Heparin, Fondaparinux, and Novel Oral Anticoagulants - Pathophysiology Anticoagulation with parenteral (intravenous or subcutaneous) and oral anticoagulants is the mainstay of VTE therapy. Typically, one of the parenteral agents (e.g. heparin, LMWH, or fondaparinux) or a new oral anticoagulant (e.g. rivaroxaban) is started first. The patient may be transitioned to a traditional oral anticoagulant (e.g. warfarin) for chronic anticoagulation. - Unfractionated heparin (UFH): Inhibits the function of thrombin as well as Xa by inducing conformational changes in antithrombin, allowing it to bind the enzymes better. - Low molecular weight heparin (LMWH): Functions similar to UFH, but due to the smaller average heparin chain length, accelerates the bridging of AT with Xa only, and not thrombin. - Fondaparinux: A pentasaccharide sequence that directly binds to AT (at an allosteric site) and induces a conformational change allowing it to bind and inhibit factor Xa only. - Rivaroxaban: A new oral anticoagulant that inhibits factor Xa by binding to its active site. #Pharmacology #Pathophysiology #Heparins #LMWH #UFH #DOAC #Dabigatran #Apixaban #Rivaroxaban #Fondaparinux #NOAC #Mechanism