Xanthine Oxidase Inhibitor — Uric Acid Stone Prevention Pregnancy: Avoid in pregnancy — limited safety data

Allopurinol

Brand names: Zyloric

Adult dose

Dose: 100-300 mg once daily

Route: Oral

Frequency: Once daily after food

Max: 300 mg/day for renal stone prophylaxis

Used for uric acid renal calculi prevention and hyperuricosuria-associated calcium oxalate stones. Maintain high fluid intake (above 2.5 L/day urine output)

Paediatric dose

Dose: Seek specialist opinion N/A/kg

Route: Oral

Frequency: Seek specialist opinion

Max: Seek specialist opinion

Seek specialist opinion

Dose adjustments

Renal

Significant reduction required — eGFR 30-59: 100-200 mg/day; eGFR 10-29: 100 mg on alternate days; eGFR under 10: 100 mg at longer intervals

Hepatic

Reduce dose in hepatic impairment

Paediatric weight-based calculator

Patient weight (kg)

Seek specialist opinion

Clinical pearls

EAU Stone Guidelines: Allopurinol indicated for uric acid stone formers with hyperuricaemia or hyperuricosuria unresponsive to dietary measures — reduces uric acid production
Also reduces calcium oxalate stones in patients with hyperuricosuria — purine metabolism affects calcium oxalate crystal nucleation
Urine alkalinisation (potassium citrate) plus allopurinol: dual strategy for uric acid stones — target urine pH 6.5-7.0
Rash is the most important early warning sign — any rash mandates immediate cessation; rechallenge is contraindicated
HLA-B*5801 screening recommended before starting in Han Chinese, Korean, and Thai patients — high SJS/DRESS risk in carriers

Contraindications

Active acute gout attack (do not start during attack)
Hypersensitivity to allopurinol — HLA-B*5801 screening in high-risk ethnic populations

Side effects

Rash (stop immediately — risk of SJS or DRESS)
GI upset
Acute gout flare on initiation
Hepatotoxicity (rare)
DRESS syndrome

Interactions

Azathioprine / mercaptopurine (reduce dose by 75% — fatal interaction if not dose-reduced)
Warfarin (enhanced anticoagulant effect)
Ampicillin / amoxicillin (increased rash rate)
ACE inhibitors (increased hypersensitivity risk)

Monitoring

Serum urate (target below 360 micromol/L)
eGFR
LFTs
Skin surveillance (rash)

Reference: BNFc; BNF 90; EAU Urolithiasis Guidelines 2024; NICE CG177 (Gout). Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways