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Generic Name

azathioprine (ay za THI oh preen)


Trade Name



What is azathioprine?

This drug effects the immune system. It was originally developed for kidney transplant patients to prevent rejection of the transplanted organ. However, it was then found to have effects in medical conditions where the immune system was overly active. In other words, by bringing the immune system down more toward normal, the tissue damage that occurs with certain disorders decreases and patients improve.


What is it used for?

The drug has been approved by the FDA for use in kidney transplantation and rheumatoid arthritis. In gastroenterology, the drug has now been demonstrated to be very useful in Crohn’s disease, autoimmune hepatitis and even ulcerative colitis. The drug has also found some use in many other immune type disorders such as myasthenia gravis and Behcet’s syndrome.


How do I take it?

Follow your physician’s instructions carefully. Take azathioprine with food to reduce stomach irritation. If nausea or vomiting develops, try eating dry foods such as toast or crackers, soups or unsweetened juices. Eat small meals throughout the day. The tablets may be crushed and sprinkled on food. Store in a tightly closed container at room temperature away from light. 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 double up on this medication.


Are there interactions with food or beverages?

There are no known interactions with azathioprine and any food or beverage.


Are there interactions with other drugs?

An interaction generally means that one drug may increase or decrease the effect of another drug. Also, the more medications a person takes, the more likely there will be a drug interaction.

Interactions with this drug may occur with the following:

  • Certain blood pressure medications known as ACE inhibitors (Capoten, Zestril, Prinivil, Vasotec)
  • allopurinol (Zyloprim)
  • methotrexate
  • blood thinners (Coumadin)
  • cyclosporine (Sandimmune, Neoral)


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

At times, a drug may have a different or enhanced effect when other diseases are present. At other times, the drug may worsen or effect another disease. The physician generally will test the red and white blood cells to be sure the proper amount of the drug is being taken. If anemia, a low white cell count, or bone marrow problems are already present, be sure to notify your physician. Also, alert your physician if you have a tendency to infections, have any liver condition or have had pancreatitis.


What about allergies?

People who have known allergies or asthma may be at an 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 itching. Of course, a personshould not take azathioprine if there has been a previous reaction to this or other chemotherapy drugs.

There is a related drug called 6MP (Purinethol) that may have a cross reaction with azathioprine. You should discuss this with your physician.


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. Always consult your physician before taking any drug during or when planning pregnancy. However, it is comforting to know that some authorities on this drug have reported a large series of patients who became pregnant while on this medication. There were no described problems with either mother or baby.


What are the effects on sexual function?

This drug may cause a lower sperm count or a reduction in sperm viability.


Are there other precautions?

Inform your physician if you develop any signs of infection (fever, chills) or abnormal bleeding or bruising, or if you have been exposed to chicken pox or shingles. Avoid immunizations with live virus vaccines and people who have recently taken oral polio virus vaccine.


How long is it safe to take azathioprine?

This drug can be taken long-term. There was an initial concern about developing a tumor called lymphoma. In the early kidney transplant reports, there was an increased incidence of this tumor. However, in gastroenterology, the dose is only 1/3 to 1/2 that used in renal transplants. There have been no reports of increased malignancies above that seen in the general population. Long-term use requires periodic blood work and evaluation by a physician. It may take several months before the full effect of this drug occurs.


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:


  • loss of appetite
  • lip and mouth sores
  • loss of hair
  • rash
  • unusual fatigue
  • weakness
  • nausea
  • vomiting


  • severe joint pain
  • severe abdominal pain (pancreatitis)
  • fever
  • sore throat
  • abnormal bleeding or bruising
  • cough
  • difficult breathing
  • yellow color to skin or eyes


A physician’s comment…

This drug is becoming increasingly important in the treatment of Crohn’s disease. It seems to be especially effective in closing draining fistulas around the anus. The drug should always be taken under a physician’s care.