Safety outcomes in 2132 Danish patients with inflammatory arthritis treated with biosimilar infliximab (GP1111) in routine care

Background: Biosimilar biologic disease-modifying antirheumatic drugs (bDMARDs) are increasingly used in clinical practice; however, real-world evidence regarding safety outcomes is currently limited. Denmark has rapidly implemented biosimilars through nationwide mandatory switches, introducing infliximab biosimilars CT-P13 in 2015 and GP1111 in 2019.Objectives: To investigate the incidence of serious safety outcomes among Danish real-world arthritis patients (including biosimilar-to-biosimilar switchers) during the first year of infliximab biosimilar GP1111 treatment.Methods: Patients with rheumatoid arthritis, psoriatic arthritis, or axial spondyloarthritis initiating GP1111 during April 1, 2019-April 1, 2022 were identified in the nationwide DANBIO registry. Comorbidities at treatment start (=baseline) and safety outcomes (major adverse cardiac events (MACE), venous thromboembolic events (VTEs), deaths, severe allergic reactions, and serious infections) during 1-year follow-up were captured through linkage to nationwide registries by using diagnoses registered from hospital contacts. Each safety outcome was assessed separately in the overall GP1111 cohort and in five sub-cohorts (based on bDMARD treatment history). We calculated 1-year crude and age- and sex-adjusted incidence rates (IRs) of each safety outcome. Furthermore, baseline factors associated with risks were assessed in the overall cohort.Results: In total, 2132 patients initiating GP1111 treatment were included, whereof 1534 (72%) were infliximab-biosimilar-to-biosimilar switchers. For the overall cohort, adjusted IRs for MACE, VTEs, death, and allergic reactions were very low (<= 1.0/100 person-years). For serious infections, the adjusted IR was 3.2 (95% confidence interval (CI) 2.5-4.2) for the overall cohort, varying across sub-cohorts (IRs 2.1-5.6). Prior serious infection increased risk of serious infection (hazard ratio = 2.06 (95% CI 1.19-3.57), whereas other baseline factors, including biologic treatment history did not. Due to few events, similar analyses were not presented for other safety outcomes.Conclusion: This study demonstrated that 1 year of treatment with biosimilar infliximab GP1111 was safe regardless of treatment history. The rate of serious infections was comparable to originator tumor necrosis factor inhibitors.