AZATHIOPRINE

immunosuppressive drug that is used to treat rheumatoid arthritis and to suppress the body's rejection of transplanted kidneys. Azathioprine decreases the number of lymphocytes that can migrate to inflammatory sites. Azathioprine is beneficial in maintaining transplanted kidneys and other tissues. Leukopenia (an abnormally low number of white blood cells in the circulation) is the drug's major undesirable side effect, although anemia and bleeding may also occur. When used with allopurinol, azathioprine's pharmacological effect is increased. The drug is readily absorbed after oral administration. Azathioprine is a derivative of 6-mercaptopurine, which is an important drug in the treatment of acute leukemia.