Cyclophosphamide is a synthetic DMARD. Its major active metabolite is phosphoramide mustard, which cross-links DNA to prevent cell replication. It suppresses T-cell and B-cell function by 30–40%; T-cell suppression correlates with clinical response in the rheumatic diseases.
Cyclophosphamide is active against rheumatoid arthritis when given orally at dosages of 2 mg/kg/d but not intravenously. It is used regularly to treat systemic lupus erythematosus, vasculitis, Wegener’s granulomatosis, and other severe rheumatic diseases.