Mercaptopurine (Puri-Nethol®)

Mercaptopurine (Puri-Nethol®) is a chemotherapy drug used to treat acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL) and chronic myeloid leukaemia (CML).

It is best to read this information with our general information about chemotherapy and the type of cancer you have.

Mercaptopurine is given as tablets. You usually have it as an outpatient. Your cancer doctor or nurse will tell you how often you will have it.

Like all chemotherapy drugs, mercaptopurine can cause side effects. Some of the side effects can be serious, so it is important to read the detailed information below.

Your healthcare team can give you advice on how to manage any side effects.

Tell your doctor or nurse straight away if you:

  • have a temperature
  • feel unwell
  • have severe side effects, including any we do not mention here.

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

If you need medical attention for any reason other than cancer, always tell the healthcare staff that you are having this treatment.

What is mercaptopurine?


How mercaptopurine is given

You may have your treatment during a stay in hospital, or as an outpatient. A chemotherapy nurse will give it to you.

During treatment, you will usually see a cancer doctor, a chemotherapy nurse or a specialist nurse in the outpatient clinic. This is who we mean when we mention doctor or nurse in this information.

How you have mercaptopurine will depend on your individual treatment plan. Your doctor or nurse will tell you when to take your mercaptopurine and how long to take it for.

Before and during your course of treatment, a nurse or person trained to take blood (phlebotomist) will take a blood sample from you. This is to check that it is okay for you to have chemotherapy.

Your doctor or nurse will check the results of each blood test you have and tell you what dose to take until your next test.


Taking your mercaptopurine tablets

Mercaptopurine is taken as tablets. Usually, the nurse or pharmacist gives you the tablets to take when you are at home. Always take them exactly as explained. This is important to make sure they work as well as possible. The number of tablets you need to take may vary depending on your blood test results. Your doctor or nurse will talk to you about this. They will also give you anti-sickness (anti-emetic) drugs to take.

Mercaptopurine tablets are usually taken once a day, preferably in the evening. They should be taken on an empty stomach, at least one hour before and three hours after having food or milk. Swallow them whole with a glass of water.

If you are sick just after taking the tablets, contact the hospital. You may need to take another dose. If you forget to take a tablet, do not take a double dose. Keep to your regular schedule and let your doctor or nurse know.

Other things to remember about your tablets:

  • Keep them in their original packaging at room temperature.
  • Keep them safe and out of the reach of children.
  • Return any remaining tablets to the pharmacist if your treatment is stopped.


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 haven’t 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 of mercaptopurine

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 (99.5F)
  • 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 chemotherapy. If your white blood cell count is low, your doctor may delay your treatment for a short time.

Bruising and bleeding

Chemotherapy can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot. Tell your doctor or nurse if you have any bruising or bleeding that you can’t 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)

Chemotherapy 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 chemotherapy. 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 don’t 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.

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.

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.

Diarrhoea

If you have diarrhoea, contact the hospital for advice. Try to drink at least two litres (three and a half pints) of fluids every day. It can help to avoid alcohol, caffeine, milk products, high-fat foods and high-fibre foods.

Tummy pain

You may get pain or discomfort in your tummy (abdomen), feel bloated or have indigestion or wind. Your doctor can prescribe drugs to help improve these symptoms. Tell them if the pain doesn’t improve, or if it gets worse.

Hair loss

Your hair may get thinner but you are unlikely to lose all the hair from your head. Hair loss usually starts after your first or second treatment. It is almost always temporary and your hair will usually grow back after treatment ends. Your nurse can talk to you about ways to cope 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 two litres (three and a half pints) of fluids each day to help protect your kidneys.


Less common side effects of mercaptopurine

Swollen pancreas (pancreatitis)

Rarely, mercaptopurine can cause this. Tell your doctor straight away if you get sharp pain in the upper tummy (abdomen) with sickness and vomiting. They will examine your tummy, prescribe drugs to help the symptoms and give you any treatment you need.

Changes in the way the liver works

Mercaptopurine causes 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

Rarely, this treatment can cause an allergic reaction. Signs of a reaction can include

  • a rash
  • feeling itchy
  • wheeziness
  • shortness of breath
  • swelling of your face or lips
  • feeling unwell.

Tell your nurse straight away if you have any of these symptoms. If you develop any of these symptoms after you get home, contact the hospital on the numbers you’ve been given immediately or go to the nearest accident and emergency department.


Other information about mercaptopurine

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 interact with chemotherapy or be harmful when you are having chemotherapy. Mercaptopurine interacts with allopurinol, olsalazine or mesalazine and sulfasalazine. It may also affect the way drugs such as warfarin work. Medicines you can buy in a shop or chemist may also be harmful when you are having chemotherapy. Tell your doctor about any medicines you are taking, including over-the-counter drugs, complementary therapies and herbal drugs.

Fertility

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

Contraception

Your doctor will advise you not to get pregnant or father a child while having this treatment. The drugs may harm the developing baby. It is important to use effective contraception during your treatment.

Sex

If you have sex in the first few days after chemotherapy, you need to use a condom. This is to protect your partner in case there is any chemotherapy in semen or vaginal fluids.

Changes to your periods

Chemotherapy can sometimes stop the ovaries working. You may not get a period every month and they may eventually stop. In some women, this is temporary, but for others it is permanent and they start the menopause.

Breastfeeding

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

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.