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Recurrent calcium oxalate nephrolithiasis with hypocitraturia — MSRA MCQ

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HardNephrolithiasisRecurrent calcium oxalate nephrolithiasis with hypocitraturiaMSRA

A 61-year-old man is reviewed after his third symptomatic stone episode in 3 years. Analysis of two retrieved stones showed more than 80% calcium oxalate. He has implemented previous dietary advice: he drinks approximately 3 L water daily, avoids carbonated drinks, maintains normal dietary calcium intake and restricts salt to less than 6 g daily. A 24-hour urine collection shows hypocitraturia with normal urinary calcium and urate. Serum adjusted calcium is normal. He has hypertension and albuminuric chronic kidney disease treated with ramipril. His eGFR is stable at 51 mL/min/1.73 m² and potassium is 4.8 mmol/L (laboratory reference range 3.5–5.0). He has no urinary tract infection, urinary obstruction, diabetes or peptic ulcer disease. Which is the most appropriate next management to reduce stone recurrence?

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Correct answer: B — Start modified-release potassium citrate with renal function and potassium monitoring

This patient has recurrent predominantly calcium oxalate stones despite appropriate fluid, salt and calcium advice, and has hypocitraturia. NICE recommends considering potassium citrate in adults with recurrent stones that are predominantly calcium oxalate. The currently licensed modified-release potassium citrate preparation is also indicated for kidney stones with hypocitraturia and chronic calcium oxalate stones. His eGFR of 51 mL/min/1.73 m² does not contraindicate this formulation: the SmPC contraindicates use at GFR 44 mL/min/1.73 m² or lower. However, his stage 3a CKD and concomitant ramipril increase the risk of hyperkalaemia, so potassium and renal function require monitoring at initiation and following dose changes. Ramipril should not be stopped solely to permit citrate therapy; the interaction requires monitoring rather than routine withdrawal. A thiazide would be appropriate if recurrent calcium oxalate stones were accompanied by hypercalciuria after salt restriction, which is not present. Allopurinol is not the appropriate empirical preventive treatment here, particularly with normal urinary urate. Continuing lifestyle measures remains important but misses an indicated pharmacological option in a recurrent stone former.

Reference: NICE NG118: Renal and ureteric stones: assessment and management — Preventing recurrence (Published January 2019; current recommendations checked August 2026) — https://www.nice.org.uk/guidance/ng118/chapter/Recommendations NICE NG118: Update information (May 2026) — https://www.nice.org.uk/guidance/NG118/chapter/update-information Renodyra 1080 mg modified-release tablets — Summary of Product Characteristics (SmPC revised December 2025; emc page updated January 2026) — https://www.medicines.org.uk/emc/product/101807/smpc