FVIIa

Factor VIIa (FVIIa) is the activated form of factor VII, a vitamin K–dependent serine protease produced in the liver. It circulates primarily as the zymogen FVII and gains hemostatic function when it forms a complex with tissue factor (TF) exposed at sites of vascular injury.

In the presence of TF, the TF–FVIIa complex initiates the extrinsic pathway of coagulation by activating factor X to Xa and, to a lesser extent, factor IX to IXa. This triggers thrombin generation and thrombus formation. FVIIa can also contribute to hemostasis by promoting FX activation on TF-bearing surfaces, with amplification of the coagulation cascade. The overall effect is rapid formation of a fibrin clot at the site of injury.

Recombinant activated FVII (rFVIIa) is used clinically under brand names such as NovoSeven. Approved indications include control of bleeding in patients with hemophilia A or B who have inhibitors to FVIII or FIX, congenital FVII deficiency, and acquired hemophilia. It is sometimes employed off-label for uncontrolled bleeding in surgical, traumatic, obstetric, or other critical bleeding situations, though such use requires careful assessment of thrombotic risk.

Adverse effects include thromboembolism and, less commonly, hypersensitivity reactions. Its use is cautioned in patients with elevated thrombotic risk. Pharmacokinetically, FVIIa has a relatively short half-life and is administered intravenously, with dosing individualized to the specific indication and clinical response.

History and context place FVIIa as a key, tightly regulated component of coagulation, leveraged therapeutically in select bleeding disorders where standard factor replacement is inadequate or contraindicated.