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Carbamazepine-Warfarin Interaction — SCE Neurology MCQ

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ModerateEpilepsy & Seizure DisordersCarbamazepine-Warfarin InteractionSCE Neurology

A 60-year-old man with epilepsy on enzyme-inducing AEDs (carbamazepine) requires warfarin for new atrial fibrillation. What effect does carbamazepine have on warfarin metabolism?

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Correct answer: A — Carbamazepine induces CYP enzymes and increases warfarin metabolism, reducing its anticoagulant effect — higher warfarin doses may be needed

Carbamazepine is a potent hepatic enzyme inducer (CYP3A4, CYP2C9, CYP1A2). It increases the metabolism of warfarin, reducing its anticoagulant effect and necessitating higher doses to achieve therapeutic INR. Close INR monitoring is essential when starting, stopping, or adjusting enzyme-inducing AEDs in warfarin-treated patients. A: There is a significant interaction. C: The effect is induction, not inhibition. D: The interaction is metabolic, not absorptive. E: Both carbamazepine and phenytoin are enzyme inducers.

Reference: BNF – Carbamazepine Drug Interactions; NICE NG217 (2025)