Moderate
Established
Mô tả
Trimethoprim (alone or in combination as TMP-SMX) increases warfarin's anticoagulant effect through CYP2C9 inhibition, raising INR and bleeding risk.
Cơ chế
Trimethoprim inhibits CYP2C9, reducing the metabolism of S-warfarin; the sulfonamide component of TMP-SMX also displaces warfarin from plasma proteins.
Ý nghĩa lâm sàng
INR elevations averaging 50–100% have been documented; bleeding complications including epistaxis, bruising, and GI hemorrhage have been reported.
Xử trí
Monitor INR within 3–5 days of starting TMP or TMP-SMX; consider reducing warfarin dose by ~10–25% preemptively in high-risk patients.