• Stephen Boulanger

Warfarin Part One: Overview of Use and Dosing

Warfarin is used to treat people with deep vein thrombosis, pulmonary embolism, artificial heart valves and other conditions. Some patients with a moderate to high risk of stroke benefit from Warfarin as well. Monitoring and Dosing The International Normalized Ratio (INR) is used to measure blood clotting time. The higher the INR, the longer it takes for the blood to clot and the “thinner” the blood is considered. The goal INR for most indications is 2.0-3.0, but for people with mechanical heart valves or recurrent clots the goal is 2.5-3.5.

The goal of warfarin therapy is to decrease the clotting tendency of blood, not to prevent clotting completely. A patient’s response to warfarin must therefore be monitored carefully through daily blood tests that determine their INR which, in turn, will determine how to adjust their next dose. The clotting factors dependent upon vitamin K have a long half life (60 hours), so it can take 5-7 days for warfarin to inhibit them and bring them down to a therapeutic level. INR should be monitored every 2-3 days when warfarin is initiated, and then every 1-4 weeks based on stability.