Suggested management strategies for warfarin pharmacokinetic drug interactions: S-warfarin (CYP2C9/CYP3A4) and R-warfarin (CYP1A2/CYP3A4/CYP2C19)7
| Inducers26-32 . | Inhibitors18-21,24,32,33 . |
|---|---|
| Monitor the INR within at least 5 d of inducer initiation and then at least once to twice weekly | Monitor the INR 3-5 d after inhibitor initiation (after 1 wk with amiodarone) and adjust warfarin dose accordingly |
| Consider aggressive warfarin dose increases until therapeutic INR is reached | Expect that patients may need a 20%-50% decrease in warfarin dose from baseline |
| Expect that patients may need at least a 50%-100% increase in warfarin dose from baseline | Consider other factors that may independently contribute to elevated INR, such as acute infection and dietary Vitamin K changes |
| Consider seeking an alternative noninteracting drug | Consider seeking an alternative noninteracting drug |
| Monitor the INR within at least 5 d of inducer discontinuation and then at least once to twice weekly | Allow 3-5 d for inhibitor offset (longer for amiodarone) |
| Expect to decrease warfarin dose to approximately preinducer levels | Expect to decrease warfarin dose to approximately preinhibitor levels |
| Inducers26-32 . | Inhibitors18-21,24,32,33 . |
|---|---|
| Monitor the INR within at least 5 d of inducer initiation and then at least once to twice weekly | Monitor the INR 3-5 d after inhibitor initiation (after 1 wk with amiodarone) and adjust warfarin dose accordingly |
| Consider aggressive warfarin dose increases until therapeutic INR is reached | Expect that patients may need a 20%-50% decrease in warfarin dose from baseline |
| Expect that patients may need at least a 50%-100% increase in warfarin dose from baseline | Consider other factors that may independently contribute to elevated INR, such as acute infection and dietary Vitamin K changes |
| Consider seeking an alternative noninteracting drug | Consider seeking an alternative noninteracting drug |
| Monitor the INR within at least 5 d of inducer discontinuation and then at least once to twice weekly | Allow 3-5 d for inhibitor offset (longer for amiodarone) |
| Expect to decrease warfarin dose to approximately preinducer levels | Expect to decrease warfarin dose to approximately preinhibitor levels |