In the U.S.—

In Canada—

• Antigout agent
• Antihyperuricemic
• Antiurolithic, calcium oxalate calculi
• Antiurolithic, uric acid calculi

Allopurinol (al-oh-PURE-i-nole) is used to treat chronic gout (gouty arthritis). This condition is caused by too much uric acid in the blood.

This medicine works by causing less uric acid to be produced by the body. Allopurinol will not relieve a gout attack that has already started. Also, it does not cure gout, but it will help prevent gout attacks. However, it works only after you have been taking it regularly for a few months. Allopurinol will help prevent gout attacks only as long as you continue to take it.

Allopurinol is also used to prevent or treat other medical problems that may occur if too much uric acid is present in the body. These include certain kinds of kidney stones or other kidney problems.

Certain medicines or medical treatments can greatly increase the amount of uric acid in the body. This can cause gout or kidney problems in some people. Allopurinol is also used to prevent these problems, and can be given as either a tablet or an injection if necessary

Allopurinol is available only with your doctor's prescription in the following dosage form:

Oral
• Tablets (U.S. and Canada)

Parenteral
• Injection (U.S.)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For allopurinol, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to allopurinol. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Although studies on birth defects have not been done in pregnant women, allopurinol has not been reported to cause problems in humans. In one study in mice, large amounts of allopurinol caused birth defects and other unwanted effects. However, allopurinol did not cause birth defects or other problems in rats or rabbits given doses up to 20 times the amount usually given to humans.

Breast-feeding—Allopurinol passes into the breast milk. Mothers who are taking this medicine and who wish to breast-feed should discuss this with their doctor.

Children—This medicine has been tested in children and, in effective doses, has not been shown to cause different side effects or problems than it does in adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of allopurinol in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking allopurinol, it is especially important that your doctor and pharmacist know if you are taking any of the following:

• Anticoagulants (blood thinners)—Allopurinol may increase the chance of bleeding; changes in the dose of the anticoagulant may be needed, depending on blood test results

• Azathioprine (e.g., Imuran) or
• Mercaptopurine (e.g., Purinethol)—Allopurinol may cause higher blood levels of azathioprine or mercaptopurine, leading to an increased chance of serious side effects

• Congestive heart disease or
• Diabetes mellitus (sugar diabetes) or
• High blood pressure or
• Kidney disease—There is an increased risk of severe allergic reactions or other serious effects; a change in the dose of allopurinol may be needed

If this medicine upsets your stomach, it may be taken after meals. If stomach upset (indigestion, nausea, vomiting, diarrhea, or stomach pain) continues, check with your doctor.

In order for this medicine to help you, it must be taken regularly as ordered by your doctor.

To help prevent kidney stones while taking allopurinol, adults should drink at least 10 to 12 full glasses (8 ounces each) of fluids each day unless otherwise directed by their doctor. Check with the doctor about the amount of fluids that children should drink each day while receiving this medicine. Also, your doctor may want you to take another medicine to make your urine less acidic. It is important that you follow your doctor's instructions very carefully.

For patients taking allopurinol for chronic gout:

• After you begin to take allopurinol, gout attacks may continue to occur for a while. However, if you take this medicine regularly as directed by your doctor, the attacks will gradually become less frequent and less painful. After you have been taking allopurinol regularly for several months, the attacks may stop completely.
• Allopurinol is used to help prevent gout attacks. It will not relieve an attack that has already started. Even if you take another medicine for gout attacks, continue to take this medicine also.

Dosing—

The dose of allopurinol will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of allopurinol. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets that you take each day and the number of times that you take the medicine every day depend on the strength of the medicine, on the dose that you need, and on the reason you are taking allopurinol. Up to 300 milligrams (mg) of allopurinol can be taken at one time. Doses larger than 300 mg a day should be divided into smaller amounts that are taken two, three, or even four times a day.

• For the oral dosage form (tablets):
  • For gout:
    • Adults—At first, most people will take 100 mg a day. After about a week, your doctor will probably increase the dose gradually until the amount of uric acid in your blood has been lowered to normal levels. The total amount of allopurinol is usually not more than 800 mg a day. After the uric acid has remained at normal levels for a while, your doctor may lower your dose gradually until you are taking the smallest amount of medicine that will keep the uric acid from increasing again.
    • Children and teenagers—Use and dose must be determined by the doctor.
  • For kidney stones:
    • Adults—100 to 800 mg a day, depending on the kind of kidney stones.
    • Children and teenagers—Use and dose must be determined by the doctor.
  • For preventing or treating medical problems that may occur if certain treatments increase the amount of uric acid in the blood:
    • Adults—600 to 800 mg a day, starting one to three days before the treatment.
    • Children—The dose depends on the child's age
      • Children up to 6 years of age: 50 mg (one-half of a 100-mg tablet) three times a day.
      • Children 6 to 10 years of age: One 100-mg tablet three times a day or one 300-mg tablet a day.
      • Children 11 years of age and older: The dose may be the same as for adults.

• For the parenteral dosage form (injection):
  • For preventing or treating medical problems that may occur if certain treatments increase the amount of uric acid in the blood:
    • Adults—200 to 400 mg per square meter of body surface area (mg/m²) a day, injected into a vein. Starting one to two days before treatment, this dose may be given as a single dose or divided into smaller doses as determined by your doctor. Your doctor will check your uric acid level and may change your dose based on the level. However, the dose is usually not more than 600 mg per day.
    • Children—At first, 200 mg per square meter of body surface area (mg/m²) per day, injected into a vein. Starting one to two days before treatment, this dose may be given as a single dose or divided into smaller doses as determined by your doctor . Your doctor will check your uric acid level and may change your dose based on the level.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Your doctor should check your progress at regular visits. Blood tests may be needed to make sure that this medicine is working properly and is not causing unwanted effects.

Drinking too much alcohol may increase the amount of uric acid in the blood and lessen the effects of allopurinol. Therefore, people with gout and other people with too much uric acid in the body should be careful to limit the amount of alcohol they drink.

Taking too much vitamin C may make the urine more acidic and increase the possibility of kidney stones forming while you are taking allopurinol. Therefore, check with your doctor before you take vitamin C while taking this medicine.

Check with your doctor immediately:

• If you notice a skin rash, hives, or itching while you are taking allopurinol.
• If chills, fever, joint pain, muscle aches or pains, sore throat, or nausea or vomiting occur, especially if they occur together with or shortly after a skin rash.

Very rarely, these effects may be the first signs of a serious reaction to the medicine.

Allopurinol may cause some people to become drowsy or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are not alert.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Stop taking this medicine and check with your doctor immediately if any of the following side effects occur:

• More common
  • Skin rash or sores, hives, or itching 
  
  

• Rare
  • Black, tarry stools;  bleeding sores on lips;  blood in urine or stools;  chills, fever, muscle aches or pains, nausea, or vomiting—especially if occurring with or shortly after a skin rash;  difficult or painful urination;  pinpoint red spots on skin;  redness, tenderness, burning, or peeling of skin;  red and/or irritated eyes;  red, thickened, or scaly skin;  shortness of breath, troubled breathing, tightness in chest, or wheezing;  sores, ulcers, or white spots in mouth or on lips;  sore throat and fever;  sudden decrease in amount of urine;  swelling in upper abdominal (stomach) area;  swelling of face, fingers, feet, or lower legs ;  swollen and/or painful glands;  unusual bleeding or bruising;  unusual tiredness or weakness;  weight gain (rapid);  yellow eyes or skin 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• Rare
  • Loosening of fingernails;  numbness, tingling, pain, or weakness in hands or feet;  pain in lower back or side;  unexplained nosebleeds 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• Less common or rare
  • Diarrhea;  drowsiness;  headache;  indigestion;  nausea or vomiting occurring without a skin rash or other side effects;  stomach pain occurring without other side effects;  unusual hair loss 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.