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Digoxin-macrolide interaction — GPhC CRA MCQ

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HardCardiovascular TherapeuticsDigoxin-macrolide interactionGPhC CRA

A stable patient taking digoxin has a concentration near the top of the local target range and is newly prescribed clarithromycin. Renal function is unchanged. Which mechanism and response are most appropriate?

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

Reveal the answer and explanation

Correct answer: B — Query clarithromycin because it may increase digoxin exposure

Option B is correct: digoxin is a P-glycoprotein substrate and clarithromycin inhibits P-glycoprotein, potentially increasing digoxin exposure and toxicity. Option A reverses the direction of interaction. Option E names the wrong mechanism and dose separation would not resolve it. Option D invents a binding interaction. Option C invents reduced antibiotic absorption and would create unsafe overdosing.

Reference: Clarithromycin SmPC: https://www.medicines.org.uk/emc/product/15000/smpc; digoxin SmPC: https://www.medicines.org.uk/emc/product/5463/smpc