Medications and Drugs

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Pharmacy Author: Annette O. Gbemudu, PharmD, MBA
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: azathioprine

BRAND NAME: Imuran, Azasan

DRUG CLASS AND MECHANISM: Azathioprine is an immunosuppressant, that is, a drug that is used to suppress the immune system. It is used to treat patients who have undergone kidney transplantation and for diseases in which activity of the immune system is important. Azathioprine is a prodrug (a precursor of a drug) which is converted in the body to its active form called mercaptopurine (Purinethol). The exact mechanism of action of azathioprine is not known.

Like other immunosuppressants, it suppresses the proliferation of T and B lymphocytes, types of white blood cells that are part of the immune system and defend the body against both infectious diseases and foreign materials. For example, in the case of organ transplantation, immunosuppressants prevent the body from immunologically rejecting the new organ. In the case of autoimmune diseases (diseases caused by an abnormal immune reaction against the body's own tissues) such as rheumatoid arthritis, suppressing the immune system reduces the inflammation that accompanies immune reactions and slows damage to the joints caused by the inflammation.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablet: 50, 75, 100 mg. Injection: 100 mg

STORAGE: Azathioprine should be stored at 15-25 C (59-77 F) in a dry place and protected from light.

PRESCRIBED FOR: Azathioprine is used for preventing rejection of transplanted kidneys. Azathioprine also is used for the treatment of severe, active, rheumatoid arthritis in patients who do not respond to rest, aspirin, or other nonsteroidal antiinflammatory drugs.

Non-FDA approved uses for azathioprine include multiple sclerosis, where several clinical trials have shown decreases in relapses but no slowing in progression of the disease. There also is limited data on the safety of azathioprine in multiple sclerosis. Other non-FDA (off-label) uses of azathioprine include Crohn's disease, myasthenia gravis, chronic ulcerative colitis, and autoimmune hepatitis (in combination with prednisone).

DOSING: Azathioprine should be taken with food.

DRUG INTERACTIONS: Allopurinol (Zyloprim) that is used for treating increased blood levels of uric acid and preventing gout increases azathioprine levels in the blood which may increase the risk of side effects from azathioprine. Therefore, it is important to reduce the dose of azathioprine by approximately 1/3 to 1/4 in patients taking allopurinol. The use of angiotensin-converting enzyme (ACE) inhibitors to control high blood pressure in patients taking azathioprine has been reported to induce anemia (low levels of red blood cells) and severe leukopenia (low levels of white blood cells). Azathioprine reduces blood levels of the blood thinner, warfarin (Coumadin), and thus may reduce the blood thinning effect of warfarin. Safety and efficacy of azathioprine in children have not been established

PREGNANCY: Azathioprine can cause fetal harm when given to pregnant women and whenever possible should be avoided.

NURSING MOTHERS: Azathioprine is found in breast milk and should not be used in nursing mothers.

SIDE EFFECTS: The most common serious side effects of azathioprine involve the cells of the blood and gastrointestinal system. Azathioprine can cause serious lowering of the white blood cell count, resulting in an increased risk of infections. This effect is reversed when the dose of azathioprine is reduced or temporarily discontinued. Azathioprine can cause nausea, vomiting, and loss of appetite, which may resolve when the daily dose is reduced or divided and taken more than once a day. Azathioprine can cause liver toxicity (for example, in less than 1% of rheumatoid arthritis patients). All patients taking azathioprine require regular testing of blood for blood cell counts and liver tests to monitor for side effects of azathioprine. Other side effects encountered less frequently include fatigue, hair loss, joint pains, and diarrhea.

Reference: FDA Prescribing Information

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