POS0652 LONG-TERM EFFECTIVENESS OF ULTRA-LOW DOSES OF RITUXIMAB IN RHEUMATOID ARTHRITIS

Background The optimal rituximab (RTX) dose for the treatment of rheumatoid arthritis remains unclear. RTX 1000mg per 6 months and 2000mg were shown to be similarly efficacious (1). REDO trial showed comparable 6-month efficacy continued with 500mg 200mg compared 1000mg, though formal non-inferiority could not established (2). Objectives To assess long-term effects ultra-low (1×500mg 1×200mg) in RA patients previously responding well conventional low (1×1000mg). Methods Patients from invited participate this study. Treatment decisions left at discretion rheumatologist patient. Disease activity (DAS28-CRP), medication use (b/tsDMARD, csDMARD, gluccocorticoids [GC]) collected start censoring April 2021. primary outcome was disease activity, secondary outcomes persistence, doses intervals, comedication. analyzed using a longitudinal mixed model random intercepts account intra-patient correlations, two ways: 1. By original randomization stratification factors (RF/ACPA csDMARD use). 2. time-varying total received year preceding each measurement, adjusted current or GC use, RF/ACPA. DAS28-CRP (NI) margin 0.6 used. Results 118 out 142 included analyses (Table 1) Reasons exclusion were: continuing elsewhere (n=3), no informed consent (n=9) data yet 2 study centers (n=12). Mean follow up 3.2 years (total 377 patient-years), 7 switching another b/tsDMARD (Figure upon which they censored analyses. Table Patient characteristics by (n=24) (n=48) (n=46) Age (years) 65 (9) 64 (11) (12) Female 15 (63%) 28 (58%) 34 (74%) Meeting ACR1987 ACRU/EULAR 2010 criteria 22 (92%) 47 (98%) 43 (93%) duration 14 (9-24) (7-21) 13 (8-20) RF ACPA positive 44 40 (87%) Duration 3.0 (1.6-5.5) 2.0 (1.0-5.5) 3.7 (2.0-5.7) Concomitant 17 (71%) 29 (60%) 27 (59%) Previous number b/tsDMARDs used (2-2) (1-3) (1-2) csDMARDs 3 (1-4) Oral baseline (13%) 8 (17%) 5 (11%) Baseline 2.3 (0.9) 2.5 (1.1) Data are n (%), mean (SD), median (IQR). Figure Rituximab persistence during up. both groups non-inferior group, (95% CI) follow-up 2.2 (2.0-2.4) (2.1-2.4) group (2.2-2.5) group. Analyzed dose, lower significantly associated higher DAS28-CRP: 0.15 CI: 0.04-0.26) points more RTX. upper limit relevant below prespecified NI margin, excluding effect on activity. Median (IQR) yearly 978mg (704mg-1425mg). Final infusion 37 (31%), (40%) (29%), final interval between infusions 6.0 (5.7-6.5), 6.2 (6.0-7.4) 6.4 (6.0-9.6) respectively. rate injections 0.38 0.32-0.44) patient-year initiation oral 0.05 (0.03-0.08) patient-year. Conclusion A majority treated remained 4 years, while did relevantly differ doses, either according dose. Switching other b/tsDMARDS rarely required. References [1]Bredemeier M et al. Clin Rheumatol 2015 Oct;34(10):1801-5. [2]Verhoef LM Lancet Rheumatol. 2019; 1: e145-e153. Disclosure Interests Nathan den Broeder: None declared, L.M. Verhoef: Yaël A. de Man: Marc R Kok: R.M. Thurlings: W. van der Weele: Bart Bemt Speakers bureau: UCB, Pfizer, Sanofi-Aventis, Galapagos, Amgen Eli Lilly, Frank Hoogen: Aatke Maas: Alfons Broeder Grant/research support from: Abbvie, Novartis, Sanofi, Gilead