context: In cancer treatment, chemotherapy refers to particular class of drugs used to kill or slow the reproduction of rapidly multiplying cells. In rheumatology, chemotherapy is designed to decrease the abnormal behavior of cells, rather than kill cells. The doses of medication used for rheumatic or autoimmune conditions are generally lower than the doses used for cancer treatment. In many rheumatic diseases, inflammation causes damage to parts of the body; for example - causing painful joints as in rheumatoid arthritis. In many cases, inflammation results from autoimmunity, a malfunction of the immune system where one's own tissues or organs are not recognized as such and are attacked by the body's immune system. Chemotherapy helps people with certain inflammatory and autoimmune diseases because it slows cell reproduction and decreases certain products made by these cells that cause an inflammatory response to occur. Although there are many chemotherapy drugs, only some are used to treat rheumatic diseases today. These include: Methotrexate ( Rheumatrex, Trexall). Methotrexate is the chemotherapeutic drug most widely used by rheumatologists because it is effective in treating rheumatoid arthritis and certain other rheumatic diseases (such as certain forms of vasculitis, or inflammation of blood vessels), and it is relatively safe. Most patients can take methotrexate by mouth in a single, weekly dose. Some patients prefer to take it as an injection once a week. Its common side effects are relatively easy to monitor, treat, and prevent. Imuran. Imuran has been used for many years as an immunosuppressive drug to prevent organ rejection in patients receiving kidney transplants. Usually taken in a single or twice daily dose by mouth, Imuran also is used to suppress the abnormal immune response in some patients with vasculitis, systemic lupus erythematosus (lupus), and rheumatoid arthritis. Cytoxan. Cytoxan is a more powerful drug and has more side effects than methotrexate and Imuran. It is usually given intravenously to treat the most aggressive and dangerous rheumatic diseases and their complications, such as severe lupus and some forms of vasculitis. Rapidly reproducing or growing cells, such as immune cells, are destroyed by Cytoxan. Other rapidly reproducing cells in the body may also be affected by Cytoxan and this accounts for some of the side effects of the drug. Cytoxan also destroys good immune cells and this results in an increased risk of infection. Side effects of chemotherapy drugs are fairly common, even though the doses are typically lower than the doses used to treat cancer. All of these drugs can suppress the formation of blood cells, resulting in: Anemia or low red blood cell count. Red blood cells are the cells that carry oxygen throughout your body Leukopenia/ Neutropenia or low white blood cell count that may cause decreased ability to fight infection Thrombocytopenia or low platelet count that may cause impaired blood clotting In addition, methotrexate and Imuran can damage the liver, and Cytoxan can damage the urinary bladder lining and cause bleeding. Cytoxan also causes hair loss and sterility. Methotrexate and Cytoxan can cause damage to the lungs. Since no drug is entirely safe, your doctor will talk to you about the possible benefits of these drugs, as well as their side effects. The occurrence of side effects depends on the dose, type of drug, and length of treatment. It is very important to have the appropriate follow-up exams and lab testing while taking chemotherapy drugs. Careful monitoring can minimize all of these risks. Although there are some differences among the drugs and how they are used to treat certain rheumatologic and autoimmune diseases, these drugs usually produce benefits gradually, requiring weeks to months for full effectiveness. Generally, if there is no benefit within four months, it is unlikely that continuing the chemotherapy drug at the same dose will be helpful. Methotrexate and Imuran can be used for prolonged periods (many years) if necessary, as long as they do not cause serious side effects. Cytoxan is generally used for more limited periods because of its greater side effects. However, in certain cases more prolonged use may be necessary.