Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ZYLOPRIM vs ALOPRIM
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
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.
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
FDA-approved: Management of hyperuricemia in gout, management of hyperuricemia in patients with recurrent uric acid stones, and prevention of tumor lysis syndrome in patients receiving chemotherapy.,Off-label: Prevention of calcium oxalate calculi, management of hyperuricemia in patients with renal impairment, and treatment of Lesch-Nyhan syndrome.
100-300 mg orally once daily, maximum 800 mg/day.
300 mg orally once daily; may be increased to 600-800 mg/day in divided doses for severe gout.
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: 1-2 h; Oxypurinol: 18-30 h (prolonged in renal impairment, up to 7 days in severe CKD)
Allopurinol is metabolized primarily by aldehyde oxidase to its active metabolite, oxypurinol; both are excreted renally.
Allopurinol is metabolized primarily by xanthine oxidase to its active metabolite, oxypurinol. Both allopurinol and oxypurinol are further metabolized to a lesser extent by aldehyde oxidase.
Renal: allopurinol ~10% unchanged, oxypurinol ~70% unchanged; total renal elimination ~76% (allopurinol + oxypurinol); fecal/biliary: minor (~12-20% as allopurinol, ~3-5% as oxypurinol).
Renal: ~70% (30% as allopurinol, 40% as oxypurinol); fecal: ~20%; biliary: minor (<5%)
Allopurinol: <1% bound; oxypurinol: ~17-20% bound (primarily to albumin).
Allopurinol: <1%; Oxypurinol: ~20% (primarily to albumin)
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.
Allopurinol: 0.6-1.6 L/kg (suggests distribution in total body water); Oxypurinol: 0.6-1.0 L/kg
Oral: allopurinol 67-90% (mean ~80%); oxypurinol formed via first-pass metabolism has an effective systemic exposure.
Oral: 67-90% (allopurinol); rapidly converted to oxypurinol
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.
GFR 30-60 m L/min: start at 200 mg/day; GFR 10-29 m L/min: 100 mg/day; GFR <10 m L/min: 100 mg every other day or 50 mg/day.
No specific guidelines; use with caution in severe hepatic impairment.
No specific adjustment recommended; use with caution in severe hepatic impairment.
6-10 years: 150 mg/day; 11-16 years: 300 mg/day; <6 years: 50 mg/day; all given orally once daily.
Children 10-20 mg/kg/day in 2-3 divided doses, maximum 400 mg/day.
Start at lower dose (100 mg daily) due to reduced renal function; titrate to achieve serum urate target.
Initiate at lower doses (e.g., 100 mg/day) due to age-related renal decline; monitor for adverse effects.
None
Allopurinol has been associated with hypersensitivity reactions including severe skin reactions such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), which can be life-threatening. The risk is higher in patients with renal impairment and those receiving thiazide diuretics. Discontinue at first sign of rash or other signs of hypersensitivity.
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.
Risk of severe hypersensitivity reactions including SJS/TEN; increased risk in patients with renal impairment or concomitant thiazide use. Monitor for rash. Acute gout attacks may increase during early therapy; prophylaxis with colchicine or NSAIDs is recommended. Hepatic and renal function should be monitored. May cause drowsiness or dizziness.
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.
Absolute: Patients with a history of a severe hypersensitivity reaction to allopurinol. Relative: Renal impairment (dose adjustment needed), pregnancy (only if benefit outweighs risk), and lactation (use caution).
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.
Avoid high-purine foods (e.g., organ meats, anchovies, sardines, mussels, scallops, red meat, beer) as they may increase serum uric acid levels and reduce drug efficacy. Maintain adequate hydration to prevent urate nephropathy. Grapefruit juice has no known interaction. No significant interaction with caffeine.
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.
First trimester: No evidence of teratogenicity in humans; animal studies show no fetal harm. Second/third trimester: No known risks; allopurinol crosses placenta but no congenital anomalies reported. Postnatal: No adverse effects reported.
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).
Allopurinol and its metabolite oxypurinol are excreted in breast milk; M/P ratio not established. No adverse effects reported in nursing infants. Use with caution, especially in infants with G6PD deficiency.
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.
No dose adjustment required based on pregnancy alone. However, dose may need adjustment if renal function declines. Allopurinol pharmacokinetics not significantly altered in pregnancy; maintain dose based on renal function and uric acid levels.
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.
Initiate therapy after acute gout flare has subsided; consider gradual dose titration to reduce flare risk; monitor for hypersensitivity reactions, especially in patients with renal impairment; use with caution in patients on thiazide diuretics or ACE inhibitors due to increased risk of hypersensitivity; assess renal function before starting and during therapy; adjust dose in renal impairment (Cr Cl <60 m L/min); avoid use with azathioprine or mercaptopurine unless dose reduction of these agents is implemented; educate patient to report rash, fever, or lymphadenopathy immediately.
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.
Take this medication exactly as prescribed, usually once daily.,Do not start or stop taking this medication during an acute gout attack; wait until the flare has resolved.,Drink plenty of fluids (at least 2 liters of water per day) unless otherwise directed by your doctor.,Avoid alcohol and foods high in purines (e.g., red meat, organ meats, shellfish) as they may increase uric acid levels.,Report any skin rash, itching, swelling, or difficulty breathing to your doctor immediately.,Inform your doctor of all medications you are taking, including over-the-counter drugs and supplements.,Do not take this medication with azathioprine, mercaptopurine, or theophylline unless specifically instructed by your doctor.,Store at room temperature away from moisture and heat.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ZYLOPRIM vs ALOPRIM, answered by our medical review team.
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.. ALOPRIM 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ZYLOPRIM and ALOPRIM 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 ZYLOPRIM is: 100-300 mg orally once daily, maximum 800 mg/day.. The standard adult dose of ALOPRIM is: 300 mg orally once daily; may be increased to 600-800 mg/day in divided doses for severe gout.. 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 ZYLOPRIM and ALOPRIM 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. 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 . ALOPRIM is classified as Category C. First trimester: No evidence of teratogenicity in humans; animal studies show no fetal harm. Second/third trimester: No known risks; allopurinol crosses placenta but no congenital . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.