Drug interactions
Fluorouracil + Warfarin
Severity: Major
Fluorouracil and Warfarin: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Fluorouracil can substantially raise INR in patients taking warfarin, leading to bleeding. The effect may be unpredictable and has been reported with systemic fluorouracil regimens.
What this interaction means in plain words
Fluorouracil and Warfarin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Fluorouracil belongs to Oncology; Warfarin belongs to Cardiovascular.
Why it happens
Likely inhibition of CYP2C9-mediated warfarin metabolism, though the mechanism is not fully established.
What to do
Monitor INR closely, at least weekly during chemotherapy cycles, and reduce the warfarin dose as required. Consider alternative anticoagulation if INR control is erratic.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Other interactions of Fluorouracil
Frequently asked questions
Can I take Fluorouracil with Warfarin?
MediHelp rates the interaction as major. Fluorouracil and Warfarin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Fluorouracil can substantially raise INR in patients taking warfarin, leading to bleeding. The effect may be unpredictable and has been reported with systemic fluorouracil regimens.
How serious is the interaction between Fluorouracil and Warfarin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor INR closely, at least weekly during chemotherapy cycles, and reduce the warfarin dose as required. Consider alternative anticoagulation if INR control is erratic.
What other medicines interact with Warfarin?
MediHelp also lists interactions of Warfarin with, for example, Defibrotide, Ketorolac, Abciximab. The full list is on the Warfarin page.
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