azathioprine (Azasan)

What is azathioprine, and how does it work (mechanism of action)?

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 modifying the 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. The FDA approved azathioprine in March 1968.

What brand names are available for azathioprine?

Imuran, Azasan

Is azathioprine available as a generic drug?


Do I need a prescription for azathioprine?


What are the side effects of azathioprine?

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.

What is the dosage for azathioprine?

The initial dose for preventing organ rejection is 3 to 5 mg/kg (oral or IV) daily, starting at the time of transplantation or in some cases 1 to 3 days before transplantation. The initial off-label dose for treating rheumatoid arthritis is 1.0 mg/kg (50 to 100 mg, oral or IV) as a single dose or twice daily. Doses may be increased by 0.5 mg/kg daily up to a maximum dose of 2.5 mg/kg per day. Dosing for other off-label use may vary according to what disease is being treated; in general, off-label use should be done by an experienced medical specialist. Azathioprine should be taken with food.


What Is Rheumatoid Arthritis (RA)? Symptoms, Treatment, Diagnosis See Slideshow

Which drugs or supplements interact with azathioprine?

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.

Is azathioprine safe to take if I'm pregnant or breastfeeding?

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

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

What else should I know about azathioprine?

What preparations of azathioprine are available?

Tablet: 25, 50, 75, 100 mg. Injection: 100 mg

How should I keep azathioprine stored?

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


Azathioprine (Imuran, Azasan) is a drug prescribed for prevention of organ rejection in kidney transplants. Off label uses for azathioprine (Imuran, Azasan) include rheumatoid arthritis, multiple sclerosis, Crohn's disease, myasthenia gravis, ulcerative colitis, and autoimmune hepatitis. Side effects, drug interactions, and safety during pregnancy information should be reviewed prior to taking this drug.

Treatment & Diagnosis

Medications & Supplements

Prevention & Wellness

Health Solutions From Our Sponsors

FDA Logo

Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

See more info: azathioprine on RxList
Medically reviewed by John P. Cunha, DO, FACOEP; Board Certified Emergency Medicine


FDA Prescribing Information