Mercaptopurine

Mercaptopurine is a type of chemotherapy. It is a treatment for:

• acute lymphoblastic leukaemia (ALL)

• a rare type of acute myeloid leukaemia (AML) called acute promyelocytic leukaemia (APL)

Find out more about ALL

• Find out more about APL

How does mercaptopurine work?

Mercaptopurine is a type of chemotherapy drug called an anti metabolite. These stop cells making and repairing ​DNA​ . Cancer cells need to make and repair DNA  so that they can grow and multiply.

How do you take mercaptopurine?

You take mercaptopurine as tablets or as a liquid (oral suspension). The oral suspension is called Xaluprine. It is only used to treat ALL.

You should take mercaptopurine at the same time each evening.

You can take it with food or on an empty stomach. But you should continue take it the same way as you started. This means if you started taking it:

• with food, you should take it with food every evening

• on an empty stomach, you should take it on an empty stomach every evening

You should not take mercaptopurine at the same time as milk or dairy products. You can take it:

• 1 hour before milk or dairy products

• 2 hours after milk or dairy products

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

Talk to your healthcare team before you stop taking a cancer drug, or if you miss a dose.

Mercaptopurine suspension

Your nurse or pharmacist will show you how to measure the right amount of the suspension using a syringe. You wear disposable gloves while doing this so that the drug doesn't come into contact with your skin.

You should drink some water after taking the suspension.

How often do you have mercaptopurine?

You usually take mercaptopurine as ​cycles of treatment​ . Each cycle might be a different length. And you may have to take it for a different number of days each cycle.

Your doctor, nurse or pharmacist will tell you when to take mercaptopurine and for how long.

Tests

You have blood tests before 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.

Before treatment starts you may have a blood test to check for viruses such as hepatitis B, hepatitis C, and ​HIV​ . This is called a viral screen.

It’s important for your doctor to know if you have had any of these viruses. This is because this treatment can weaken your ​immune system​ and can cause the virus to become active again (reactivation). 

Testing for gene changes

Before starting treatment with mercaptopurine you may have a blood test to check if you have any changes to the following genes:

• thiopurine methyltransferase (TPMT)

• nudix hydrolase 15 (NUDT15)

People with these gene changes may have severe side effects from mercaptopurine. So, you may start treatment with a lower amount (dose) of the drug or have a different treatment. Your doctor, pharmacist or nurse will talk to you about this.

Side effects

Side effects can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

• you have severe side effects 

• your side effects aren’t getting any better

• your side effects are getting worse

Early treatment can help manage side effects better. 

We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.

Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Increased risk of getting an infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, cough, headaches, feeling cold and shivery, pain or a burning feeling when peeing, or generally feeling unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Bruising, bleeding gums or nosebleeds

This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs. This is known as petechiae.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

• breathlessness and looking pale due to a drop in ​red blood cells​ - this is called anaemia.

• loss of appetite

• loose watery poo (diarrhoea) – if you are taking mercaptopurine suspension

• feeling or being sick

• your liver stops working properly. Less often the liver cells may start to die - symptoms include feeling sick, weak, tummy (abdominal) pain and ​jaundice​ . Call your advice line if you have any of these

• the flow of ​bile​ slows down and your ​bile ducts​ may become blocked

Rare side effects

These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:

• a rash – this could be a sign of an allergic reaction. You should contact your advice line if you have a rash

• swelling of the face – this can be caused by a reaction to the medication. You should see a doctor urgently if you have this

• inflammation of the pancreas (pancreatitis) - this happens less often if you are taking mercaptopurine tablets. Symptoms include severe abdominal pain, feeling or being sick, a high temperature and ​jaundice​ . You should call your advice line if you have any of these symptoms

• joint pain

• a high temperature caused by the body reacting to the medication

• ulcers in your mouth – this happens less often if you are taking mercaptopurine tablets

• an increased risk of developing another cancer

• ulcers in your bowel

Other side effects

There isn't enough information to work out how often these side effects might happen. You might have one or more of them. They include:

• a low blood sugar in children

• a low level of vitamin B3 (niacin) in your body - especially in people with a long term inflammatory bowel problem. Symptoms include a rash, diarrhoea and feeling confused. Contact your advice line straight away if you have any of these symptoms

• your skin being more sensitive to the sun or UV light - don’t use sunbeds or sit in the sun. You should cover up and wear a hat if you are out in the sunshine. You should also wear sunscreen with a sun protection factor (SPF) of 50 or higher

• swellings under the skin, normally on your legs and arms

• soreness and inflammation of your lips, mouth and food pipe (oesophagus). It might go down to your intestines and bottom

• a problem with your blood clotting – your doctor will do regular blood tests to check for this

Coping with side effects

We have more information about side effects and tips on how to cope with them.

Read more about how to cope with side effects

What else do I need to know?

Other medicines, food and drink

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Having blood after this treatment

After having this treatment you should only have blood or platelets that are first treated with radiation (irradiated). The radiation lowers the risk of a reaction between your blood cells and the cells in the transfusion. No harm comes from the irradiated blood.

In your medical records there is a note saying you should only have irradiated blood. You have a card to carry with this information. This is in case you need treatment at another hospital.

Loss of fertility

It is not known whether this treatment affects ​fertility​ in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant 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. Let them know straight away if you or your partner become pregnant while having treatment.

Breastfeeding

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

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

Immunisations

Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having.

Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, and yellow fever.

You can usually have:

• other vaccines, but they might not give you as much protection as usual

• the flu vaccine (as an injection)

• the coronavirus (COVID-19) vaccine

Talk to your doctor or pharmacist about the best time to have a vaccine in relation to your cancer treatment.

Contact with others who have had immunisations 

You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your ​immune system​ is weakened.

Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.

Read more about immunisations and cancer treatment

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

eMC website

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

Report a side effect to the MHRA