Warfarin is an anti-coagulant used to prevent heart attacks, strokes and the formation of blood clots. It interferes with the use of vitamin K in the required carboxylation of several vitamin K-dependent proteins in the clotting cascade, preventing the initiating of clotting. (±)-Warfarin is a racemic mixture of two optically active isomers. (-)-Warfarin differs from (+)-warfarin by being five times more potent as a vitamin K antagonist. However, the two isomers are metabolized in vivo by different pathways, and (-)-warfarin has a shorter terminal elimination half-life (24-33 hours) than (+)-warfarin (35-58 hours).