rFVIIa mechanisms of action. At pharmacologic levels, rFVIIa complexes with tissue factor (TF) from the subendothelium and on the surface of cells at the site of tissue damage. rFVIIa also binds to the surface of activated platelets. Factor X (FX) is activated by rFVIIa-TF and rFVIIa on the surface of platelets to FXa, which complexes with FVa to catalyze the conversion of prothrombin (FII) to thrombin (FIIa). Xa indicates FXa; Va, Fva; II, FII; Iia, FIIa. Adapted from Poon.⁶