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Generic Name

azathioprine (ay za THYE oh preen)


Trade Name



What is azathioprine?

Azathioprine is an immunosuppressant, meaning that it controls the activity of the immune system.  More specifically, 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.


What is it used for?

This drug is used to treat patients who have undergone kidney transplantation and for diseases in which activity of the immune system is important, such as rheumatoid arthritis and Crohn’s disease.


How do I take it?

Follow your physician’s instructions carefully. The medication is dispensed in either pill or injection form.  Swallow the pill or capsule whole and do not break, crush or chew. Keep all medications away from children. Never share your medications with anyone else.


What do I do for a missed dose?

If you miss a dose of this medicine, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and return to your regular schedule. Do not take a double dose of this medicine.


Are there interactions with food or beverages?

The drug may be taken with food.  There are no known interactions with food or beverages.


Are there interactions with other drugs?

An interaction generally means that one drug may increase or decrease the effect of another drug.  Interactions with this drug may occur with 5-ASA derivatives (Asacol, Pentasa), ACE inhibitors, allopurinol (Zyloprim), Echinacea, mercaptopurine (Purinethol), natalizumab (Tysabri), sulfamethoxazol – trimethoprime (Bactrim), trastuzumab (Herceptin), vitamin K antagonists (Warfarin) and various vaccines.


Is there a problem if I have another disorder or disease?

Do not take this medication if you have hepatic impairment, renal impairment or TPMT deficiency.


What about allergies?

People who have known allergies or asthma may be at increased risk for a reaction from any new medication.  The physician should always know a patient’s allergy history.  Signs of an allergic reaction are skin rash, hives or fever.  Of course, a person should not take azathioprine if there has been a previous reaction to this.


What if I’m pregnant, considering pregnancy or breast-feeding?

Most females now know that, if possible, no drug, including alcohol, should be taken during pregnancy or lactation. The potential danger, of course, is an injury to the baby. However, some drugs are much safer than others in this regard. So, the FDA has a grading system for each drug which reflects what is known medically. It ranks drugs from A, where medical studies show no evidence for danger to the fetus or mother, to B, C, D and X, where the medical evidence indicates that the risk to the fetus outweighs any benefit to the mother. Azathioprine is ranked D and, as such, does pose a potential risk to the fetus.  More importantly, however, is a healthy mother during pregnancy and azathioprine is often continued during pregnancy to keep both the mother and fetus healthy.


What are the effects on sexual function?

In animal studies, azathioprine has been shown to cause reduction in sperm development, sperm viability and sperm count.


Are there other precautions?

Severe or recurrent pain and high or continued fever may indicate a serious illness. If pain persists for more than 5 days or if redness or swelling are present, contact your physician.


How long is it safe to take azathioprine?

A period of a few weeks is usually necessary to determine the drug’s effectiveness.  Long-term use of months to years is generally necessary and safe but does require a physician’s supervision and periodic evaluation.


How about side effects?

Adverse reactions can occur with any drug, even over-the-counter medications. Some of these are mild such as a stomach upset, which may be avoided by taking the medication with food. Minor reactions may go away on their own but, if they persist, contact the physician. For major reactions, the patient should contact the physician immediately.

For azathioprine, the following are the observed side effects:


  • nausea
  • diarrhea
  • fever
  • rash


  • vomiting
  • abnormal liver enzymes
  • pancreatitis
  • hypotension


A physician’s comment…

Azathioprine is a drug used often for long-term immunosuppressive treatment.  It can be used to treat a variety of disorders.  Gastroenterologists use it frequently for Crohn’s disease and ulcerative colitis.  Please be sure to discuss other medications you are taking with your physician, as this drug has a high number of drug interactions.  Also, if you plan to become pregnant, it is not advisable to take this medication.