Cardiovascular Drugs and Medications Q 52
Parenteral anticoagulants work by disrupting:
A. Formation of thromboplastin.
B. Conversion of prothrombin to thrombin.
C. Vitamin K-dependent clotting factors.
D. Conversion of prothrombin to fibrin.
Correct Answer: B. Conversion of prothrombin to thrombin
Parenteral anticoagulants such as heparin work by disrupting the conversion of prothrombin to thrombin. Prothrombin is transformed into thrombin by a clotting factor known as factor X or prothrombinase; thrombin then acts to transform fibrinogen, also present in plasma, into fibrin, which, in combination with platelets from the blood, forms a clot (a process called coagulation).
Option A: Tissue thromboplastin is formed in the extrinsic pathway as tissue is damaged. Blood clotting is known as tissue factor or tissue thromboplastin. Tissue factor is found in many of the cells of the body but is particularly abundant in those of the brain, lungs, and placenta.
Option C: Oral anticoagulants work by interfering with vitamin K-dependent clotting factors. The vitamin K-dependent coagulation factors are factors II, VII, IX, X, proteins C and S. Combined deficiency of the vitamin K-dependent factors may result from missense mutations in the genes for vitamin K reductase (VKORC-1) or gamma-glutamyl carboxylase.
Option D: Prothrombin does not convert to fibrin. Thrombin is produced by proteolytic activation of the precursor, prothrombin, in the first committed step of the pathway to thrombus formation. Thrombin catalyzes thrombus formation and also a series of reactions that both positively and negatively regulate flux through the coagulation cascade.