Vitamin K antagonizes
Corticosteroids
Thrombin formation
Bishydroxy coumarin
Production of clotting factors by liver
Bishydroxy coumarin (dicoumarol), a vitamin K antagonist may be considered as an oral anticoagulant. 
This acts by reducing  the synthesis of certain clotting factors (ll, Vll, lX and X).

Ref : Lippincott’s illustrated reviews for biochemistry , 7th edition.