Therapy Type Mechanism No. of Interventional Clinical Trials b Unfractionated heparin or Low molecular weight heparins (Enoxaparin, Dalteparin, Tinzaparin, and others) Sulfated glycosaminoglycans Activation of antithrombin to inhibit thrombin and factor Xa ~23 Aspirin (Acetylsalicylic acid) Small molecule Cyclo-oxygenase inhibitor ~8 Rivaroxaban(Xarelto) Small molecule Direct factor Xa inhibitor ~5 Dipyridamole(Aggrenox) Small molecule Nucleoside transport inhibitor and a phosphodiesterase 3 inhibitor ~3 Clopidogrel(Plavix) Small molecule Irreversible adenosine diphosphate receptor blocker ~3