330. Treatment Efficacy of Biosimilar Rituximab Compared to the originator in Patients with ANCA associated Vasculitis

Background: Truxima is a biosimilar version of rituximab. It was licensed & launched in the United Kingdom in April 2017. A biosimilar medicine is made to be similar in quality, safety and efficacy to existing licensed “reference” biological medicine and the cost is often significantly lower. A recent systematic review showed comparable long-term efficacy and safety of biosimilar rituximab to the originator ug in treatment of rheumatoid arthritis and non-Hodgkin’s lymphoma. Few data are available regarding the efficacy of biosimilar rituximab in treatment of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). A retrospective study was thus conducted in our centre to examine the efficacy of Truxima when compared to the reference rituximab (MabThera) in the treatment of patients with AAV. Methods: All patients with new or relapsing AAV who received first ever rituximab therapy between 1/1/2016 and 31/12/2018 were identified via our hospital dispensing database, and stratified into Truxima or MabThera treatment groups depending on the version of rituximab administered. Primary outcomes that were assessed included: time to B cell depletion (defined as absolute B cell count (ABC) 10 cells/µL) and repletion (i.e ABC >10 cells/µL and >20 cells/µL); time to myeloperoxidase (MPO)/proteinase 3(PR3)-ANCA negativity.Secondary outcomes included: overall survival, time to major relapse (defined as relapse requiring further course of rituximab for remission induction); adverse events including episodes of neutropenia, hypogammaglobulinemia and major infusion reactions. Subgroup analysis in patients who received concomitant cyclophosphamide and rituximab or other induction therapy was performed to examine its impact on treatment efficacy and safety. Results: 59 and 60 patients received Truxima and MabThera, respectively, for treatment of new or relapsing AAV. The baseline characteristic (age, gender, entry estimated Glomerular Filtration Rate, proportion of patients received concomitant cyclophosphamide, ANCA serology, and pattern of organ involvement) of both group were comparable. All patients achieved clinical remission following induction treatment. Using Kaplan Meier analysis and log rank test, no difference was identified in time to B cell depletion or repletion (Figure 1A & 1B), MPO/PR3-ANCA negativity (Figure 1C), overall survival or major relapses requiring further rituximab as induction therapy. Treatment efficacy of Truxima and MabThera did not differ in subgroup analysis. However, we observed that patients who received concurrent cyclophosphamide during induction therapy achieved MPO/PR3-ANCA negativity more rapidly compared to those who did not, irrespective of the version of rituximab received (Figure 1D). No difference in adverse events such as major infusion reactions was seen in either group upon first rituximab exposure. Two patients in each group developed reactions following repeated dosing of rituximab. Conclusions: Biosimilar rituximab Truxima appears to have comparable B cell depletion kinetics and treatment efficacy compared to the reference ug in our cohort of patients with AAV. Combination of rituximab, regardless of ug type, to cyclophosphamide may lead to more rapid ANCA-negative seroconversion. Disclosures: Non