Review Question - QID 101370

Unfractionated heparin and low-molecular weight heparin (LMWH) bind to antithrombin III. Enoxaparin (trade name Lovenox) is a LMWH.

When unfractionated or LMWH bind to antithrombin III (ATIII), they enhance ATIII's ability to inactivate factor Xa, thereby disrupting the coagulation cascade. Additionally, unfractionated heparin has a long pentasaccharide chain that allows it to bind to both antithrombin and thrombin itself, deactivating thrombin. LMWHs, such as enoxaparin, have a shorter pentasaccharide chain, making them unable to bind to both antithrombin and thrombin. Therefore, LMWH has greater activity against Factor Xa than it does thrombin, while unfractionated heparin has equal activity against both Factor Xa and thrombin.

deBreuil et al. report that the safety and efficiacy of LMWH is equal to that of inpatient unfractionated heparin for the treatment of venous thromboembolism. The authors also note that patients with venous thromboembolism who have cancer show a survival advantage beyond treatment for venous thromboembolism when treated with LMWH compared to unfractionated heparin. For this reason, the ACCP recommend 3-6 months of treatment with LMWH in these patients.

Bauer gives an overview of newer anticoagulants including direct thrombin inhibitors and factor Xa inhibitors. Researchers continue to attempt to develop an oral anticoagulant that is as safe and effective as warfarin but does not require regular monitoring of INR. LMWH are administered subcutaneously.

Illustration A shows the difference between unfractionated heparin and LMWH as they bind to ATIII.

Incorrect answers:
Answer 1: Aspirin is an antiplatelet agent.
Answer 2: Warfarin is a vitamin K antagonist.
Answer 3: Dabigatran is a direct thrombin inhibitor.
Answer 4: Rivaroxaban is a direct factor Xa inhibitor.