Allopurinol: uses, dosing, side effects & brands

ALOPRIM (allopurinol) for Injection, a xanthine oxidase inhibitor, is a sterile, white, lyophilized powder or cake, in a single-dose vial for reconstitution. Each vial contains 500 mg of allopurinol equivalent to 580.7 mg of allopurinol sodium and 148 mg of sodium hydroxide as a solubilizer. Sodium hydroxide is also used as a pH adjuster. ALOPRIM (allopurinol) for Injection contains no preservatives. Allopurinol is a xanthine oxidase inhibitor.

The FDA classifies allopurinol as a xanthine oxidase inhibitor. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

The elimination half-life of allopurinol is about 1 to 2 hours (parent drug) — that is how long the body takes to clear half of a dose. The ~1-2 hour figure is for allopurinol itself, but it barely reflects how long the drug works. Allopurinol is converted to an active metabolite, oxypurinol (oxipurinol / alloxanthine), which is also a xanthine-oxidase inhibitor and is generally believed to mediate allopurinol's uric-acid-lowering action. Oxypurinol has a much longer plasma half-life of about 15 hours, so the therapeutic effect far outlasts the parent. Allopurinol is cleared by glomerular filtration, but oxypurinol is reabsorbed in the kidney tubules; in people with severely impaired renal function (or reduced urate clearance) the oxypurinol half-life is greatly prolonged. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run allopurinol against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 3 allopurinol-containing products in the U.S.: Aloprim, Allopurinol and Zyloprim. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, allopurinol is currently marketed as injectable and tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Yes. Our catalog lists 1 generic allopurinol product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.

The FDA's Enforcement database lists 1 recall record whose product description mentions allopurinol. The most recent: Allopurinol Tablets (Jun 7, 2024). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.

Because dropping your uric acid level stirs up the crystals already sitting in your joints, flares are common in the first weeks to months of treatment. The FDA label expects this and states that maintenance doses of colchicine generally should be given prophylactically when allopurinol is begun; in practice some clinicians use an anti-inflammatory instead. The mistake that undoes months of progress is stopping allopurinol when a flare hits. Treat the flare, keep taking the allopurinol. Flares thin out as your uric acid stays down and the crystal deposits dissolve, which takes months, not days. Take it after meals with enough fluid to keep urine output up, which reduces stomach upset and kidney stone risk.

Stop the drug and call your doctor the same day. Rash is the most frequently reported reaction to allopurinol, and the label instructs that it be discontinued at the first appearance of skin rash or other signs of an allergic reaction, because a rash can be followed by far more severe hypersensitivity reactions — including Stevens-Johnson syndrome, generalized vasculitis, irreversible liver damage and, on rare occasions, death. The ones that kill are SJS and toxic epidermal necrolysis (painful rash that blisters and peels, sores in the mouth or eyes) and DRESS (rash with fever, facial swelling, swollen lymph nodes, organ inflammation). Warning signs to treat as an emergency: fever with the rash, blistering, peeling, mouth or eye sores, or a rash that spreads quickly.

Yes, for some people. The label says to consider screening for HLA-B*58:01 before starting allopurinol in patients from populations where the allele is common, and that allopurinol is not recommended in HLA-B*58:01-positive patients unless the benefits clearly outweigh the risks. The label puts the allele at 8 to 10% in Han Chinese, about 8% in Thai and about 6% in Korean populations, about 4% in Blacks, about 1 to 2% in Hispanic and indigenous American populations, and under 1% in people of European or Japanese descent; it names African, Asian and Native Hawaiian/Pacific Islander ancestry as the higher-frequency groups. If that applies to you — especially with reduced kidney function — ask specifically about testing before your first dose rather than after a rash. One caveat the label states outright: SJS and TEN can still occur in people who test negative, whatever their ancestry, so a negative result is never a reason to ignore a new rash.

Azathioprine and mercaptopurine are the dangerous pair: allopurinol blocks the enzyme that breaks them down, so normal doses can build up and wipe out your bone marrow. The label states that patients taking either one need the dose cut to roughly one third to one fourth of the usual amount when allopurinol 300 to 600 mg a day is added. If you take either — for transplant, inflammatory bowel disease or autoimmune conditions — this has to be handled before the first allopurinol tablet. Anticoagulant effect can be increased, so INR needs closer watching. Rash is more likely if you take ampicillin or amoxicillin at the same time; in one series, 13.9% of patients given ampicillin with allopurinol developed a rash. Report fever, sore throat, unusual bruising or bleeding, extreme fatigue, dark urine or yellowing skin right away — those point to marrow, liver or kidney injury rather than a nuisance side effect.