Xanthine Oxidase Inhibitors for Gout

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Xanthine Oxidase Inhibitors for Gout


Generic NameBrand Name

These medicines are taken in tablet form (oral). They are taken in low dosages at first. The dose may be adjusted if the uric acid level is still not low enough.

How It Works

Allopurinol and febuxostat have different chemical structures, but they both prevent the release of a substance called xanthine oxidase, which helps in the formation of uric acid. In treatment for gout, these drugs block the production of uric acid in the body.

Why It Is Used

Xanthine oxidase inhibitors may be prescribed to prevent gout attacks. They also may be used because of:

  • Overproduction of uric acid.
  • Frequent gout attacks.
  • Presence of gritty, chalky clumps of uric acid crystals (tophi).
  • Failure of other medicines to adequately reduce uric acid levels.
  • Allergy to uricosuric medicines, which increase the elimination of uric acid, or serious side effects from these medicines. Uricosuric medicines include probenecid and sulfinpyrazone.
  • Poor kidney function.
  • History of uric acid kidney stones.

Allopurinol may also be used for the prevention of kidney disease in people going through treatment for cancer.

The dose of xanthine oxidase inhibitors may need to be lower for people who have chronic kidney disease.

Allopurinol is not recommended for people who have a known sensitivity to allopurinol.

Xanthine oxidase inhibitors should not be started for the first time by people who are still having symptoms caused by a gout attack.

How Well It Works

Xanthine oxidase inhibitors lower the amount of uric acid in the body.1 After the proper dose is reached, the uric acid levels should return to normal. Your doctor will monitor your uric acid level within one month of starting or changing a dose of a xanthine oxidase inhibitor.

Treatment with xanthine oxidase inhibitors can reduce the size of tophi.1

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.

Call 911 or other emergency services right away if you have:

  • Trouble breathing.
  • Swelling of your face, lips, tongue, or throat.
  • Skin rash, especially if you are taking allopurinol.

Call your doctor if you have:

  • Hives.

Common side effects of allopurinol include:

  • Rash. This is a common side effect, but it can be a sign of a very serious or life-threatening condition.
  • Diarrhea and nausea.
  • Increased gout attacks at first. To avoid this, your doctor may also prescribe either colchicine, which blocks the inflammation caused by uric acid crystals, or low-dose nonsteroidal anti-inflammatory drugs (NSAIDs). After normal uric acid levels have been maintained for 6 to 12 months and no further attacks occur, colchicine or NSAIDs do not need to be taken.

Common side effects of febuxostat include:

  • Abnormal liver function.
  • Dizziness.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Xanthine oxidase inhibitors interfere with many other medicines. They may increase or decrease the levels of other medicines, which may raise the toxicity of these medicines or reduce their effectiveness. Be sure your doctor knows about all prescription and over-the-counter medicines and dietary supplements you are taking.

Xanthine oxidase inhibitors should not be used until the symptoms of a gout attack are gone. But if you are already taking one of these medicines, continue to take it (even during an attack).

Gout attacks may increase at first for some people who take allopurinol. To avoid this, doctors may also prescribe either colchicine, which blocks the inflammation caused by uric acid crystals, or low-dose nonsteroidal anti-inflammatory drugs (NSAIDs). After uric acid levels have been normal for 6 to 12 months and no further attacks occur, colchicine or NSAIDs can be discontinued.

Liver and kidney function studies may be done after a few months of using xanthine oxidase inhibitors. These studies can be repeated as needed.

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

If you are pregnant, breast-feeding, or trying to get pregnant, do not use any medicines unless your doctor tells you to. Some medicines can harm your baby. This includes prescription and over-the-counter medicines, vitamins, herbs, and supplements. And make sure that all your doctors know that you are pregnant, breast-feeding, or planning to get pregnant.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Colchicine and other drugs for gout. (2009). Medical Letter on Drugs and Therapeutics, 51(1326).


ByHealthwise Staff
Primary Medical ReviewerAnne C. Poinier, MD - Internal Medicine
Specialist Medical ReviewerNancy Ann Shadick, MD, MPH - Internal Medicine, Rheumatology
Last RevisedJune 12, 2012

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