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Simvastatin and clarithromycin — GPhC CRA MCQ

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ModerateDrug InteractionsSimvastatin and clarithromycinGPhC CRA

A prescription for clarithromycin 500 mg twice daily is presented for a 70-year-old man taking simvastatin 40 mg at night, amlodipine 5 mg daily and metformin 500 mg twice daily. He has normal renal function and no known drug allergies. What is the most important interaction to flag?

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Correct answer: C — Clarithromycin can increase simvastatin exposure and myopathy risk

Clarithromycin inhibits CYP3A4 and can markedly increase simvastatin concentrations. This increases the risk of myopathy and rhabdomyolysis, so simvastatin should usually be withheld during the macrolide course or an alternative antibiotic considered. Metformin is not the main safety concern in this scenario.

Reference: https://www.pharmacyregulation.org/students-and-trainees/pharmacist-education-and-training/registration-assessment