Which agent is categorized as unfractionated heparin?

• A. Low-molecular-weight heparin
• B. Unfractionated heparin
• C. Fondaparinux
• D. Argatroban

Answer: (B)

Unfractionated heparin is the older, heterogeneous mix of heparin chains that requires antithrombin to inactivate thrombin and factor Xa. Because its effect varies based on chain length and interactions with blood proteins and the endothelium, its anticoagulant activity is monitored and adjusted using the aPTT, and dosing can be rapidly reversed with protamine. The other agents are different kinds of anticoagulants: low-molecular-weight heparins are shorter chains with more predictable pharmacokinetics and mainly inhibit factor Xa with less impact on thrombin; fondaparinux is a synthetic Xa inhibitor that acts via antithrombin; and argatroban is a direct thrombin inhibitor not based on heparin.