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 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 the patient or specified by the 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. The number of patients switching to RTX-B was 255/337 (75.7%) while 82 (24.3%) remained on RTX-O. There was no difference in DAS28-CRP(3) 4 months post-RTX-B switch vs the 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 hazard ratio 1.52 (95% CI: 0.85, 2.73)]. The number of patients who discontinued RTX-B for loss of effectiveness (LOE) was 42/255 (16.5%), five (2.0%) for adverse effects (AEs). Risk of RTX-B discontinuation was associated with comorbidities and >= 2 previous biologic DMARDs. 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. The number of patients who switched back to RTX-O was 34/255 (13.3%) (LOE: 30, AEs: 4), while 13/255 (5.1%) started other biologic/targeted synthetic DMARDs. Of patients who switched back for LOE, 28/30 remained on RTX-O at a 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 biologic DMARDs, and RTX-O treatment history, may inform switch decisions. Most patients who switched back to RTX-O for LOE remained on treatment at short-term follow-up.