Minor
Suspected
Description
Amoxicillin may slightly potentiate warfarin by reducing gut flora that synthesize vitamin K2, though the effect is generally small and inconsistent.
Mechanism
Broad-spectrum antibiotic activity against intestinal bacteria that produce menaquinones (vitamin K2), potentially reducing cofactor availability for hepatic coagulation factor synthesis.
Clinical Significance
The interaction is usually modest; however, patients with marginal dietary vitamin K intake may show clinically significant INR increases.
Management
Consider INR check midway through and after completing a course of amoxicillin, especially in patients with variable diets.