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Trade/Other Name(s): Zyloprim, Aloprim, Lopurin

Why would this drug be used?

Allopurinol belongs to a group of drugs that may be called cytoprotective (cell-protecting) agents. It is used to lower blood levels of uric acid, especially in people who are getting chemotherapy or radiation therapy that is likely to kill a large number of cancer cells in a short amount of time. This helps prevent kidney damage.

Allopurinol is also used to prevent or treat other medical problems caused by too much uric acid in the body, including gout and some kinds of kidney stones.

How does this drug work?

The goal of cancer treatments such as chemotherapy or radiation therapy is to kill cancer cells. But in some cases, killing large numbers of cancer cells in a short amount of time can be dangerous. As the cells die, they break open and spill their contents into the bloodstream. Some of these substances can cause serious kidney damage and other problems, a condition known as tumor lysis syndrome. One of these substances, uric acid, is formed from the breakdown of DNA and RNA. Uric acid is hard for the body to get rid of quickly and can form harmful crystals in the kidneys.

Allopurinol works by blocking the enzyme (xanthine oxidase) that converts other substances into uric acid.

Before taking this medicine

Tell your doctor…

  • If you are allergic to any medicines, dyes, additives, or foods.
  • If you have any type of kidney problems. This drug is cleared from the body mainly by the kidneys. Reduced kidney function might result in more drug than expected staying in the body, which could lead to unwanted side effects. Your doctor may need to adjust your dose accordingly.
  • If you have any type of liver disease (including hepatitis). In rare cases this drug may affect liver function. Your doctor will likely do blood tests to monitor your liver function during treatment.
  • If you have ever had gout. This drug may raise your risk of an attack when first given.
  • If you have any other medical conditions such as heart disease, congestive heart failure, lung disease, diabetes, or infections. You may need closer monitoring of these conditions while being treated.
  • If you are pregnant, trying to get pregnant, or if there is any chance of pregnancy. This drug might cause problems if it is taken at the time of conception or during pregnancy. Check with your doctor about what kinds of birth control can be used with this medicine. This drug should be used during pregnancy only if the potential benefit is thought to justify the potential risk to the fetus.
  • If you are breast-feeding. This drug passes into breast milk and may affect the baby. Your doctor may want to monitor the baby if you are breast-feeding while taking this drug.
  • If you think you might want to have children in the future. It is not known whether or not this drug can affect fertility. Talk with your doctor about the possible risk with this drug and the options that may preserve your ability to have children.
  • About any other prescription or over-the-counter medicines you are taking, including vitamins and herbs. In fact, keeping a written list of each of these medicines (including the doses of each and when you take them) with you in case of emergency may help prevent complications if you get sick.

Interactions with other drugs

  • Allopurinol may interact with a number of other drugs. It is very important that your doctor know if you are taking any of the following:
  • antibiotics such as amoxicillin (Amoxil) or ampicillin (Polycillin)
  • blood thinners such as warfarin (Coumadin) or dicumarol
  • chemotherapy drugs such as cyclophosphamide (Cytoxan) or mercaptopurine (Purinethol)
  • thiazide diuretics (water pills) such as hydrochlorothiazide
  • medicines to suppress the immune system such as azathioprine (Imuran) or cyclosporine (Neoral, Sandimmune)
  • medicines for gout such as probenecid (Benemid) or sulfinpyrazone (Anturane)
  • drugs for diabetes such as tolbutamide (Orinase) or chlorpropamide (Diabinese)

No other serious interactions are known at this time. But this does not necessarily mean that none exist. Check with your doctor, nurse, or pharmacist about all of your medicines, herbs, and supplements, and whether alcohol can cause problems with this medicine.

Interactions with foods

No serious interactions with food are known at this time. Check with your doctor, nurse, or pharmacist about whether some foods may be a problem.

Tell all the doctors, dentists, nurses, and pharmacists you visit that you are taking this drug.

How is this drug taken or given?

To prevent tumor lysis syndrome, allopurinol is usually taken as a pill, starting 1 to 3 days before cancer treatment. Taking the pills after meals may reduce the chance of an upset stomach. For people who can't take allopurinol as a pill, it can also be given as an injection into a vein (intravenous, or IV).

The daily dose depends on your body size and how well your kidneys are working. Smaller daily doses may be taken once a day, while larger daily doses may be divided into 2 or 3 doses. Your doctor will check your uric acid levels during treatment and adjust or stop the allopurinol as needed.

If you are taking pills, keep the medicine in a tightly closed container away from heat and moisture and out of the reach of children and pets.


While getting this drug, other measures to help reduce the risk of tumor lysis syndrome should also be used, including good fluid intake and possibly intravenous (IV) fluids to get enough liquid. Talk to your doctor about how much fluid you should drink each day.

This drug may make you feel drowsy. Do not drive or operate heavy machinery until you know how the drug affects you. Use caution if consuming alcohol while taking this medicine. Talk to your doctor or nurse if you feel too drowsy or it does not go away.

Your doctor will likely test your blood throughout your treatment, looking for possible effects of the drug on blood chemistry levels and especially on liver and kidney function. Based on the test results, your doctor may need to reduce or delay your next dose of this drug, or even stop it altogether. Tell your doctor right away if you have trouble urinating or notice blood in the urine or yellowing of the eyes or skin.

Tell your doctor right away if you get any type of skin rash while on this drug. Rarely, a serious type of rash can develop and cause serious illness or death. This kind of reaction can also produce fever, shaking chills, and yellowed skin or eyes.

Call your doctor if you have pain when you pass urine, blood in your urine, or irritated eyes.

In rare cases, this drug can cause allergic reactions when the drug is given. Mild reactions may consist of skin rash or itching, fever, chills, or feeling flushed. More serious reactions happen rarely, but can be dangerous. Symptoms can include feeling lightheaded or dizzy (due to low blood pressure), chest pain or tightness, shortness of breath, back pain, or swelling of the lips, face, tongue, or throat. Tell your doctor or nurse right away if you notice any of these symptoms during or after being given the drug.

Possible side effects

You will probably not have most of the following side effects, but if you have any talk to your doctor or nurse. They can help you understand the side effects and cope with them.


  • none

Less common

  • skin rash or itching*
  • feeling drowsy*
  • headache
  • upset stomach


  • allergic reaction (may include skin rash or hives, dizziness, shortness of breath, chest pain or tightness, swelling in the mouth or throat, flushing, or fever)*
  • abnormal blood tests suggesting the drug may be affecting the liver or kidneys (Your doctor will discuss the importance of this finding, if any.)*
  • severe skin rash with peeling of the skin*
  • sores or swelling in the mouth or lips
  • trouble urinating or blood in the urine*
  • red or irritated eyes

*See "Precautions" section for more detailed information.

There are other side effects not listed above that can also occur in some patients. Tell your doctor or nurse if you develop these or any other problems.

FDA approval

Yes – first approved before 1984 (FDA cannot verify dates of drugs approved before 1984.)

Disclaimer: This information does not cover all possible uses, actions, precautions, side effects, or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for talking with your doctor, who is familiar with your medical needs.

Last Medical Review: 10/21/2009
Last Revised: 10/21/2009