Allopurinol

About

Allopurinol is a medicine used to lower uric acid levels in the blood. It belongs to a class of drugs known as xanthine oxidase inhibitors, which work by reducing the production of uric acid — a substance that can build up and cause gout or kidney stones.

It is commonly prescribed for:

• Gout (to prevent attacks)
• Kidney stones caused by high uric acid
• High uric acid levels due to cancer treatments (tumor lysis syndrome)
• Other conditions associated with excess uric acid

Allopurinol is usually available in the form of:

• Tablets (100 mg, 300 mg)
• Occasionally as an injectable form (hospital use)

How and When to Use It

Take allopurinol exactly as prescribed by your doctor.

Dosage: The dose varies depending on your uric acid levels and kidney function. For adults, the usual starting dose is 100 mg once daily, which may be increased gradually (up to 300–600 mg daily).

Take allopurinol after food with a full glass of water. Drink plenty of fluids during treatment to help prevent kidney stones.

Allopurinol is used to prevent gout attacks — it should not be started during an acute gout attack. Continue taking it regularly, even when you feel well.

Contraindications

Allopurinol should not be used if you have:

• Allergy to allopurinol or any of its ingredients
• Severe liver or kidney disease (unless dose is adjusted by your doctor)
• Current acute gout attack (wait until it settles before starting)
• Rare genetic enzyme disorders affecting purine metabolism

Side Effects

Like all medicines, allopurinol can cause side effects, although not everyone gets them.

Common side effects:

• Skin rash (usually mild)
• Upset stomach, nausea, or diarrhea
• Drowsiness or dizziness
• Changes in liver enzyme tests

Serious but rare side effects:

• Severe allergic reactions (Stevens–Johnson syndrome, toxic epidermal necrolysis)
• Fever, sore throat, or mouth ulcers (possible sign of low blood cells)
• Liver inflammation (hepatitis)
• Kidney problems or stones

Seek medical attention immediately if you develop a widespread rash, blistering, fever, or swelling of the face or throat.

Pregnancy, Breastfeeding & Fertility

Allopurinol can be used during pregnancy only if clearly necessary and prescribed by a doctor. There is limited evidence, but it is not known to cause harm when used under medical supervision.

Small amounts may pass into breast milk, but no harmful effects have been reported.

There is no evidence that allopurinol affects fertility in men or women.

Interactions With Other Medications

Allopurinol can interact with several medicines:

• Azathioprine and mercaptopurine — doses of these should be reduced (risk of toxicity)
• Warfarin — may increase the effect; monitoring is required
• Antibiotics such as ampicillin or amoxicillin — may increase risk of skin rash
• Diuretics (e.g., thiazides) — can increase risk of hypersensitivity reactions
• Other gout medicines (e.g., colchicine or NSAIDs) — may be used together as directed by a doctor

Frequently Asked Questions