Allopurinol

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 and urinary urate.

Prescribing in practice

• It can rarely cause severe, life-threatening hypersensitivity including DRESS and Stevens-Johnson syndrome, so start at a low dose, warn the patient, and stop immediately and permanently at the first sign of rash; risk is higher in renal impairment and HLA-B*5801 carriers.
• Starting therapy can precipitate an acute attack, so introduce it with gout prophylaxis cover and not during an acute flare.
• It markedly increases the toxicity of azathioprine and mercaptopurine and interacts with ciclosporin; reduce the dose in renal impairment.

Monitoring

Monitor serum urate to guide titration to target and check renal function periodically, especially in renal impairment.

Counselling the patient

• Stop the tablets and seek urgent medical advice if you develop a rash.
• Keep taking it regularly even when free of attacks, and continue it during a flare once established.
• Drink plenty of fluids.

Evidence & guidelines

Allopurinol is the first-line urate-lowering therapy with efficacy and safety established in the SPC and NICE and British gout guidance.