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Simvastatin and clarithromycin — GPhC CRA MCQ

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ModerateDrug InteractionsSimvastatin and clarithromycinGPhC CRA

A 58-year-old man taking simvastatin 40mg at night is prescribed clarithromycin 500mg twice daily for pneumonia. He has muscle aches after a recent gym session and eGFR is 70mL/min/1.73m2. What is the most important interaction to flag?

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Correct answer: D — Clarithromycin increases simvastatin exposure and myopathy risk

Clarithromycin strongly inhibits CYP3A4 and can increase simvastatin levels, increasing risk of myopathy and rhabdomyolysis. The prescriber should be contacted to withhold simvastatin temporarily or choose an alternative antibiotic where appropriate. Existing muscle aches make counselling and safety-netting important. The interaction is not loss of statin effect.

Reference: BNF Simvastatin interactions; BNF Clarithromycin