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

Used in: Gout

Allopurinol is a urate-lowering medicine used for the long-term prevention of gout and to reduce uric acid in some other settings. It is not used to treat an acute attack.

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

Introduce at low dosage (e.g. 100 mg/day) to reduce risk of adverse reactions and increase only if serum urate response is unsatisfactory. If dosing on a mg/kg basis, use 2–10 mg/kg bodyweight/day. Adjust dose by monitoring serum urate and urinary urate/uric acid at appropriate intervals. Exercise extra caution if renal function is poor. Reduced doses in hepatic impairment (with periodic LFTs early in therapy). For high urate turnover conditions (e.g. neoplasia, Lesch-Nyhan): correct hyperuricaemia before cytotoxic therapy, ensure adequate hydration, dose at lower end of range. 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.

US labelling (FDA)

Reference — US labelling, may differ from UK

Gout : Prior to initiating treatment assess serum uric acid level, complete blood count, chemistry panel, liver and kidney function tests. Prophylactic treatment for gout flares is recommended. ( 2.1 , 2.2 ) Patients with normal kidney function: Initial dosage is 100 mg orally daily. Increase by 100 mg weekly increments until serum uric acid of 6 mg/dl or less is reached (maximum 800 mg daily). ( 2.3 ) Patients with impaired kidney function: The initial dosage is 50 mg orally daily. Follow recommendations for titration in patients with renal impairment until target serum uric acid level is reached. ( 2.6 ) See complete information in the Full Prescribing Information (FPI). Hyperuricemia …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-07-08. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

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 inhibits xanthine oxidase, reducing production of uric acid.

Prescribing in practice

Start at a low dose and titrate to a target serum urate; provide anti-inflammatory cover (e.g. colchicine or an NSAID) during initiation, as starting can trigger a flare.
Do not stop it during an acute attack already established on treatment.
Rare but serious hypersensitivity can occur (higher risk in certain HLA-B*5801 backgrounds and in renal impairment); it interacts with azathioprine and mercaptopurine, whose doses must be markedly reduced.

Monitoring

Monitor serum urate and titrate to target; check renal function and remain alert to early rash or hypersensitivity.

Counselling the patient

Keep taking it long-term to prevent attacks, and do not stop it during a flare.
Report any rash promptly.
Drink plenty of fluids.

Evidence & guidelines

First-line urate-lowering therapy for gout, titrated to a urate target, per NICE NG219.

Reference: NICE NG219 (Gout); BSR Gout Guidelines 2017; 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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