Figure 125

Urinary cystine crystals. Excessive urinary excretion of cystine (250 to 1000 mg/d of cystine/g of creatinine) coupled with its poor solubility in urine causes cystine precipitation with the formation of characteristic urinary crystals and urinary tract calculi. Stone formation often causes urinary tract obstruction and the associated problems of renal colic, infection, and even renal failure. The treatment objective is to reduce urinary cystine concentration or to increase its solubility. High fluid intake (to keep the urinary cystine concentration below the solubility threshold of 250 mg/L) and urinary alkalization are the mainstays of therapy. For those patients refractory to conservative management, treatment with sulfhydryl-containing drugs, such as D-penicillamine, mercaptopropionylglycine, and even captopril can be efficacious [14,15].

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