Mercaptopurine (Puri-Nethol ®)
This information should ideally be read with our general information about chemotherapy and your type of cancer.
How mercaptopurine is given
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You will have your treatment as an outpatient or during a stay in hospital. A chemotherapy nurse will give it to you. Mercaptopurine can be given in combination with other chemotherapy drugs.
During treatment, you 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.
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 it is okay for you to have chemotherapy.
You will also see a doctor or nurse before you have chemotherapy. They will ask you about how you have been. If your blood results are alright on the day of your treatment, the pharmacist will prepare your chemotherapy. Your nurse will tell you when your treatment is likely to be ready.
Taking your chemotherapy tablets
Mercaptopurine is taken as tablets. Sometimes, 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 results. Your doctor or nurse will talk to you about this. They will also give you anti-sickness drugs to take.
Mercaptopurine tablets are usually taken once a day. 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 the original package 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.
Your course of chemotherapy
You will have chemotherapy as a course of several sessions (or cycles) of treatment over a few months.
Mercaptopurine can be given on its own or in combination with other chemotherapy drugs. This will depend on the type of cancer you have. Your doctor or nurse will tell you more about this and the number of cycles you are likely to have.
Possible side effects of mercaptopurine
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We explain the most common side effects of mercaptopurine here. But we don’t include all the rare ones that are unlikely to affect you.
You may get some of the side effects we mention but you are very unlikely to get all of them. If you are having other chemotherapy drugs as well, you may have some side effects that we don’t list here. Always tell your doctor or nurse about the side effects you have.
Your doctor can prescribe drugs to help control some side effects. It is very important to take them exactly as your nurse or pharmacist has explained. This means they will be more likely to work better for you. Your nurse will give you advice about managing your side effects. After your treatment is over, the side effects will start to improve.
Contact the hospital
Your nurse will give you telephone numbers for the hospital. You can call them if you feel unwell or need advice any time of day or night. Save these numbers in your phone or keep them somewhere safe.
Risk of infection
Mercaptopurine can reduce the number of white blood cells in your blood. This will make you more likely to get an infection. When the number of white blood cells is low, it’s called neutropenia.
Contact the hospital straight away on the contact number you’ve been given if:
your temperature goes over 37.5°C (99.5°F) or over 38°C (100.4°F), depending on the advice given by your chemotherapy team
you suddenly feel unwell, even with a normal temperature
you have symptoms of an infection – this can include feeling shaky, a sore throat, a cough or needing to pass urine often.
The number of white blood cells usually increases steadily and returns to normal before your next chemotherapy. You will have a blood test before having more chemotherapy. If your white blood cells are still low, your doctor may delay your treatment for a short time.
Bruising and bleeding
Mercaptopurine 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 you can’t explain. This includes nosebleeds, bleeding gums, blood spots or rashes on the skin. Some people may need a drip to give them extra platelets.
Anaemia (low number of red blood cells)
Chemotherapy can reduce the number of red blood cells that carry oxygen around the body. But this isn’t common with mercaptopurine. 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.
This may happen in the first few days after chemotherapy. Your doctor will prescribe anti-sickness (anti-emetic) drugs to help prevent or control sickness. Take the drugs exactly as your nurse or pharmacist explains to you. It’s easier to prevent sickness than to treat it after it has started.
If you still feel sick or are vomiting, contact the hospital as soon as possible. They can give you advice and change the anti-sickness drug to one that works better for you.
Loss of appetite
You may lose your appetite during your treatment. Try to eat small meals regularly. Don’t worry if you don’t eat much for a day or two. If your appetite doesn’t improve after a few days, let your nurse or dietitian know. They can give you advice on getting more calories and protein in your diet. They may give you food supplements or meal replacement drinks to try. Your doctor can prescribe some of these and you can buy them from chemists.
Feeling very tired is a common side effect. It’s often worse towards the end of treatment and for some weeks after it’s finished. Try to pace yourself and get as much rest as you need. It helps to balance this with some gentle exercise, such as short walks. If you feel sleepy, don’t drive or operate machinery.
Your mouth may become sore and you may get ulcers. This can make you more likely to get an infection in your mouth. Gently clean your teeth and/or dentures morning and night and after meals. Use a soft-bristled or children’s toothbrush. Your nurse might ask you to rinse your mouth regularly or use mouthwashes. It’s important to follow any advice you are given and to drink plenty of fluids.
Tell your nurse or doctor if you have any problems with your mouth. They can prescribe medicines to prevent or treat mouth infections and reduce any soreness.
Your doctor can prescribe drugs to control diarrhoea. Let them know if it is severe or if it doesn’t get better. Make sure you drink at least two litres (three and a half pints) of fluids every day if you have diarrhoea.
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 gets worse.
Your hair may thin but you’re unlikely to lose all the hair from your head. This usually starts after your first or second cycle of chemotherapy. It is almost always temporary and your hair will grow back after chemotherapy ends. Your nurse can give you advice about coping with hair loss.
Changes in the way the kidneys work
Mercaptopurine 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. Your nurse will ask you to drink plenty of fluid.
Less common side effects of mercaptopurine
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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.
Rarely, mercaptopurine can cause an allergic reaction. Signs of a reaction can include: a rash, feeling itchy, joint pain, swelling of your face or lips, or 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
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Blood clot risk
Cancer increases the chance of a blood clot (thrombosis) and chemotherapy can add to this. A clot can cause symptoms such as pain, redness and swelling in a leg, breathlessness and chest pain. Contact your doctor straight away if you have any of these symptoms. A blood clot is serious but your doctor can treat it with drugs that thin the blood. Your doctor or nurse can give you more information.
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.
Mercaptopurine may affect your fertility (being able to get pregnant or father a child). If you are worried about this, you can talk to your doctor or nurse before treatment starts.
Your doctor will advise you not to become pregnant or to father a child during treatment. This is because the drugs may harm a developing baby. It’s important to use effective contraception during and for a few months after chemotherapy. You can talk to your doctor or nurse about this.
If you have sex while having chemotherapy you need to use a condom. This is to protect your partner in case there is any chemotherapy in semen or vaginal fluid.
Women are advised not to breastfeed during treatment and for a few months after. This is in case there is chemotherapy in their breast milk.
Medical and dental treatment
If you need to go into hospital for any reason other than cancer, always tell the doctors and nurses that you are having chemotherapy. Explain you are taking chemotherapy tablets that no one should stop or restart without advice from your cancer doctor. Give them contact details for your cancer doctor.
Talk to your cancer doctor or nurse if you think you need dental treatment. Always tell your dentist you are having chemotherapy.
This section has been compiled using information from a number of reliable sources including:
electronic Medicines Compendium (eMC). medicines.org.uk (accessed July 2013).
Perry MC. The Chemotherapy Source Book. 5th edition. 2012. Lippincott Williams andWilkins.
With thanks to Man-Chie Chow, Lead Pharmacist Haemato-Oncology, who reviewed this edition.
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