medicinal substances that suppress the activity of the clotting system of the blood and obstruct the formation of thrombi.

Anticoagulants affect various links in the process of blood clotting. One may distinguish anticoagulants with direct effect (heparin, hirudin, etc.), which lower the activity of thrombin in the blood; and anticoagulants with indirect effect (dicoumarin, “neodikumarin,” or Pelentan, phenin-dione, “sinkumar,” etc.), which disrupt the formation in the liver of prothrombin, which participates in blood coagulation. Certain preparations that are not classed as anticoagulants also decrease the coagulability of the blood, such as sodium citrate, sodium salicylate, and acetylsalicylic acid. (These bind the calcium in blood, which plays a part in blood clotting.) Anticoagulants are used in myocardial and pulmonary infarctions, in thrombotic and embolic insults, in cases of thrombophlebitis, and in other cases; they are used prophylactically in atherosclerosis of the coronary arteries and the cerebral blood vessels and in rheumatic mitral defects of the heart; in surgery they are used to prevent formation of thrombi in the postoperative period. Anticoagulants are contraindicated in cases of ulcers, kidney stones, diseases that incline to hemorrhage, and pregnancy.