Background/Purpose: Immunobiological drugs emerged as a revolutionary option for treating inflammatory chronic rheumatic diseases, particularly rheumatoid arthritis (RA). However, the extremely high costs associated with originator drugs caused an overload in the health systems worldwide. At the end of patent period, biosimilars (BS) were announced as a cost-effective alternative. BS are biological drugs containing a version of the active substance of an already authorized original biological product. Few studies have assessed the switch from originator Rituximab (RTX) MabtheraⓇ (MBT) to the biosimilar RiximyoⓇ (RIX) in RA patients. Our purpose was to evaluate safety and treatment response in RA patients receiving RTX for the first time by comparing MBT and RIX presentations, focusing on articular response.

Methods: A single-center retrospective analysis was conducted using a medical electronic database in a tertiary center in Brazil. Inclusion criteria comprised individuals aged over 18 years with RA who were prescribed MBT or RIX between January 2010 and October 2023. Data were collected at baseline and after six months of the first cycle of RTX, regardless of whether it was originator or BS.

Results: A total of 76 patients treated with MBT and 63 treated with RIX were included. Due to the historical access to bDMARDs in Brazil, patients who received MBT were different from those who received RIX: they were younger (mean age: 55.1 vs 58.7, p=0.017), with a more frequent indication for treatment due to articular activity (90.8% vs 73.0%, p=0.007) and less due to pulmonary involvement (10.5% vs 23.8%, p=0.041), and were less refractory, with a lower number of failures to previous bDMARDs [1(0-2) vs 2(1-4), p=0.005]. When considering the subgroup of patients who had previously used up to two bDMARDs and only articular indication for RTX, patients with RIX were still older (63.3 vs 54.1, p=0.012) and presented a longer disease duration at the beginning of treatment (18.6 vs 12.7, p=0.036). There was no difference of sDMARDs associated with RTX in both groups (p >0.05). Regarding treatment efficacy, the two groups MBT and RIX presented similar responses after six months as evidenced by the following measures: SDAI [11.1(6.0-19.9) vs 16.3(9.6-23.5), p=0.381], CDAI [10.0(5.0-19.6) vs 16.0(9.0-22.0), p=0.415), DAS28 [ 3.8 ± 1.5 vs 4.3 ± 1.4, p=0.387) and DAS28-CRP (3.6 ± 1.5 vs 3.8 ± 1.6, p=0.580), 50% reduction in baseline SDAI (SDAI50%) (42.1%vs21.4%, p=0.209) and reduction in DAS28-CRP >1.2(deltaDAS28-CRP >1.2) (65.8%vs42.9%, p=0.203), respectively. Furthermore, there were no statistical differences in infusion-related reactions (7.9% vs 14.3%, p=0.602) or final prednisone dose [5(5-10) vs 5(0-7.5), p=0.220].

Conclusion: In this real-life retrospective analysis, we found a similar pattern of articular response and infusional safety among patients who received originator MBT and biosimilar RIX, confirming data from pharmacokinetic and phase III clinical studies used to RIX approval. However, historical discrepancies regarding the availability and indication of the drug precludes a definitive conclusion.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-the-safety-and-effectiveness-of-originator-rituximab-mabthera-versus-biosimilar-riximyo-in-rheumatoid-arthritis-a-retrospective-unicentric-analysis/