Urinary-Tract Stones Resulting from the Excretion of Oxypurinol

COMPOUNDS that inhibit the enzyme, xanthine oxidase, are useful in the treatment of disorders of purine metabolism. They are of particular value in disorders resulting from the overproduction of uric acid. Xanthine oxidase is inhibited by both allopurinol (4-hydroxypyrazolo [3,4-d] pyrimidine), an analogue of hypoxanthine, and oxypurinol (4,6-dihydroxypyrazolo [3,4-d] pyrimidine), which is an analogue of xanthine. Xanthine oxidase catalyzes the conversion of hypoxanthine to xanthine to uric acid. It also catalyzes the conversion of allopurinol to oxypurinol. A major percentage of administered allopurinol is rapidly oxidized to oxypurinol.1 After the administration of a xanthine oxidase inhibitor such as allopurinol or . . .