How does unfractionated heparin work?

How does unfractionated heparin work?

• A. Inhibits IIa (thrombin) by binding to antithrombin III
• B. Directly inhibits factor Xa
• C. Activates plasmin
• D. Inhibits fibrinogen conversion to fibrin

Answer: (A)

Unfractionated heparin works by binding to antithrombin III and dramatically increasing ATIII’s ability to inactivate key coagulation enzymes. The hallmark effect is the inactivation of thrombin (IIa) through the heparin-ATIII complex, which forms a bridge to thrombin and stops its activity. This ATIII-mediated inhibition is the main reason UFH is an effective anticoagulant. It also reduces activity against factor Xa via ATIII, but the classic description focuses on thrombin inhibition through ATIII. The other options describe mechanisms you’d see with different drugs or processes: directly activating plasmin to dissolve clots, or directly blocking the conversion of fibrinogen to fibrin, are not how UFH works. So the statement that UFH inhibits thrombin by binding to antithrombin III best captures its primary mechanism.

Unfractionated heparin works by binding to antithrombin III and dramatically increasing ATIII’s ability to inactivate key coagulation enzymes. The hallmark effect is the inactivation of thrombin (IIa) through the heparin-ATIII complex, which forms a bridge to thrombin and stops its activity. This ATIII-mediated inhibition is the main reason UFH is an effective anticoagulant. It also reduces activity against factor Xa via ATIII, but the classic description focuses on thrombin inhibition through ATIII.

The other options describe mechanisms you’d see with different drugs or processes: directly activating plasmin to dissolve clots, or directly blocking the conversion of fibrinogen to fibrin, are not how UFH works. So the statement that UFH inhibits thrombin by binding to antithrombin III best captures its primary mechanism.