Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALLOPURINOL vs ULORIC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Allopurinol inhibits xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and xanthine to uric acid, thereby reducing serum and urinary uric acid concentrations. It also inhibits de novo purine synthesis through feedback inhibition.
ULORIC (febuxostat) is a xanthine oxidase inhibitor that reduces serum uric acid levels by inhibiting the enzyme xanthine oxidase, which catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid.
Gout (management of recurrent uric acid stones),Hyperuricemia associated with malignancy (tumor lysis syndrome),Uric acid nephropathy,Prevention of calcium oxalate calculi in hyperuricosuric patients,Recurrent uric acid stones,Gouty arthritis (prophylaxis of acute attacks),Secondary hyperuricemia (various causes)
Chronic management of hyperuricemia in patients with gout,Off-label: Prevention of tumor lysis syndrome (not FDA-approved)
100-600 mg orally once daily; initial 100 mg/day with weekly increases of 100 mg/day; maximum 800 mg/day.
40 mg orally once daily; may increase to 80 mg once daily if serum uric acid not at target after 2 weeks.
Allopurinol: 1–2 hours; oxypurinol: 18–30 hours (prolonged in renal impairment).
Terminal elimination half-life is approximately 5-8 hours. This short half-life supports once-daily dosing for maintenance of therapeutic urate-lowering effect.
Allopurinol is metabolized primarily by aldehyde oxidase to its active metabolite oxypurinol (alloxanthine), which also inhibits xanthine oxidase. Oxypurinol is further metabolized and eliminated renally.
Primarily metabolized by UGT1A1, UGT1A3, UGT1A9, and CYP2C8; minor metabolism by CYP1A2, CYP2C9, and CYP2D6. Approximately 22% excreted unchanged in urine.
Renal: ~76% as unchanged drug and metabolites; oxypurinol (active metabolite) is primarily excreted renally. Biliary/fecal: minor, <5%.
Renal excretion of unchanged drug accounts for approximately 40-45% of the dose. Biliary/fecal excretion eliminates about 50-55% of the dose, primarily as oxidative metabolites.
Allopurinol: <1%; oxypurinol: ~50% (mainly to albumin).
Approximately 99% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Allopurinol: ~1.6 L/kg; distributes into total body water.
Apparent volume of distribution is about 50 L (approximately 0.7 L/kg). This suggests distribution into total body water and some tissue binding.
Oral: ~79–90% for allopurinol; oxypurinol is formed rapidly via first-pass metabolism.
Oral bioavailability is approximately 85% (range 60-100%). Tablets are well absorbed, with food having no significant effect on overall absorption.
GFR >50: no adjustment; GFR 10-50: 200 mg/day; GFR <10: 100 mg/day or dosing interval every 48-72 hours.
No dose adjustment required for mild to moderate renal impairment (GFR 30-89 m L/min). Not recommended for use in patients with severe renal impairment (GFR <30 m L/min) or end-stage renal disease on dialysis due to lack of efficacy data.
No specific guidelines; use with caution in severe hepatic impairment (Child-Pugh C); consider dose reduction.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh Class A or B). Not recommended in severe hepatic impairment (Child-Pugh Class C) due to lack of data.
Children <6 years: 150 mg/day; 6-10 years: 300 mg/day; 11-16 years: 300-600 mg/day; initial dose 10 mg/kg/day divided in 2-3 doses, max 300 mg/day.
Safety and efficacy not established in pediatric patients; no FDA-approved dosing.
Start at lowest dose (100 mg/day) and titrate slowly; monitor renal function and adjust per GFR.
No specific dose adjustment required; clinical studies included patients aged 65 and older with no overall differences in safety or efficacy observed.
No FDA black box warning.
Increased risk of cardiovascular death compared to allopurinol in patients with gout and cardiovascular disease. Febuxostat should be used only in patients who have not responded adequately to allopurinol or have contraindications to allopurinol.
Hypersensitivity reactions (including Stevens-Johnson syndrome, toxic epidermal necrolysis) occur more frequently in patients with renal impairment or thiazide diuretic use.,Discontinue at first sign of rash or other signs of hypersensitivity.,Increased risk of bone marrow suppression in patients with renal impairment.,Hepatotoxicity (monitor liver function tests).,Acute gout flare may occur during initiation; prophylaxis with colchicine or NSAIDs recommended.,Dose adjustment required in renal impairment.,Azathioprine or 6-mercaptopurine dose reduction required due to inhibited metabolism.
Cardiovascular events: Increased risk of cardiovascular death, especially in patients with pre-existing cardiovascular disease.,Gout flare: May increase frequency of gout flares during initiation; prophylaxis with NSAIDs or colchicine recommended.,Liver enzyme elevations: Monitor liver function tests; discontinue if persistent elevation or signs of liver injury.,Thyroid disorders: Can increase TSH levels; monitor thyroid function.,Renal impairment: Dose adjustment not required; limited data in severe renal impairment.,Drug interactions: Use with caution with azathioprine, mercaptopurine, or theophylline; increase risk of toxicity.
Hypersensitivity to allopurinol or any component of the formulation.,Idiopathic hemochromatosis (relative contraindication due to potential for increased iron storage).,Concurrent use with didanosine (increased risk of pancreatitis and peripheral neuropathy).
History of hypersensitivity to febuxostat,Concurrent use with azathioprine, mercaptopurine, or theophylline (absolute)
Avoid high-purine foods such as organ meats (liver, kidney), anchovies, sardines, mussels, and scallops; limit red meat and shellfish; avoid excessive alcohol, especially beer and spirits; maintain adequate fluid intake.
No specific food interactions; however, high-purine foods (e.g., organ meats, anchovies, sardines, scallops, game meats, beer) may counteract efficacy by raising uric acid. Grapefruit juice has no known interaction with febuxostat. Avoid excessive alcohol, especially beer and spirits, as they increase urate levels.
FDA Pregnancy Category C. First trimester: limited human data, no clear teratogenic signal; animal studies show fetal anomalies at high doses. Second/third trimester: potential for neonatal complications (e.g., hypersensitivity, rash) if used near term; avoid if possible.
Pregnancy Category C: In animal studies, febuxostat caused fetal toxicity (reduced fetal weights, increased incidence of fetal malformations) at doses equivalent to 2-4 times the human exposure. There are no adequate and well-controlled studies in pregnant women. Use during pregnancy only if potential benefit justifies potential risk to fetus. First trimester: limited data; second and third trimesters: theoretical risk of uric acid reduction impacting fetal growth due to role of uric acid in fetal development.
Excreted in breast milk; M/P ratio ~0.9. Relative infant dose ~1-2% of maternal weight-adjusted dose. Considered compatible with breastfeeding; monitor infant for rash or diarrhea.
Excretion in human milk unknown; M/P ratio not determined. Because many drugs are excreted in human milk and potential for serious adverse reactions in nursing infants, a decision should be made to discontinue nursing or discontinue drug, taking into account importance of drug to mother.
Pregnancy can increase renal clearance and plasma volume, potentially lowering drug levels. Monitor serum uric acid and symptomatic response; dose adjustment may be needed, but data insufficient for specific recommendations. Use lowest effective dose.
No specific dose adjustments recommended for pregnancy due to lack of pharmacokinetic data. Physiological changes in pregnancy (increased plasma volume, renal blood flow, and glomerular filtration rate) may reduce serum uric acid levels; however, no dose modification studies have been conducted. Use lowest effective dose if treatment necessary.
Start at low dose (100 mg/day) and titrate every 2-4 weeks to reduce risk of gout flare; check renal function before dosing and adjust accordingly; allopurinol hypersensitivity syndrome (AHS) is rare but life-threatening, discontinue immediately if rash or signs of hypersensitivity occur; avoid use with azathioprine or 6-mercaptopurine unless dose of these agents is reduced by 60-80%; monitor liver function tests periodically.
ULORIC (febuxostat) is a non-purine xanthine oxidase inhibitor indicated for chronic management of hyperuricemia in gout. Avoid use in patients with ischemic heart disease or heart failure due to increased cardiovascular events in the CARES trial. Do not use in asymptomatic hyperuricemia. Titrate from 40 mg to 80 mg if serum urate target not reached. SCr monitoring is not required, but caution with severe renal impairment (Cr Cl <30 m L/min) – no data. Avoid concomitant with azathioprine, 6-mercaptopurine, or theophylline due to XO inhibition. Coadministration with NSAIDs or colchicine is safe for flare prophylaxis. Check liver enzymes periodically as ALT elevations >3x ULN occurred in 2%.
Take exactly as prescribed, usually once daily with food.,Do not stop or change dose without consulting your doctor.,Report any rash, hives, itching, or swelling of face/lips immediately.,Drink plenty of fluids (8-10 glasses per day) to prevent kidney stones.,Avoid alcohol, especially beer, as it may increase uric acid levels.,It may take weeks or months to prevent gout attacks; do not skip doses.,During initial therapy, gout attacks may still occur; continue treatment as directed.,Store at room temperature away from moisture and heat.
Take ULORIC once daily with or without food. Do not crush or chew tablets.,You may experience a gout flare when starting ULORIC; you will be prescribed medication (e.g., colchicine, NSAID) to prevent flares for at least 6 months.,Seek immediate medical attention if you develop chest pain, shortness of breath, rapid heartbeat, or sudden numbness/weakness – these may indicate a cardiovascular event.,Avoid drinking large amounts of alcohol or consuming high-purine foods (e.g., red meat, shellfish) as they can increase uric acid levels.,Tell your doctor if you have a history of heart disease, heart failure, stroke, or liver problems.,Report persistent nausea, right upper abdominal pain, dark urine, or yellowing of eyes/skin – signs of liver injury.
"Concurrent use of bumetanide, a loop diuretic, and allopurinol, a xanthine oxidase inhibitor, may increase the risk of allopurinol hypersensitivity reactions, including Stevens-Johnson syndrome and acute gout flares. This interaction is thought to result from bumetanide-induced volume depletion and reduced renal clearance of oxypurinol, the active metabolite of allopurinol, leading to elevated serum oxypurinol levels and enhanced toxicity. Clinically, patients may present with rash, fever, eosinophilia, or acute gouty arthritis, particularly in those with renal impairment."
"The combination of allopurinol and captopril increases the risk of hypersensitivity reactions, including Stevens-Johnson syndrome and angioedema, due to a pharmacodynamic interaction that potentiates immune-mediated adverse effects. This is particularly concerning in patients with renal impairment, where both drugs may accumulate, and can lead to severe cutaneous adverse reactions or hematologic toxicities."
"Allopurinol inhibits xanthine oxidase, an enzyme involved in the catabolism of purine analogs. Tegafur is a prodrug of 5-fluorouracil and is metabolized via the same pathway. Coadministration of allopurinol may reduce the conversion of tegafur to its active metabolite, thereby decreasing the therapeutic efficacy of tegafur. This can lead to suboptimal antineoplastic effect and potential treatment failure."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALLOPURINOL vs ULORIC, answered by our medical review team.
ALLOPURINOL is a Xanthine Oxidase Inhibitor that works by Allopurinol inhibits xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and xanthine to uric acid, thereby reducing serum and urinary uric acid concentrations. It also inhibits de novo purine synthesis through feedback inhibition.. ULORIC is a Xanthine Oxidase Inhibitor that works by ULORIC (febuxostat) is a xanthine oxidase inhibitor that reduces serum uric acid levels by inhibiting the enzyme xanthine oxidase, which catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALLOPURINOL and ULORIC depend on the specific clinical indication. These are both Xanthine Oxidase Inhibitor agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ALLOPURINOL is: 100-600 mg orally once daily; initial 100 mg/day with weekly increases of 100 mg/day; maximum 800 mg/day.. The standard adult dose of ULORIC is: 40 mg orally once daily; may increase to 80 mg once daily if serum uric acid not at target after 2 weeks.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ALLOPURINOL and ULORIC in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ALLOPURINOL is classified as Category C. FDA Pregnancy Category C. First trimester: limited human data, no clear teratogenic signal; animal studies show fetal anomalies at high doses. Second/third trimester: potential for. ULORIC is classified as Category C. Pregnancy Category C: In animal studies, febuxostat caused fetal toxicity (reduced fetal weights, increased incidence of fetal malformations) at doses equivalent to 2-4 times the h. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.