Heparin-derivative anticoagulants include unfractionated heparin (UFH), low molecular weight heparin (LMWH), pentasaccharide (fondaparinux), and ultralow molecular weight heparin (ULMWH). Heparin contains an active pentasaccharide sequence that binds to antithrombin (AT). This bond produces conformational changes that accelerate its binding with AT and inactivation of coagulation factors XIIa, XIa, Xa, and IXa and thrombin (IIa). Thrombin and factor Xa are the most sensitive to inhibition by the heparin-AT complex, and the strength of inhibiting thrombin is ten times more sensitive than factor Xa. The UFH anticoagulant response is monitored using activated partial thromboplastin time (APTT), a measurement that is sensitive to inhibition of thrombin and factor Xa. Protamine titration examination is the standard for measuring UFH concentrations in plasma. Recommendations from the American College of Chest Physicians (ACCP) suggest that the APTT target range for the UFH therapy is equivalent to 0.2–0.4 IU/mL with protamine titration or 0.35–0.7 IU/mL with an anti-Xa examination. A new examination is thrombodynamics (TD), measuring the level of development of clots. This method is considered most able to mimic the coagulation process that occurs in vivo compared to other examinations.
Part of the book: Anticoagulation Drugs