Major
simvastatin × warfarin
HMG-CoA reductase inhibitors (statins)×Vitamin K antagonist anticoagulants
Mechanism
Simvastatin inhibits CYP3A4 and to a lesser extent CYP2C9, raising warfarin concentration. Average INR rise is 0.5–1.5 units, with significantly larger increases in some patients.
Management
Check INR 1–2 weeks after starting simvastatin and after dose changes. In warfarin patients, statins with minimal interaction – pravastatin or rosuvastatin – are preferred.
Sources
- Lexicomp: Lexicomp Drug Interactions (2024)— Wolters Kluwer Clinical Drug Information, Inc. Lexi-Interact Online, 2024
- Pharmaceutical Press: Stockley's Drug Interactions, 12th edition (2024)— Preston CL (ed.). Stockley's Drug Interactions. 12th ed. London: Pharmaceutical Press; 2024