What is allopurinol?
Allopurinol is used for the long-term treatment and prevention of gout. Taken regularly, it can stop attacks of gout and help prevent damage to your joints.
Gout occurs in people who have high levels of urate in their blood. Every day, the body naturally produces urate. This normally dissolves in your blood until it is passed out of the body, mainly in your pee.
But if too much urate is produced, or your body cannot get rid of it properly, urate crystals can form in and around your joints. These crystals can slowly form for years without you knowing. Once many crystals have formed, they can shed into the joint, causing painful inflammation.
Allopurinol works by lowering the amount of urate in your blood. Because of this, it’s sometimes called a urate lowering therapy (ULT). Once your urate level is low enough, new crystals will stop forming and existing crystals will slowly dissolve.
After a few years, all the crystals may dissolve. If this happens, there will be no more joint damage or gout attacks caused by these crystals, as long as you are taking allopurinol.
Because it can take a long time to dissolve the crystals, you may have more attacks of gout while this is happening. This is more likely if your urate levels are very high to begin with, or if you have had gout for a long time.
If this happens to you, it does not mean that the allopurinol is not working.
Who can take allopurinol?
Allopurinol is often recommended as the first choice of treatment to control gout. If your doctor prescribes it as soon as you are diagnosed, it may prevent future attacks and joint damage.
You will usually be offered allopurinol if blood tests show that your urate level is high enough for urate crystals to form, especially if one or more of the following applies:
- you are having frequent attacks of gout.
- your joints have been damaged by gout.
- your skin has visible deposits of urate crystals. These are firm white lumps, which are called tophi.
You may not be offered allopurinol, or you may be given a lower dose, if you:
- have ever had an allergic reaction to allopurinol.
- are currently having an attack of gout.
- have problems with your liver or kidneys.
- are of Han Chinese, Thai or Korean origin.
- have thyroid problems.
How is it taken?
Allopurinol is taken as a tablet once a day. It is usually better to take it just after eating and the tablet should be swallowed with water. It is important to drink plenty of water during the day because this will help you get rid of more urate through your kidneys.
Your dose of allopurinol may change over time, depending on the amount of urate in your body. Your doctor will monitor your urate levels with blood tests every 2-4 weeks, until they are sure that the dose that you’re taking is high enough to reduce the amount of urate in your body.
You may need to remain on a lower dose if you have kidney or liver problems.
Your doctor may recommend that you do not start taking allopurinol until after an attack of gout has passed to avoid triggering further attacks. If this is not possible, it may be started when your inflammation is not too bad.
Allopurinol doesn’t treat the immediate pain caused by attacks of gout. But it’s a long-term treatment to get rid of the urate crystals which causes gout attacks.
It is likely that you will need to take allopurinol for the rest of your life to manage your urate levels. You should keep taking allopurinol even if:
- you are experiencing more gout attacks, or it doesn’t seem to help the pain and inflammation at first
- you stop having gout attacks – stopping your treatment can cause urate crystals to form again, which will lead to more gout attacks.
To reduce the effects of gout attacks in the first three to six months of taking allopurinol, your doctor may prescribe a low dose of colchicine or a non-steroidal anti-inflammatory drug (NSAID), such as:
You should be offered another tablet, known as a proton pump inhibitor, to protect your stomach while taking NSAIDs. If you cannot take NSAIDs, colchicine or steroids may be given instead.
Side effects and risks
Most people who take allopurinol do not get any serious side effects. However, some side effects of allopurinol include:
- feeling drowsy or dizzy
- feeling or being sick
- changes to your sense of taste.
If you develop a rash, redness or flu-like symptoms, you should contact your doctor straight away. If you become dizzy or drowsy while taking allopurinol, do not drive or operate machinery, and see your doctor as soon as possible. You should also speak to your doctor if you develop any new symptoms that worry you.
Sometimes starting allopurinol can trigger a gout attack. This is because some of the crystals can dislodge into the joint as they get smaller which can cause an attack.
You may be given another medicine to reduce the risk of these attacks. However, if you do have an attack of gout while you’re on allopurinol, it’s important that you carry on taking it.
Very rarely, allopurinol can lower the number of blood cells that fight infection in your body. This is called allopurinol hypersensitivity syndrome.
The symptoms of allopurinol hypersensitivity syndrome include:
- severe rashes and blisters
- fever and flu-like symptoms
- yellowing of the eyes or skin, known as jaundice
- bleeding gums
- unexplained bleeding
- unusual thirst
- needing to pee a lot
This mainly occurs in people who have chronic kidney disease and have started a higher dose of allopurinol.
Allopurinol is usually the first urate lowering therapy (ULT) recommended for gout. But if you’re unable to continue taking allopurinol because of the side effects, you may be able to take another drug instead, such as febuxostat, which works in a similar way to allopurinol.
Effects on other treatments
Some drugs interact with allopurinol, so you should discuss any new medication with your doctor before starting it. You should also tell anyone else treating you that you’re taking allopurinol.
Do not use complementary treatments, such as herbal remedies, without discussing this first with your doctor or pharmacist. Some of them could react with allopurinol.
You should avoid taking aspirin while you’re being treated for gout. If you’re in pain, you can take paracetamol and NSAIDs. But remember you should only take one NSAID at a time – so do not take another if you have already been prescribed one to reduce the effects of gout attacks.
Allopurinol can also react with drugs that are often prescribed for high blood pressure, such as bendroflumethiazide, indapamide, lisinopril, ramipril.
It can also reduce the breakdown of the leukaemia drug mercaptopurine, so the dose of mercaptopurine will need to be reduced if you take this drug.
Allopurinol may also increase the risk of developing a rash if you take them with the antibiotics ampicillin or amoxicillin.
Allopurinol may also increase the effect of warfarin and other drugs that thin the blood. These are known as anticoagulants. If you’re taking blood thinners, you may need your clotting time tested more frequently to check you’re still on the right dose.
You can have vaccinations while on allopurinol.
Having an operation
If you need surgery, your doctor will discuss with you whether you should continue taking allopurinol.
Allopurinol can be continued when you have surgery but, your doctor may recommend that you temporarily stop allopurinol and then restart it again 5-7 days later at the same dose.
If you still have urate crystals in your joints, an operation can trigger an acute attack, usually within the first few days of the surgery, while you are still in hospital.
It's important to discuss any medications with your doctor before having surgery.
Alcohol is not thought to affect allopurinol. However, alcohol increases the amount of urate in the blood, and excessive drinking can trigger an attack of gout.
Guidelines state that adults shouldn’t have more than 14 units a week, and that they should spread them out over the course of the week. In some circumstances your doctor may advise lower limits.
You can find out more about units of alcohol at www.drinkaware.co.uk.
Fertility, pregnancy and breastfeeding
Allopurinol is unlikely to affect your fertility. However, it is not recommended during pregnancy or while you are breastfeeding, because we don’t know what effect it may have on your baby.
Talk to your doctor if you’re planning a family or become pregnant while taking allopurinol, they may be able to recommend a safe alternative treatment.