Moderate
Probable
Description
Doxycycline may enhance warfarin's anticoagulant effect, particularly in patients whose vitamin K intake is already limited.
Mechanism
Doxycycline reduces intestinal flora that produce vitamin K2, potentially decreasing cofactor availability for synthesis of clotting factors II, VII, IX, and X.
Clinical Significance
INR elevations are typically modest but can be clinically relevant in elderly patients or those with dietary vitamin K insufficiency.
Management
Monitor INR after starting doxycycline; counsel patients on consistent dietary vitamin K intake during antibiotic therapy.