Rituximab is a chimeric murine/human immunoglobulin g1 kappa monoclonal antibody targeting the cluster of differentiation 20 antigen found on pre-B and mature B lymphocytes, but not on hematopoietic stem cells, pro-B cells, normal plasma cells or the cells of other normal tissues. In the United States it was approved by the US Food and Drug Administration in 1997 for non-Hodgkin's lymphoma and was later approved for rheumatoid arthritis. Intravenous administration of rituximab results in rapid, selective, prolonged B cell depletion.