Argatroban-d3 is intended for use as an internal standard for the quantification of argatroban by GC- or LC-MS. Argatroban is a reversible inhibitor of thrombin (IC50s = 0.01 and 0.09 μM for the free and clot-bound forms, respectively). It is selective for thrombin over factor Xa, trypsin, plasmin, and tissue plasminogen activator (Kis = 0.0045, 53, 0.19, 25.7, and 87.7 μM, respectively). It inhibits thrombin-induced platelet aggregation in washed isolated guinea pig platelets with an IC50 value of 0.077 μM. Argatroban (3.2 mg/kg, s.c.) decreases thrombus formation in a guinea pig model of iron chloride-induced arterial thrombosis. Formulations containing argatroban have been used in the prevention or treatment of thrombosis in patients with heparin-induced thrombocytopenia.