Allopurinol
1 medicine
Allopurinol lowers uric acid to prevent gout attacks and kidney stones, and in rare cases it triggers a severe, potentially fatal skin reaction, so any new rash means stopping the drug and seeking care immediately.
Key facts
- Allopurinol is a xanthine oxidase inhibitor. It blocks the enzyme that makes uric acid, lowering blood uric acid over weeks to prevent gout attacks and uric-acid kidney stones.
- It's taken once or twice daily with food; the dose starts low and rises gradually, guided by blood uric-acid levels.
- Rarely, allopurinol triggers a severe skin reaction, including Stevens-Johnson syndrome or toxic epidermal necrolysis, that can be fatal. Any new rash, especially with fever or mouth sores, means stopping the drug immediately and seeking care.
- Starting allopurinol can trigger a gout flare before it prevents future ones, so it's often started alongside a short anti-inflammatory course.
What Allopurinol treats
Allopurinol treats gout by lowering uric acid so crystals stop forming in joints, and it prevents uric-acid kidney stones. It's also used to prevent tumour lysis syndrome, a sudden surge in uric acid that can occur when cancer treatment destroys large numbers of cells quickly.
How Allopurinol works
Uric acid forms when the body breaks down purines, using an enzyme called xanthine oxidase. Allopurinol blocks this enzyme, so less uric acid is produced. Over weeks, blood uric acid falls, existing crystal deposits gradually dissolve, and gout attacks become less frequent.
Before you take it
- People of Southeast Asian, Han Chinese or African descent may carry a gene, HLA-B*5801, that raises the risk of severe skin reactions; testing is recommended for these groups before starting.
- Do not start allopurinol during an acute gout attack. Wait until the flare settles, but keep taking it if you're already on treatment when a flare occurs.
- Tell your prescriber about kidney disease, and about azathioprine or mercaptopurine, since allopurinol raises their levels to a dangerous degree and their doses must be cut.
- Diuretics and ACE inhibitors raise the risk of allopurinol side effects in people with reduced kidney function.
Side effects
Common effects include mild rash, nausea and diarrhoea.
Stop and seek urgent medical care for:
- A spreading or blistering rash, mouth sores, or skin peeling.
- Fever, swollen glands, or yellowing of the skin or eyes.
- Facial swelling or difficulty breathing.
Safety essentials
- Any new rash is a stop-and-call-your-doctor sign. Severe skin reactions to allopurinol are rare but can be life-threatening, and most occur in the first two months of treatment.
- Never combine allopurinol with azathioprine or mercaptopurine without a dose adjustment supervised by your prescriber.
- Kidney function guides your dose, so tell your prescriber about any change in kidney health.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.