Change in inhibitory potential in urine of hyperuricosuric calcium oxalate stone formers effected by allopurinol and orthophosphates.

Allopurinol and orthophosphates were used in the treatment of 25 hyperuricosuric calcium oxalate stone formers. Their urines were tested by the Discriminating Index method, which measures the potential of a urine to retard calcium oxalate precipitation in vitro. The tests were performed before any treatment was begun and about 10 days after the commencement of drug intake. An insignificant effect by allopurinol and a markedly significant effect of orthophosphates on Discriminating Index were found. In a few of the patients, allopurinol seemed to cause a decrease in the urine's potential to retard calcium oxalate precipitation. Therefore the effect of allopurinol in 11 hyperuricosuric patients with no history of calcium oxalate stone formation was tested. In 5 of the 11 patients, the urine's potential to retard calcium oxalate precipitation decreased to levels similar to those of calcium oxalate stone formers. The results of this study suggest that hyperuricosuric calcium oxalate stone formers suffer from the same yet-undefined etiology of stone formation as other calcium oxalate stone formers. The results also question the role of uric acid in calcium oxalate stone formation and the efficacy of allopurinol in preventing this disease. It is suggested that allopurinol may even be related to stone formation in some patients.