 anticoagulants are drugs which prevent formation of clots. First thing is not to confuse anticoagulant drugs with antiplatelet drugs. Antiplatelet drugs are mainly required to counter excess hemostatic process in arteries where there is high shear stress. While anticoagulant drugs are mainly required for excess hemostatic process in veins like deep venous thrombosis, pulmonary emboli. However, in treatment protocols they may be given together to supplement each other. So we know this is coagulation pathway and both pathways converge on to the formation of thrombin. This factor 2 is nothing but pro-thrombin and the activated factor 2 is thrombin. Now thrombin is required in bust for conversion of fibrinogen to fibrin. This factor 1 is fibrinogen. Anticoagulant drugs focus on limiting thrombin generation or inhibiting thrombin activity. So either you limit the generation of thrombin or whatever is formed inhibit its activity. Thrombin generation is limited by giving vitamin K antagonist. Now vitamin K is required for regeneration of factors 2, 7, 9 and 10. How to remember this? By anemonic toss not. T for 2, S for 7, N for 9 and again T for 10. Toss not. Factor 10 activity is also inhibited by giving heparin. So if factor 10 is inhibited there will be no formation of thrombin. So heparin inhibits this activity. Actually it binds with antithrombin 3 and inhibits factor 9, 10, 11 and 12. Now factor 10, 8 direct inhibitors are also available. Direct thrombin inhibitors like dabicatran inhibit the activity of thrombin.