PHAR3816 Lecture Notes - Lecture 13: Vitamin K Antagonist, Lactone, Warfarin
22 Jul 2018
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With warfarin, primarily the extrinsic pathway we"re stopping. Regeneration step inhibited, thus formation of activated clotting factors inhibited. Warfarin activity in the liver, metabolized by cyp2c9 but also r- enantiomer is metabolized by other enzymes. S-warfarin has the major effect in patient"s body- as vitamin k reductase. Some effect with r enantiomer but s is 4x potent. It acts as a reductase stopping the formation of vitamin k (via oxidization)- Vitamin k is good for converting clotting factors to pre functional state to functional state. i. e. proclotting factors exist but not in functional form. Warfarin is a vitamin k antagonist, and blocks vitamin k being recycled because they are similar in structure. A correction factor the international sensitivity index or isi is applied to pr as the sensitivity of commercial thromboplastin reagents is variable. We don"t measure warfarin, but prothrombin time i. e. activity of warfarin and clotting time. Prothrombin ratio and inr relative to international sensitivity index.
