Allopurinol is used as a long-term tablet for gout prevention.
Uric acid (urate) is a waste product naturally found in the blood. It is created when the body breaks down chemicals called purines.
Normally, the kidneys filter uric acid out, but if levels become too high, it can form sharp, needle-like crystals in the joints and tissues.
Allopurinol (brand name Zyloric) is the most common medication used to lower uric acid levels. It belongs to a group of medicines called ‘xanthine oxidase inhibitors.’
Unlike painkillers that treat a sudden attack, allopurinol is a preventative treatment designed to stop gout attacks from happening in the first place.
A Urate-Lowering Therapy (ULT): It is a specific type of medicine used to reduce the amount of uric acid produced by your body.
Preventative Medicine: It is not a painkiller. It does not treat the pain of an active gout flare; instead, it works over time to dissolve existing crystals and prevent new ones from forming.
Lifelong Management: For most people with chronic gout, allopurinol is a long-term (often lifelong) medication to keep the condition under control.
Gout: It is primarily used to prevent gout attacks, joint damage, and “tophi” (visible lumps of crystals under the skin).
Kidney Stones: It helps prevent the formation of certain types of kidney stones made of uric acid.
Cancer Treatment Support: It is sometimes used for patients undergoing chemotherapy to prevent “Tumour Lysis Syndrome,” where rapid cell breakdown causes a dangerous spike in uric acid.
Dose: Treatment usually starts at a low dose (e.g. 100mg daily) to reduce the risk of triggering a flare. It is then increased every few weeks based on blood test results.
Maintenance: The typical maintenance dose is between 300mg and 600mg daily, though some may require up to 900mg.
Schedule: It is taken once a day, ideally at the same time each day.
Note on Starting 1: When you first start allopurinol, the shift in uric acid levels can actually trigger a gout flare. Because of this, doctors may prescribe a low-dose anti-inflammatory (like colchicine) to take alongside it for the first few months.
Note on Starting 2. Allopurinol should not be started during a gout attack, but between attacks. This is because its function is to prevent (i.e. reduce frequency of attacks) gout, not treat it whilst you have it.
Common side-effects
Skin Rash: This is the most common side-effect. If you develop any rash, you must stop the medication and speak to a doctor immediately.
Nausea: Feeling sick can occur but is usually managed by taking the tablet after a meal.
Drowsiness: Some people feel a bit sleepy when they first start the treatment.
Less common (but more serious) side-effects
Severe Hypersensitivity: A very rare but serious allergic reaction involving the skin and internal organs.
Liver Issues: Occasional changes in liver function tests.
Blood Disorders: Rare effects on the number of white or red blood cells.
Enzyme Blocking: Allopurinol works by blocking an enzyme (protein) in the body called xanthine oxidase. This enzyme is responsible for turning purines into uric acid.
Lowering Production: By “switching off” this enzyme’s activity, the body produces significantly less uric acid, leading to lower levels in the bloodstream.
Crystal Dissolution: When blood levels stay low (usually below a specific target), the crystals that have built up in your joints over years slowly begin to dissolve and wash away.
Your doctor will need to monitor:
Serum Urate Levels: Regular blood tests to ensure your uric acid is below the “target level” (usually <300 or <360 µmol/L).
Kidney Function: Since allopurinol is cleared by the kidneys, your dose may need to be lower if your kidney function (e.g. CKD) decreases.
Liver Function: Occasional checks to ensure your liver is healthy.
| Feature | Colchicine | Allopurinol |
| Main Action | Reduces inflammation and pain during a flare. | Lowers the production of uric acid in the body. |
| Primary Goal | Short-term relief of intense pain. | Long-term prevention of future attacks. |
| Timing | Taken at the first sign of a gout attack. | Taken every day, even when you feel well. |
| Duration | Usually taken for a few days at a time. | Usually a lifelong daily commitment. |
| Side-effects | Primarily stomach upset/diarrhoea. | Primarily skin rashes or nausea. |
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