Mercaptopurine (6-MP, Purinethol)

Mercaptopurine is a chemotherapy drug used to treat some types of cancer, including acute leukaemia. It 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.

Mercaptopurine comes as fawn coloured 50mg tablets that you swallow with lots of water. You should take them at the same time each day, 30 to 60 minutes before eating.

It is very important that you take tablets according to the instructions your doctor or pharmacist gave you. For example, whether you have a full or empty stomach can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

You usually have chemotherapy as a course of several cycles of treatment. The treatment plan for mercaptopurine depends on which type of cancer you have. There is detailed information about planning chemotherapy in the main chemotherapy section.

The side effects of mercaptopurine are listed below. You can use the links to find out more about each side effect or go to the cancer drug side effects section.

More than 10 in every 100 people have one or more of the side effects listed below.

Temporary drop in the number of blood cells made by the bone marrow, causing

• Increased risk of getting an infection from a drop in white blood cells – it is harder to fight infections and you can become very ill. You may have headaches, aching muscles, a cough, sore throat, pain passing urine or feel cold and shivery
• Tiredness and breathlessness due to a drop in red blood cells (anaemia) – you may need a blood transfusion
• Bruising more easily due to a drop in platelets – you may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)

Some of these side effects can be life threatening, particularly infections. You should contact your doctor if you have any of these side effects. Your doctor will check your blood counts regularly to see how well your bone marrow is working.

This drug may also cause

• Fatigue (tiredness) during and after treatment – most people find their energy levels are back to normal within 6 months to a year

Between 1 and 10 in every 100 people have one or more of these.

• Diarrhoea – drink plenty of fluids and tell your doctor or nurse if diarrhoea becomes severe, or continues for more than 3 days
• Feeling or being sick is usually well controlled with anti sickness medicines
• A sore mouth and throat
• Liver changes that are very mild and unlikely to cause symptoms – the liver will almost certainly go back to normal when treatment is finished, but you will have regular blood tests to check how well your liver is working
• Loss of fertility – we don’t know exactly how this drug affects fertility so do talk with your doctor before starting treatment if having a baby is important to you
• Women may stop having periods (amenorrhoea) but this may only be temporary
• Mercaptopurine may have a harmful effect on a developing baby so talk to your doctor or nurse about contraception before having treatment if there is any chance that you or your partner could become pregnant
• Doctors recommend that you don't breastfeed while taking mercaptopurine in case the drug could be passed on in the milk
• An itchy rash
• Headaches

Fewer than 1 in 100 people have these.

• Hair loss – this is rare, but can begin 2 to 5 weeks after treatment starts
• Kidney changes that are mild and unlikely to cause symptoms may occur – they will almost certainly go back to normal when treatment finishes, but you will have regular blood tests to check how well your kidneys are working
• Reddening of the skin in areas where you have had radiotherapy in the past, and the skin may get dry and flaky and feel sore and hot – this goes away on its own but keep affected areas out of the sun
• Fever and chills

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

• How many times you've had the drug before
• Your general health
• The amount of the drug you have (the dose)
• Other drugs you are having

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. Your chemotherapy nurse, clinic or ward nurse will give you a contact number. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and other over the counter remedies – some drugs can react together. If you are taking a drug called allopurinol it is very important to let your doctor know because they may need to lower the dose of mercaptopurine for you.

You should not have immunisations with live vaccines while you are having this treatment or for at least 6 months afterwards. In the UK, live vaccines include rubella, mumps, measles (usually given together as MMR), BCG and yellow fever. You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with oral vaccines, but not many people in the UK have oral vaccines now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.