Renal clearance of oxipurinol, the chief metabolite of allopurinol

Abstract Oxipurinol (4,6-dihydroxypyrazolo(3,4-d)pyrimidine; alloxanthine) is the chief metabolite of allopurinol in vivo . Like allopurinol, although to a lesser degree, oxipurinol suppresses xanthine oxidase and lowers the serum and urinary uric acid levels; indeed, for reasons indicated, much of the effect of allopurinol may well be due to oxipurinol. Unlike allopurinol, but like uric acid, oxipurinol appears to be reabsorbed by the tubules, since its renal clearance is much less than the glomerular filtration rate in man and the mongrel dog, although it is not bound to plasma proteins. Moreover, uricosuric drugs increase the clearance of oxipurinol in man, but not in the Dalmatian dog. Oxipurinol apparently is not secreted by the tubules. In the presence of marked kidney damage the renal clearance of oxipurinol is impaired and the plasma oxipurinol concentration in patients given usual allopurinol dosages is elevated. Patients with marked renal insufficiency appear to exhibit a higher incidence of side reactions than do patients with normal renal function.