Tiopronin Cystinuria — ESENeph MCQ

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ModerateRenal Stone DiseaseTiopronin CystinuriaESENeph

A 38-year-old man with cystinuria has been on high fluid intake and potassium citrate for alkalinisation but continues to form cystine stones. Urine pH is 7.5 (at target). What additional pharmacological agent can be used?

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Correct answer: E — Tiopronin (or D-penicillamine)

When conservative measures (high fluid intake, urinary alkalinisation, dietary sodium/protein restriction) fail to prevent cystine stones, thiol agents are used. Tiopronin (alpha-mercaptopropionylglycine) binds cystine to form a more soluble mixed disulfide, reducing urinary cystine saturation. D-penicillamine has a similar mechanism but worse side effect profile (marrow suppression, proteinuria, lupus-like syndrome). Captopril has thiol properties but is insufficiently effective for stone prevention. Target urinary cystine is <250 mg/L.

Reference: https://guidelines.ukkidney.org