Allopurinol: Uses, Dosage & Side Effects

Allopurinol is a xanthine oxidase inhibitor that decreases uric acid production by inhibiting the final steps of purine metabolism, effectively reducing serum and urinary uric acid levels.

• Chronic gout (prevention of attacks and management of tophaceous gout)
• Asymptomatic hyperuricemia (serum urate >13 mg/dL or with risk factors)
• Uric acid nephrolithiasis (kidney stones)
• Tumor lysis syndrome prophylaxis
• Secondary hyperuricemia (from chemotherapy, hemolytic anemia)

Gout Prevention:

• Initial: 50-100 mg daily (some clinicians use 100-200 mg)
• Increase by 50-100 mg every 2-4 weeks until serum urate <6 mg/dL
• Maintenance: 300-800 mg daily in 1-3 divided doses
• Maximum: 800 mg daily (higher doses rarely used)

Tumor Lysis Syndrome:

• 200-400 mg daily divided into 3-4 doses
• Start 1-3 days before chemotherapy

Common: Rash (maculopapular), GI upset, diarrhea, headache Serious: Allopurinol hypersensitivity syndrome (fever, rash, eosinophilia, organ dysfunction), hepatotoxicity, Stevens-Johnson syndrome, toxic epidermal necrolysis

• Asymptomatic hyperuricemia without complications (not routinely indicated)
• Acute gout attack (use colchicine or NSAIDs first; start allopurinol after attack resolves)
• Severe hepatic disease
• HLA-B*5801 allele positive patients (very high hypersensitivity risk, especially in Han Chinese and Thai populations)

• Azathioprine/6-mercaptopurine: increased toxicity; reduce dose to 1/3-1/4
• Theophylline: increased levels; monitor theophylline concentration
• Warfarin: potential increased anticoagulant effect; monitor INR
• Ampicillin: increased rash incidence
• Thiazide diuretics: increased hyperuricemia risk; monitor urate levels

Multiple RCTs demonstrate allopurinol effectively reduces gout attack frequency and resolves tophi. CARES trial (NEJM 2020) showed febuxostat (alternative xanthine oxidase inhibitor) increased cardiovascular events; allopurinol remains preferred agent.

• Baseline assessment before initiating therapy
• Regular clinical follow-up per indication
• Laboratory parameters as specified in sections above
• Drug interaction screening at each visit

Dosing adjustments may be necessary in:

• Renal impairment
• Hepatic impairment
• Elderly patients
• Pregnancy and lactation
• Pediatric patients

• Take exactly as directed; do not modify dose without consulting healthcare provider
• Report any unusual symptoms or adverse effects
• Maintain regular follow-up appointments
• Store at room temperature away from moisture and light
• Keep out of reach of children

Disclaimer: This information is for educational purposes only and should not substitute for professional medical advice. Always consult with a qualified healthcare provider before starting, stopping, or modifying any medication.