Effect of captopril on urinary cystine excretion in homozygous cystinuria.

We determined if captopril could reduce urinary cystine excretion in homozygous cystinuric patients. Seven patients were treated with 150 mg. captopril daily after determination of baseline 24-hour urine cystine excretion. All patients had a history of multiple cystine stones, and were on chronic fluid and alkalization therapy. Five patients had previously been on D-penicillamine. Cystine excretion studies were repeated 1 to 5 months after institution of captopril. Baseline 24-hour urinary cystine excretion ranged from 580 to 970 mg. per gm. creatinine (mean 744). After institution of captopril these levels decreased to a range of 113 to 581 mg. per gm. creatinine (mean 371). These values on treatment represented a statistically significant decrease to between 18 and 89% of baseline levels (p equals 0.0045). We conclude that captopril can significantly, and at times profoundly, decrease urinary cystine excretion in patients with homozygous cystinuria. Further studies are required to elucidate fully the mechanism of urinary cystine reduction and to help define a possible role for this drug in routine maintenance or dissolution therapy.