Mercaptopurine

Mercaptopurine is an immunosuppressant drug used in the treatment of Crohn’s disease or ulcerative colitis. It decreases your immune response and thereby decreases inflammation. It may help keep you well (maintain remission) and thereby decrease the number of flares (or relapses). I tend to recommend treatment with mercaptopurine early in the management of patients with Crohn’s disease but after the use of mesalazine or steroids in patients with ulcerative colitis.

How is it taken?

By mouth, once daily. The dosage is based upon your body weight and is started usually at a dose of 1mg/kg each day and may be increased to 1.5mg/kg daily.

Are there any side effects?

A small number of patients may experience side effects that will prevent them from continuing with treatment. Should you develop symptoms that might be related to your treatment please let me know.

Side effects that you should look out for include:

Nausea / vomiting and loss of appetite (<20% and often during second week of treatment)
Abdominal pain – should this develop, the drug should be stopped immediately. There may be inflammation in the pancreas gland; this is rare however.
Hair loss
Adverse effects on the blood so that the bone marrow does not make enough blood cells (1-2%)
Fever, weakness and fatigue (rare)
Unusual bleeding / bruising (rare)
Inflammation in the liver or jaundice (rare; <1%)
Rashes (rare)
There is some evidence to suggest that the risk of lymphoma may be increased slightly. In addition, some forms of skin cancer are more common whilst taking mercaptopurine. It is sensible to use sunscreens and or protective clothing to reduce sunlight exposure.

How long does it take to work?

Usually 6-12 weeks.

Can I drink alcohol whilst taking mercaptopurine?

Yes, there is no known interaction with alcohol.

Is it safe to take mercaptopurine in pregnancy and breast feeding?

Mercaptopurine is safe to take in pregnancy. These is no evidence that it increases the risk of miscarriage or low birth weight above that associated with inflammatory bowel disease per se.

Women receiving mercaptopurine ideally should avoid breast feeding.

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

Do I need any special monitoring whilst taking mercaptopurine?

Whilst taking this treatment, you will need regular blood tests to monitor blood cell counts and liver function. Once the dose of treatment is stable, the frequency of blood testing will be reduced. The testing will be performed at your GP surgery, your GP and I will be responsible for keeping an eye on the blood test results.

For the first 8 weeks of treatment a blood test (full blood count and liver function test) will need to be performed every week and if these are satisfactory, then every 12 weeks thereafter.

Other information

Immunisation with LIVE vaccines should be avoided (Influenza and pneumovax can be given). Please discuss with your GP if necessary.
Other medicines that you are prescribed may interact with mercaptopurine such as allopurinol (for gout), warfarin (for blood thinning) and certain antibiotics (co-trimoxazole and trimethoprim). You should discuss these with your GP.


At Digestive Health City & Docklands, we work hard to provide our patients with top-class care. You will enjoy friendly, fast and modern treatment by a highly experienced gastroenterologist. We carefully review patient satisfaction and feedback, and at Digestive Health we are continuously making improvements to our services, ensuring the highest level of care possible.

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