Allopurinol belongs to a class of medications called xanthine oxidase inhibitors. It works by reducing the production of uric acid in the body. High levels of uric acid may cause gout attacks or kidney stones.

Allopurinol is used to treat gout (a type of arthritis in which uric acid, a naturally occurring substance in the body, builds up in the joints and causes sudden attacks of redness, swelling, pain, and heat in one or more joints). Allopurinol is used to prevent gout attacks, not to treat them once they occur.

Allopurinol is also used to treat high levels of uric acid that builds up in the blood as tumors break down in people with certain types of cancer who are being treated with chemotherapy medications. It is also used to treat kidney stones that have come back in people who have high levels of uric acid in their urine.

You should not use this medicine if you have ever had an allergic reaction to allopurinol.

Allopurinol can lower blood cells that help your body fight infections. This can make it easier for you to bleed from an injury or get sick from being around others who are ill. Your blood may need to be tested often. Visit your doctor regularly.

In rare cases, allopurinol may cause a severe allergic reaction. Stop taking this medicine and call your doctor right away if you have painful urination, blood in your urine, burning in your eyes, swelling in your face or throat, skin redness or a rash that spreads and causes blistering and peeling.

Avoid drinking alcohol. It can make your condition worse. Allopurinol may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Allopurinol comes as a tablet to take by mouth. It is usually taken once or twice a day, preferably after a meal. To help you remember to take allopurinol, take it around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take allopurinol exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor will probably start you on a low dose of allopurinol and gradually increase your dose, not more than once a week.

It may take several months or longer before you feel the full benefit of allopurinol. Allopurinol may increase the number of gout attacks during the first few months that you take it, although it will eventually prevent attacks. Your doctor may prescribe another medication such as colchicine to prevent gout attacks for the first few months you take allopurinol. Continue to take allopurinol even if you feel well. Do not stop taking allopurinol without talking to your doctor.

Take allopurinol exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Take the tablets with a full glass of water. To reduce your risk of kidney stones, drink 8 to 10 full glasses of fluid every day, unless your doctor tells you otherwise.

Take with food if allopurinol tablets upsets your stomach.

Allopurinol injection is injected into a vein by a healthcare provider. The injection is usually only used if you are unable to take medicine by mouth.

You may need frequent medical tests while using this medicine, even if you have no symptoms.

Your kidney and liver function may also need to be tested. Your doctor may change your dose if your kidney function changes.

You may have gout attacks when you first start taking allopurinol tablets. Your doctor may recommend another gout medication to take with allopurinol. Keep taking the medicine as directed.

Your symptoms may not improve for up to 2 to 6 weeks. Call your doctor if your symptoms do not improve after 6 weeks.

You may need to follow a special diet to help prevent kidney stones. Follow all instructions of your doctor or dietitian. Learn about the foods you should eat or avoid.

Store at room temperature away from moisture and heat.

You should not use allopurinol if you are allergic to it.

To make sure this medicine is safe for you, tell your doctor if you have ever had:

• diabetes;

• congestive heart failure;

• high blood pressure;

• if you are receiving chemotherapy;

• if you have a gene variation called HLA-B*58:01 allele (your doctor can test you for this);

• liver disease; or

• kidney disease.

Allopurinol may harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Do not breastfeed while using this medicine, and for at least 1 week after your last dose.

Take allopurinol as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Call your doctor for instructions if you miss an appointment for your allopurinol injection.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Drink at least eight 8-ounce (240-milliter) cups of water or other liquids each day while taking allopurinol unless directed to do otherwise by your doctor.

Avoid driving or hazardous activity until you know how allopurinol will affect you. Your reactions could be impaired.

Avoid drinking alcohol.

Get emergency medical help if you have signs of an allergic reaction to allopurinol (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.

Allopurinol may cause serious side effects. Stop using this medicine and call your doctor at once if you have:

• any skin rash, no matter how mild;

• painful urination, blood in the urine;

• inflammation of your blood vessels - numbness or tingling, skin rash, fever, headache, body aches, night sweats, weight loss, feeling or weak or tired;

• signs of infection - fever, chills, sore throat, body aches, unusual tiredness, loss of appetite, bruising or bleeding; or

• liver problems - loss of appetite, weight loss, stomach pain (upper right side), itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common allopurinol side effects may include:

• an increase in gout attacks when you first start taking this medicine;

• rash;

• drowsiness;

• abnormal liver function tests;

• nausea, vomiting, diarrhea; or

• kidney problems - swelling, urinating less, feeling tired or short of breath.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Tell your doctor about all your other medicines, especially:

• azathioprine or mercaptopurine;

• chlorpropamide;

• cyclosporine;

• cancer medicine;

• other gout medications;

• an antibiotic such as ampicillin or amoxicillin;

• a blood thinner such as warfarin, Coumadin, Jantoven; or

• a diuretic or "water pill".

This list is not complete. Other drugs may interact with allopurinol, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body's response to allopurinol.

Before having any laboratory test, tell your doctor and the laboratory personnel that you are taking allopurinol.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.