Real-world experience of effectiveness of non-medical switch from originator to biosimilar rituximab in rheumatoid arthritis

Objective: To evaluate the impact of non-medical switch from rituximab originator (RTX-O) to biosimilar (RTX-B) in patients with rheumatoid arthritis (RA).Methods: Between October 2017 and October 2019, all patients on RTX-O in our centre requiring re-treatment were switched to RTX-B unless declined by patient or specified by treating clinician. Switch strategy effectiveness was assessed retrospectively using DAS28-CRP(3) and RTX retention, with patients remaining on RTX-O as a comparator group.Results: 255/337 patients (75.6%) switched to RTX-B while 82 (24.3%) remained on RTX-O. There was no difference in DAS28-CRP(3) 4 months post-RTX-B switch versus same time-point post-RTX-O previous cycle (paired data available in 60%). Eighteen month retention estimates were 75.6% (95% CI 69.4–80.7) for RTX-B group and 82.3% (95% CI 70.4–89.8) for RTX-O [adjusted HR 1.52 (95% CI 0.85-2.73)]. 42/255 patients (16.5%) discontinued RTX-B for loss of effectiveness (LOE), 5 (2.0%) for AE. Risk of RTX-B discontinuation was associated with comorbidities and ≥2 previous bDMARDs. Risk of adverse outcome RTX cessation was associated with comorbidities, and reduced risk with number of previous RTX-O cycles and pre-switch cycle B-cell depletion. 34/255 patients (13.3%) switched back to RTX-O (LOE=30, AE=4), while 13/255 (5.1%) started other b/tsDMARDs. Of patients switched back for LOE, 28/30 remained on RTX-O at mean 7.7 months follow-up. Conclusion: Non-medical switch to RTX-B was largely effective. Factors associated with RTX-B discontinuation, including comorbidities, previous bDMARDs, and RTX-O treatment history, may inform switch decisions. Most patients switched back to RTX-O for LOE remained on treatment at short-term follow-up.