Effect sites of anticoagulation agents. The new oral anticoagulation agents directly inhibit one of two major targets in the coagulation cascade. Rivaroxaban and apixaban directly inhibit factor Xa, and dabigatran directly inhibits thrombin. The parenteral anticoagulants that inhibit factor Xa include low-molecular-weight heparin (LMWH) and fondaparinux by antithrombin (AT)-dependent binding. Parenteral direct thrombin inhibitors include argatroban, bivalirudin, and desirudin that also directly inhibit thrombin independent of AT.