Xanthine Oxidase Inhibitor — Urate-Lowering Therapy Pregnancy: Inadequate evidence of safety in human pregnancy; use only when there is no safer alternative and the disease carries risk to mother or unborn child.

Allopurinol

Brand names: Zyloric

Allopurinol is a xanthine oxidase inhibitor used as first-line urate-lowering therapy to prevent recurrent gout and uric acid stones; this page concerns its use in older adults, in whom renal impairment is common.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Start 100 mg/day; 100–200 mg daily (mild), 300–600 mg daily (moderately severe), 700–900 mg daily (severe)

Route: Oral

Frequency: Daily

Older people: in the absence of specific data, use the lowest dosage which produces satisfactory urate reduction, paying particular attention to renal impairment advice (see below). General adult regimen: introduce at low dosage (e.g. 100 mg/day) and increase only if serum urate response is unsatisfactory; if dosing on a mg/kg basis, use 2–10 mg/kg bodyweight/day. Patients treated for hypertension or cardiac insufficiency (e.g. with diuretics or ACE inhibitors) may have concomitant renal impairment — use allopurinol with care. Adjust dose by monitoring serum urate and urinary urate/uric acid. Paediatric: Children under 15 years: 10 to 20 mg/kg bodyweight/day up to a maximum of 400 mg daily. Use in children is rarely indicated, except in malignant conditions (especially leukaemia) and certain enzyme disorders such as Lesch-Nyhan syndrome.

Dose adjustments

Renal

In severe renal insufficiency, may be advisable to use less than 100 mg/day or single 100 mg doses at intervals longer than one day; adjust to maintain plasma oxipurinol below 100 micromol/L if monitoring available. On dialysis (2–3×/week): consider 300–400 mg immediately after each dialysis with none in the interim.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to allopurinol or to any component of the formulation

Side effects

Rash (common); rarely Stevens-Johnson syndrome/toxic epidermal necrolysis
Hypersensitivity (uncommon); rarely anaphylactic reaction
Nausea, vomiting, diarrhoea (uncommon)
Liver function test abnormal (uncommon); rarely hepatitis
Blood thyroid stimulating hormone increased (common)

Interactions

Thiazide diuretics — increased risk of hypersensitivity reactions/SJS/TEN, especially with concomitant renal impairment
ACE inhibitors — concomitant renal function impairment; use allopurinol with care
Ampicillin/amoxicillin — increased risk of skin rash

Clinical monograph

How it works

It and its active metabolite oxypurinol inhibit xanthine oxidase, reducing the conversion of hypoxanthine and xanthine to uric acid and thereby lowering serum urate.

Prescribing in practice

In the elderly, age-related and renal impairment increase the risk of allopurinol hypersensitivity syndrome, so start at a low dose and titrate slowly against renal function and serum urate.
Do not start during an acute attack, and provide gout flare prophylaxis when initiating, as urate-lowering can transiently trigger flares.
It markedly potentiates azathioprine and mercaptopurine, and increases the effect of these and certain other drugs, requiring dose adjustment or avoidance.

Monitoring

Monitor serum urate to target, renal and liver function, and remain alert for early rash or hypersensitivity, particularly during initiation.

Counselling the patient

Keep taking it regularly even when gout-free, and continue any flare-prevention medicine as advised.
Stop and seek urgent advice if a rash, fever or mouth ulcers develop.
Maintain good hydration and attend blood-test appointments.

Evidence & guidelines

Use reflects NICE and British Society for Rheumatology gout guidance recommending treat-to-target urate lowering with cautious dose titration in renal impairment.

Reference: NICE CG177 (Gout); BSR Gout Guidelines 2017; MHRA HLA-B*5801 guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways