Allopurinol metabolism in a patient with xanthine oxidase deficiency

A patient with complete deficiency of xanthine oxidase would not be expected to oxidase allopurinol to oxipurinol if allopurinol did not have any alternative metabolic pathway. 400 mg of allopurinol was administered to a patient with xanthine oxidase deficiency, and plasma allopurinol, oxipurinol, hypoxanthine, and xanthine levels were determined serially by the use of high-performance liquid chromatography (HPLC). Plasma oxipurinol as well as allopurinol was increased after the administration of allopurinol, and oxipurinol reached a maximum level of 13.1 micrograms/ml at 6 hours after the administration. This was the same pattern as that of normal controls. This result demonstrated the existence of some other oxidising enzyme of allopurinol than xanthine oxidase.