Rituximab is a medication used to treat certain autoimmune diseases and types of cancer. specifically it is used for non-hodgkin s lymphoma, chronic lymphocytic leukemia, rheumatoid arthritis, idiopathic thrombocytopenic purpura, and pemphigus vulgaris. it is given by slow injection into a vein.rituximab is a monoclonal antibody against the protein cd20, which is primarily found on the surface of immune system b cells. when it binds to this protein it triggers cell death.