Edoxaban-d6 is intended for use as an internal standard for the quantification of edoxaban by GC- or LC-MS. Edoxaban is an orally bioavailable and potent inhibitor of factor Xa (Kis = 0.561 and 0.903 nM for free and complexed human factor Xa, respectively). It is >10,000-fold selective for factor Xa over thrombin, FVIIa/sTF, FXIa, tPA, aPC, trypsin, plasmin, and chymotrypsin. Edoxaban prolongs prothrombin, activated partial thromboplastin, and thrombin clotting times in a concentration-dependent manner ex vivo in human plasma. Oral administration of edoxaban (0.5-12.5 mg/kg) reduces thrombus formation and prolongs prothrombin time in a dose-dependent manner in rat and rabbit models of venous stasis thrombosis. It also reduces thrombus formation in a rat model of platinum wire-induced venous thrombosis. Formulations containing edoxaban have been used to prevent stroke in patients with atrial fibrillation.