OBJECTIVES: Biosimilars have similar efficacy and safety profiles to the originator biologics such that their introduction into Ireland is expected to increase competition, lower prices and improve the affordability of costly therapies. The objective of this study sought to estimate the budget impact of introducing an infliximab biosimilar (CT-P13) as a treatment option for rheumatoid arthritis (RA) patients in Ireland. METHODS: An Excel-based budget impact model was developed over a five-year time horizon. The annual population in Ireland receiving treatment with a biologic was based on national population statistics and published literature including: prevalence and incidence of RA; proportion of patients eligible for treatment with a biologic; and proportion of patients receiving treatment with a biologic. After the first year, an annual population growth rate of 1.1% was assumed. Maximum conversion of all existing and new infliximab patients to the infliximab biosimilar was assumed for years one to five. The total cost/patient was based on published literature and included drug acquisition, administration, and monitoring costs. Outcomes are reported as the annual and cumulative budget impact over five years. RESULTS: In year one, 3,776 prevalent and 119 incident patients entered the model. Of these, 13% received the infliximab biosimilar with the total cost/patient calculated as €15,754 in the first year of treatment and €12,789 in subsequent years. The drug acquisition cost for the infliximab biosimilar was assumed to discount infliximab by 20%. Annual budget saving estimations following introduction of the infliximab biosimilar were €579,631, €1,165,400, €1,177,553, €1,189,463 and €1,201,137 for years one to five, with a cumulative budget saving of €5,313,184. CONCLUSIONS: Introducing an infliximab biosimilar as a treatment option for RA patients in Ireland represents a cost saving of up to €5,313,184 over five years; equivalent to treating an extra 337 new patients with a biosimilar for one year.