Cystine-binding Agents in Urinary Disease
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.