LMWH shows increased inactivation of Factor Xa compared to unfractionated heparin, and fondaparinux, an agent based on the critical pentasacharide sequence of heparin, shows more selectivity than LMWH. This inactivation of Factor Xa by heparins is termed "indirect" since it relies on the presence of AT and not a direct interaction with Factor Xa. Recently a new series of specific, direct acting inhibitors of Factor Xa has been developed. These include the drugs rivaroxaban, apixaban, betrixaban, LY517717, darexaban (YM150), edoxaban and 813893. These agents have several theoretical advantages over current therapy. They may be given orally. They have rapid onset of action. And they may be more effective against Factor Xa in that they inhibit both free Factor Xa and Factor Xa in the prothrombinase complex. History
American and British scientists described deficiency of factor X independently in 1953 and 1956, respectively. As with some other coagulation factors, the factor was initially named after these patients, a Mr Rufus Stuart (1921) and a Miss Audrey Prower (1934). At that time, those investigators could not know that the human genetic defect they had identified would be found in the previously characterized enzyme called thrombokinase. Thrombokinase was the name coined by Paul Morawitz in 1904 to describe the substance that converted prothrombin to thrombin and caused blood to clot. That name embodied an important new concept in understanding blood coagulation – that an enzyme was critically important in the activation of prothrombin.
In 2019, it was the 110th most commonly prescribed medication in the United States, with more than 5 million prescriptions. Society and culture
Brand names
It is marketed by GlaxoSmithKline under the brand names Valtrex and Zelitrex. Valaciclovir has been available as a generic drug in the U.S. since November 2009. References
External links
"Valaciclovir". Drug Information Portal. U.S. National Library of Medicine. "Valacyclovir hydrochloride". Drug Information Portal. U.S. National Library of Medicine.