ARC19499 sodium is an aptamer that inhibits tissue factor pathway inhibitor (TFPI) , thereby enabling clot initiation and propagation via the extrinsic pathway. The core aptamer binds tightly and specifically to TFPI. ARC19499 sodium blocks TFPI inhibition of both factor Xa and the TF/factor VIIa complex. ARC19499 sodium corrects thrombin generation in hemophilia A and B plasma and restores clotting in FVIII-neutralized whole blood.