and the General Mortality Register through the Central Statistics Office — to provide comprehensive data on drug-related deaths. The NDRDI classifies drug-related deaths as poisonings or non-poisonings (fatal overdoses), where ‘poisonings’ are deaths resulting from the toxic effects of the consumption of a drug(s) and/or other substances, and excludes adverse reactions to prescribed medications. Included in the current study were methadone-related poisoning deaths.

Findings

Methadone was implicated in 182 poisoning deaths that occurred during the study period. Just over half of the deaths were among persons aged 34 years or less (54%), and the majority of deaths were among males (78%). During the two-year period, more people died off OAT treatment (61%) than on OAT treatment (39%).

The study further found that a large number of methadone-related deaths were among persons previously treated for substance dependency, and many involved more than one substance. It was not possible to identify how many of those dying of fatal overdose were opioid dependent or were using diverted methadone for recreational or self-medicating purposes, nor was it clear how many had previous contact with OAT providers. Nonetheless, the findings suggest the targeting of overdose prevention interventions (such as overdose recognition, cardiopulmonary resuscitation, and naloxone) to those accessing all types of drug treatment services and not just those offering OAT. Over one-third of the fatal overdoses involving methadone were in patients registered for OAT, highlighting the unique position of OAT providers in risk assessment and overdose prevention. The finding that a high number of deaths occurred in a private dwelling and in the presence of others suggests that family and peers should also be involved in overdose prevention initiatives.

Limitations

A key limitation of the study is that the number of deaths off treatment may have been underestimated, as patients are not removed from the CTL until 28 days after treatment ceases. A further limitation is that it was not possible to differentiate between groups not registered for OAT, in particular those on waiting lists for OAT; those who just completed treatment; and those on buprenorphine. The study was also limited by the incomplete data for some variables, resulting from missing data in the original data sources accessible to the NDRDI. Access to a greater number of data sources would ensure more comprehensive data that could further inform the development and targeting of overdose prevention. The authors conclude that knowledge of patient characteristics, along with improved risk assessment and OAT retention strategies, can be used to inform any future national drug overdose plan.

2  Cousins G, Boland F, Courtney B, Barry J, Lyons S and Fahey T (2016) Risk of mortality on and off methadone substitution treatment in primary care: a national cohort study. Addiction, 111(1): 73—82. https://www.drugsandalcohol.ie/24374/