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Mercaptopurine (Xaluprine)

Find out what mercaptopurine is, how you have it and other important information about taking this drug. 

What is it

Mercaptopurine is also called Xaluprine. It is a chemotherapy drug used to treat some types of leukaemia. 

How it works

Mercaptopurine is one of a group of chemotherapy drugs known as anti metabolites. These drugs stop cells making and repairing DNA. Cancer cells need to make and repair DNA so that they can grow and multiply. 

How you have it

Mercaptopurine comes as pale yellow tablets and as a pinky brown liquid (oral suspension). The liquid medicine is called Xaluprine. 

Taking mercaptopurine tablets

You swallow the tablets whole with lots of water. If you need to break them in half, wash your hands afterwards and make sure that you don't breathe in any of the powder released by the tablet.

You should take the tablets at the same time each day, at least 1 hour before or 3 hours after food or milk. 

Taking mercaptopurine liquid

Your nurse or pharmacist will show you how to measure the dose of liquid mercaptopurine (Xaluprine) using a syringe. You need to wear disposable gloves while doing this so that the drug doesn't contact your skin.

You take Xaluprine in the evening, with food or on an empty stomach. But whichever you choose, you should do the same thing each day.

Milk and dairy products can make this drug less effective so you should take Xaluprine at least 1 hour before or 2 hours after milk or dairy products.   

If you take too much mercaptopurine

If you accidentally take more mercaptopurine than you should you might feel sick, be sick or have diarrhoea. 

Tell your doctor or go to a hospital straight away. Take the medicine pack with you.

If you forget to take mercaptopurine

Don't take a double dose to make up for the dose that you forgot. Tell your doctor or nurse. 

Taking your tablets or capsules

You must take tablets and capsules according to the instructions your doctor or pharmacist gives you.

You should take the right dose, not more or less.

Never stop taking a cancer drug without talking to your specialist first.

When you have it

You usually have mercaptopurine as a course of several cycles of treatment. The treatment plan for mercaptopurine depends on which type of cancer you have. 

Tests during treatment

You have blood tests before starting treatment and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

Side effects

Important information

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 3 months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


You may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future. Men may be able to store sperm before starting treatment. Women may be able to store eggs or ovarian tissue but this is rare.


Don’t breastfeed during this treatment because the drug may come through in your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.

Mercaptopurine can cause very severe side effects if you have a condition where your body makes too little of something called TPMT (thiopurine methyltransferase). Your doctor might do blood tests to check the levels before you start treatment. 

Lactose and mercaptopurine

This drug contains lactose (milk sugar). If you have an intolerance to lactose, contact your doctor before taking this medicine.


Don’t have immunisations with live vaccines while you’re having treatment and for at least 6 months afterwards.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and shingles vaccine (Zostavax).

You can:

  • have other vaccines, but they might not give you as much protection as usual
  • have the flu vaccine
  • be in contact with other people who've had live vaccines as injections

Avoid contact with people who’ve had live vaccines taken by mouth (oral vaccines). This includes the rotavirus vaccine given to babies. The virus is in the baby’s urine for up to 2 weeks and can make you ill. So, avoid changing their nappies for 2 weeks after their vaccination if possible. Or wear disposable gloves and wash your hands well afterwards.

You also need to avoid anyone who has had oral polio or typhoid vaccination recently.

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Information and help

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