A 35-year-old man with recurrent calcium oxalate renal stones has a 24-hour urine: calcium 420 mg, oxalate 48 mg, citrate 95 mg (low), pH 5.9, and volume 900 mL. Which is the MOST important pharmacological intervention to reduce stone recurrence?
- A Thiazide diuretic (hydrochlorothiazide)
- B Allopurinol
- C Sodium cellulose phosphate
- D Potassium citrate ✓
Explanation
This patient has hypercalciuria, hyperoxaluria mild, and importantly hypocitruria (citrate <320 mg/day) with acidic urine pH — hypocitruria is a major risk factor for calcium oxalate stones as citrate normally chelates urinary calcium and inhibits stone nucleation. Potassium citrate increases urinary citrate, alkalinises urine, and reduces calcium ion activity. Hydrochlorothiazide is effective for hypercalciuria but does not address hypocitruria and alkalinise urine. Allopurinol reduces urate-induced calcium oxalate crystallisation but is indicated mainly for hyperuricosuria. Increasing fluid intake (target >2.5 L urine/day) is the most important non-pharmacological measure.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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