Phenprocoumon (marketed under the brand names Marcoumar, Marcumar and Falithrom) is an anticoagulant drug, a derivative of coumarin. It is a vitamin K antagonist that inhibits coagulation by blocking synthesis of coagulation factors II, VII, IX and X. It is used for the prophylaxis and treatment of thromboembolic disorders (thrombosis/pulmonary embolism).