Measuring the Impact of the Substitution of Innovator Biologics With Biosimilars on Uptake and Costs Among Ontario Public Drug Benefit Recipients

In Ontario, biologics have historically represented a small proportion of public drug claims but a large proportion of spending. Biosimilars, lower cost alternatives to biologics, offer a potential solution to the rising spending on biologics. From March 2023 to January 2024, the Ontario Ministry of Health required public drug program beneficiaries on eight innovator biologics to transition to biosimilars. Clinicians were reimbursed for supporting patients who transitioned. To evaluate the impact of this biosimilar switch policy, we conducted a repeated cross-sectional study using administrative data from April 2019 to June 2024. For the biologics (innovator and biosimilar) included in the policy, we reported the biosimilar market share, public drug program spending, and clinician support fees. We used interrupted time series analyses to evaluate the policy's impact, and forecasting to estimate drug cost savings. From March 2023 to June 2024, the percentage of affected individuals on biosimilars increased from 21.7% to 96.5%. Drug cost savings were $65.2 million between April 2023 to June 2024, with most savings attributed to non-insulin biosimilars. We estimated savings of $46.6 million in Year 1 (April 2023 to March 2024) and $95.9 million in Year 2 (April 2024 to March 2025). Clinician support fees totaled $3.4 million across the study period. Ontario's biosimilar policy achieved high biosimilar uptake and substantial cost savings. Future research should examine the impact of this policy on clinical outcomes to assess its broader implications for patient care and long-term sustainability.