Warfarin Overdose Answers 1. Heparin binds to AT III to enhance its action from a slow to rapid inactivator of thrombin, Xa, IXa. Describe your laboratory evaluation and your reasoning and indicate the most likely diagnosis. This is a case of warfarin overdose caused by potentiation by cimetidine which competes for protein binding and increases the free plasma level of warfarin. Drugs may also reduce the anticoagulant effect by stimulating hepatic enzymes and warfarin metabolism - sedatives, oral contraceptives, steroids, antacids.
Appropriate therapy is to decrease warfarin dose or discontinue cimetidine.
Fresh frozen plasma or Vitamin K can be given to normalize the PT and PTT rapidly if severe bleeding is occuring.