Reviewed on 6/1/2022

What Is Allopurinol and How Does It Work?

Allopurinol is a prescription medication used to treat gout and certain types of kidney stones. It is also used to prevent increased uric acid levels in patients receiving chemotherapy. These patients can have increased uric acid levels due to the release of uric acid from the dying cancer cells. Allopurinol works by reducing the amount of uric acid made by the body. Increased uric acid levels can cause gout and kidney problems.

  • Allopurinol is available under the following different brand names: Zyloprim and Aloprim.

What Are Side Effects Associated with Using Allopurinol?

Side effects associated with the use of Allopurinol, include the following:

Tell your doctor if you experience rare but very serious side effects of Allopurinol including:

  • numbness or tingling of arms or legs,
  • easy bleeding or bruising,
  • signs of infection (e.g., fever, persistent sore throat),
  • unusual tiredness,
  • painful or bloody urination,
  • change in the amount of urine,
  • yellowing eyes or skin,
  • severe stomach or abdominal pain,
  • persistent nausea or vomiting,
  • dark urine,
  • unusual weight loss,
  • eye pain, or
  • vision changes.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Are Dosages of Allopurinol?

Dosages of Allopurinol:

Adult and pediatric dosages:


  • 100 mg
  • 300 mg

Powder for injection

  • 500 mg/vial

Dosage Considerations – Should be Given as Follows:


  • Adult dosage:
  • Mild: 100 mg per day orally initially, increased weekly to 200-300 mg per day
  • Moderate to severe: 100 mg per day orally initially, increased weekly to 400-600 mg per day

Excess of Uric Acid (Hyperuricemia)

  • Pediatric dosage:
  • 10 mg/kg per day orally divided every 12 hours, not to exceed 600 mg/day

Antineoplastic-Induced Excess of Uric Acid (Hyperuricemia)

  • Pediatric dosage:
    • 10 mg/kg per day orally divided every 12 hours, not to exceed 600 mg/day
  • Adult dosage:
    • 600-800 mg divided every 8-12 hours, starting 1-2 days before chemotherapy
    • Intravenously: 200-400 mg/m2 per day, not to exceed 600 mg/m2 per day, may administer as a single infusion or in equally divided doses at 6, 8, and 12-hour intervals beginning 1-2 days before chemotherapy
  • Dosing considerations:
    • Minimum oral dosage: 100-200 mg/day
    • Maximum oral dosage: 800 mg/day
  • Dosing modifications:
  • Renal impairment:
    • Creatinine clearance 10-20 ml/min: 200 mg/day
    • Creatinine clearance 3-10 ml/min: 100 mg/day
    • Creatinine clearance less than 3 ml/min: 100 mg/day at extended intervals
  • Pediatric dosage:
    • Children under 6 years old: 150 mg orally daily divided every 8 hours
    • Children 6-10 years old: 300 mg orally daily in a single dose or divided every 8 hours
    • Children 10 years and older: 600-800 mg orally daily, starting 1-2 days before chemotherapy
    • Intravenously: 200 mg/m2 per day initially, starting 1-2 days before chemotherapy

What Other Drugs Interact with Allopurinol?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist about all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns, or more information about this medicine.

What Are Warnings and Precautions for Allopurinol?


  • Hypersensitivity to allopurinol
  • This medication contains allopurinol. Do not take Zyloprim or Aloprim if you are allergic to allopurinol or any ingredients contained in this drug
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately


  • Hypersensitivity to allopurinol

Effects of Drug Abuse

  • No information provided

Short-Term Effects

  • See "What Are Side Effects Associated with Using Allopurinol?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Allopurinol?"


  • Discontinue at the first sign of allergic reactions, the first sign of rash, inflammation of blood vessels, or Stevens-Johnson syndrome
  • If the decrease in bone marrow activity (myelosuppression) is reported, use caution when administering other drugs known to cause a decrease in bone marrow activity
  • Liver damage (hepatotoxicity) was reported (reversible)
  • Not for the treatment of asymptomatic hyperuricemia, elevated levels of serum urate with no other symptoms of gout
  • Use with caution in renal impairment
  • The risk of hypersensitivity increased in patients treated with angiotensin-converting enzyme (ACE) inhibitors
  • When taken with amoxicillin or ampicillin, may increase the risk of skin rash
  • During concomitant treatment, reduce dosages of azathioprine and mercaptopurine to 25-33% of the usual dose
  • Maintain fluid intake necessary to yield urine output of at least 2 liters per day in adults

Pregnancy and Lactation

  • Use allopurinol during pregnancy with caution if the benefits outweigh the risks. Animal studies show risk and human studies are not available, or neither animal nor human studies were done
  • Allopurinol is distributed into breast milk, use with caution when breastfeeding.
Medscape. Allopurinol.

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