Assessing the impact of the introduction of generic methadone to the Ontario public drug formulary

Background — Two new generic methadone products—Jamp-methadone and Odan-methadone—were added to Ontario’s public drug formulary in August 2022 and listed as interchangeable with the brand-name product, Methadose®. Concerns have been raised by people receiving methadone and their prescribers about potential risks of treatment destabilization as a result of switching between methadone-containing products.

Methods — We conducted a retrospective population-based time series analysis of weekly methadone claims in Ontario, Canada between January 5, 2017, and March 31, 2023. Using interventional autoregressive integrated moving average models, we assessed the impact of the formulary listing on product market-share, maximum dose dispensed, methadone discontinuation, and opioid toxicities.

Results — The market share of Methadose® declined from 99.7 % to 52.3 % between the listing of generic methadone and March 2023, whereas generic products increased from 0.27 % to 40.0 % (Jamp-methadone) and 0.0 % to 7.7 % (Odan-methadone). We observed a significant short-term increase in the percentage of individuals dispensed methadone doses ≥130 mg (+1.30 %; 95 % CI: 0.85 %, 1.76 %) following formulary listing; however the introduction of generic methadone did not result in a significant change in methadone discontinuation among those stabilized (p > 0.5) and not yet stabilized on treatment (p > 0.7) or opioid-related toxicity events (p > 0.1).

Conclusion — Our findings did not indicate broad treatment destabilization or increased opioid-related toxicity among methadone recipients in the months following the introduction of generic products. Early notification of formulary changes, phased implementation of the policy, as well as information resources developed for patients and clinicians may have played a role in mitigating potential disruptions for this population.