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Overview: Azathioprine is used for rheumatoid arthritis in certain people and to prevent organ rejection after a kidney transplant. Common side effects include nausea and vomiting. The most serious side effects include an increased risk of infections, cancer, and liver damage. It is usually prescribed as an oral tablet but is also available in an injectable form that is given by health care providers.

Uses

What is azathioprine used for?

Azathioprine is commonly used to prevent organ rejection after a kidney transplant. Azathioprine is also used to treat rheumatoid arthritis in certain people.

Azathioprine may also be used for other conditions as determined by your health care provider.

How does azathioprine work (mechanism of action)?

Azathioprine works by weakening the immune system and making immune cells less active. This lowers the risk of your immune system attacking your new kidney after a transplant. It also slows or stops the immune system from attacking the joints, which helps reduce symptoms of rheumatoid arthritis.

How is azathioprine supplied (dosage forms)?

Brands and other names

  • Azasan
  • Imuran

Dosage forms and strengths

  • 25 mg, 50 mg, 75 mg, 100 mg oral tablets

Azathioprine is also available in injectable forms.

How should I store azathioprine?

Oral Tablet. Azathioprine tablets should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place and protect from light.

Injectable Forms. Azathioprine injections are usually given by a health care provider in a hospital or clinic. You will not store it at home.

Side Effects

What are the most common side effects of azathioprine?

The most common side effects of azathioprine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Blood disorders (see below)
  • Infections (see below)
  • Nausea and vomiting

There may be other side effects of azathioprine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of azathioprine?

While less common, the most serious side effects of azathioprine are described below, along with what to do if they happen. These side effects may vary depending on the condition being treated.

Severe Allergic Reactions. Azathioprine may cause allergic reactions, which can be serious. Get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain
  • Nausea and vomiting that may happen along with diarrhea, rash, fever, muscle aches, or stomach pain

Infections. Azathioprine can increase your risk of infections, including serious infections that may be life-threatening. Call your health care provider right away if you have an infection or any of the following symptoms.

  • Fever, sweats, chills, or muscle aches
  • Feeling more tired than usual
  • Sore throat
  • Cough or coughing up blood
  • Burning or stinging when you pee
  • Shortness of breath
  • Diarrhea or stomach pain
  • Weight loss

Blood Disorders. Azathioprine can cause blood disorders, such as low white blood cell levels (leukopenia), low platelet levels (thrombocytopenia), and low red blood cell levels (anemia). Keep all appointments to have your blood checked while using azathioprine. Call your health care provider right away if you have any of the following symptoms of blood disorders.

  • Fever
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or unusual bleeding
  • Frequent infection
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Cancer. Azathioprine can cause a new cancer to develop, including certain blood cancers (lymphomas) or skin cancer. It may also cause a previously treated cancer to come back. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin. Tell your health care provider about any new symptoms or skin changes.

Progressive Multifocal Leukoencephalopathy (PML). People using azathioprine may develop a brain disease called PML. It is caused by a virus called the JC virus. While rare, PML is very serious and can lead to death. Call your health care provider right away if you have any of the following symptoms of PML.

  • Clumsiness or loss of coordination
  • A hard time walking or speaking
  • Facial drooping
  • Vision problems
  • Thinking, memory, or personality changes
  • Weakness on one side of your body that gets worse
  • Seizures

Liver Damage. Liver damage, also called hepatotoxicity, can happen while using azathioprine. Call your health care provider right away if you have any of the following symptoms.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Warnings & Precautions

Who should not use azathioprine?

Allergies to Ingredients. People who are allergic to any of the following should not use azathioprine.

  • Azasan
  • Azathioprine
  • Imuran
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific azathioprine products they stock.

Certain People With Rheumatoid Arthritis. People with rheumatoid arthritis should not use azathioprine if they are pregnant. See the Pregnancy section for more details. People with rheumatoid arthritis who have used certain medicines known as alkylating agents should not use azathioprine. People who have used alkylating agents, such as cyclophosphamide, chlorambucil, and melphalan, may have a higher risk of cancer. 

What should I know about azathioprine before using it?

Do not use azathioprine unless it has been prescribed to you by a health care provider. Use it as prescribed.

Do not share azathioprine with other people, even if they have the same condition as you. It may harm them.

Keep azathioprine out of the reach of children.

Keep all appointments for blood tests after starting azathioprine.

What should I tell my health care provider before using azathioprine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if azathioprine is right for you.

In particular, make sure that you discuss any of the following.

Vaccines. Talk with your health care provider about any vaccines that you may need. You should not receive certain vaccines right before or while using azathioprine. Tell your health care provider about any vaccines you have recently received or have scheduled.

Other Medicines and Supplements. Azathioprine may interact with other medicines and supplements. Before starting azathioprine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Enzyme Deficiency. Tell your health care provider if you have an enzyme deficiency called thiopurine S-methyltransferase (TPMT) or nucleotide diphosphatase (NUDT15) deficiency. When someone has a deficiency, or lack, of these enzymes, their body may not process azathioprine properly, leading to a higher risk of serious side effects.

Other Current and Past Health Conditions. Tell your health care provider if you have any of the following.

Pregnancy. Azathioprine may cause harm to an unborn baby and is not to be used for rheumatoid arthritis if you are pregnant. If you can become pregnant, talk to your health care provider about birth control options that may be right for you. Tell your health care provider right away if you are pregnant or plan to become pregnant. If you are using azathioprine to prevent organ rejection, your health care provider will let you know if you should use azathioprine while you are pregnant or trying to get pregnant.

Breastfeeding. Azathioprine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should stop breastfeeding or stop azathioprine.

Interactions

Does azathioprine interact with foods or drinks?+

There are no known interactions between azathioprine and foods or drinks. Taking azathioprine after meals may help reduce side effects such as nausea or vomiting.

It is unknown if drinking alcohol will affect azathioprine, but heavy drinking can slow your immune response and make it harder for your body to fight infections. Infections, including some serious infections, are a possible side effect of azathioprine. See the Side Effects section for more details. Both azathioprine and alcohol can increase your risk of liver damage. It is best to limit the amount of alcohol you drink.

Does azathioprine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using azathioprine.

  • Allopurinol, which is a medicine used for gout, certain types of kidney stones, or high levels of uric acid in the blood 
  • Febuxostat (Uloric), which is a medicine used for gout
  • Mercaptopurine (Purixan), which is a medicine used to treat a type of blood cancer
  • Ribavirin, which is a medicine used to treat hepatitis C
  • Sulfasalazine (Azulfidine) or olsalazine (Dipentum), which is a medicine used for certain inflammatory conditions, such as ulcerative colitis 
  • Warfarin, which is a blood thinner
  • An angiotensin-converting enzyme (ACE) inhibitor, such as enalapril or lisinopril, which is a medicine for high blood pressure, heart failure, and certain kidney problems

This may not be a complete list of medicines that can interact with azathioprine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much azathioprine?

If you or someone else has used too much azathioprine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of azathioprine?

Missing doses of azathioprine can cause it to not work as well over time. So, it is important not to miss or skip doses.

Oral Tablets. If you miss an azathioprine tablet dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.

Injection. Azathioprine injection is usually given by a health care provider in a hospital. Your health care provider will make sure you are receiving azathioprine as scheduled.

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