The effect of allopurinol on oxypurine excretion in xanthinuria

In a patient with xanthine urolithiasis secondary to hereditary xanthinuria (xanthine oxidase deficiency), allopurinol administration resulted in a 20 per cent increase in oxypurine excretion and an elevation of the urinary xanthine/hypoxanthine ratio from 4.08 to 6.53. The rise in this ratio suggests that residual xanthine oxidase activity may have been present. It is possible that the excessive re-utilization of hypoxanthine and xanthine in this disease prevents the allopurinol-induced inhibition of de novo purine biosynthesis that is seen in normal subjects.