Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALLOPURINOL vs ZYLOPRIM
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.
Allopurinol is a xanthine oxidase inhibitor that reduces the production of uric acid by inhibiting 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)
Gout: management of chronic, primary, or secondary gout,Hyperuricemia associated with chemotherapy: prevention of acute uric acid nephropathy in patients with leukemia, lymphoma, and solid tumor malignancies receiving chemotherapy,Recurrent calcium oxalate calculi: prevention in patients with hyperuricosuria
100-600 mg orally once daily; initial 100 mg/day with weekly increases of 100 mg/day; maximum 800 mg/day.
100-300 mg orally once daily, maximum 800 mg/day.
Allopurinol: 1–2 hours; oxypurinol: 18–30 hours (prolonged in renal impairment).
Allopurinol: 1-2 hours; oxypurinol: 18-30 hours (prolonged to 48-72 hours in renal impairment). Clinical context: oxypurinol half-life determines dosing interval; dose adjustment required for Cr Cl < 20 m L/min.
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.
Allopurinol is metabolized primarily by aldehyde oxidase to its active metabolite, oxypurinol; both are excreted renally.
Renal: ~76% as unchanged drug and metabolites; oxypurinol (active metabolite) is primarily excreted renally. Biliary/fecal: minor, <5%.
Renal: allopurinol ~10% unchanged, oxypurinol ~70% unchanged; total renal elimination ~76% (allopurinol + oxypurinol); fecal/biliary: minor (~12-20% as allopurinol, ~3-5% as oxypurinol).
Allopurinol: <1%; oxypurinol: ~50% (mainly to albumin).
Allopurinol: <1% bound; oxypurinol: ~17-20% bound (primarily to albumin).
Allopurinol: ~1.6 L/kg; distributes into total body water.
Allopurinol: ~1.6 L/kg; oxypurinol: ~0.4-0.6 L/kg. Clinical meaning: allopurinol distributes widely into total body water, while oxypurinol has a smaller Vd consistent with limited tissue distribution.
Oral: ~79–90% for allopurinol; oxypurinol is formed rapidly via first-pass metabolism.
Oral: allopurinol 67-90% (mean ~80%); oxypurinol formed via first-pass metabolism has an effective systemic exposure.
GFR >50: no adjustment; GFR 10-50: 200 mg/day; GFR <10: 100 mg/day or dosing interval every 48-72 hours.
Cr Cl >60 m L/min: no adjustment; Cr Cl 30-60 m L/min: 200 mg daily; Cr Cl 10-30 m L/min: 100 mg daily; Cr Cl <10 m L/min: 100 mg every 2-3 days or 50 mg daily.
No specific guidelines; use with caution in severe hepatic impairment (Child-Pugh C); consider dose reduction.
No specific guidelines; use with caution in severe hepatic impairment.
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.
6-10 years: 150 mg/day; 11-16 years: 300 mg/day; <6 years: 50 mg/day; all given orally once daily.
Start at lowest dose (100 mg/day) and titrate slowly; monitor renal function and adjust per GFR.
Start at lower dose (100 mg daily) due to reduced renal function; titrate to achieve serum urate target.
No FDA black box warning.
None
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.
Allopurinol hypersensitivity syndrome (AHS) including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN); increased risk in patients with HLA-B*5801 allele; renal impairment requires dose adjustment; use with caution in patients with liver dysfunction; may cause drowsiness or dizziness; discontinue at first sign of rash or other signs of hypersensitivity.
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).
Absolute: known hypersensitivity to allopurinol or any component of the formulation. Relative: concomitant use with didanosine; severe renal impairment (Cr Cl <10 m L/min) unless used for prevention of uric acid nephropathy during chemotherapy.
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.
High-purine foods (e.g., organ meats, anchovies, sardines, mussels, beer) should be avoided as they increase uric acid levels. No significant food-drug interactions besides alcohol.
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.
Allopurinol (Zyloprim) is a xanthine oxidase inhibitor. First trimester: Limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second and third trimesters: No known increased risk; use only if clearly needed. Overall FDA pregnancy category C.
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.
Allopurinol and its metabolite oxypurinol are excreted into human breast milk. Milk-to-plasma ratio approximately 0.9-1.4 for allopurinol and 0.5-0.9 for oxypurinol. No adverse effects reported in infants. Considered compatible with breastfeeding given very low infant dose (<2% of maternal weight-adjusted dose).
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 adjustment required during pregnancy. However, pregnancy can increase renal clearance; monitor serum uric acid levels and adjust dose if necessary. Maintain lowest effective dose.
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.
Monitor serum uric acid levels monthly until goal is achieved; titrate every 2-4 weeks. Avoid use in acute gout flares; start after inflammation subsides. Check renal function and adjust dose accordingly (Cr Cl <30 m L/min: max 200 mg/day). Consider HLA-B*5801 screening in Han Chinese, Thai, or Korean patients to prevent severe hypersensitivity. Allopurinol hypersensitivity syndrome is rare but life-threatening; discontinue at first sign of rash. Concomitant azathioprine or 6-mercaptopurine requires dose reduction to 25-33% of original.
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 exactly as prescribed; do not miss doses.,Drink at least 8 glasses of water daily to prevent kidney stones.,Report rash, itching, or swelling immediately; may indicate severe allergic reaction.,Avoid alcohol, especially beer and liquor, which can increase uric acid.,Use with caution if you have kidney disease; your dose may need adjustment.,Do not start or stop other medications like diuretics without consulting your doctor.,This drug prevents gout attacks, so continue even if you feel well.
"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 ZYLOPRIM, 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.. ZYLOPRIM is a Xanthine Oxidase Inhibitor that works by Allopurinol is a xanthine oxidase inhibitor that reduces the production of uric acid by inhibiting 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 ZYLOPRIM 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 ZYLOPRIM is: 100-300 mg orally once daily, maximum 800 mg/day.. 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 ZYLOPRIM 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. ZYLOPRIM is classified as Category C. Allopurinol (Zyloprim) is a xanthine oxidase inhibitor. First trimester: Limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.