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Xanthine oxidase inhibitor / Urate-lowering therapy Pregnancy: Avoid unless essential. Limited data. Consider stopping and using conservative management.

Allopurinol

Brand names: Zyloric

Adult dose

Dose: 100 mg daily initially; titrate to serum urate <360 micromol/L (target <300 if tophi)
Route: Oral (after meals)
Frequency: Once daily
Max: 900 mg/day
Start 100 mg/day. Increase by 100 mg every 4 weeks. Target serum urate <360 micromol/L (or <300 with tophi). DO NOT start during acute gout attack. Cover first 3–6 months with colchicine 500 mcg OD or low-dose NSAID to prevent flare. Adequate hydration.

Paediatric dose

Dose: 10 mg/kg
Route: Oral
Frequency: Once daily
Max: 400 mg/day
<15 years (tumour lysis prophylaxis): 10–20 mg/kg/day in 2–3 divided doses (max 400 mg/day). 6–12 years: 150 mg/day. <6 years: 150 mg/day. Gout prophylaxis in children: specialist guidance.

Dose adjustments

Renal

eGFR 10–20: max 100 mg/day; eGFR <10: 50–100 mg with increased interval; haemodialysis: 100 mg after each session.

Hepatic

Reduce dose in severe hepatic impairment.

Paediatric weight-based calculator

<15 years (tumour lysis prophylaxis): 10–20 mg/kg/day in 2–3 divided doses (max 400 mg/day). 6–12 years: 150 mg/day. <6 years: 150 mg/day. Gout prophylaxis in children: specialist guidance.

Clinical pearls

  • NEVER start during an acute gout attack — wait 2–4 weeks after attack resolves
  • Prophylactic colchicine essential for first 3–6 months of ULT to prevent flares
  • HLA-B*5801 allele — associated with severe cutaneous reactions in Han Chinese/Thai — screen before starting
  • Critical interaction: azathioprine + allopurinol — reduce aza dose to 25% of normal
  • Check serum urate every 4 weeks during titration; target <360 micromol/L

Contraindications

  • Acute gout attack (do not initiate — wait until attack resolved for 2–4 weeks)

Side effects

  • Gout flare on initiation (paradoxical — use prophylaxis)
  • Rash (stop immediately — can progress to Stevens-Johnson Syndrome or TEN)
  • GI upset
  • Hypersensitivity syndrome (DRESS) — rare but serious
  • Elevated LFTs

Interactions

  • Azathioprine/mercaptopurine — MAJOR: allopurinol inhibits xanthine oxidase, causing 4× increase in azathioprine levels (reduce azathioprine by 75%)
  • Ampicillin/amoxicillin — increased rash frequency
  • Warfarin — increased anticoagulant effect
  • Theophylline — increased levels
  • Ciclosporin — increased ciclosporin levels

Monitoring

  • Serum urate (every 4 weeks during titration then 6-monthly)
  • LFTs and U&E (baseline and periodically)
  • Rash and skin reactions (especially in first weeks)

Reference: BNFc; BNF; NICE NG219 Gout; BSR Gout Guidelines; EULAR 2022. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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