In cystinuria, what therapy is used for refractory stones?

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In cystinuria, when stones keep forming despite good hydration and urine alkalinization, the therapy that helps reduce recurrent stones is chelation therapy. The problem in cystinuria is excessive cystine in the urine, because the defective transporter lets cystine spill into the urine and it remains poorly soluble, especially at lower pH. Hydration and alkalinization help by increasing cystine solubility, but some patients still form stones. Chelation therapy uses thiol-containing drugs such as tiopronin or penicillamine. These drugs bind to cystine to form a soluble mixed disulfide, lowering the urinary cystine concentration and preventing new stones from forming. Diuretics alone won’t address the underlying solubility issue, and acidifying the urine would actually worsen cystine precipitation. High fluid intake remains supportive but is not sufficient for refractory stones, whereas chelation specifically targets the cystine that’s driving stone formation.