AB0235 RITUXIMAB (BIOSIMILAR) IN RHEUMATOID ARTHRITIS: CLINICAL & IMMUNOLOGICAL RESPONSE TO VARYING DOSES- EXPERIENCES FROM A TERTIARY CARE CENTER IN SOUTH INDIA

Background: Rituximab (RTX) is a chimeric monoclonal antibody against CD20. There is a paucity of studies done with RTX biosimilars. This is a Retrospective and Observational study from January 2018 to December 2019 done in the Department of Clinical Immunology & Rheumatology, Sri Ramachandra Institute of Higher Education and Research, Chennai, India. Objectives: 1.To find the effects of varying doses of RTX in attaining clinical remission in RA. 2.To find if CD19, CD20 & IgG help in identifying impending flare & if these levels help in deciding the timing of the next dose of RTX. Methods: Rheumatoid arthritis (RA) cases who were given Rituximab from January 2018 were selected. Clinical Response at 6 & 12 months & wherever feasible at 18 & 24 months was assessed by Simplified Disease Activity index (SDAI). RTX initial dose was given at 0 and 14 days followed by fixed dose at six months interval.CD19, CD20 B cell count, IgG levels were tested in patients in whom it was feasible at baseline & 6 months (select patients at 12,18 &24 months). Patients were divided in to 5 groups (DMARD naive, DMARD resistant & Interstitial Lung disease (ILD) [Lung involvement>20% in Computed Tomography (CT)]) and (500mg & 1g). Patients were divided into three clinical groups, (DMARD naive, DMARD resistant & Interstitial Lung disease (ILD) [Lung involvement>20% in Computed Tomography (CT)]) and two treatment groups (500mg & 1g) based on clinical indication for RTX and dose of RTX, respectively. In patients with ILD, CT scan & FVC were compared at baseline & 12 months. Results: 29 patients (seropositive 28 (RF/Anti CCP/BOTH+VE), seronegative 1) were given RTX for RA over a 2-year period of which 12 had CD19, CD20 & IgG tested. Mean SDAI reduction from baseline to 6 months post treatment was 30%, 32% & 14% while complete remission (SDAI 20% reduced from 53.3% to 46.7%. Flare was observed in one patient who received 500mg RTX. CD19, CD20 & IgG levels increased from 7.9%, 8% & 9.8g/L to 27%, 25% & 13g/L respectively. 3 patients in the 1g group were followed up at 12,18 & 24 months. In these patients there were no flares or worsening symptoms. 1 patient was double negative for RF & Anti CCP and this patient did not attain clinical remission even after 2 doses of 1g RTX. Conclusion: [1]Patients with early arthritis (diagnosis made within 1 year) and who were DMARD naive had an excellent response to Rituximab. [2]Complete remission was observed in more patients the 1g compared to 500mg group. [3]Reduction in CD19 & CD20 was associated with significant reduction in the SDAI score. [4]There was no significant reduction of CD19 & CD20 with 500mg dose of Rituximab where either a partial remission or mild flare was observed. [5]There was reduction in the lung involvement to less than 20%(CT) in few patients with 1g dose. [6]Double negative Rheumatoid arthritis poorly responded to Rituximab. [7]The positive effects of 1g Rituximab could be noted up to 24 months. [8]Flare of RA was associated with significant increase in CD19 & CD20. Disclosure of Interests: None declared