Cystinuria, with subsequent cystine urolith formation, results from an inherited disorder of renal tubular transport. Cystine stones are dissolved by dietary modification, urinary alkalinization or neutralization, and the use of cystine-binding agents. Urinary alkalinization or neutralization is accomplished as described above. Tiopronin at 15 mg/kg, PO, bid, or d-penicillamine at 15 mg/kg, PO, bid, given with food, are both cystine-binding agents. Tiopronin has fewer adverse effects and is the recommended choice. Both agents can cause Coombs’-positive anemia, thrombocytopenia, increased liver enzyme activity, glomerulonephritis, lymphadenopathy, cutaneous hypersensitivity, and delayed wound healing. Penicillamine also causes vomiting. Once stones are dissolved, a prevention protocol can be instituted. Dietary modification with or without urinary alkalinization may be all that is needed to prevent stone formation; however, tiopronin may also be needed if uroliths recur.
