Please read this information in conjunction with our general information on chemotherapy, and with the information in relation to your specific type of cancer.

What is mercaptopurine?

Mercaptopurine is a chemotherapy drug used to treat certain types of cancers. Its main use is in the treatment of leukaemias.
Mercaptopurine belongs to a group of drugs known as antimetabolites. It resembles a normal cell nutrient needed by cancer cells to grow. The cancer cells take up mercaptopurine which then interferes with their growth.

 What does it look like?

Mercaptopurine is available in:

  • a 50mg  yellow coloured tablet.
  • a 500mg vial of powder to be mixed with sterile water.

How is it given?

  • Tablets should be taken with a glass of water as directed by your doctor. The amount of mercaptopurine tablets you will have to take each week will depend on how the drug is affecting your blood counts.
  • It is given in the form of a drip through a cannula or central line or PICC line. This normally takes about 60 mins.

Side effects:

The side effects mentioned below may not affect everyone, as each patient’s reaction to chemotherapy is different. It will also depend on how many chemotherapy drugs you are receiving. If you experience any side effects that you think are related to your chemotherapy, please discuss them with your oncology doctor or chemotherapy nurse.


You will be more prone to infection as mercaptopurine affects your white cell production from the bone marrow. This effect usually occurs about 7 days after your chemotherapy and can continue throughout the treatment. You will have blood tests to check your levels before every chemotherapy dose to ensure your blood levels have returned to normal. Occasionally your treatment may be delayed until your blood levels come back to normal.  If you notice any signs of infection visit your doctor for assessment.
You should contact your doctor or the Oncology Unit straight away if you if you have a sore throat,cough, pain passing urine, redness and swelling at e.g. at a catheter site. Or have a temperature of 38 degrees° C or greater.


Mercaptopurine can also affect the production of platelets, which can cause bleeding or bruising. Inform your doctor if you notice any unexplained bleeding or bruising.


You may feel very tired. This can last for a few months after your treatment. Inform your doctor or nurse of how you are feeling.

Liver problems

Mercaptopurine may alter the way the liver works. Once the treatment has finished your liver function will return to normal. Your doctor will monitor your liver function very closely while you are on treatment by checking your bloods but this temporary disturbance to your liver function is very unlikely to cause you harm.

Less common side-effects

Nausea and vomiting

Mercaptopurinecan make you feel sick nausea   or to to be sick vomit  . When this occurs can vary. Your doctor will prescribe some medications to prevent this anti-emetics  . If you continue to feel sick it is important to inform your doctor.

Sore mouth

You may develop a sore mouth or ulcers due to your chemotherapy. You will be prescribed some mouthwashes. Inform your doctor or nurse if your mouth becomes sore or you develop ulcers. You may also experience some taste changes, which will resolve after you finish your treatment.


If Diarrhoea occurs it can be easily controlled with medicine. It is important to drink plenty of fluid if you experience diarrhoea and to inform your doctor or nurse.

Skin changes

Mercaptopurine can cause a rash, which may be itchy. Your doctor can prescribe medicine to help with this.

Additional information

Mercaptopurine interacts with a number of drugs, including allopurinol, warfarin and muscle relaxants.

  • Allopurinol is a medicine that is commonly given to people having chemotherapy to help reduce a high uric acid in the blood.  To prevent the interaction you will usually be told to stop taking allopurinol before you start taking mercaptopurine.
  • Warfarin is an anticoagulatant used to thin a persons blood. Mercaptopurine can intervere with the working of this drug, so it is important that the doctor monitors your clotting levels regularly.
  • Mercaptopurine can also decrease the effectiveness of muscle relaxant tables and close monitoring is required.

Your doctor can give you further advice about this. It is important to follow the instructions given to you by the doctor. 

Other medications

It is important to inform your doctor of any medications that you are taking, including over the counter medications or herbal drugs as they can interfere with some chemotherapy drugs.


It is important to discuss this with your doctor as your fertility may be affected by mercaptopurine.


It is important to use a reliable form of contraception while you are on treatment and for at least two years after your treatment has completed. It is not advised to get pregnant or father a child while on treatment as the drugs may affect the foetus.


  • Store the  tablets in a cool, dry place
  • Keep the tablets in a safe place where children cannot reach them.
  • Take your capsules at the right times as directed by your doctor.
  • If your doctor decides to stop the treatment, return any remaining capsules to the pharmacist. Do not flush them down the toilet or throw them away
  • If you forget to take a capsule do not take a double dose. Tell your doctor.
  • If you vomit soon after taking your tablets inform your doctor.


  • British National Formulary. British Medical Association and Royal Pharmaceutical Society of Great Britian, March 2002
  • The Chemotherapy Source Book (2rd edition). Ed. Perry. Lippincott Williams and Wilkins, 1997
  • The Royal Marsden Hospital Handbook of Cancer Chemotherapy. Ed. Brightwood, D., Ford, H., Johnston, S., Ross, P. and Wood, M.

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