Azathioprine belongs to the group of medications known as immunosuppressive agents. It is used to prevent the rejection of kidney transplants and to treat severe rheumatoid arthritis that is not responding to conventional treatment. Azathioprine prevents rejection of kidney transplant and reduces the inflammation and pain in rheumatoid arthritis by suppressing the body's natural defense, or immune system.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

When used to prevent kidney transplant rejection, azathioprine is usually started on the day of transplant. The initial dose is based on body weight at 3 mg to 5 mg per kilogram of body weight daily. After the transplant, the dose is then generally reduced to a maintenance dose of 1 mg to 3 mg per kilogram of body weight per day.

For treatment of rheumatoid arthritis, azathioprine is usually given at a dose of approximately 1 mg per kilogram of body weight (50 mg to 100 mg) per day by mouth, in a single daily dose or on a twice-daily schedule. After 6 to 8 weeks, your doctor may increase your dose by 0.5 mg per kilogram daily if needed. Additional increases may be prescribed by your doctor every 4 weeks up to the maximum daily dose of 2.5 mg per kilogram per day.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose and you are taking the pills once a day, do not take the missed dose at all, but go back to your regular dosing schedule.

If you are taking pills more than once a day, skip the missed dose and go back to your regular schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light, and keep it out of the reach of children.

50 mg tablet
Each pale yellow, peanut-shaped tablet, engraved "AZ 50" on one side and score lines on the other, contains 50 mg of azathioprine. Nonmedicinal ingredients: lactose, magnesium stearate, microcrystalline cellulose, and starch.

Injection

Do not use azathioprine if you are allergic to azathioprine or any ingredients of the medication.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• hair loss
• nausea

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• feeling tired, dizzy, or generally unwell
• fever or chills
• new marks or change in marks on your skin
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• symptoms of a lung infection (e.g., shortness of breath, cough, chest pain)
• symptoms of a urinary tract infection (e.g., pain when urinating, urinating more often than usual, low back or flank pain, strong odour)
• tender, red bumps on shins

Stop taking the medication and seek immediate medical attention if any of the following occur:

• muscle or bone pain
• severe skin reaction such as redness or blisters on skin or peeling skin
• severe nausea, vomiting, diarrhea, or stomach pain
• dizziness or faintness especially when you stand up
• signs of kidney problems (e.g., increased urination at night, decreased urine production, blood in the urine, change of urine colour)
• signs of a severe allergic reaction, e.g.:
• difficulty breathing
• hives
• swelling of the face, mouth, throat, or tongue

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Allergy: Some people who are allergic to or have had a hypersensitivity reaction to mercaptopurine also experience reactions to azathioprine. Contact your doctor at once if you experience signs of an allergic reaction, such as skin rash, itching, difficulty breathing, or swelling of the face and throat.

Anemia: Azathioprine may cause low levels of red blood cells. If you experience symptoms of reduced red blood cell count (anemia) such as shortness of breath, feeling unusually tired, or pale skin, contact your doctor as soon as possible.

Cancer: This medication may increase your risk of developing certain types of cancer, specifically hepatosplenic T-cell lymphoma, a particularly severe cancer of the immune cells, and skin cancer.

To reduce the risk of skin cancer, limit your exposure to sunlight and ultraviolet light, wear protective clothing, and use sunscreen with a high sun protection factor. Report any unusual growths on your skin to your doctor as soon as possible.

Bleeding: This medication can decrease the number of platelets (component of the blood that helps blood to clot). Your doctor will monitor your platelet levels regularly while you are taking this medication. If you notice any unusual signs of bruising or bleeding (e.g., bleeding gums, blood in urine, dark-tarry stools), contact your doctor immediately or get immediate medical attention.

Hypersensitivity reaction: A severe allergic reaction affecting the digestive system has been reported by some people using azathioprine. This type of reaction can cause severe nausea and vomiting, and may also cause diarrhea, rash, or fever and affect liver organ function. It should be treated as an emergency. Get immediate medical attention if you have symptoms of a severe allergic reaction, including these symptoms or swollen glands, yellowing of the skin or eyes, or flu-like symptoms with skin rash or blistering.

Infection: This medication reduces the number of white blood cells that fight infection in the body and can increase the risk of bacterial, fungal, and viral infections. If you notice any signs of infection (e.g., fever, chills, cough, painful urination) or any other unusual symptoms, contact your doctor. Contact your doctor immediately if you come into contact with someone who has chickenpox or shingles. Your doctor will monitor your white blood cell levels regularly while you are taking this medication.

Kidney function: Azathioprine may be removed from the body more slowly for people with reduced kidney function. If you have reduced kidney function discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver damage or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Azathioprine may reduce liver function and can cause liver failure. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Vaccines: The effectiveness of giving other vaccines while using this medication has not been studied. Vaccinations should be completed before starting azathioprine or should be postponed until at least 3 months after treatment with azathioprine is complete.

Pregnancy: Azathioprine can cause harm to the baby when taken by pregnant women. This medication should not be used during pregnancy unless the benefits outweigh the risks. Effective birth control should be practiced while using this medication. If you become pregnant while you are taking this medication, contact your doctor at once.

Breast-feeding: This medication may pass into breast milk. If you are breast-feeding and taking azathioprine it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

Seniors: The safety and effectiveness of using this medication have not been established for people over the age of 65. Discuss the risks and benefits of taking azathioprine with your doctor.

There may be an interaction between azathioprine and any of the following:

• 5-ASA medications (e.g., mesalamine, olsalazine, sulfasalazine)
• abrocitinib
• adalimumab
• allopurinol
• angiotensin-converting enzyme (ACE) inhibitors (e.g., enalapril, ramipril)
• baricitinib
• certolizumab
• cladribine
• clozapine
• cyclophosphamide
• deferiprone
• denosumab
• etanercept
• febuxostat
• golimumab
• infliximab
• leflunomide
• mercaptopurine
• natalizumab
• ocrelizumab
• ofatumumab
• pimecrolimus
• ribavirin
• ruxolitinib (topical)
• sphingosine 1-phosphate (S1P) receptor inhibitors (e.g., fingolimod, ponesimod, siponimod)
• sulfamethoxazole
• tacrolimus
• tofacitinib
• trimethoprim
• upadacitinib
• vaccines
• warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking.

Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.