Rituximab biosimilar(BioIntegrator LLC)

This is a multicenter, double-blind, randomized clinical study of safety, tolerability, pharmacokinetics and pharmacodynamics of biosimilar drug Ritumax® compared to original drug MabThera® in patients with rheumatoid arthritis, receiving stable doses of Methotrexate.
At Week -2, after signing the Patient Information Sheet and Informed Consent Form, patients with rheumatoid arthritis receiving stable doses of Methotrexate (10-25 mg per week orally or parenterally) will pass screening procedures.
Patients meeting all the inclusion/exclusion criteria will be invited to the investigational site for Visit 2 (Week 0) to be randomized into one of two treatment arms:
* Ritumax® 1000 mg х 2 intravenous infusions
* MabThera® 1000 mg х 2 intravenous infusions After being assigned to the treatment arm patients will receive a course of study treatment, including two i/v infusions at 14-day interval: at Week 0 and Week 2.
After that, patients will be followed up for the next 22 weeks. Safety, pharmacokinetic and pharmacodynamic parameters will be monitored at this visits.