विवरण
Levothyroxine enhances the catabolism of vitamin K-dependent clotting factors, amplifying warfarin's anticoagulant effect and raising the risk of bleeding when thyroid replacement is initiated or doses are increased.
तंत्र
Thyroid hormone accelerates the hepatic catabolism of vitamin K-dependent coagulation factors (II, VII, IX, X); as circulating factor levels fall, warfarin's anticoagulant effect is potentiated, resulting in INR elevation.
नैदानिक महत्व
Well-documented pharmacodynamic interaction; INR may increase by 20–50% when levothyroxine is initiated or dose-escalated in patients on stable warfarin therapy.
प्रबंधन
Monitor INR within 4–6 weeks of starting or adjusting levothyroxine; reduce warfarin dose prophylactically by 10–25% when initiating thyroid replacement; increase monitoring until INR is stable.