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Objectives There are limited data to support non-medical switch from originator rituximab (RTX-O) to biosimilar (RTX-B) or between biosimilars in SLE and other connective tissue disease and vasculitis (CTD-VAS) due to a concern with cross-reactivity of antibodies compared with rheumatoid arthritis. This study evaluated the effectiveness of non-medical biosimilar RTX switch programme in SLE and CTD-VASMethods We conducted a retrospective observational cohort study of all CTD-VAS patients in a centre between October 2017 (Index date) and November 2024. Patients were encouraged to switch from RTX-O to RTX-B and between biosimilars RTX as per contractual agreement. Consultants’ assessment of clinical response was recorded, as well as data on CD20+ cells depletion using highly sensitive flow cytometry. 5-year RTX retention rate between patients who underwent non-medical switch (Group 1) vs those remained on RTX-O or started RTX-B (Group 2) was analysedResults At Index date, of 300 CTD-VAS patients studied, 90(30%) underwent non-medical switch, Group 1 [RTX-O to RTX-B=68%; between biosimilars=32%]. Their mean (SD) age was 51 (15) years, 72% were female, 71% were of European ancestry, median (IQR) disease duration of 8.7 (5-15) years, and diagnoses were SLE (53%), AAV (31%), Sjogren (4%), and other CTD-VAS (12%). 16/300 (5%) patients remained on RTX-O, while 194/300 (65%) initiated treatment with RTX-B; therefore Group 2=210/300 (70%).In Group 1, of 87/90 and 77/90 patients with paired clinical response and B-cells data in the RTX cycle before and after switch respectively, there was no difference in response rate and CD20+ cell complete depletion, p=0.289 and p=1.00 respectively.At 5 years, 9/90 (10%) patients discontinued RTX in Group 1 [inefficacy=7; 2 deaths], while in Group 2, 28/210 (13%) discontinued therapy [inefficacy=16; side effects=3; and deaths=9]. 44% and 32% respectively had a diagnosis of SLE. Kaplan-Meier analysis showed no difference in 5-year RTX retention between groups; adjusted HR 0.71 (95% CI 0.30-1.71), p=0.448 (figure 1).Abstract PO:12:311 Figure 1Conclusions Our findings support non-medical switch either from RTX-O to RTX-B or between biosimilars in SLE and CTD-VAS. Given its low cost and durability, future studies should assess the cost-effectiveness of first-line use of rituximab biosimilars in patients with CTD-VAS.