SSRI-Induced Hyponatraemia — RACP Adult Medicine MCQ

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ModerateClinical PharmacologySSRI-Induced HyponatraemiaRACP Adult Medicine

A 50-year-old woman with a history of depression is found to have a serum sodium of 124 mmol/L, 6 weeks after commencing sertraline. She is euvolaemic. Urine osmolality is 480 mOsm/kg, urine sodium is 50 mmol/L. What is the mechanism?

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Correct answer: B — Sertraline-induced SIADH

SSRIs (including sertraline, fluoxetine, paroxetine) are a common cause of SIADH, particularly in elderly patients (though can occur at any age). The mechanism involves enhanced ADH release centrally. It typically occurs within the first few weeks of treatment. Management involves fluid restriction and consideration of switching to an alternative antidepressant with lower risk of hyponatraemia (e.g. mirtazapine). Sodium levels should be monitored within 2 weeks of commencing an SSRI in at-risk patients.

Reference: AMH – 2025 – SSRIs; eTG – 2025 – Psychotropic