Warfarin is an anti-coagulant, b/c reduces VitK dependent clotting factor production in the plasma.
It has a narrow therapeutic index: with a little Warfarin, the INR = 2, but with a little more, INR = 6+. Highly bound to plasma (95%).
Too much Warfarin leads to bleeding.
Interactions: Increased bleeding (asprin), GI bleeding (NSAIDS), Impairment of Warfarin metabolism and increased bleeding (Quinolone or phenytoin), increased bleeding, maybe bc less VitK (sulfa drugs). Bartituates like phenobarbital increase metabolism, so need more Warfarin.
Also: cholesteramine causes decreased abosorption.