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Phenytoin and doxycycline contraception not, phenytoin — GPhC CRA MCQ

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ModerateDrug InteractionsPhenytoin and doxycycline contraception not, phenytoinGPhC CRA

A woman taking phenytoin for epilepsy is prescribed a short course of doxycycline and asks whether the antibiotic affects seizure medicines. What is the most important interaction to flag?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Phenytoin can reduce doxycycline exposure through enzyme induction

Phenytoin is an enzyme inducer and can reduce exposure to some medicines, including doxycycline. The clinical relevance depends on infection severity and duration. The prescriber may need to consider an alternative.

Reference: BNF