Which of the following is true about Warfarin?

A) Warfarin inhibits Vitamin E dependant clotting factors 6 and 8.
B) Warfarin promotes production of endogenous anticoagulants such as protein S.
C) Warfarin inhibits carboxylation of clotting factors 9 and 10.
D) Warfarin inhibits only the extrinsic pathway and so Heparin is commonly prescribed as well.
E) Warfarin is used in the acute setting for thrombolysis.


The answer is C.

Warfarin acts an an anticoagulant by blocking the ability of Vitamin K to carboxylate the Vitamin K dependent clotting factors, this results in the production of non-functional clotting factors 2,7,9 and 10 but also the production of non-functional protein C and protein S which are endogenous anticoagulants. This means that initially warfarin makes patients hypercoagulable for the first 24-48 hours - during this initial period heparin is commonly prescribed.

Heparin inhibits antithrombin with immediate action and through indirect inhibition heparin will impair clotting factors 7a, 9a, 10a, 11a and thrombin.