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Xanthine Oxidase Inhibitor Pregnancy: C

Allopurinol

Brand names: Zyloprim, Zyloric

Adult dose

Dose: 100–300mg once daily

Route: Oral

Frequency: Once daily

Start low (100mg/day) and titrate up. Reduce dose in renal impairment: eGFR 10–50: max 100mg/day; eGFR <10: 100mg every 2–3 days.

Clinical pearls

Start at 100mg/day AFTER acute gout attack resolves — never start during flare
HLA-B*58:01 allele increases risk of severe cutaneous reactions — screen in Han Chinese, Thai, Korean populations before starting
Flare prophylaxis with colchicine 500mcg BD for first 3–6 months of treatment
Target urate <360 µmol/L (or <300 µmol/L with tophi)
Febuxostat is alternative if intolerant, but higher cardiovascular risk

Contraindications

Acute gout attack (do not initiate during acute attack)
Azathioprine or 6-MP use without dose reduction

Side effects

Rash (can progress to SJS/TEN)
Hypersensitivity syndrome (DRESS)
Nausea
Hepatitis
Renal failure

Interactions

Azathioprine/6-mercaptopurine — allopurinol inhibits their metabolism → toxicity (reduce AZA dose by 75%)
Warfarin — increases anticoagulant effect
Ampicillin — increased rash risk

Monitoring

Serum uric acid (4–6 weeks after dose change)
Renal function
LFTs
FBC

Reference: BSR Guidelines for Gout 2017; ACR Gout Guidelines 2020. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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