Allopurinol dosage, forms, and strengths

Allopurinol is a generic drug commonly used to manage symptoms of gout, as well as other medical conditions. It is also sold under the brand names Aloprim and Zyloprim. It belongs to a class of medications called xanthine oxidase inhibitors, which work by lowering the levels of uric acid in the body. 

Other medications used to lower uric acid levels include febuxostat (also a xanthine oxidase inhibitor), probenecid, and Elitek (rasburicase). This article will focus on how allopurinol is prescribed for different medical conditions, as well as general guidelines for its safe use.

Allopurinol forms and strengths

Allopurinol and its brand name Zyloprim are available in tablet form and are taken by mouth for gout and kidney stones. Allopurinol is also available as a solution for intravenous injection for hyperuricemia induced by chemotherapy. The injection is available as a generic and under the brand name Aloprim.

• Tablet: 10 mg, 300 mg

• Solution for intravenous injection: 20 mg/mL*

*The contents of a single 500 mg vial are reconstituted with 25 mL of sterile water for injection, yielding a solution with a concentration of 20 mg/mL. The solution will then be diluted with 0.9% sodium chloride injection or 5% dextrose for injection to a final concentration no greater than 6 mg/mL, before being administered to the patient.

Allopurinol dosage for adults

Allopurinol is FDA approved for the prevention of gout in patients who have recurring gout attacks, as well as management of recurrent calcium oxalate calculi (a type of kidney stone) and management of hyperuricemia caused by chemotherapy. The dose range for adults is typically around 200-300 mg per day, although the exact range is different for each indication. See the dosing chart below for details:

Check our best Allopurinol prices

Allopurinol dosage for gout

Unlike colchicine, ibuprofen, or prednisone, allopurinol is not used to treat a gout flare. Instead, it is used to reduce the frequency of gout flares in patients who experience two or more flares per year. Allopurinol is known as a urate-lowering therapy (ULT) and is the preferred first-line agent for lowering uric acid. Urate lowering therapy may be discontinued if the patient has not experienced flares for a year or more and no tophi are present.

• Starting dosage for gout: 100 mg per day, to which may be added

• Standard dosage for gout: 200-600 mg per day given as a single dose or as two to four divided doses (any single oral dose should not exceed 300 mg)

Allopurinol dosage for hyperuricemia due to chemotherapy

Uric acid is released from tumor cells when they are destroyed by chemotherapy. Thus, one of the side effects of chemotherapy is hyperuricemia (elevated uric acid in the blood). Tumor cells also release potassium, phosphates, and calcium into the blood when destroyed. Together, these contents released from tumor cells can lead to a dangerous metabolic condition known as tumor lysis syndrome (TLS). Seizures, heart arrhythmias, and acute kidney injury may result from TLS. 

• Standard dosage to lower serum uric acid: 200 to 400 mg per square meter of body surface area per day given as a single infusion or in equally divided infusions given at six-, eight-, or 12-hour intervals.

The concentration of infusion should not exceed 6 mg/mL. Allopurinol therapy should begin 24 to 48 hours before the start of chemotherapy. The max dose is 600 mg per day. Dosages are adjusted based on serum uric acid measurements.

Allopurinol dosage for recurrent calcium oxalate calculi

Allopurinol is indicated for the management of recurrent calcium oxalate kidney stones in male patients whose daily uric acid excretion exceeds 800 mg per day and female patients whose daily uric acid excretion exceeds 750 mg per day. While uric acid is often responsible for causing a different type of kidney stone called uric acid stones, it can also contribute to the formation of calcium oxalate stones. Patients with calcium acid stones who do have elevated levels of uric acid in the urine (hyperuricosuria) are not likely to benefit from allopurinol. 

• Standard dosage for recurrent calcium calculi: 200 to 300 mg per day as a single dose or divided into two to three doses

Dosage adjustments are made based on levels of uric acid in the urine, measured by a 24-hour urine sample. Patients may also benefit from dietary changes including reduced calcium, animal protein, sodium, and sugar intake, as well as increased hydration and fiber intake.

Allopurinol dosage for children

Allopurinol is approved for the management of hyperuricemia caused by chemotherapy in pediatric patients. The standard allopurinol dosage for children ages 2 years and above is 300 mg per square meter of body surface area per day, divided into two to four doses.

• Maximum dosage for children ages 11 years and above: 800 mg per day, any single dose should not exceed 300 mg

• Maximum dosage for children ages 6-10 years: 300 mg per day

• Maximum dosage for children ages 2-6 years: 150 mg per day

Allopurinol dosage restrictions

Allopurinol is primarily eliminated through the kidneys. Therefore, patients with kidney disease may require lower doses of allopurinol to avoid accumulation of allopurinol levels to toxic levels. The manufacturer recommends the following dosage guidelines based on a commonly used measurement of renal (kidney) function known as “creatinine clearance.”

Patients taking allopurinol for gout prevention:

• Creatinine clearance greater than 30 mL per minute: 100 mg daily

• Creatinine clearance is less than 30 mL per day: 50 mg or less daily

For patients on hemodialysis:

• 100 mg daily and an additional 50 mg supplement dose after

  dialysis. Dose may be titrated up or down based on uric acid levels

Patients with poor renal function taking allopurinol for other indications should follow the following dosage guidelines: 

• Creatinine clearance of 10-20 mL per minute: 200 mg daily

• Creatinine clearance of 3-10 mL per minute: 100 mg daily

• Creatinine clearance less than 3 mL: 100 mg per dose and time intervals between doses may need to be extended

Other cautions and contraindications

Allopurinol should not be used in patients with a history of a severe allergic reaction to allopurinol or any of the ingredients in allopurinol tablets or solutions for injection. An example of a severe allergic reaction is anaphylaxis, which is characterized by difficulty breathing, skin rash, and/or swelling of the face, tongue, or throat.

Allopurinol hypersensitivity syndrome (AHS) is a rare but potentially fatal adverse reaction that is more likely to occur in patients of Korean, Han Chinese, and Thai descent with a particular drug-metabolism gene called the “HLA-B*5801 genotype.” This reaction is characterized by a life-threatening skin rash (Stevens-Johnson syndrome or toxic epidermal necrolysis), inflammation of the blood vessels, irreversible liver injury, acute kidney injury, fever, and increased white blood cells.

Allopurinol should generally not be used in pregnant or breastfeeding mothers. The potential risks of harm to the fetus may be weighed against potential benefits to the mother. The data surrounding allopurinol use during pregnancy and possible increases in birth defects are inconclusive. If allopurinol is used during breastfeeding, infants should be monitored for adverse effects related to allopurinol.

Allopurinol dosage for pets

Allopurinol is used to treat urate bladder stones (uroliths) in cats and dogs. The dose for dogs is 3-5 mg per pound (or 10 mg per kilogram) every eight hours. For cats, a dose of 3.5 mg per pound (7.5 mg/kg) twice daily may be used. Give with food. Pregnant or nursing pets should not be given allopurinol. Allopurinol treatment should be combined with an alkalinizing and protein-restricted diet (low in purine proteins). To achieve a diet low in protein it is often best to avoid meat protein sources such as beef, using protein sources such as egg or wheat instead.

How to take allopurinol

• Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

• Drink extra fluids so you will urinate more often and help prevent renal impairment. Drink about 10 to 12 full glasses of water each day, unless otherwise directed by your doctor.

• Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take your usual dose. Do not take extra medicine to make up for a missed dose.

• You should also increase your fiber intake.

• Your doctor will tell you how much medicine to use. Do not use more than directed.

• You may have more gout attacks when you start using this medicine. Keep using the medicine even if this happens. Your doctor may give you other medicines (including colchicine, NSAIDs) to prevent gout attacks. The attacks should become shorter and less severe after you take allopurinol for several months.

• Swallow the allopurinol tablets with water, ideally after meals to prevent stomach upset.

Allopurinol dosage FAQs

How long does it take allopurinol to work?

In patients taking allopurinol for gout, a decrease in serum and urine uric acid typically occurs within two to three days, with the peak effect occurring after one week or longer. Generally, normal uric acid levels are achieved within one to two weeks for patients starting allopurinol therapy. Gout symptoms may initially become worse when starting allopurinol – if a gout flare occurs during treatment, allopurinol does not need to be discontinued.

In a study examining patients with hyperuricemia induced by chemotherapy, the average time to normal uric acid levels was 27 hours after starting allopurinol monotherapy. Patients treated for chemotherapy-induced hyperuricemia often receive Elitek (rasburicase) along with allopurinol. The average time to normal uric acid levels in patients receiving the two drugs together was only four hours.

How long does allopurinol stay in your system?

Healthcare professionals measure the time it takes to eliminate a chemical from the body using a metric called a half-life. The half-life of oxypurinol is 15 hours in patients with normal renal function. The active form of allopurinol will not be entirely gone from the body until three days after it is taken. Allopurinol will be removed more slowly in patients with impaired kidney function. Other drugs such as salicylates can increase the rate at which the kidney eliminates certain drugs. These medications decrease the total time that the active metabolite of allopurinol remains in the body and can make allopurinol less effective.

What is the maximum dosage for allopurinol?

The maximum daily dosage for allopurinol is 800 mg per day for oral tablets and 600 mg per day for intravenous injection. Any single oral dose should not exceed 300 mg. Children under the age of 11 should not take more than 300 mg by mouth per day, and children less than 6 years old should not take more than 150 mg by mouth per day.

Can you overdose on allopurinol?

Severe adverse reactions have occurred in patients with poor kidney function receiving too high a dose of allopurinol. In these cases, the kidney cannot remove allopurinol fast enough, which leads to the accumulation of allopurinol to unsafe levels. This puts patients at much greater risk of experiencing a severe hypersensitivity syndrome characterized by a potentially life-threatening rash (Stevens-Johnson syndrome), irreversible liver damage, and inflammation of the blood vessels (vasculitis). ­­­­­­­­While there are very few cases of allopurinol overdoses in patients with normal kidney function, extreme doses of allopurinol are likely to cause similar severe side effects. 

If you suspect an overdose of allopurinol in a child or adult, immediately seek medical attention at the nearest emergency room or call Poison Control Center at 1-800-222-1222.

What interacts with allopurinol?

Taking salicylates can lower the effects of allopurinol. Examples of salicylates include Pepto-Bismol (bismuth subsalicylate), magnesium salicylate, methyl salicylate, and trolamine salicylate. Other non-salicylate drugs that may decrease the effects of allopurinol include niacin (vitamin B3), pyrazinamide, and ethambutol.

Medications containing certain metals can decrease the levels of allopurinol. Examples include the antacid medications aluminum hydroxide, magnesium citrate, magnesium hydroxide, magnesium carbonate, and magnesium trisilicate. Other examples include the supplement chromium and the phosphate binder lanthanum (also known as Fosrenol). 

Combining an ACE inhibitor or certain antibiotics with allopurinol is associated with a higher risk of potentially life-threatening hypersensitivity reactions such as Stevens-Johnsons syndrome. 

Allopurinol may increase levels of certain medications, leading to increased side effects. Taking allopurinol with theophylline, for example, can increase risk of heart arrhythmias, seizures, and other side effects of theophylline. Coumadin (warfarin) is another medication that has increased effects when combined with allopurinol. Other agents that may require a decrease in dose when combined with allopurinol include:

• aminophylline

• azathioprine

• bendamustine

• chlorpropamide

• clozapine

• cyclosporine

• mercaptopurine

• tizanidine

This is not a complete list of all possible drug interactions involving allopurinol. For medical advice about drug interactions, consult your doctor or pharmacist and provide them with a full list of your current medications.

What happens when you mix allopurinol and alcohol?

There is no known interaction between allopurinol and alcohol, so it is safe for people taking allopurinol to drink in moderation–this means two drinks daily for men and one drink per day for women. However, it is important to be aware that alcohol can lead to dehydration, which can increase uric acid levels in the blood. This can increase risk of gout attacks, so people taking allopurinol for gout need to be particularly cautious about how much they are drinking.

Is it safe to take allopurinol during pregnancy?

The U.S. Food and Drug Administration (FDA) categorizes allopurinol under "category C" pregnancy risk. This means that there is not enough data to demonstrate whether it is safe to take allopurinol during pregnancy. According to the manufacturer, there have been case reports of fetal birth defects after allopurinol was used during pregnancy. However, another report showed no difference in the rates of birth defects among women taking allopurinol during pregnancy, compared to those who did not. Since fetal harm cannot be ruled out, it is not recommended that women take allopurinol during pregnancy or while breastfeeding, unless absolutely necessary.

Related resources:

• ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats

• Aloprim prescribing information

• Allopurinol

• Allopurinol

• Allopurinol overdose

• Allopurinol – Drug Summary

• Feline uroliths

• Control of plasma uric acid in adults at risk for tumor lysis syndrome: efficacy and safety of rasburicase alone and rasburicase followed by allopurinol compared with allopurinol alone—results of a multicenter phase III study

• Zyloprim prescribing information

• 2020 American College of Rheumatology guideline for the management of gout