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Doxycycline and antacid interaction — GPhC CRA MCQ

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ModerateDrug InteractionsDoxycycline and antacid interactionGPhC CRA

A patient prescribed doxycycline 100 mg daily for acne buys an over-the-counter antacid containing magnesium and aluminium. He takes the antacid at breakfast with doxycycline because of nausea. What would you advise the patient?

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

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Correct answer: E — Separate doxycycline from antacids and take with water

Multivalent cations in antacids reduce absorption of doxycycline. The patient should separate doses and take doxycycline with plenty of water while remaining upright to reduce oesophageal irritation. Nausea can be managed by taking it with food if permitted, but not with interacting antacids.

Reference: BNF