Why is the patient initially started on heparin rather than warfarin?
Heparin acts within seconds by enhancing the rate of inactivation of clotting factors by antithrombin III to produce an anticoagulant effect, as measured by the partial thromboplastin time (PTT). In contrast, warfarin is a vitamin K antagonist that affects the production of clotting factors II, VII, IX, and X in the liver, and the half-life of these factors is measured in hours to days. Factor VII has the shortest half-life--about 6 hours. Thus, several days of warfarin therapy may be needed to produce adequate anticoagulation, as measured by the prothrombin time (PT).
How does one reverse the effects of warfarin?
Depending upon how quickly the effects need to be reversed, one can give vitamin K and, if the need is relatively urgent, fresh frozen plasma.
How does one reverse the effects of heparin?
Protamine sulfate will reverse the action of heparin within minutes. This is a situation where the correction studies mentioned above are quite useful. With a patient who has heparin in his/her system, the coagulation parameters will not correct when normal plasma is added to their sample. This is effectively what happens in the patient--you can give FFP until the "cows come home" and it will not reverse the effects of heparin. Protamine in the proper dosage is needed for urgent reversal. Otherwise, the half-life of heparin is generally short and, if time allows, one can discontinue the drug and wait for it to degrade.
