Fluorouracil and Warfarin interaction
Fluorouracil 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 Fluorouracil label · effective 2026-02-09
Increased Risk of Elevated INR with Warfarin: Concurrent administration with warfarin can result in clinically significant increases in coagulation parameters: Closely monitor INR and prothrombin time.
Increased Risk of Elevated International Normalized Ratio (INR) with Warfarin Clinically significant elevations in coagulation parameters have been reported during concomitant use of warfarin and fluorouracil.
While pharmacokinetic data are not available to assess the effect of fluorouracil administration on warfarin pharmacokinetics, the elevation of coagulation times that occurs with the fluorouracil prodrug capecitabine is accompanied by an increase in warfarin concentrations.
Closely monitor patients receiving concomitant coumarin-derivative anticoagulants such as warfarin for INR or prothrombin time in order to adjust the anticoagulant dose accordingly [see Drug Interactions (7) ].
Anticoagulants and CYP 2C9 Substrates Elevated coagulation times have been reported in patients taking fluorouracil concomitantly with warfarin.
From the Warfarin (Warfarin Sodium) label · effective 2026-06-24
Inhibitors of CYP2C9, 1A2, and/or 3A4 have the potential to increase the effect (increase INR) of warfarin by increasing the exposure of warfarin.
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.