POS0639 LONG-TERM EFFECTIVENESS OF THE RITUXIMAB HALF DOSE REGIMEN FOLLOWING A RESPONSE TO THE LICENSED DOSE IN RHEUMATOID ARTHRITIS
Authors: L. Garcia-Montoya, M. Y. Md Yusof, G. Eugénio, J. B. Candelier, S. Das, E. Vital, P. Emery
Journal: Annals of the Rheumatic Diseases (2021)

Background: Following initial treatment with rituximab (RTX) full dose (2x1000mg), B-cell numbers are often lower than baseline. The half dose regime (2x500mg) has been reported to be similarly effective [1]; however, there is limited long-term data on the effectiveness of switching to RTX half-dose from the real-world perspective. Objectives: To compare the 3-year RTX regime retention between patients receiving retreatment with half-dose and full-dose of RTX, and assess factors associated with maintenance of 2x500mg, with a view to establish an optimal long-term retreatment strategy in RA. Methods: An observational study was conducted on 755 consecutive RTX-treated RA patients in a single centre for over 20 years. Of these, 165/755 (22%) received at least one cycle of 2x500mg. Long-term effectiveness was assessed using RTX retention rate. Drug survival of patients treated with 2x500mg was compared with 200 RA patients receiving 2x1000mg throughout the study, matched to the number of cycle when the 2x500mg regime was initiated. Results: Of the 165 patients who received 2x500mg, 81.8% were female; mean age was 63.4 (26-91) years; mean disease duration 15.5 (2-53) years; 57 (34.5%) were bDMARDs-naïve; 121 (74%) were on concomitant DMARDs and mean DAS-28 was 3.9 (SD 1.29) at the half dose initiation. At 3 years, the retention rate was 38% for patients recieving 2x500mg compared to 87% for those on 2x1000mg; HR for half dose discontinuation was 6.17 [95%CI (3.91-12.27); p&lt;0.001] (Figure 1A). The main reasons for 2x500mg discontinuation were poor EULAR response (30%); moderate EULAR response (30%); shorter duration of response compared to the full dose (22%); and incomplete B-cell depletion (17%). The majority of these patients (87.9%) were switched back to 2x1000mg, 5.1% received other bDMARDs and 7.1% did not receive further DMARDs. In multivariable analysis, previous TNFi use was associated with 3-year maintenance of the 2x500mg dose [OR 2.63 (1.12-6.10); p=0.024]; while higher plasmablasts at 2x500mg initiation was associated with shorter maintenance of this regime [OR 0.78 (0.67-0.97); p=0.028]. There were no significant differences in 5-year RTX retention rates between patients receiving 2x500mg and switched back to 2x1000mg vs those receiving 2x1000mg throughout the study (Log-Rank=0.186) (Figure 1B). Conclusion: The use of RTX half-dose regimen was associated with poor retention at 3 years. Nevertheless, where loss of effectiveness occurs post-2x500mg initiation, switching back to 2x1000mg appears to be a pragmatic option. Patients with previous TNFi exposure and lower plasmablasts may be most suited to be commenced on the 2x500mg dose for long-term disease control. References: [1]Mariette X, et al. ARD 2014 Acknowledgements: Leeds Cares Disclosure of Interests: Leticia Garcia-Montoya: None declared, Md Yuzaiful Md Yusof: None declared, Gisela Eugénio: None declared, Jean Baptiste Candelier: None declared, Sudipto Das Speakers bureau: Dr Das has received honoraria from Roche, Edward Vital Speakers bureau: Dr Vital has received honoraria from Roche, Consultant of: Dr Vital has received honoraria a from Roche, Grant/research support from: Dr Vital has received research grant support from Roche, Paul Emery Speakers bureau: Professor Emery has received honoraria from Roche, Consultant of: Professor Emery has received consultant fees from Roche, Grant/research support from: Professor Emery has received research grants paid to his employer from Roche.