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Azithromycin Drug Interactions — MFDS Part 1 MCQ

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HardPharmacologyAzithromycin Drug InteractionsMFDS Part 1

A 74-year-old woman taking citalopram and stable-dose warfarin is to receive azithromycin following microbiological advice for an odontogenic infection. Which option correctly identifies the principal potentially life-threatening drug interaction and its mechanism?

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Correct answer: A — Additive QT prolongation with citalopram, increasing the risk of torsade de pointes

Azithromycin can delay cardiac repolarisation and prolong the QT interval. Combining it with another QT-prolonging medicine such as citalopram produces an additive risk of ventricular arrhythmia and torsade de pointes; older women are particularly susceptible. Warfarin remains clinically relevant because potentiated anticoagulation has been reported, so additional INR/prothrombin-time monitoring should be considered. However, option E is incorrect: azithromycin is only a weak CYP450 inhibitor, and the mechanism of the reported warfarin interaction is unknown rather than strong CYP2C9 inhibition. Azithromycin does not characteristically inhibit aldehyde dehydrogenase or monoamine oxidase, so it does not cause disulfiram-like reactions, serotonin syndrome through MAO inhibition, or tyramine-associated hypertensive crises.

Reference: Sandoz Limited. Azithromycin 500 mg Tablets, Summary of Product Characteristics, sections 4.4 and 4.5. Updated 2026. https://www.medicines.org.uk/emc/product/6541/smpc