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Carbamazepine-Induced Hyponatraemia — SCE Neurology MCQ

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ModerateEpilepsy & Seizure DisordersCarbamazepine-Induced HyponatraemiaSCE Neurology

A 45-year-old woman with known epilepsy on carbamazepine develops hyponatraemia (Na⁺ 124 mmol/L). She is asymptomatic. What is the mechanism and what should be done?

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Correct answer: C — Carbamazepine causes SIADH-like syndrome by increasing ADH sensitivity — monitor sodium, consider fluid restriction, and consider switching to an alternative AED if recurrent or symptomatic

Carbamazepine (and oxcarbazepine, which has a higher incidence) causes hyponatraemia through an SIADH-like mechanism — it enhances the action of ADH on the renal collecting duct, leading to water retention and dilutional hyponatraemia. Management includes monitoring sodium levels, fluid restriction if symptomatic, and considering switching to a non-sodium-channel-blocking AED if hyponatraemia is recurrent or symptomatic. A: The mechanism is not renal sodium wasting. C: Carbamazepine is a well-recognised cause. D: Increasing the dose would worsen hyponatraemia. E: Sodium supplementation does not address the underlying mechanism.

Reference: BNF – Carbamazepine; NICE NG217 (2025)