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What is Allopurinol (Zyloprim)?

Allopurinol is a xanthine oxidase inhibitor (XOI) medication that you take orally to treat gout, kidney stones, and other conditions. If you’re undergoing chemotherapy, it prevents an increase in your blood levels of uric acid, which is released by dying cancer cells.

Allopurinol reduces the amount of uric acid produced by your body. When uric acid levels are too high, they can cause gout and damage your kidneys.

What does allopurinol treat?

Allopurinol can treat many different medical conditions. These include:


You can take allopurinol if you have symptoms of primary or secondary hyperuricemia (an elevated uric acid level in the blood). Symptoms include acute gout attacks, gouty arthritis, tophi, joint damage, and neuropathy.

Certain types of kidney stones

Doctors prescribe allopurinol for recurrent calcium stone disease where the daily urine oxalate excretion exceeds 750mg in females and 800mg in males. Physicians may also use it if you have uric acid stones. Your doctor should carefully evaluate your treatment periodically to determine whether the benefits outweigh the risks.

If you’re undergoing chemotherapy

You can take allopurinol before starting a course of chemotherapy. Chemotherapy medication can cause kidney damage by releasing uric acid crystals into the bloodstream. Allopurinol prevents these crystals from forming.

You should stop taking allopurinol if you’re no longer experiencing increased uric acid levels.

How do you take allopurinol?


The usual dose of allopurinol is 100-300mg a day. Before taking any medication, consult your doctor for recommendations on dosage and how often you should take it. This will ensure the drug is the best possible treatment for your condition.

Take allopurinol with a glass of water, preferably after eating. You'll usually take one pill daily, but if you need to take two, your doctor might suggest splitting the dose into two.

For gout

Oral dosages for mild gout:

  • 200-300mg daily for maintenance

Oral dosage for severe tophaceous gout:

  • 100-200mg daily for minimal effective dosage

  • 800mg daily is the maximum recommended dosage 

Guidelines recommend beginning with a low allopurinol dose and increasing weekly until you reach a uric acid level of 6mg/dl or less. Doctors should not exceed the maximum recommended dosage to prevent an attack of acute gouty arthritis.

Doctors should administer lower than recommended doses if you have decreased renal function. They should monitor you closely during the early stages of treatment.

For calcium oxalate/urate calculi (kidney stones)

Oral dosage for adults:

  • 200-300mg once a day or in divided doses

For treating recurrent calcium oxalate stones if your daily urinary oxalate excretion exceeds 800mg in males or 750mg in females.

For hyperuricemia secondary to chemotherapy:

Oral dosage for adults:

  • 600-800mg in divided doses for the initial dosage

  • 800mg per day is the maximum recommended dosage

  • Adjust dose as needed depending on your serum uric acid levels for maintenance 

Ideally, you should take doses over 300mg/day in divided doses to minimize gastric irritation.

Therapy should be initiated at least 24 hours before the start of chemotherapy. Your doctor should discontinue treatment when the risk of overproduction of uric acids has passed.

Drink enough water to keep your urine output above two liters per day.

When to take it

Allopurinol may be taken at any time of the day, although you should attempt to take your dosages at the same time each day.

Doctor's recommendation:

When taking allopurinol, drink 2-3 liters of water every day unless instructed otherwise.

Seeing results

It generally takes 1-3 weeks for this drug to start preventing gout. You may have multiple gout attacks for the first few months while your body gets rid of extra uric acid. Your doctor may prescribe medication to treat acute flares while your body stabilizes its uric acid level.

Potential side effects of allopurinol

Allopurinol can sometimes cause adverse effects, although most people don't get any.

Common side effects of allopurinol include:

  • Drowsiness

  • Headache

  • Diarrhea

  • Vomiting

  • Stomach discomfort

  • Muscle pain

Serious side effects

Some side effects can be serious, and you should look out for them. These include:

  • Tingling sensation in the arms or legs

  • Severe weight loss

  • Tiredness

  • Eye problems (changes in vision or eye pain)

  • Dark, bloody, or painful urination

  • Changes in the amount of urine

  • Yellowing eyes or skin (jaundice)

  • Severe pain in the abdomen

  • Nausea or vomiting

If you experience these effects, stop taking allopurinol and immediately contact your doctor.

Rare side effects

Allopurinol hypersensitivity syndrome (AHS) is a severe and sometimes life-threatening side effect. It involves multiple organs and skin reactions.

Characteristics of this hypersensitivity syndrome are:

  • A prolonged illness with fever at the start

  • A prominent skin reaction

  • Eosinophilia (high white blood cell count)

  • Liver failure

  • Acute kidney failure

  • Gastrointestinal bleeding

AHS is a rare side effect of allopurinol with an incidence of about one in 1000, with a mortality rate of 20%-25%¹. The mechanism is an immune response to oxypurinol.

The highest risk is during the first few months of treatment, especially when starting with high doses of allopurinol.

Studies² show that Han-Chinese, Korean, and Thai carriers of the HLA-B58 gene are at a very high risk of developing AHS.

Long-term use of allopurinol

Allopurinol is a drug that is safe for prolonged use. Although taking allopurinol is unlikely to have any long-term consequences, discussing it with your doctor is wise.

Missed doses

If you forget to take your medication and it’s close to the time for your next dose, don’t take the missed dose. Instead, take the next one as usual. Never take two doses of medication to make up for a forgotten dose.

If you often forget to take your prescription on time, it may help to use an alarm or reminder to keep you on your dose schedule. You could also ask a pharmacist or your doctor for advice.


Like any other medication, overdoses of allopurinol are possible. If you take too much, there could be dangerous levels of allopurinol in your body. Symptoms can include:

Symptoms of an overdose:

  • Diarrhea

  • Rash

  • Nausea

  • Gout flare-up if you have gout

If you think you or a family member has overdosed on allopurinol, call your local poison control center at 1-800-222-1222 or go to an emergency room immediately.

What to discuss with your doctor before you start taking allopurinol

When starting allopurinol, you must tell your doctor about any health problems and all other medications you are taking. Allopurinol can interact with some medicines.

It’s also important to tell your doctor if you:

  • Are allergic to allopurinol or any other medications such as amoxicillin, ampicillin, and blood thinner drugs like anticoagulants

  • Take any vitamins, nutritional supplements, and herbal products

  • Take mercaptopurine (Purinethol) and cyclophosphamide (Cytoxan) for chemotherapy

  • Take chlorpropamide, diuretics, immunosuppressants, or gout medications 

  • Have a history of gout

  • Have a kidney problem

  • Have liver disease

  • Have high blood pressure

  • Are pregnant or thinking of becoming pregnant

  • Are breastfeeding

Stopping allopurinol

If you stop allopurinol treatment suddenly, there is a high risk that gout may worsen or you will experience serious side effects. Only stop taking allopurinol if a doctor tells you to.

If you need to stop taking allopurinol, your doctor will slowly decrease your daily dose to avoid serious side effects.

Allopurinol and pregnancy

Doctors don’t usually recommend allopurinol during pregnancy as there is limited evidence of its safety. Talk to a doctor if you plan on becoming pregnant. There may be safer alternatives.


Studies³ have found allopurinol in the milk of women who took allopurinol for gout. Because the impact of allopurinol on an infant is unknown, nursing mothers should use caution.

Interactions with other drugs

Interactions between allopurinol (Zyloprim) and other medications

Allopurinol can react with other medicines and supplements, so it's crucial to tell your doctor about all your medications. The following are some of the most common drug interactions:

Moderate interactions

  • Aluminum hydroxide

  • Amoxicillin

  • Calcium carbonate

  • Cyclophosphamide

  • Dichlorphenamide

Serious interactions

  • Enalapril

  • Perindopril

  • Protamine

  • Theophylline

  • Warfarin

Severe interactions

  • Didanosine

Allergy information

If you feel any new symptoms after starting allopurinol, contact your doctor. Symptoms of an allergic reaction can range from mild to life-threatening. If you have a severe reaction, seek immediate medical attention.

Symptoms of an allergic reaction to allopurinol may include:

  • Hives

  • Itching

  • Swelling of your face, lips, tongue, or throat

  • Difficulty breathing

  • Tightness in your chest

  • Severe dizziness

  • Fainting

Clinical trial history

A 2014 study⁴ established the effectiveness of allopurinol, comparing it with other urate-lowering drugs in patients with gout.

Researchers concluded that allopurinol is slightly better than other gout treatments. Further studies are needed to evaluate higher doses or longer-term safety.

Tips and advice for taking allopurinol

If you're taking allopurinol, follow your doctor's instructions closely. Here are several tips to get the most out of your treatment:

  • Take allopurinol with food or milk to reduce stomach upset.

  • If your kidneys are impaired, exercise extra caution when taking allopurinol.

  • You should take allopurinol daily or according to your doctor's instructions.

  • Drink plenty of fluids while taking allopurinol to help flush uric acid from your body.

  • Keep all appointments with your doctor so that they can monitor your treatment.

  • Don't stop taking allopurinol without first consulting with your doctor.

  • Store allopurinol tablets at room temperature, away from heat and moisture.

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Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.

However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.

It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.

Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.

Curious about clinical trials?

Access the latest treatments and medications. unavailable elsewhere - entirely free of charge. We make it easy to take part.