The decreased viscosity is directly attributable to lowered fibrinogen levels and leads to important improvements in blood flow and perfusion of the microcirculation. Erythrocyte flexibility is not affected by normal doses of ancrod. The rheological changes are readily maintained and the viscosity approaches pretreatment values very slowly (within about 10 days) after stopping ancrod. One of the cleavage fibrinogen products, termed 'desAA-Fibrin', acts as cofactor for the tPA-induced plasminogen activation and an increased fibrinolysis results in return (profibrinolytic activity of ancrod). Ancrod decreases the blood viscosity in affected arteries, leads to less intense pain, improves physical limb mobility, and facilitates physical and ergo therapy. Finally, ancrod decreases the likelihood of local thrombotic events. These mechanisms also account for ancrod's activity in other diseases. Effects on other clotting factors: Unlike thrombin, ancrod does not directly activate Factor XIII, nor does it produce platelet aggregation nor cause the release of ADP, ATP, potassium, or serotonin from platelets. Platelet counts and survival time remain normal during ancrod therapy. Ancrod was originally isolated from the venom of the Malayan pit viper ("Calloselasma rhodostoma", formerly "Agkistrodon rhodostoma") and is a serine protease. It is one of the Venombin A enzymes. Two genes encoding for such enzymes have been found in the viper genome. The form used in clinical trials was not made recombinantly, but was purified from harvested venom. Under the brand name Arwin, ancrod was marketed for several decades in Germany and Austria, until it was withdrawn in the 1980s. Arwin was a brand name of Knoll Pharma. In 2001 Knoll was acquired by Abbott Laboratories, and in 2002 Abbott licensed the rights to ancrod to Empire Pharmaceuticals, a startup that included a Knoll employee who had worked on ancrod. In 2004 Empire was acquired by Neurobiological Technologies. NTI also acquired a lot of unpurified venom in the acquisition, and had that purified for use in its clinical trials. The failure of ancrod in the 6-hour window for ischemic stroke trial in 2008 led to cuts in staff, an effort to sell off the company's assets, and finally to the dissolution of NTI in August 2009.