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Information for parents of children prescribed mercaptopurine

Patient information A-Z

Who is this leaflet for?

This leaflet is for parents of children who have been prescribed mercaptopurine for treatment of inflammatory bowel disease.

The information leaflet provides parents with details of mercaptopurine use to ensure the child receives the medicines safely and side effects can be monitored.

Name of drug

Brand names:
Puri-Nethol® Xaluprine®

What is mercaptopurine?

Mercaptopurine belongs to a group of medicines called immunosuppressants. It is used in different conditions including inflammatory bowel disease and hepatitis.

It works by helping to stop your child’s immune system from fighting against their bowel/ liver. This reduces the inflammation in the bowel/ liver and so reduces the painful symptoms.

What is mercaptopurine available as?

  • Tablets 10mg and 50mg
  • Liquid medicine can be ordered specially from your pharmacist

When should I give mercaptopurine?

  • Mercaptopurine is usually given once a day. This can be in the morning or the evening.
  • Your doctor may tell you to give it twice a day. This should be once in the morning and once in the evening. Ideally, 10 to 12 hours apart.
  • Give the medicine at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

How should I give it?

Mercaptopurine should be given after your child has eaten and with a glass of water.

Tablets should be swallowed with a glass of water, milk or juice. Your child should not chew the tablet. The tablets should not be crushed owing to the risk of inhaling the powder.

Liquid medicine: Measure out the right amount using an oral syringe. You can get these from your pharmacist. Do not use a kitchen teaspoon as it will not give the right amount.

When should the medicine start working?

Mercaptopurine takes several weeks or even months to start working properly. It may take up to three months before you start to see any improvement in your child. It is important that you continue to give mercaptopurine during this time.

What if my child is sick? (vomits)

  • If your child is sick less than 30 minutes after having a dose of mercaptopurine, give them the same dose again.
  • If your child is sick more than 30 minutes after having a dose of mercaptopurine, you do not need to give them another dose. Wait until the next normal dose.

What if I forget to give it?

If you usually give it once a day in the morning:
Give the missed dose when you remember during the day, as long as this is at least 12 hours before the next dose is due.

If you usually give it once a day in the evening:
If you remember before bedtime, give the missed dose. You do not need to wake a sleeping child to give them the missed dose. You can give the missed dose in the morning, as long as this is at least 12 hours before the evening dose is due.

If you normally give it twice a day:
If you remember up to four hours after you should have given a dose, give your child the missed dose. For example, if you usually give a dose at about 07:00 (7am), you can give the missed dose at any time up to 11:00 (11am).

If you remember after that time, do not give the missed dose. Wait until the next normal dose. Never give a double dose of mercaptopurine.

What if I give too much?

It is unlikely that mercaptopurine will cause any harm if you give your child an extra dose by mistake. If you are worried that you may have given your child too much mercaptopurine, contact a member of the paediatric gastroenterology team.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side effects).

Side effects you must do something about

If your child gets flu-like symptoms, sore throat, or unusual bleeding or bruising, contact a member of the paediatric gastroenterology team.

If your child starts being sick every few hours, has stomach pains, is very sleepy or has jaundice (the skin or eyes look yellow), contact a member of the paediatric gastroenterology team or take them to hospital straight away.

Other side effects you need to know about

Your child may get these side effects when they first start taking mercaptopurine. They will usually settle down within a week or so as their body gets used to the medicine. Continue to give mercaptopurine to your child as your doctor has told you to. Contact a member of the paediatric gastroenterology team if the side effects go on for longer than a week.

  • Your child may feel sick (nausea) and have some diarrhoea. It may help to give mercaptopurine with some food or shortly afterwards.
  • Your child may feel less hungry (lose their appetite). Encourage them to eat small meals often.
  • Your child may become sensitive to sunlight so make sure to avoid too much sun, ensure they cover up and use sunscreen.

Can other medicines be given at the same time?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.
  • Mercaptopurine should not be taken with some medicines that you get on prescription. Tell your doctor and pharmacist about any other medicines your child is taking before giving mercaptopurine.
  • Always check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal or complementary medicines.

If your child is due to have an immunisation (vaccination), tell the nurse or doctor that your child is taking mercaptopurine.

Chickenpox/ shingles infection

Infection with chickenpox and shingles can be severe in patients taking immunosuppressive medicine.

  • If your child comes into close contact with someone who has chickenpox/ shingles you should contact a member of the paediatric gastroenterology team.
  • If your child develops a cold sore, you should contact your GP. Your child may need a medicine called aciclovir to help treat the virus infection causing the cold sore.


Your child will require blood tests whilst taking mercaptopurine. This will monitor for any of the side effects with the blood and liver.

Your child will require blood tests at the following times after starting mercaptopurine:

  • First month: A weekly blood test.
  • Second month: A fortnightly blood test.
  • If your child’s blood tests have been reported as normal the frequency of the tests will then be every three months.

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that you always have enough medicine. Order a new prescription at least two weeks before you will run out.
  • Make sure that the medicine you have at home has not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight. It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in its original container.

Contacts/ further information

Paediatric gastroenterology team: 01223 274757

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Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151