Name: Warfarin (Coumadin)
Class: Antithrombotic Agent (Oral Anticoagulant)
Mechanism: Vitamin K antagonist ® ¯ g-carboxylation of thrombin, factors, VII, IX, & X, and proteins C & S ® inhib. of synth. of active coagulation factors. Does not alter organized clots.
Absorption: Oral.
Dist.: Almost completely bound (99%) to plasma proteins (mainly albumin).
Metabolism.: Microsomal enzymes in liver and kidneys.
Excretion, t½: Urine and stool.
Toxicity/S.E.s: Hemorrhage, hypersensitivity rxns., fetal toxicity. “Purple Toe” synd. (necrosis) assoc. w/protein C deficiency. During pregnancy, can cause birth defects and abortion. Many drug interactions.
Utility: Prevention of recurrent thrombotic events following acute Rx w/heparin. Valvular heart disease, prosthetic cardiac valves, AMI, atrial fibrillation.
Special Features: Max. effects require 2-7 days. Init. response may be procoagulant due to inhib. of protein C. Should have 6 day overlap w/heparin. Monitor PT.