Coagulation Factor XI / activated Factor XIa

Class

Monoclonal antibody anticoagulant, dual-acting (blocks both activation of Factor XI and downstream activity of Factor XIa)

Pathway

Intrinsic (contact activation) coagulation cascade — developed for dialysis-vascular-access thrombosis prevention without impairing hemostasis

Factor XI (FXI) is a plasma protein that participates in the intrinsic, or contact activation, pathway of blood clotting. Once activated to Factor XIa, it propagates the coagulation cascade by activating Factor IX, amplifying thrombin generation and stabilizing clot formation. Unlike the tissue factor-driven pathway that initiates hemostasis after injury, the intrinsic pathway is thought to contribute mainly to pathological clot amplification, particularly on artificial or damaged vascular surfaces such as catheters, stents, or dialysis vascular access sites. Because people with inherited Factor XI deficiency generally have only mild bleeding tendencies, blocking this factor is viewed as a way to reduce thrombosis while largely sparing the hemostatic clotting needed to stop bleeding after injury. This mechanism uses a monoclonal antibody engineered to act at two points: preventing the activation of Factor XI to XIa, and independently neutralizing the enzymatic activity of any XIa that still forms. This dual action is intended to provide more complete pathway suppression than blocking either step alone. Such approaches are being explored for prevention of clot formation in settings of recurrent vascular injury or foreign-surface exposure, including chronic hemodialysis access, where reducing device-related thrombosis without substantially raising bleeding risk is a central clinical goal.