Critical
Fluorouracil × Warfarin
Antineoplastic, pyrimidine analogue (5-FU)×Vitamin K antagonist anticoagulants
Mechanism
5-FU inhibits CYP2C9 (S-warfarin metabolism) and impairs vitamin K-dependent clotting factor synthesis through direct myelotoxicity. INR rises 2-4 fold within 5-10 days. Fatal bleeding cases reported.
Symptoms
Gum/nose bleeding, haematuria, bloody stool within 5-10 days. INR above 5.0.
Management
If possible – switch warfarin to LMWH during chemotherapy. If warfarin needed – reduce by 30-50% with weekly INR.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Sources
- AEMPS: Ficha tecnica de Fluorouracilo (5-FU) (2023)– AEMPS CIMA, 2023