Atorvastatin × tacrolimus

Tacrolimus is a weak CYP3A4 inhibitor; atorvastatin is a substrate. Atorvastatin plasma levels rise by 30–50%, raising myalgia risk. Tacrolimus itself can cause myopathy.

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 transplant patients needing a statin, use pravastatin up to 20 mg/day or fluvastatin (minimal tacrolimus interaction). Atorvastatin is acceptable when no alternative exists, capped at 10 mg/day with creatine kinase every 4 weeks.