Cystine calculi in children: the results of a metabolic evaluation and response to medical therapy.

Purpose: We describe baseline metabolic abnormalities and evaluate mercaptopropionylglycine plus potassium citrate treatment for urinary abnormalities and to prevent new stone formation in children with cystine stones.

Materials And Methods: Daily urinary excretions of calcium, oxalate, citrate, magnesium, urate and phosphorus were determined in 18 children with cystine stone and 24 healthy children. The cystine stone cases were treated with 10 to 15 mg./kg. alpha-mercaptopropionylglycine and 1 mEq./kg. potassium citrate daily for a median 15 months. The potassium citrate dose was adjusted to render urinary pH 6.5 to 7.5.

Results: There was no significant difference in baseline metabolic profile between the cystine stone and control groups except for citrate. The cystine stone group excreted less citrate than the control group (p = 0.044). After treatment median plus or minus standard deviation urinary cystine 245 +/- 233 to 140 +/- 106 mmol./mol. creatinine decreased from (p = 0.015), and urinary citrate increased from 255 +/- 219 to 729 +/- 494 mg./1.73 m.2 (p = 0.003). No serious adverse reaction was noted. Of the 15 patients with followup data 5 (33%) had 8 recurrent calculi (recurrence rate 0.64 per patient year).

Conclusions: Our results suggest that further investigation of low citrate excretion is needed in cystinuric children. Potassium citrate therapy is effective in increasing urinary pH and urinary citrate. However, high recurrence rate and persistent cystinuria in our patients emphasize the inadequacy of our treatment schedule in the prevention of recurrent cystine calculi.