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Erythromycin-simvastatin interaction — GPhC CRA MCQ

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ModerateDrug InteractionsErythromycin-simvastatin interactionGPhC CRA

A 60-year-old man with type 2 diabetes and a penicillin allergy (rash) presents with a prescription for erythromycin 500 mg four times daily for community-acquired pneumonia. He is also taking simvastatin 40 mg at night. What is the most important interaction to flag?

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Correct answer: B — Erythromycin inhibits CYP3A4, increasing simvastatin levels and the risk of rhabdomyolysis

Erythromycin is a potent inhibitor of CYP3A4. Simvastatin is extensively metabolised by CYP3A4, and inhibition by erythromycin can lead to markedly elevated simvastatin levels, significantly increasing the risk of myopathy and rhabdomyolysis. The BNF advises that this combination should be avoided. The prescriber should be contacted to discuss either withholding simvastatin during the antibiotic course or choosing an alternative antibiotic.

Reference: BNF Drug Interactions