Xanthine-containing calculi during allopurinol therapy.

We report a case of urate overproduction owing to the Lesch-Nyhan syndrome (deficiency of hypoxanthine-guanine phosphoribosyltransferase). Urate crystalluria was controlled by allopurinol therapy but renal calculi developed, which contained a variety of purines, particularly the relatively insoluble xanthine, as well as oxypurinol and hypoxanthine. The potential hazard from the increased amounts of xanthine that are produced during allopurinol therapy for urate overproduction is stressed, as well as the importance of maintaining a high urine flow rate even during such therapy.