Fosaprepitant and Warfarin interaction
Fosaprepitant and Warfarin: both prescribing labels describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Fosaprepitant (FOCINVEZ) label · effective 2026-03-30
Warfarin (a CYP2C9 substrate): Risk of decreased INR of prothrombin time; monitor INR in 2–week period, particularly at 7 to 10 days, following initiation of FOCINVEZ.
Decrease in INR with Concomitant Warfarin Coadministration of fosaprepitant with warfarin, a CYP2C9 substrate, may result in a clinically significant decrease in the International Normalized Ratio (INR) of prothrombin time [see Clinical Pharmacology ( 12.3 )] .
Monitor the INR in patients on chronic warfarin therapy in the 2-week period, particularly at 7 to 10 days, following initiation of FOCINVEZ with each chemotherapy cycle [see Drug Interactions ( 7.1 )] .
Examples birth control pills, transdermal systems, implants, and certain intrauterine systems CYP2C9 Substrates Warfarin Clinical Impact Decreased warfarin exposure and decreased prothrombin time (INR) [see Warnings and Precautions ( 5.4 ) and Clinical Pharmacology ( 12.3 )] .
Intervention In patients on chronic warfarin therapy, monitor the prothrombin time (INR) in the 2-week period, particularly at 7 to 10 days, following administration of FOCINVEZ with each chemotherapy cycle.
From the Warfarin (Warfarin Sodium) label · effective 2026-06-24
Closely monitor INR if a concomitant drug is a CYP2C9, 1A2, and/or 3A4 inhibitor or inducer.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.