BACKGROUND: Use of costly biologic drugs for the treatment of chronic inflammatory diseases has increased significantly in recent years. However, biosimilar drugs offer an opportunity to ensure health system sustainability with robust uptake. OBJECTIVE: To study the effect of formulary listing strategies on the use of infliximab and etanercept innovator and biosimilar biologics. METHODS: This is a cross-sectional study of individuals in Ontario, Canada, dispensed a biologic prescription for infliximab or etanercept through Ontario's public drug program between January 1, 2010, and June 30, 2019. Quarterly utilization and costs were forecasted using Holt-Winters' exponential smoothing models to the second quarter (Q2) of 2022. Secondary analyses explored utilization for rheumatic conditions (RC) and inflammatory bowel disease (IBD). RESULTS: From Q1 2010 to Q2 2019, infliximab and etanercept users increased by 75.7% (n = 4,073 to 7,158), with a forecasted increase of 13.7% (n = 8,142; 95% CI = 7,438-8,847) by Q2 2022. Biosimilar users represented 13.8% (n = 539 of 3,905) of total infliximab users in Q2 2019, although this differed by indication with 6.9% for IBD (n = 187 of 2,712) and 26.6% for RC (n = 203 of 764). Etanercept biosimilar users represented 20.2% (n = 659 of 3,256) of total etanercept users for RC in Q2 2019. Biologics expenditures increased 109.7% during the study, amounting to $49.9 million in Q2 2019. CONCLUSIONS: Despite differing reimbursement restrictions between innovator infliximab and etanercept biologics, the uptake of their biosimilars was low and not noticeably different in the treatment of RC. Dynamic policy strategies are needed to improve the uptake of biosimilars, particularly for IBD. DISCLOSURES: Funding for this study was contributed by the Ontario Ministry of Health. The authors have no conflicts of interest to disclose.