Amgen (NASDAQ:AMGN) today announced that the U.S. Food and Drug Administration (FDA) has approved RIABNI™ (rituximab-arrx), a biosimilar to Rituxan®, in combination with methotrexate for adults with moderate to severely active rheumatoid arthritis (RA) who have had an inadequate response to one or more tumor necrosis factor (TNF) antagonist therapies.