Atorvastatin × Metronidazole

Metronidazole does not block CYP3A4 but increases myopathy risk with statins (mechanism not fully established; reported in post-marketing data). The effect is rare.

Pain and weakness in large muscle groups (thighs, shoulders, calves), dark urine, elevated creatine kinase. Symptoms usually appear 2–6 weeks after starting the combination.

For short metronidazole courses (5–7 days), no special adjustment. In patients with myopathy risk factors, check creatine kinase on muscle symptoms. For prolonged metronidazole therapy, temporarily reduce atorvastatin.