Real-world experience of rituximab biosimilar GP2013 in rheumatoid arthritis patients naïve to or switched from reference rituximab.

Randomized controlled trials showed high comparability of biosimilar rituximab (bs-RTX) GP2013 to biologic originator RTX (bo-RTX). Data on effectiveness of switching from bo-RTX to bs-RTX, starting therapy with bs-RTX, and bs-RTX drug survival in real-world setting are sparse. To explore long-term drug effectiveness and survival of bs-RTX GP2013 in rheumatoid arthritis (RA) patients both naïve to and mandatory switched from bo-RTX, and to clarify reasons for treatment cessation. Retrospective observational cohort study including RA outpatient clinic patients treated with bs-RTX between 2018 and 2021 in Norway. Patients were examined and monitored using recommended measures for disease activity and patient-reported outcomes (PROs). For description of population medians and interquartile range were used. Difference between observation times was assessed with Signed-Rank test, drug survival with Kaplan-Meier survival analysis. Reasons for discontinuation were ascertained. Among 110 patients, at baseline, 88 were mandatory switched from bo-RTX and 22 were RTX-naïve. During 2-year follow-up, disease activity and PROs measures remained stable in switchers subgroup and improved in subgroup starting bs-RTX for the first time. Overall drug survival was 80.0% after 1 year and 57.7% after 2 years and was significantly higher in bs-RTX-switched than in bs-RTX-naïve patients (p = 0.036). Two most frequently reported reasons for drug discontinuation were remission (38.6%) and doctor's decision (27.1%). RA patients treated with bs-RTX had satisfactory treatment response and drug retention rates which supports equivalence of bs-RTX GP2013 to bo-RTX, both in patients naïve to and mandatory switched from bo-RTX.