Allopurinol
Allopurinol is a structural analogue of hypoxanthine. It reduces uric acid production by inhibiting xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid. Zyloprim is used for gout and for uric acid that rises when tumour cells break down during some cancer treatment.
Key points
- Allopurinol works by inhibiting xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid.
- Allopurinol has a measured plasma half-life of about 1 to 2 hours, and its active metabolite oxipurinol has a longer measured half-life of about 15 hours.
- Allopurinol is itself metabolised to oxipurinol, which is also an inhibitor of xanthine oxidase.
- NICE lists allopurinol as a first-line option for starting long-term, treat-to-target urate-lowering therapy.
How allopurinol lowers uric acid, and what it treats
Allopurinol is a structural analogue of hypoxanthine, and the Zyloprim label describes it as an inhibitor of xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid. Allopurinol is itself metabolised to oxipurinol, which is also an inhibitor of xanthine oxidase; allopurinol has a measured plasma half-life of about 1 to 2 hours, and oxipurinol’s measured half-life runs longer, at about 15 hours.
The Zyloprim label covers the management of primary or secondary gout, including acute attacks, tophi, joint destruction, uric acid lithiasis and nephropathy. The label separately covers raised uric acid in patients with leukaemia, lymphoma and other malignancies undergoing cancer therapy that elevates serum and urinary uric acid. NICE treats allopurinol as a first-line option for starting long-term, treat-to-target urate-lowering therapy, describing gout as a lifelong condition that benefits from such therapy to eliminate urate crystals, prevent flares, shrink tophi and prevent long-term joint damage. NICE gives a gout flare itself a separate first-line treatment of an NSAID, colchicine or a short course of an oral corticosteroid.
A rash is a warning sign
The Zyloprim label states that a skin rash may be followed by more severe hypersensitivity reactions, including Stevens-Johnson syndrome, generalised vasculitis, irreversible hepatotoxicity and, on rare occasions, death.
Zyloric: a regional name for allopurinol
The Emirates Drug Establishment’s drug directory records Zyloric 100 mg with allopurinol as its tablet ingredient, a familiar regional name for readers who know the medicine this way.