Which of the following statements is false about unfractionated heparin?
**Core Concept**
Unfractionated heparin (UFH) is a highly sulfated glycosaminoglycan that acts as an anticoagulant by enhancing the activity of antithrombin III (AT III), thereby inhibiting the conversion of prothrombin to thrombin and subsequent clot formation. UFH is commonly used for the treatment and prevention of thromboembolic disorders.
**Why the Correct Answer is Right**
UFH works by binding to the serpin antithrombin III (AT III), which is then able to inactivate several key enzymes in the coagulation cascade, including thrombin (factor IIa) and factors Xa, IXa, XIa, and XIIa. This results in a decrease in the formation of fibrin clots and the prevention of thrombosis. UFH also has a high affinity for the thrombin-thrombomodulin complex, which further enhances its anticoagulant effects.
**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true, as UFH is indeed a highly charged molecule that binds to the antithrombin III (AT III) molecule.
**Option B:** This statement is true, as UFH is commonly used for the treatment and prevention of thromboembolic disorders, such as deep vein thrombosis and pulmonary embolism.
**Option C:** This statement is false, as UFH is not a vitamin K antagonist. Instead, it works by enhancing the activity of antithrombin III (AT III) to inhibit the coagulation cascade.
**Clinical Pearl / High-Yield Fact**
UFH requires careful monitoring of activated partial thromboplastin time (aPTT) to prevent both thrombosis and bleeding. It is essential to adjust the dosing of UFH based on the patient's aPTT levels to achieve an optimal therapeutic effect.
**Correct Answer:** C. UFH is not a vitamin K antagonist.