Association between early methadone dose titration and treatment discontinuation and opioid toxicity: a retrospective cohort study

Background — Clinical guidance in Canada and the United States recommends faster methadone dose titration for individuals using fentanyl. An initial dose increase is recommended between days 4 and 6, but the impact on patient outcomes remains unclear, particularly when provided in an outpatient setting. Therefore, we evaluated the association between early methadone dose titration (i.e., within treatment days 4–6) and treatment discontinuation and opioid toxicity.

Methods and findings — We conducted a retrospective propensity-score weighted cohort study of Ontario residents who initiated methadone in an outpatient setting between January 2017 and December 2022. Exposure was defined as provision of a dose titration between treatment days 4–6, with the index date defined as the first date of dose increase. For unexposed individuals, the index date was randomly assigned and followed the same distribution as those exposed. Individuals were followed for up to 181 days following index date for study outcomes. Primary outcomes included methadone discontinuation and opioid toxicity, using an intention-to-treat approach. Secondary outcomes included methadone versus non-methadone-related toxicity while on treatment. We fit a propensity-score model to estimate the probability of dose titration, conditional on baseline demographic and clinical (e.g., comorbidities, past medication use) variables. Propensity score weighted Cox proportional hazard models were then estimated to determine the association between early dose titration and study outcomes. Among 13,560 incident methadone recipients (61.4% [N = 8,322] provided early dose titration), the mean age was 36.5 years old, and approximately one-third were female. Individuals who received an early dose titration had a lower weighted hazard of discontinuation, which was most pronounced during the first seven days of follow-up (weighted hazard ratio [wHR]: 0.55; 95% confidence interval [CI]: 0.51, 0.60), with attenuation towards the null over time. The observed weighted rate of opioid toxicity was lower among those exposed versus unexposed (10.1 versus 12.3 per 100 person-years; wHR: 0.82; [95% CI: 0.69, 0.97]). Early dose titration was not associated with opioid toxicity while on treatment. Most toxicities were attributed to non-methadone opioids (exposed: 3.89 per 100 person-years versus unexposed: 4.06 per 100 person-years; wHR: 1.00; [95% CI: 0.70, 1.44]). Methadone-related toxicity while on treatment remained low and comparable between exposed and unexposed groups (2.02 versus 2.65 per 100 person-years; wHR: 0.80; [95% CI: 0.46, 1.41]). The main study limitation is the lack of information on drug use history and time-varying clinical factors that may influence both dose titration and subsequent outcomes, introducing the potential for residual confounding.

Conclusions — This population-based analysis demonstrated that early methadone dose titration was associated with improved treatment retention and lower hazard of opioid toxicity. Logistical barriers that hinder timely provision of dose increases must be addressed to improve methadone retention among people who use fentanyl.