Patients with active moderate-to-severe rheumatoid arthritis diagnosed according to the 2010 ACR criteria will be randomized to receive a blinded treatment course of either MabionCD20, EU-Rituximab (MabThera®) or US-Rituximab (Rituxan®) on the top of a stable methotrexate therapy. Two infusions of investigational drug at a dose of 1000 mg will be given at Day 1 and 15. Patients will be then followed for a minimum of 24 weeks to establish PK and therapeutic similarity and to compare PD, safety and immunogenicity parameters between the three rituximab products (Main Phase). Patients may receive a second course of investigational therapy at Week 24, provided that they meet re-treatment eligibility criteria specified in the study protocol. Subjects in MabionCD20 and EU-Rituximab groups will be continued on their assigned treatments, while all subjects in US-Rituximab group will be switched to MabionCD20. All subjects (re-treated and not re-treated) will continue the follow-up until Week 48 to collect long-term safety, immunogenicity and efficacy data.
Primary objective of the study is to establish a 3-way PK similarity bridge between MabionCD20 (candidate biosimilar to rituximab), MabThera® (EU-sourced rituximab) and Rituxan® (US-sourced rituximab) following the administration of these drugs to patients with moderate-to-severe rheumatoid arthritis. Main secondary objective is to confirm therapeutic similarity between MabionCD20 and the reference rituximab.