NCIt definition : The sodium form of allopurinol, which is a structural isomer of hypoxanthine. Allopurinol
inhibits xanthine oxidase, an enzyme that converts oxypurines to uric acid. By blocking
the production of uric acid, this agent decreases serum and urine concentrations of
uric acid, thereby providing protection against uric acid-mediated end organ damage
in conditions associated with excessive production of uric acid, i.e. the massive
cell lysis associated with the treatment of some malignancies. (NCI04);