Indications
Azathioprine is an immunosuppressant, a medicine that calms the immune system. It is used to help prevent rejection of transplanted organs such as kidneys, and to treat autoimmune and inflammatory conditions, including rheumatoid arthritis, systemic lupus erythematosus, autoimmune hepatitis, inflammatory bowel disease (Crohn’s disease and ulcerative colitis), and some skin, blood and muscle disorders. It also helps reduce the need for steroids.
How It Works
Azathioprine is converted in the body into substances that interfere with the making of DNA in rapidly dividing cells. This mainly slows the multiplication of white blood cells (lymphocytes) that drive immune attacks and inflammation. Its full effect usually takes several weeks to months to appear.
Dosage and Administration
The dose depends on the condition, body weight, blood test results and the activity of an enzyme called TPMT, and is taken as prescribed. Tablets are usually taken once or twice daily with or after food to reduce stomach upset, swallowed whole with water. Do not stop or change the dose without speaking to your doctor.
- Regular blood tests (blood counts and liver tests) are needed, especially in the first months.
- Carers should avoid handling broken or crushed tablets; wash hands after handling.
Interactions
Allopurinol and Febuxostat greatly increase Azathioprine levels and can cause dangerous bone marrow suppression; Febuxostat should not be used with it, and if Allopurinol is needed the Azathioprine dose must be greatly reduced by the doctor. Other medicines that lower blood counts, such as Co-trimoxazole, Methotrexate, Clozapine and some ACE inhibitors, add to this risk. It can reduce the effect of Warfarin. Live vaccines (such as BCG, oral polio, measles, rubella, yellow fever) should be avoided.
Contraindications
- Allergy to Azathioprine or Mercaptopurine.
- Very low or absent TPMT enzyme activity, unless a specialist directs very low doses.
- Receiving live vaccines.
- Pregnancy, unless the specialist decides the benefit outweighs the risk.
Side Effects
Common side effects include nausea, vomiting, loss of appetite, a lower white blood cell count, a higher chance of infections, and changes in liver tests. Hair thinning, rash, joint and muscle pain, and pancreatitis can occur. Long-term use slightly increases the risk of skin cancer and lymphoma.
Get urgent medical help if you have fever, sore throat, mouth ulcers or other signs of infection, unusual bruising or bleeding, severe tiredness or paleness, yellowing of the skin or eyes, severe stomach pain, or a sudden reaction with fever, dizziness, rash and muscle pain soon after starting.
Pregnancy and Lactation
Azathioprine may be continued during pregnancy in some conditions under specialist care, when stopping it would be riskier for mother and baby. Do not stop it on your own; discuss pregnancy plans with your specialist. Small amounts pass into breast milk; breastfeeding is often possible under medical advice, with the baby monitored.
Precautions and Warnings
A TPMT test may be done before starting. Report any sign of infection promptly. Avoid strong sunlight and use sunscreen and protective clothing, and have your skin checked regularly. Avoid contact with people who have chickenpox or shingles and tell your doctor if exposed. Use with care in liver or kidney disease. Men and women should use reliable contraception during treatment unless advised otherwise.
Overdose
Overdose may cause severe bone marrow suppression, leading to infections, bleeding and anaemia, as well as nausea, vomiting and diarrhoea. Seek emergency medical help; blood counts must be monitored closely in hospital.
Therapeutic Class
Immunosuppressant (purine antimetabolite).
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.