Azathioprine and Mercaptopurine

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This medication information leaflet is designed to answer any common questions that you may have if you have been prescribed Azathioprine or Mercaptopurine to treat your Crohn’s Disease or Ulcerative Colitis (two main forms of Inflammatory Bowel Disease).

Azathioprine and Mercaptopurine are thiopurines that have been considered to be effective treatment for patients with moderate to severe inflammatory bowel disease for many years.

Azathioprine is generally the immunosuppressant of choice, but if azathioprine treatment fails, its active metabolite mercaptopurine may be tolerated. Mercaptopurine is unlicensed for inflammatory bowel disease but has been used for many years in treating this condition and is in line with national guidelines.

Why am I being treated with this medicine?

You may have been given azathioprine or mercaptopurine because you have Crohn’s disease or Ulcerative Colitis and are having relapses despite any medication that you are currently taking. The aim of using this drug is to allow you to come off steroids completely or to significantly reduce the dose of steroid that you need to control your symptoms.

How do azathioprine and mercaptopurine work?

Azathioprine and mercaptopurine belong to a group of medicines called immunosuppressants. In inflammatory bowel disease cells in the immune system attack the body’s own tissue and cause inflammation. Azathioprine and mercaptopurine work by dampening down the over activity. Azathioprine and mercaptopurine are chemically closely related. Azathioprine is converted to mercaptopurine in the body and both medications act in a very similar way.

Although they are similar, some people who cannot tolerate azathioprine because of side effects may still be able to take mercaptopurine.

What are other names for these medications?

Azathioprine is occasionally referred to by the brand name which is ‘Imuran’. Mercaptopurine is occasionally called 6-mercaptopurine or 6-MP or the brand name which is ‘Puri-nethol’.

How much will I need to take and how often?

Your dose will be calculated depending on your TPMT level, weight and severity of your condition, your health care professional will advise you how much you should take. You will need to take your medication every day.

Azathioprine dose is usually between 2-2.5 mg per kilogram of body weight per day.

Mercaptopurine dose is usually between 1-1.25 mg per kilogram of body weight per day.

It is important to check the label on your tablet container so you know which strength tablets you have been given as this will affect the number of tablets you need to take.

How long do they take to work?

You will not have any immediate benefit from this drug.  It can take up to three months for you to notice an improvement in your symptoms and you will need to continue taking your other medicines during this time, unless advised differently by your IBD team.

How long will I need to take this medication for?

If you tolerate this then you will be on this medication for some years, treatment continues for a minimum of two years if there is a good clinical response. Do not stop taking your medication unless your health professional tells you to, even if you feel well.

How do I take this medication?

It is best to take the tablets with, or immediately after food.

What do I do if I miss a dose?

If you forget a dose, take it as soon as you remember as long as it is within 12 hours. Do not double up on your next dose, just continue taking the tablets as directed but make a note of it in your diary and remember to tell your doctor on your next visit. If you take too much, then contact your health professional as soon as possible.

Can I take other medicines and alcohol with this drug?

Azathioprine and mercaptopurine are compatible with most other medicines but always remind your health professional that you are taking azathioprine or mercaptopurine if a new medication is being prescribed for you. You will also need to tell the Pharmacist if you buy any “over the counter medicines” that you are taking azathioprine or mercaptopurine.

Certain medications interact with azathioprine and mercaptopurine, these include

  • Allopurinol (used to treat gout)
  • Warfarin (used to thin the blood) possibly inhibits the anticoagulant effect.
  • Phenytoin, sodium valproate, carbamazepine (epilepsy) absorption may be reduced.
  • Co-trimazole (antibiotic)
  • Trimethoprim (antibiotic)

Alcohol can be taken in moderation, however for general health reasons it is best to remain within the Department of Health advised limits.

What checks will I need?

Your treatment monitoring may be managed by your hospital team or shared between the hospital and GP.

You will be monitored closely whilst you are taking this medicine. You will need a blood test at the start of your treatment, you will need two weekly blood tests for the first 8 weeks, then a monthly blood test for a further 8 weeks, and finally if within normal parameters on a three monthly basis until you stop taking this medication. You may have a blood test during your treatment which will check the level of the medication in your blood, this will help to make sure you are on the correct dose.

Can I have immunisations whilst I am on this medication?

The Department of Health advises you should have an annual flu vaccine, please book one at your local GP practice in the Autumn. You should have a pneumococcal vaccination with a booster every 5 years. It may be unsafe to have certain vaccines, you should not have any live vaccines, as these contain live viruses such as:

Polio, yellow fever, rubella, MMR, BCG.

However you may be able to have the inactivated polio vaccine. It is important that you check with your health professional prior to having any vaccines.

Will I need to take any special precautions while I am taking this medication?

Your body’s resistance to infection is likely to be reduced whilst taking Azathioprine.  Therefore, you should avoid contact with people who have an obvious infection. You should contact your health professional if you begin to feel unwell and think you may have caught an infection. You can potentially become seriously unwell from the viruses that cause chickenpox, measles, shingles, and pneumococcal disease. If you are not already immune it may be a good idea to have a vaccination against these diseases before you start treatment. If you come into contact with anyone who has these conditions tell your health professional as soon as possible.

You may experience side effects initially and therefore should avoid hazardous work and driving until you have learned how the medication affects you.

The skins sensitivity to sunlight and the risk of developing skin cancer is increased whilst you are taking this medication and therefore you should use factor fifty sunblock and wear a hat when out in the sunshine. You should not use sunbeds (UV light).

Will this medication affect fertility or pregnancy?

Inform your health professional if you are thinking about pregnancy or are pregnant. Azathioprine and mercaptopurine are not known to affect fertility, there has previously been a small amount of evidence that with a man taking this medication the risk of miscarriage and birth defects is increased, however recent research has not confirmed these findings and your health professional will advise you to continue taking your medication, rather than risk a flare-up.

The risk of having a flare-up for a woman that is pregnant has a greater risk to mother and baby than taking this medication. The evidence suggests that these medications are well tolerated and safe for women with inflammatory bowel disease in pregnancy. If you do have any questions, then discuss them with your health professional and they will discuss your personal risks and benefits of continuing the medication whilst pregnant.

Can I breastfeed whilst taking this medication?

There is no evidence of harm in children of mothers who have breastfed while on these medications, very little of the drug is secreted into breast milk and therefore it is considered low risk to breastfeed (Low dose excretion occurs into breast milk for four hours following ingestion, therefore consider expressing and wasting milk during this time period ). The benefit of breastfeeding outweighs any small potential risk.

What are the possible side effects of taking this medication?

All medicines can cause unwanted side effects. Some people taking azathioprine and mercaptopurine will experience unwanted side effects initially, however not everyone will get them and as your body adjusts to the medication the side effects may improve over a few weeks. The monitoring of your blood will enable early identification of some adverse effects.

Nausea / Vomiting/ loss of appetite

This is less likely if you take the tablets with a meal. If they persist then you can try taking your tablets in two smaller doses instead of all at once. A temporary dosage reduction may help if severe effects are experienced. You will need to speak to your health professional before you make any changes to how you take your medication, or dosage. Do not stop taking your medication until you have spoken to your health professional.

Flu like illness/ general aches and pains

You may experience a few days or weeks after starting your treatment. Contact your health professional if you begin to feel unwell in this way.

Weakness/ breathlessness/ infection /bruise or bleed easily

Anaemia, reduction in the number of platelets and white blood cells can be caused by suppression of the normal bone marrow function. By attending for your regular blood tests and regular monitoring the abnormal blood values should be picked up early. If you develop any of these then contact your health professional as soon as possible.

Liver inflammation

As part of your treatment monitoring the regular blood tests will include monitoring your liver function. If you notice yellowing or discoloration of your skin it may be a sign of jaundice. You will need to contact your health professional as soon as possible.


If you experience acute pain in your abdomen it is possible that your pancreas (a digestive gland in the abdomen) is inflamed. Contact your health professional as soon as possible.


This is a type of cancer affecting the lymph glands and being on this medication does increase the risk. However the potential benefits of being on this medication outweigh the small risk of Lymphoma and when the medication is discontinued the risk returns to normal.

Skin cancer

There is an increased risk of certain types of skin cancer. This risk can be reduced by using high factor sun block and avoiding sunbeds (UV light).

Dizziness/hair loss/ skin rash/oral ulceration/sore throat

If you do experience any of these symptoms, then contact your health professional.

Keep all medicines out of the reach of children. Never give any medicine prescribed for you to anyone else. It may harm them even if their symptoms are the same as yours.

Contact details:

Should you have any further questions or need advice, consult the specific health professional using the contact numbers below:

  • Inflammatory Bowel Disease Nursing team (please contact as first contact)
  • Telephone: 01908 996955 email: [email protected]
  • Dr Prakash Gupta MD FRCP, Consultant Physician / Gastroenterologist
  • Telephone: 01908 997115 (Secretary)
  • Dr Ravi Madhotra MD FRCP, Consultant Physician / Gastroenterologist
  • Dr Wamedh Taj-Aldeen MD FRCP, Consultant Physician / Gastroenterologist
  • Telephone: 01908 997103 (Secretary)
  • Dr George MacFaul MD FRCP, Consultant Physician / Gastroenterologist
  • Telephone: 01908 997138 (Secretary)