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Antacid tetracycline interaction — GPhC CRA MCQ

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EasyGastrointestinal TherapeuticsAntacid tetracycline interactionGPhC CRA

A patient prescribed doxycycline for acne asks to take magnesium trisilicate mixture for indigestion at the same time. What is the most important interaction to flag?

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Correct answer: E — Reduced doxycycline absorption from chelation

Antacids containing polyvalent cations can bind tetracyclines and reduce absorption. Doses should be separated and counselling given. In this scenario, the correct option is reduced doxycycline absorption from chelation. The other options are plausible but do not address the key clinical, legal or safety issue as directly. This aligns with UK pharmacy practice guidance cited in the reference field.

Reference: BNF; Stockley's Drug Interactions