Thrombin-like snake venom serine protease that acts as an anticoagulant. It cleaves fibrinogen (FGA) to split off the A-fibrinopeptides (A, AY and AP), but not the B-fibrinopeptide. The resulting fibrin polymers are imperfectly formed and much smaller in size (1 to 2 um long) than the fibrin polymers produced by the action of thrombin. These ancrod-induced microthrombi are friable, unstable, urea-soluble and have significantly degraded alpha chains. They do not cross-link to form thrombi. They are markedly susceptible to digestion by plasmin and are rapidly removed from circulation by either reticuloendothelial phagocytosis or normal fibrinolysis, or both. Anticoagulation through the removal of fibrinogen from the blood is rapid, occurring within hours following its administration. It does not activate plasminogen and does not degrade preformed, fully cross-linked thrombin fibrin. It also reduces the level of plasminogen activator inhibitor (PAI) and may stimulate the release of tissue plasminogen activator (PLAT) from the endothelium. The profibrinolytic effect of these 2 actions appears to be limited to local microthrombus degradation. Selective cleavage of Arg-|-Xaa bond in fibrinogen, to form fibrin, and release fibrinopeptide A. The specificity of further degradation of fibrinogen varies with species origin of the enzyme. Monomer. Expressed by the venom gland. Used for the treatment of acute ischemic stroke. Until 2002 was available under the brand name Arvin or Arwin (Knoll). Is actually available under the brand name Viprinex (Abbott). Belongs to the peptidase S1 family. Snake venom subfamily. Ancrod entry Viprinex entry