Allopurinol: Uses, Side Effects & Safety

What it is and what it's used for

Allopurinol is a medicine that lowers the level of uric acid in the blood. Uric acid is a natural waste product in the body; when too much of it builds up, sharp crystals can form in the joints and cause gout — sudden, very painful swelling, often in the big toe — and, over time, lumps under the skin or kidney stones.

Allopurinol is mainly used for the long-term prevention of gout attacks in people with high uric acid levels, and sometimes to prevent certain uric acid kidney stones or high uric acid caused by some cancer treatments. It is not a painkiller and it does not treat a gout attack that has already started.

In India, allopurinol is a prescription medicine (Schedule H). It should only be taken on a doctor's advice, and it is usually taken for a long period, often for years, to keep uric acid levels down.

How it works (simple language)

Allopurinol is thought to work by blocking an enzyme called xanthine oxidase, which the body uses to make uric acid. With less uric acid being produced, blood levels fall gradually, and over time the crystals already in the joints can slowly dissolve, so gout attacks become less frequent and less severe. Because this process is gradual, allopurinol does not relieve pain quickly, and gout attacks may even occur more often in the first few weeks of treatment before things improve.

Dosage forms available in India (general info only)

Allopurinol is commonly available in India as 100 mg and 300 mg tablets. Well-known Indian brand names include Zyloric and Zyrik, though brands vary.

Never decide the dose yourself from this article. Always follow your doctor's prescription or the directions on the pack, and check with your pharmacist if you are unsure — especially for children, where the dose depends on the child's weight and age.

Side effects

Common: Skin rash or itching, nausea, vomiting, diarrhoea, stomach pain, drowsiness, headache, and a metallic or altered taste in the mouth.

Serious — seek medical care: Widespread skin rash, peeling or blistering skin, sores in the mouth, swelling of the face, lips or tongue, difficulty breathing, fever with rash, yellowing of the skin or eyes, dark urine, severe stomach pain, blood in the urine, or very little or no urine. Stop the medicine and seek urgent medical help if any of these occur, as a serious skin or allergic reaction needs immediate attention.

Precautions and warnings

• Do not start during a gout attack: Allopurinol is for preventing future attacks, not treating one that has started. Starting it during an attack can make the attack worse; your doctor will usually advise when to begin, and may give another medicine for pain and inflammation in the meantime.
• Report any rash immediately: Even a mild rash should be reported to your doctor straight away and the medicine should not be continued without medical advice, because a rash can rarely develop into a severe, life-threatening skin reaction.
• Kidney or liver disease: Tell your doctor if you have kidney or liver problems, as the dose may need to be lower and blood tests may be needed to check how the medicine is affecting you.
• Drink plenty of fluids: Unless your doctor has limited your fluid intake, drinking enough water helps the kidneys flush out uric acid and may reduce the risk of kidney stones.
• Avoid alcohol: Alcohol, especially beer, raises uric acid levels and can trigger gout attacks, so it is best avoided or kept to a minimum while taking allopurinol.
• Do not stop suddenly without advice: Stopping allopurinol can allow uric acid levels to rise again and bring gout attacks back, so talk to your doctor before stopping, even if you feel well.
• Driving and alertness: Allopurinol can cause drowsiness or dizziness in some people, so be careful when driving or operating machinery until you know how it affects you.

Interactions (general)

Allopurinol can interact with medicines such as azathioprine and mercaptopurine (used for immune conditions and some cancers), the blood thinner warfarin, some water pills (diuretics), and ampicillin or amoxicillin (which may increase the chance of a rash). It can also interact with some diabetes medicines and with theophylline. Alcohol should be avoided. Always tell your doctor about ALL medicines you take, including herbal and ayurvedic products, before starting allopurinol.

Pregnancy and breastfeeding (general guidance)

Allopurinol should only be used in pregnancy if your doctor considers it clearly necessary, as its safety in pregnancy is not fully established. It is generally not recommended while breastfeeding unless your doctor advises it. Always consult your doctor first if you are pregnant, planning pregnancy, or breastfeeding.

Storage

Store allopurinol tablets at room temperature, away from heat and moisture, and out of the reach of children. Do not use tablets past their expiry date, and do not share your medicine with others even if their symptoms seem similar.

When to see a doctor

See a doctor if: you develop any skin rash or itching, your gout attacks do not become less frequent over time, you have persistent nausea, stomach pain, or unusual tiredness, or you notice yellowing of the skin or eyes or changes in urination. Seek emergency care immediately for a widespread rash, peeling skin, swelling of the face or lips, difficulty breathing, or signs of a severe allergic reaction.

FAQs

1. Does allopurinol cure gout?

No, allopurinol does not cure gout, but it lowers uric acid levels over time, which can prevent attacks and allow crystals in the joints to slowly dissolve. Most people need to keep taking it long-term to keep gout under control.

2. Can I take allopurinol when I have a gout attack?

Allopurinol is not a treatment for an ongoing attack and should not be started during one, as it may make the attack worse. Your doctor may prescribe a painkiller or anti-inflammatory medicine for the attack and advise when to start or continue allopurinol.

3. How long does it take for allopurinol to work?

Uric acid levels fall gradually over weeks, and gout attacks may even be more frequent at first before they improve. It can take several months of regular use before attacks become clearly less frequent, so patience and regular follow-up blood tests are important.

4. What should I do if I get a rash while taking allopurinol?

Stop taking the medicine and contact your doctor straight away, even if the rash seems mild. A rash can rarely be the first sign of a serious skin reaction, so it should never be ignored or treated by simply continuing the medicine.