What is mercaptopurine?

Mercaptopurine is a chemotherapy drug used to treat acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML) and acute promyelocytic leukaemia (a rare form of AML).

It may sometimes be used to treat other cancers. It is best to read this information with our general information about chemotherapy and the type of cancer you have.

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to treatment.

How mercaptopurine is given

During treatment, you usually see a blood cancer doctor (haematologist), a chemotherapy nurse or a specialist nurse, and a specialist pharmacist. This is who we mean when we mention doctor, nurse or pharmacist in this information.

Before or on the day of treatment, a nurse or person trained to take blood (phlebotomist) will take a blood sample from you. This is to check that your blood cells are at a safe level for you to have chemotherapy.

You will see a doctor or nurse before you have chemotherapy. They will talk to you about your blood results and ask you how you have been feeling. If your blood results are okay, the pharmacist will prepare your chemotherapy. Your nurse will tell you when your treatment is likely to be ready.

Your course of chemotherapy

Mercaptopurine comes in tablets. It also comes as a liquid called Xaluprine®. You can take it at home or while you are in hospital. Mercaptopurine may be given on its own, or with other chemotherapy drugs.

Chemotherapy is usually given as a course of several cycles of treatment over a few months. Your nurse or doctor will discuss your treatment plan with you. They may give you a copy of the treatment plan to take home with you.

The nurse or pharmacist will give you the tablets or liquid to take home. Always take the tablets or liquid exactly as explained. This is important to make sure they work as well as possible for you.

Your nurse or pharmacist may also give you anti-sickness (anti-emetic) drugs and other medicines to take home. Take all your medicines exactly as they have been explained to you.

Taking mercaptopurine

You can take mercaptopurine with food, or on an empty stomach. Xaluprine® is the liquid form of mercaptopurine. If you are taking this, it is important to take it in the evening.

You should not take either the tablets or liquid with dairy products. Avoid milk or dairy products for:

  • 1 hour before taking the drug
  • 2 hours after taking the drug.

Take the drug in the same way every day.

Mercaptopurine tablets should be swallowed whole with a glass of water. You should not chew, open or crush them. Take the tablets at the same time every day.

If you are taking Xaluprine® liquid, your nurse or pharmacist will show you how to measure your dose. You will use plastic syringes. It is important to follow your nurse or pharmacist’s advice. You need to protect your skin when handling the liquid. You must wear disposable gloves. Close the lid of the bottle tightly when you have finished. You should have a drink of water after taking the liquid.

If you forget to take either the tablets or liquid tell your doctor. Do not take a double dose.

Other things to remember about your tablets or liquids:

  • Wash your hands after taking your tablets.
  • Other people should avoid direct contact with the chemotherapy drugs.
  • Keep them in the original package at room temperature, away from heat and direct sunlight.
  • Keep the tablets or bottle safe and out of sight and reach of children.
  • If you are sick just after taking the tablets or liquid, contact the hospital. Do not take another dose.
  • If your treatment is stopped return any unused tablets or liquid to the pharmacist.

About side effects

We explain the most common side effects of this treatment here. We also include some less common side effects. You may get some of the side effects we mention, but you are unlikely to get all of them.

If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.

Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.

Serious and life-threatening side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Common side effects

Risk of infection

This treatment can reduce the number of white blood cells in your blood. These cells fight infection.

If the number of white blood cells is low, you are more likely to get an infection. A low white blood cell count is called neutropenia.

If you have an infection, it is important to treat it as soon as possible. Contact the hospital straight away on the 24-hour contact number you have if:

  • your temperature goes over 37.5°C (99.5°F)
  • you suddenly feel unwell, even with a normal temperature
  • you have symptoms of an infection.

Symptoms of an infection include:

  • feeling shivery
  • a sore throat
  • a cough
  • diarrhoea
  • needing to pass urine often.

It is important to follow any specific advice your cancer treatment team gives you.

The number of white blood cells will usually return to normal before your next treatment. You will have a blood test before having more treatment. If your white blood cell count is low, your doctor may delay your treatment for a short time.

Bruising and bleeding

This treatment can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot. 

Tell your doctor if you have any bruising or bleeding that you cannot explain. This includes:

  • nosebleeds
  • bleeding gums
  • tiny red or purple spots on the skin that may look like a rash.

Some people may need a drip to give them extra platelets. This is called a platelet transfusion.

Anaemia (low number of red blood cells)

This treatment can reduce the number of red blood cells in your blood. These cells carry oxygen around the body. If the number of red blood cells is low, you may be tired and breathless. Tell your doctor or nurse if you feel like this. If you are very anaemic, you may need a drip to give you extra red blood cells. This is called a blood transfusion.

Feeling sick

You may feel sick in the first few days after this treatment. Your doctor will give you anti-sickness drugs to help prevent or control sickness. Take the drugs exactly as your nurse or pharmacist tells you. It is easier to prevent sickness than to treat it after it has started.

If you feel sick, take small sips of fluids and eat small amounts often. If you continue to feel sick, or if you vomit more than once in 24-hours, contact the hospital as soon as possible. They will give you advice and may change the anti-sickness drug to one that works better for you.

Loss of appetite

This treatment can affect your appetite. Do not worry if you do not eat much for a day or two. But if your appetite does not come back after a few days, tell your nurse or dietitian. They will give you advice. They may give you food or drink supplements.

Sore mouth

You may get a sore mouth or mouth ulcers. This can make you more likely to get a mouth infection.

Use a soft toothbrush to clean your teeth or dentures in the morning, at night and after meals.

If your mouth is sore:

  • tell your nurse or doctor – they can give you a mouthwash or medicines to help
  • try to drink plenty of fluids
  • avoid alcohol, tobacco, and foods that irritate your mouth.

Feeling tired

Feeling tired is a common side effect. It is often worse towards the end of treatment and for some weeks after it has finished. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can give you more energy. If you feel sleepy, do not drive or operate machinery.

Diarrhoea

This treatment may cause diarrhoea. Diarrhoea means passing more stools (poo) than is usual for you, or having watery or loose stools. If you have a stoma, it will be more active than usual.

If you have diarrhoea:

  • try to drink at least 2 litres (31/2 pints) of fluids each day
  • avoid alcohol, caffeine, milk products, high-fat foods and high-fibre foods
  • contact the hospital for advice.

Tummy pain

You may experience the following side effects in your tummy (abdomen):

  • feeling pain or discomfort
  • feeling bloated
  • having indigestion or wind.

Your doctor can give you drugs to help. Tell them if the pain doesn’t improve or gets worse.

Hair loss

Your hair may thin, but you are unlikely to lose all the hair from your head. This is almost always temporary and your hair will grow back after chemotherapy ends. Your nurse can give you advice about coping with hair loss.

Effects on the kidneys

This treatment can affect how your kidneys work. This is usually mild and goes back to normal after treatment. You will have blood tests to check how well your kidneys are working.

It is important to drink at least 2 litres (3½ pints) of fluids each day to help protect your kidneys.

Less common side effects of mercaptopurine

Swollen pancreas (pancreatitis)

Mercaptopurine can make your pancreas swell (pancreatitis). This side effect is rare. Tell your doctor straight away if:

  • you get sharp pain in the upper tummy (abdomen) and
  • you are sick or vomit.

The doctor will examine your tummy. They will give you drugs to help the symptoms. The doctor will give you any other treatment you need.

Changes in the way the liver works

This drug may cause changes in the way your liver works. These will usually go back to normal after treatment finishes.

The drug may cause your skin and the whites of your eyes to become yellow (jaundice). Tell your nurse or doctor if you notice this. You will have regular blood tests to check how well your liver is working.

Allergic reaction

Mercaptopurine can cause an allergic reaction. This side effect is rare. Signs of a reaction can include:

  • a rash
  • feeling itchy
  • joint pain
  • swelling of your face or mouth and throat
  • feeling unwell.

Tell your nurse straight away if you have any of these symptoms. Contact the hospital immediately if you develop any of these symptoms after you get home. You should contact the hospital on the number they gave you or visit the nearest accident and emergency department.

Other information

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:

  • pain, redness or swelling in a leg or arm
  • breathlessness
  • chest pain.

If you have any of these symptoms, contact a doctor straight away.

A blood clot is serious, but can be treated with drugs that thin the blood. Your doctor or nurse can give you more information.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.

Lactose

Mercaptopurine contains a small amount of lactose. Talk to your doctor if you have a lactose intolerance. You must do this before taking mercaptopurine.

Vaccinations

Your doctor or nurse may talk to you about vaccinations. These help reduce your risk of getting infections.

Doctors usually recommend that you have a flu jab, which is an inactivated vaccination. People with weak immune systems can have this type of vaccination.

If your immune system is weak, you need to avoid live vaccinations such as shingles. Your cancer doctor or GP can tell you more about live vaccinations.

Contraception

Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.

Breastfeeding

Women are advised not to breastfeed while having this treatment. This is because the drugs could be passed to the baby through breast milk.

Fertility

Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.

Sex

If you have sex during this course of chemotherapy, you need to use a condom. This is to protect your partner in case there is any chemotherapy in semen or vaginal fluids.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses that you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.

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