Nephrotic syndrome during treatment with alpha-mercaptopropionylglycine.

We report 2 cases of cystinuria in which a nephrotic syndrome developed during treatment with alpha-mercaptopropionylglycine. This syndrome resolved after withdrawal of the drug and it did not recur when the alpha-mercaptopropionylglycine was given again in lower doses. The hypothesis is made that the nephrotic syndrome was dose-related. The alpha-mercaptopropionylglycine must be used in doses less than 50 mg./kg per day with regular monitoring of 24-hour urinary protein in cystinuric children.