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Class: Biologic Therapy

Generic Name: azathioprine

Trade Name: Imuran®, Azasan®

How is this drug used? Azathioprine is approved as a supplementary for the prevention of renal transplantation failure, and for adults with active rheumatoid arthritis (RA).

What is the mechanism of action? Azathioprine is an immunosuppressant that works by suppressing the immune system to prevent it from damaging tissues and joints. The immune system helps protect the body from harmful substances such as infectious agents and bacteria. In people with RA, however, the immune system attacks and destroys normal tissue—namely, the tissue around the joints. This leads to inflammation and damage to the cartilage and bone and causes pain. Specifically, azathioprine blocks the action of a certain enzyme to decrease the proliferation of rapidly dividing cells.

How is azathioprine given (administered)? Azathioprine is taken orally. Dose may be increased after an adequate and positive trial period.

How are patients monitored? Patients should have complete blood counts (CBC), including platelet counts, weekly during the first month, twice monthly for the second and third months of treatment, then monthly or more frequently if dosages have been changed, or other therapy has been added.

What are the most common side effects of treatment with azathioprine?

  • Black, tarry stools
  • Bleeding gums
  • Blood in urine or stools
  • Chest pain
  • Cough or hoarseness
  • Fever or chills
  • Lower back or side pain
  • Painful or difficult urination
  • Pinpoint red spots on the skin
  • Shortness of breath
  • Sore throat
  • Mouth sores
  • Swollen glands
  • Unusual bleeding or bruising
  • Fatigue

This is not a complete list of side effects. Some patients may experience other side effects that are not listed here. Patients may wish to discuss with their physician the other less common side effects of this drug, some of which may be serious.

Some side effects may require medical attention. Other side effects do not require medical attention and may go away during treatment. Patients should check with their physician about any side effects that continue or are bothersome.

What are some of the less common but potentially serious side effects of azathioprine?

  • Abdominal or stomach pain
  • Clay-colored stools
  • Dark urine
  • Decreased appetite
  • Fast heartbeat
  • Sudden fever
  • Headaches
  • Itching
  • Loss of appetite
  • Muscle or joint pain
  • Severe nausea, vomiting or diarrhea
  • Redness or blisters on skin
  • Swelling of feet or lower legs
  • Sudden discomfort or illness
  • Yellow skin or eyes
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Are there any special precautions patients should be aware of before starting treatment?

  • Acute myelogenous leukemia (AML) as well as solid tumors have been reported in patients with rheumatoid arthritis who have received azathioprine.
  • Severe low white blood cell counts, platelets counts, and red blood cell counts, including macrocytic anemia, and/or pancytopenia may occur in patients being treated with azathioprine. Severe bone marrow suppression may also occur.
  • Patients receiving immunosuppressants are at increased risk of developing lymphoma and other malignancies, particularly of the skin. Exposure to sunlight and ultraviolet light should be limited by wearing protective clothing and a high SPF sunscreen.
  • Pregnant or nursing women should not be treated with azathioprine, although there are no adequate studies to prove negative effects. If this drug is used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus. Women of childbearing age should be advised to avoid becoming pregnant.
  • Patients with low or absent TPMT activity are at an increased risk of developing severe, life-threatening myelotoxicity if receiving conventional doses of azathioprine. TPMT genotyping or phenotyping can help identify patients who are at an increased risk for developing toxicity.
  • Azathioprine is not recommended for patients who are hypersensitive to azathioprine.
  • Severe infections may occur when using azathioprine. Patients receiving azathioprine are at increased risk for bacterial, viral, fungal, protozoal, and opportunistic infections, including reactivation of latent infections such as tuberculosis (TB). These infections may lead to serious, including fatal outcomes.
  • Cases of JC virus-associated infection resulting in progressive multifocal leukoencephalopathy (PML), sometimes fatal, have been reported in patients treated with immunosuppressants, including azathioprine.
  • Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines and all herbal supplements as other medicines may affect each other and cause serious side effects.

When should patients notify their physician?

Contact your healthcare professional immediately in case of any of the following:

  • You have symptoms of an infection. These include: fever; unusual tiredness; cough; flu-like symptoms; and warm, red, or painful skin.
  • You have symptoms of an allergic reaction. These include: hives, rash, or mucous membrane lesions.
  • You have symptoms of liver dysfunction or disease. These include: unusual tiredness, abdominal pain, or jaundice.
  • You have symptoms of a blood deficiency. These include: bruising or bleeding easily, recurrent infections, fever, paleness, or unusual tiredness.
  • You have symptoms of lung disease. These include: cough, shortness of breath, nail deformity, unusual tiredness, or weight loss.
  • You become pregnant.
  • You notice an irregularity on your skin.

What is a package insert?

A package insert is required by the FDA and contains a summary of the essential scientific information needed for the safe and effective use of the drug for healthcare providers and consumers. A package insert typically includes information regarding specific indications, administration schedules, dosing, side effects, contraindications, results from some clinical trials, chemical structure, pharmacokinetics and metabolism of the specific drug. By carefully reviewing the package insert, you will get the most complete and current information about how to safely use this drug. If you do not have the package insert for the drug you are using, your pharmacist or physician may be able to provide you with a copy.

Important Limitations of Use

The information provided above on the drug you have selected is provided for your information only and is not a substitute for consultation with an appropriate medical doctor. We are providing this information solely as a courtesy and, as such, it is in no way a recommendation as to the safety, efficacy or appropriateness of any particular drug, regimen, dosing schedule for any particular cancer, condition or patient nor is it in any way to be considered medical advice. Patients should discuss the appropriateness of a particular drug or chemotherapy regimen with their physician.

As with any printed reference, the use of particular drugs, regimens and drug dosages may become out-of-date over time, since new information may have been published and become generally accepted after the latest update to this printed information. Please keep in mind that health care professionals are fully responsible for practicing within current standards, avoiding use of outdated regimens, employing good clinical judgment kin selecting drugs and/or regimens, in calculating doses for individual patients, and verifying all dosage calculations.



The prescribing physician is solely responsible for making all decisions relating to appropriate patient care including, but not limited to, drugs, regimens, dose, schedule, and any supportive care.