Azathioprine (Imuran)

Pill Bottle with Pills

Fast Facts

  • Azathioprine is used to treat joint swelling in rheumatoid arthritis and complications of other conditions, including lupus, vasculitis or myositis.
  • Blood counts of patients taking azathioprine should be carefully monitored to minimize their risk of infections while taking this drug.
  • Patients taking azathioprine should notify their physician if they develop fevers or nausea and vomiting as these can be signs of a serious allergic reaction or infection.

Azathioprine (Imuran) is a drug used to suppress the immune system and help treat symptoms like joint pain and swelling in certain autoimmune conditions. The most common diseases treated with Imuran are dermatomyositis, systemic lupus erythematosus (lupus), inflammatory bowel disease and vasculitis (inflammation of the blood vessels).  Azathioprine can also be used to treat rheumatoid arthritis, but it is not used as commonly as other DMARDs like methotrexate.

Azathioprine (Imuran) can be used to treat many other inflammatory conditions like inflammatory muscle diseases (dermatomyositis and polymyositis), multiple sclerosis, myasthenia gravis, autoimmune hepatitis and inflammatory bowel disease. It is also used in combination with other medications to suppress the immune system after organ transplantation to prevent rejection of transplanted organs.

Azathioprine (Imuran) belongs to a class of medications called disease-modifying antirheumatic drugs (DMARDs) or immunosuppressants. This class of medicines can decrease joint damage and disability.

How it works

Azathioprine is a prodrug (a precursor of the active drug) which is converted in the body to its active components 6-mercaptopurine and 6-thioinosinic acid. Azathioprine works by reducing the function of the body’s immune system response. Although the immune system is important for fighting infections, immune system cells sometimes mistakenly attack the body's own tissues. Azathioprine helps prevent this by interfering with deoxyribonucleic acid (also known as DNA) synthesis, which is needed for cells to grow and divide.

Dosing and time to effect

Dosage of this medication depends on the disease being treated. The initial dose for rheumatoid arthritis is approximately 1 milligram/kilogram (mg/kg) of body weight, or approximately 50 to 100 mg given as a single dose or twice daily. This can be increased every 1-2 months, up to a maximum dose of 2.5 mg/kg of body weight, or approximately 75 to 150 mg given twice a day.

A benefit in arthritis or other conditions may appear as early as 6-8 weeks. It may take up to 12 weeks to notice a full effect.

Side effects

The most common side effects of azathioprine can involve the gastrointestinal tract (which includes the stomach, intestines, liver and pancreas) and the blood cells. Approximately 10­­­­­­­-15 percent of patients may have nausea and vomiting after taking this medication, sometimes accompanied by abdominal pain or diarrhea. Taking the medication twice daily instead of all at once, or taking it after eating, may help avoid these problems. If vomiting occurs, you should contact your doctor, as this may be a sign of a serious reaction.

Less often, azathioprine may cause hepatitis (liver swelling or damage), pancreatitis (swelling or damage to the pancreas gland behind the stomach, which can cause abdominal pain) or an allergic reaction that may include a flu-like illness or a rash. Azathioprine also can lower the number of infection-fighting white blood cells.

Before or during treatment, your doctor may perform a thiopurine methyltransferase enzyme activity level (TPMT). This enzyme helps clear the medication from your system. If you have lower amounts of these enzymes, you may be at higher risk for medication toxicity.

Long-term use of azathioprine in combination with other immune-suppressing medications in transplant patients has been associated with a slightly elevated risk of cancer. There may be a similar slight increased risk of lymphoma (a form of cancer) in patients taking this medication for inflammatory bowel disease.  This risk appears to be increased when taken along with medications known as anti-TNF drugs (or TNF inhibitors) in the treatment of Crohn’s disease or ulcertative colitis. It is not clear whether arthritis patients face a similar risk.

Drug interactions

Be sure to tell your doctor about all of the medications you are taking, which may include over–the-counter drugs and natural remedies. Medications that may interfere with azathioprine and potentially cause serious problems include the gout medication allopurinol (Aloprim, Zyloprim); warfarin (Coumadin); some blood pressure medications, including some angiotensin-converting enzyme (ACE) inhibitors (Accupril or Vasotec); olsalazine (Dipentum); mesalamine (Asacol, Pentasa); and sulfasalazine (Azulfidine).

Information to discuss with healthcare providers

It is important to take azathioprine as directed and have regular blood tests. You should notify your doctor if you have these symptoms while taking this medication: fever, rash, easy bruising or bleeding, or signs of an infection.

Make sure to notify your other physicians that you are taking this drug. If you are pregnant or are considering having a child, discuss this with your doctor before starting this medication. Women taking this medication should discuss appropriate forms of birth control with their primary care physicians or gynecologists. The use of an effective form of birth control is important as long as you take this medication and for months after it is stopped. Breast-feeding should be avoided while taking azathioprine because the drug can enter breast milk.

Be sure to talk with your doctor before receiving any vaccines or undergoing any surgeries while taking this medication. Live vaccines should be avoided while on this medication, and you should discuss updating your vaccinations prior to starting this medication. It may be important to receive certain vaccines before starting this medication, such as the Pneumovax (pneumonia vaccine), hepatitis B, tetanus booster, or the Zostavax (shingles vaccine) for some patients.

Because this medication can lower your ability to fight infection, it is important you discuss this with any treating physician, as this may lead to a different evaluation or treatment.

Updated May 2015.Written by Michael Cannon, MD, and reviewed by the American College of Rheumatology Communications and Marketing Committee.

This information provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.

© 2015 American College of Rheumatology