BMA Concise Guide to Medicine & Drugs


Brand names Caplenal, Cosuric, Rimapurinol, Zyloric

Used in the following combined preparations None


Drug group Drug for gout

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Allopurinol is used to prevent gout, which is caused by deposits of uric acid crystals in joints. Allopurinol blocks an enzyme called xanthine oxidase that is involved in forming uric acid. It is also used to lower high uric acid levels (hyperuricaemia) caused by other drugs. Allopurinol should never be started until several weeks after an acute attack has subsided because it may cause a further episode. Treatment with the drug should be continued indefinitely to prevent further attacks. At the start of treatment, an acute attack may occur and colchicine or an anti-inflammatory drug may also be given, until uric acid levels are reduced. If an acute attack occurs while on allopurinol, treatment should continue along with an anti-inflammatory drug.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses 1–3 x daily after food.

Adult dosage range 100–900mg daily.

Onset of effect Within 24–48 hours. Full effect may not be felt for several weeks.

Duration of action Up to 30 hours. Some effect may last for 1–2 weeks after the drug has been stopped.

Diet advice A high fluid intake (2 litres of fluid daily) is recommended.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose If your next dose is not due for another 12 hours or more, take a dose as soon as you remember and take the next one as usual. Otherwise skip the missed dose and take your next dose on schedule.

Stopping the drug Do not stop the drug without consulting your doctor; symptoms may recur.

Exceeding the dose An occasional unintentional extra dose is unlikely to cause problems. Large overdoses may cause nausea, vomiting, abdominal pain, diarrhoea, and dizziness. Notify your doctor.


Adverse effects of allopurinol are not very common. The most serious are an allergic rash, sore throat, fever, and chills. If you experience any of these symptoms, they should be reported to your doctor and you should stop taking the drug; an alternative drug may need to be substituted. Nausea can be avoided by taking allopurinol after food. The drug may also cause drowsiness, dizziness, headache, and taste or visual disturbances. Discuss with your doctor if these occur.


ACE inhibitors Allopurinol may increase the risk of toxicity from these drugs.

Anticoagulant drug Allopurinol may increase the effects of these drugs.

Ciclosporin Allopurinol may increase the effects of this drug.

Didanosine Allopurinol increases levels of this drug.

Mercaptopurine and azathioprine Allopurinol blocks the breakdown of these drugs, requiring a reduction in their dosage.

Theophylline Allopurinol may increase levels of this drug.


Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You have had a previous sensitivity reaction to allopurinol.

· You have a current attack of gout.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk but is not known to be harmful to the baby. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 Reduced dose may be necessary.

Driving and hazardous work Avoid such activities until you have learned how allopurinol affects you because the drug can cause drowsiness.

Alcohol Avoid. Alcohol may worsen gout.


Apart from an increased risk of gout in the first weeks or months, no problems are expected.

Monitoring Periodic checks on uric acid levels in the blood are usually performed, and the dose of allopurinol adjusted if necessary.