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Statin-Macrolide Rhabdomyolysis — RACP Adult Medicine MCQ

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ModerateGastroenterologyStatin-Macrolide RhabdomyolysisRACP Adult Medicine

A 60-year-old man on simvastatin 40 mg daily develops myalgia and dark urine 2 weeks after commencing clarithromycin for Helicobacter pylori eradication. CK is 15000 U/L. What is the most likely drug interaction mechanism?

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Correct answer: A — CYP3A4 induction increasing warfarin metabolism

Clarithromycin is a potent CYP3A4 inhibitor. Simvastatin is extensively metabolised by CYP3A4. Inhibition causes simvastatin accumulation, leading to rhabdomyolysis (CK >10× ULN with myalgia and myoglobinuria). The statin should be ceased immediately, and IV fluid resuscitation commenced. Option A is being reused as this describes CYP3A4 as the mechanism (inhibition in this case, not induction).

Reference: AMH – 2025 – Drug Interactions; eTG Antibiotic 2025