Allopurinolألوبيورينول

Allopurinol is a medicine used to lower the level of uric acid in the blood.

It's prescribed for gout, for people with recurring uric-acid kidney stones, and for high uric acid levels that can occur during some cancer treatments.

Allopurinol works by blocking an enzyme called xanthine oxidase, which the body normally uses to turn other compounds into uric acid.

By blocking this enzyme, allopurinol reduces how much uric acid the body produces in the first place — it does not act as a diuretic and has no effect on how much urine the body passes.

• Gout
• Preventing recurring uric-acid-related kidney stones
• High uric acid linked to some cancer treatments

Allopurinol doses are set individually by a doctor and depend on the condition being treated.

Gout

• Initial dose: around 100 mg a day, then adjusted upward
• Maintenance dose for milder gout: 200–300 mg a day
• Maintenance dose for more severe, tophaceous gout: 400–600 mg a day
• Target uric acid level: about 6 mg/dL or below

Uric-acid-related kidney stones

• Typical dose: 200–300 mg a day

High uric acid linked to cancer treatment

• Dose: 600–800 mg a day
• Duration: 2–3 days

Splitting the dose

• The total daily dose is generally kept at or below 800 mg a day, split into more than one dose when the daily amount is above 300 mg.

This is educational background, not an individual prescription — your own doctor sets your exact dose.

Allopurinol lowers uric acid gradually, not immediately.

A noticeable change may take around 4 weeks.

It does not relieve a gout attack that is already happening.

Gout attacks can actually become more frequent for a while right after starting treatment, before things settle down — this is a recognized pattern, not a sign the medicine isn't working.

• Taken once a day
• Generally taken after a meal, which reduces the chance of stomach upset
• Drink plenty of fluids while taking it — enough to keep urine output generous through the day, which helps the body clear uric acid; ask your doctor how much fluid is right for you

• Store below 25°C
• Keep away from moisture
• Keep away from direct sunlight
• As with any medicine, keep it out of the reach of children

Common side effects can include:

• Headache
• Diarrhea
• Drowsiness
• Mild skin rash
• Itching
• Nausea (feeling or being sick) — sometimes eased by taking allopurinol after food

Many people experience no side effects at all.

A small number of people develop a severe skin reaction to allopurinol. This can include drug reaction with eosinophilia and systemic symptoms (DRESS), with rash occurring in up to 3% of cases, and rarer but more serious reactions — Stevens-Johnson syndrome and toxic epidermal necrolysis — in under 1% of cases; these can be life-threatening. Stop the medicine and contact a doctor immediately at the first sign of rash or skin reaction.

Allopurinol can, in rare cases, cause a serious hypersensitivity reaction. If sudden, severe symptoms appear after starting allopurinol, treat it as a medical emergency and seek urgent care rather than waiting to see if it passes.

Allopurinol has rarely been linked to liver problems, including reversible liver toxicity with possible rises in liver-enzyme blood tests, and rare cases of granulomatous hepatitis or liver tissue damage (each in under 1% of patients). Anyone with existing liver disease should be monitored more closely while taking it.

Bone marrow suppression has rarely been reported with allopurinol, including reduced white blood cells (agranulocytosis), aplastic anemia, low platelet counts, and increased eosinophils, together in about 0.6% of patients. The risk is higher in people also taking other medicines that can affect the bone marrow.

• Known hypersensitivity to allopurinol
• Concurrent use with didanosine (an antiviral medicine)
• A positive HLA-B*5801 genetic marker — associated with a higher risk of severe skin reactions
• Pregnancy and breastfeeding — generally avoided unless clearly needed
• Occupations requiring high concentration (such as driving) — caution advised, given the possibility of drowsiness

Very important interactions

• Azathioprine — allopurinol can significantly increase its effect; the dose of azathioprine usually needs to be substantially reduced when combined
• Didanosine — should not be combined with allopurinol

Other medicines that can interact

• Warfarin (a blood thinner)
• Captopril and enalapril (ACE inhibitors)
• Fluorouracil
• Cyclosporine
• Aluminum-hydroxide antacids
• Chlorpropamide
• Ampicillin and amoxicillin (antibiotics) — combined use has been linked to a higher rate of skin rash

Notes on diuretics

• Other diuretics can also interact with allopurinol
• If you take a thiazide diuretic together with allopurinol, your kidney function should be monitored

Always tell your doctor and pharmacist about every other medicine, supplement, and herbal product you take.

Kidney function changes how allopurinol is dosed. Staged reference points are used:

For more advanced kidney disease (stage 4 or beyond), treatment often starts as low as 50 mg a day, adjusted gradually over weeks under close monitoring. These are reference points for a prescribing doctor to apply, not a self-dosing guide.

Allopurinol is occasionally used in children for cancer-related high uric acid, each for 2–3 days unless noted otherwise:

Use in children should always be directed and monitored by a specialist — these are reference figures, not a self-dosing guide.

Allopurinol should only be used during pregnancy or while breastfeeding if your doctor decides it's clearly needed — its safety in these situations has not been firmly established, and possible harm to the baby cannot be ruled out.

Talk to your doctor before starting or continuing it if you are pregnant, planning a pregnancy, or breastfeeding.

Some situations call for closer monitoring while taking allopurinol:

• Reduced kidney function together with a thiazide diuretic — higher risk of a serious hypersensitivity reaction
• Taking another medicine that can affect the bone marrow — bone marrow suppression is more likely
• Pre-existing liver disease — liver function should be watched more closely
• Kidney-related blood markers (BUN) may rise during treatment
• Protein in the urine followed by kidney inflammation has been noted in some cases

Your own doctor will decide exactly what monitoring, if any, applies to you.