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Recurrent calcium oxalate nephrolithiasis with hypercalciuria — MSRA MCQ

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HardNephrolithiasisRecurrent calcium oxalate nephrolithiasis with hypercalciuriaMSRA

A 46-year-old man is reviewed after his fourth stone episode in 5 years. Analysis of 2 retrieved stones showed 90% calcium oxalate. He has already implemented recurrence-prevention advice: he drinks 2.5 to 3 litres of water daily, has reduced salt intake to approximately 5 g/day, maintains normal dietary calcium intake and avoids carbonated drinks. A specialist metabolic assessment shows hypercalciuria; urinary citrate and uric acid excretion are normal. Serum adjusted calcium is normal, eGFR is 88 mL/min/1.73 m² and serum potassium is 4.2 mmol/L. He takes lithium carbonate for bipolar disorder and has been psychiatrically stable for several years. Which is the most appropriate next pharmacological management plan to reduce stone recurrence?

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Correct answer: C — Consider potassium citrate and avoid initiating a thiazide unless lithium adjustment and close monitoring are coordinated

This patient has recurrent predominantly calcium oxalate stones despite appropriate fluid, salt and calcium advice. NICE supports considering potassium citrate for adults with recurrent calcium oxalate stones, irrespective of whether hypocitraturia is present. His normal eGFR and potassium do not provide an immediate biochemical reason to avoid it. A thiazide would otherwise be a reasonable targeted option because he has hypercalciuria and has already reduced salt intake to 6 g/day or less. However, thiazides reduce renal lithium clearance and can precipitate lithium toxicity. The lithium SmPC states that, if a thiazide must be prescribed, lithium dosage should be reduced and the patient re-stabilised with frequent monitoring. It is therefore inappropriate for a GP to initiate a thiazide while simply continuing lithium unchanged or applying an arbitrary dose reduction. Coordinated management with the lithium prescriber is required if thiazide treatment is later pursued. Urgent nephrology assessment is not indicated solely because he takes lithium: renal function is normal and there is no evidence of lithium nephropathy. Allopurinol is not the preferred preventive treatment here because there is no hyperuricosuria and NICE does not recommend it for this indication.

Reference: NICE NG118: Renal and ureteric stones: assessment and management — Preventing recurrence (2019; updated May 2026) — https://www.nice.org.uk/guidance/ng118/chapter/Recommendations Li-Liquid 509 mg/5 ml Oral Syrup — Summary of Product Characteristics (2024) — https://www.medicines.org.uk/emc/product/6679/smpc