A 16-year-old male presents with recurrent renal colic. Stone analysis reveals hexagonal crystals. Urinalysis shows cystine crystals, and urine chromatography confirms cystinuria. First-line therapy aimed at increasing cystine solubility is:
- A Allopurinol and urine alkalinization
- B High fluid intake, urine alkalinization, and tiopronin ✓
- C Pyridoxine supplementation and penicillamine restriction
- D Dietary methionine loading and thiazide diuretics
Correct answer: B. High fluid intake, urine alkalinization, and tiopronin
Explanation
Cystinuria stems from defective dibasic amino acid reabsorption (rBAT/b0,+AT), causing cystine stone formation since cystine is poorly soluble at acidic pH. Management begins with copious fluids and alkalinization to keep urine pH above 7.5, with chelating agents such as tiopronin or D-penicillamine added for refractory cases. Pyridoxine treats cystathionine beta-synthase deficiency, not cystinuria, and methionine loading would worsen cystine production.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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