Vardenafil (INN) is a PDE5 inhibitor used for treating impotence (erectile dysfunction) that's sold under the trade name Levitra (Bayer AG, GSK, and SP). History Vardenafil was co-marketed by Bayer Pharmaceuticals, GSK, and SP under the trade name Levitra. As of 2005, the co-promotion rights of GSK on Levitra have been returned to Bayer in many markets outside the U.S. In Italy, Bayer sells vardenafil as Levitra and GSK sells it as Vivanza, thus, because of European Union trade rules, parallel… (More on Levitra)