Encysive Pharmaceuticals ( ENCY) looks like it overplayed its hand. Prior to a bombshell announcement this weekend, the company had managed to convince investors that approval of Thelin -- its new drug for pulmonary arterial hypertension -- was essentially a sure thing. Instead, the company now faces a delayed launch of Thelin at best. Without sharing any major details, Encysive disclosed Friday night that the Food and Drug Administration has asked for more information about Thelin -- including additional clinical trial work -- before it can approve the new PAH drug. Shares of Encysive plummeted 46% to a multiyear low of $4.94 on the report. Meanwhile, shares of Myogen ( MYOG) -- which is developing a PAH drug of its own -- rose 4.1% to $36.41. Encysive had previously been hoping for first-run approval of Thelin and, in turn, a big head start against Myogen's ambrisentan. But that perceived advantage has now diminished. Brean Murray Carret analyst Jonathan Aschoff promptly downgraded Encysive from accumulate to hold as a result. The FDA's response "was almost entirely unexpected by the Street," Aschoff wrote on Monday. "Barring significant ambrisentan delays, we no longer believe that Thelin will have any meaningful lead time to market over competitor ambrisentan and will therefore have to fight it out with ambrisentan for market share on relatively equal ground without enjoying more than perhaps a few months lead time." In the meantime, Encysive has offered few clues about its surprising regulatory setback. Rather, when repeatedly questioned by analysts on Monday, Encysive insisted that the company would be best served by dealing with the FDA in a "quiet and confidential" manner. Some have speculated that Encysive ran into some classwide challenges that could ultimately hinder Myogen as well. Notably, the FDA recently ordered stricter guidelines for a PAH drug already on the market. Moreover, Encysive suggested on Monday that the FDA could treat "anybody that potentially follows us" in a similar manner.