Shares of Encysive Pharmaceuticals ( ENCY) were among the worst-performing health-related stocks Monday, plummeting 47% after the Food and Drug Administration said it needs more information about Thelin, the company's pulmonary arterial hypertension drug, before it can be approved. Encysive said the approvable letter from the FDA also includes a request for additional clinical trial work. "We will work in close collaboration with the FDA to clarify the path forward," the company said in a statement issued late Friday. "We are hopeful that this can be accomplished without the need for additional clinical work, but that will require discussion with the agency before we can be sure." Shares recently were trading down $4.28 to $4.80. Shares of Myogen ( MYOG), which is developing a rival drug, were trading up $1.63, or 5%, to $36.61. DexCom ( DXCM) jumped 11% after the FDA approved the company's STS continuing glucose monitoring system, which is used by diabetics who want to manage their blood sugar levels. The device consists of a tiny wire-like sensor that is inserted just under the skin to measure glucose levels, which are transmitted wirelessly to a cell phone-like receiver. DexCom shares were up $2.13 to $21.94. Shares of Keryx Biopharmaceuticals ( KERX) rose 3% after the biotech company laid out plans to sell almost $83 million worth of stock to two institutional investors. The company, which plans to sell 4.5 million shares at $18.40 apiece as part of a registered direct offering, expects the stock sale to close Tuesday. Shares were trading up 56 cents to $19.04. Santarus ( SNTS) rose 5% after the FDA approved the company's new drug application for Zegerid chewable tablets, an immediate-release proton pump inhibitor that's used to treat heartburn. "We are evaluating the positioning and launch timing of the chewable tablet dosage form and do not currently anticipate that the commercial launch of this product will occur in 2006," Santarus said. Shares recently changed hands at $6.57, up 32 cents.