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Erythromycin-digoxin toxicity — GPhC CRA MCQ

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ModerateDrug InteractionsErythromycin-digoxin toxicityGPhC CRA

A 72-year-old man taking digoxin 125 micrograms daily for atrial fibrillation has recently been started on erythromycin 500 mg four times daily for a chest infection. He presents with nausea, visual disturbances, and a slow pulse. What is the most likely cause?

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Correct answer: B — Erythromycin has increased digoxin levels leading to digoxin toxicity

Erythromycin inhibits P-glycoprotein and CYP3A4, which increases digoxin bioavailability and reduces its clearance, leading to elevated serum digoxin concentrations. The symptoms described — nausea, visual disturbances (classically yellow-green visual changes), and bradycardia — are classic features of digoxin toxicity. Digoxin levels should be checked urgently and the dose likely needs to be reduced or temporarily withheld. The erythromycin interaction should be managed with an alternative antibiotic if possible.

Reference: https://www.pharmacyregulation.org/registration-assessment#stage-8-order-16