Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the mechanism of action of tranexamic acid?

1. Enhances clot formation by stimulating platelets

2. Inhibits breakdown of clots by blocking plasminogen and plasmin binding to fibrin

3. Inhibits thrombin activity

4. Increases fibrinolysis

The correct answer is: Inhibits breakdown of clots by blocking plasminogen and plasmin binding to fibrin

Tranexamic acid works primarily by inhibiting the breakdown of fibrin clots, which is essential in maintaining hemostasis. It achieves this by preventing plasminogen and plasmin from binding to fibrin, thereby reducing the process of fibrinolysis—where the body breaks down clots once they are no longer needed. By blocking this action, tranexamic acid helps to stabilize clots and can be beneficial in conditions where excessive bleeding occurs, such as in trauma, surgery, or bleeding disorders. The other options suggest mechanisms that do not accurately reflect the role of tranexamic acid. For instance, enhancing clot formation by stimulating platelets implies an interaction that is not the primary function of the drug. Similarly, inhibiting thrombin activity would imply a direct effect on one of the key enzymes in the coagulation cascade, which is not the mechanism of tranexamic acid. Finally, increasing fibrinolysis directly contradicts the role that tranexamic acid plays by inhibiting this very process. Thus, the understanding of tranexamic acid's action allows for appropriate use in clinical scenarios where hemostatic support is necessary.