FREE! Stop That Clot: Haemostasis and anticoagulants
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Direct Factor Xa Inhibitors

Rivaroxaban and apixaban have only been well studied and licensed for use in the prophylaxis of VTE in major elective orthopaedic surgery, and prophylaxis of VTE in AF. This drug is administered orally and has a predictable therapeutic response. It binds to activated factor X and prevents the conversion of prothrombin to thrombin. Response can be tested via PT (Table 3) but is not normally required. There is no specific antagonist available. There are some drug-drug interactions possible with rivaroxaban, but not as many as with warfarin.

Direct Thrombin Inhibitors

Derived from hirudin found in the saliva of medicinal leeches (Rang et al., 2012), these drugs bind directly to thrombin and prevent the conversion of fibrinogen to fibrin (Figure 3). Dabigatran is an oral anticoagulant with far fewer interactions than warfarin but for which there is currently no reversal agent if haemorrhage occurs. It is also used for prophylaxis in elective major orthopaedic surgery and VTE in AF. Bivalirudin is an injectable direct thrombin inhibitor.
Trials have demonstrated increased risk for patients with AF and valve disease or those with artificial heart valves when prescribed oral anticoagulants other than warfarin (January et al., 2014).

Antiplatelet Drugs

Platelet activation is critical to haemostasis (Figure 2) but is also involved in development of arterial thrombosis in atherosclerosis. Antiplatelet drugs act to inhibit platelet activation.
Figure 2: Haemostasis

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