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Carbamazepine enzyme induction — GPhC CRA MCQ

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ModerateDrug InteractionsCarbamazepine enzyme inductionGPhC CRA

A 31-year-old man taking carbamazepine 400mg twice daily is prescribed doxycycline 100mg daily for acne. He asks why the GP later changed the antibiotic to lymecycline. What is the most important interaction to flag?

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Correct answer: ECarbamazepine may reduce doxycycline exposure through enzyme induction

Carbamazepine is an enzyme inducer and can reduce concentrations of some medicines, including doxycycline, potentially reducing efficacy. This matters for a prolonged acne course where treatment failure is possible. The interaction is not increased doxycycline exposure. The other proposed consequences are not the clinically relevant issue in this case.

Reference: BNF