The correct answer is the option (A) heparin.
DVT refers to a condition called the deep vein thrombosis when a blood clot occurs in the deep veins of the legs in the body. PE refers to the Pulmonary embolism when a blood clot is observed in the artery of the lungs.
The drugs used in the treatment of DVT and PE are called the anticogulants which interfere with the process of blood clot formation. Heparin and warfarin are the two older anticoagulants used in the prevention and treatment and prevention of DVT and PE. Heparin is given intravenously to treat DVT and PE whereas, warfarin is taken as a tablet or pill through the mouth. Heparin allows the body's clot lysis mechanism to break down the existing clots and it is also a natural anticoagulant produced by the basophils and the mast cells of the blood.
Thus, heparin is the old drug that is used subcutaneously to prevent DVT in high-risk patients and intravenously to treat DVT and PE.