Allopurinol is a xanthine oxidase inhibitor medicine used to prevent build-up of uric crystals in the body. This build up can be caused by some illnesses or as a side effect of certain medicines.This page from Great Ormond Street Hospital (GOSH) explains what allopurinol is, how it is given and some of the possible side effects. Each person reacts differently to medicines, so your child will not necessarily suffer from every side effect mentioned. If you have any questions or concerns, please speak to your doctor, nurse or pharmacist.

In adults, allopurinol can be used to prevent kidney stones and gout.

Allopurinol can be given at the start of a course of chemotherapy. When chemotherapy medicines start to kill the cancer cells, uric acid is released from these cells which can crystallise causing damage to the kidneys. Allopurinol stops these crystals from forming.

How is allopurinol given?

Allopurinol is given by mouth in tablet form. Allopurinol tablets should be taken after food with plenty of water.

What are the side effects?

Severe allergic reaction

Some people develop a severe allergic reaction to allopurinol.

Signs of a severe allergic reaction include skin rashes and itching, high temperature, shivering, redness of the face, a feeling of dizziness or a headache, as well as shortness of breath or chest pain.

If you are in hospital and your child shows signs of a severe allergic reaction, call a doctor or nurse immediately. If you are at home and your child shows signs of a severe allergic reaction, call an ambulance immediately.

If your child has a severe reaction to allopurinol, the subsequent treatment will probably be changed.

If your child experiences the following side effects, please contact your doctor immediately as the dose may need to be reduced or stopped

Skin rash

Allopurinol may cause an itchy rash. Please tell your doctor or nurse if your child develops a rash. They will advise you on the appropriate treatment to use.

Upset stomach, causing diarrhoea and/or constipation

Please tell your doctor or nurse if your child has diarrhoea and/or constipation which is very bad or continues for more than a few days. Your child should continue to drink plenty of fluids and increase the amount of fibre eaten. Sometimes additional medicines may be prescribed to reduce these effects.

Interactions with other medicines

Some medicines can react with allopurinol, altering how well it works. Always check with your doctor or pharmacist before giving your child any other medicine, including medicines on prescription from your family doctor (GP), medicines bought from a pharmacy (chemist) or any herbal or complementary medicines.


  • Keep all medicines in a safe place where children cannot reach them.
  • Allopurinol tablets should be kept in a cool, dry place away from direct sunlight or heat.
  • If your doctor decides to stop treatment with allopurinol or the medicine passes its expiry date, return any remaining medicine to the pharmacist. Do not flush it down the toilet or throw it away.
  • If your child vomits straight after taking the dose, inform your doctor or nurse, as your child may need to take another one.
  • If you forget to give your child a dose and it is within a few hours of when the dose was due, give it as soon as you remember. Otherwise, do not give this dose but wait until the next dose is due. Do not give a double dose.
Compiled by:
The Pharmacy Department in collaboration with the Child and Family Information Group.
Last review date:
September 2019