Xanthine oxidase inhibitor / Urate-lowering therapy Pregnancy: Inadequate evidence of safety in human pregnancy; use only when there is no safer alternative and when the disease itself carries risk for the mother or unborn child. Breast-feeding not recommended.

Allopurinol

Brand names: Zyloric

Allopurinol is a xanthine oxidase inhibitor used as urate-lowering therapy to prevent recurrent gout and uric acid nephrolithiasis, and to manage hyperuricaemia including tumour lysis.

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: Introduce at low dosage, e.g. 100 mg/day, increased only if serum urate response is unsatisfactory

Route: oral

Frequency: once daily

Max: 900 mg daily (severe conditions)

Suggested schedules: 100-200 mg daily in mild conditions; 300-600 mg daily in moderately severe conditions; 700-900 mg daily in severe conditions. If mg/kg basis required, 2-10 mg/kg bodyweight/day. Older people: use lowest dosage producing satisfactory urate reduction. High urate turnover conditions (e.g. neoplasia, Lesch-Nyhan): dose at lower end of schedule; correct hyperuricaemia before cytotoxic therapy with adequate hydration and urine alkalinisation. Adjust dose by monitoring serum urate and urinary urate/uric acid levels.

Paediatric dose

Dose: 10 mg/kg

Route: oral

Frequency: daily (total daily dose range 10-20 mg/kg/day)

Max: 400 mg daily

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

Impaired renal function may lead to drug/metabolite retention. In severe renal insufficiency, use less than 100 mg per day or single 100 mg doses at longer intervals than one day; if oxipurinol levels can be monitored, adjust to keep plasma oxipurinol below 100 micromol/litre. Removed by renal dialysis; if dialysis 2-3 times/week, consider 300-400 mg immediately after each dialysis with none in 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.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

Known hypersensitivity to allopurinol or to any of the components of the formulation

Side effects

Rash (common)
Liver function test abnormal (uncommon)
Hypersensitivity (uncommon)
Vomiting, nausea, diarrhoea (uncommon)
Stevens-Johnson syndrome/toxic epidermal necrolysis (rare)

Interactions

Mercaptopurine or azathioprine (reduce their dose)
Bendamustine, thiazide diuretics, ampicillin and amoxicillin (increased risk of skin rash)
Capecitabine (avoid concomitant use)
Pegloticase (discontinue allopurinol and refrain from initiating)

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

Stop immediately and seek advice if a rash develops, as allopurinol can cause severe hypersensitivity (including DRESS and Stevens-Johnson syndrome), with higher risk in those carrying HLA-B*58:01.
Do not start during an acute attack; begin under cover of an anti-inflammatory or colchicine prophylaxis to avoid precipitating a flare, and start low with slow titration in renal impairment.
It markedly potentiates azathioprine and mercaptopurine, requiring substantial dose reduction of those drugs to avoid life-threatening myelosuppression.

Monitoring

Monitor serum urate to a target, together with renal function, and review for any sign of hypersensitivity early in treatment.

Counselling the patient

Keep taking it every day, including during a gout flare, and do not stop just because an attack settles.
Report any skin rash promptly.
Maintain a good fluid intake while on treatment.

Evidence & guidelines

Urate-lowering therapy and an HLA-B*58:01-informed approach in at-risk groups are supported by NICE gout guidance and MHRA hypersensitivity advice.

Reference: NICE NG219 Gout; BSR Gout Guidelines; EULAR 2022; 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.

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