Adults

Initial dose: 100 mg once daily. Adjust dosage in increments of 100 mg at weekly intervals according to serum uric acid levels. Typical maintenance dose: 200-300 mg daily for mild gout, 400-600 mg daily for severe gout. Maximum dose: 800 mg per day.

Elderly

Start with lower doses (e.g., 50 mg daily) and gradually increase as tolerated, monitoring renal function and uric acid levels carefully.

Renal_impairment

Dosage reduction is necessary. For creatinine clearance (CrCl) 10-20 mL/min, 100-200 mg/day; for CrCl <10 mL/min, 100 mg every other day or 100 mg twice weekly.

Onset

Uric acid lowering effects begin within 24-48 hours, with maximum effects achieved after several weeks of continuous therapy.

Excretion

Approximately 20% of allopurinol is excreted unchanged in the urine, while about 60% is excreted as oxypurinol via the renal route. Some excretion also occurs via feces.

Half life

Allopurinol has a plasma half-life of 1-2 hours. Its active metabolite, oxypurinol, has a much longer half-life of 15-20 hours.

Absorption

Well absorbed orally (approximately 80%), with peak plasma concentrations occurring within 1.5 hours for allopurinol.

Metabolism

Allopurinol is rapidly metabolized by xanthine oxidase to its major active metabolite, oxypurinol.

Warfarin

May enhance the anticoagulant effect of warfarin, requiring close monitoring of INR and possible dose adjustment.

Theophylline

Allopurinol may inhibit the metabolism of theophylline, leading to increased plasma concentrations and potential toxicity.

Thiazide Diuretics

Increased risk of hypersensitivity reactions, especially in patients with impaired renal function.

Ampicillin / Amoxicillin

Increased incidence of skin rash when co-administered with allopurinol.

Azathioprine / Mercaptopurine

Allopurinol inhibits the metabolism of these drugs, significantly increasing their toxicity. Reduce their dosage by 75% or more when co-administered with allopurinol.