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Treatment for Pulmonary Arterial Hypertension (PAH)

Encysive Announces PDUFA Date for Thelin New Drug Application in Pulmonary Arterial Hypertension

HOUSTON, July 14, 2005 -- Encysive Pharmaceuticals today announced that the Cardio-Renal Division of the U.S. Food and Drug Administration (FDA), in correspondence with the Company, stated that it anticipates filing Encysive's New Drug Application (NDA) for Thelin (sitaxsentan) on July 23, 2005 under a standard review classification. Thelin 100 mg is being evaluated as a once daily oral treatment for patients with pulmonary arterial hypertension (PAH).

"We are pleased that the FDA plans to accept our NDA for Thelin. This is the largest database for a PAH orphan drug indication that has been submitted to the Cardio-Renal Division for initial marketing approval," said Bruce D. Given, M.D., President and Chief Executive Officer of Encysive Pharmaceuticals. "We are also pleased that the FDA has simultaneously requested a plan for the study of Thelin in pediatric PAH patients, a demographic with limited treatment options in which patient safety is paramount."

The FDA Prescription Drug User Fee Act (PDUFA) target action date for Thelin is March 24, 2006.

About Thelin and PAH

Thelin is a small molecule that blocks the action of endothelin, a potent mediator of blood vessel constriction and growth of smooth muscle in vascular walls. Endothelin receptor antagonists may prove to be effective in the treatment of a variety of diseases where the regulation of vascular constriction is important. Thelin is 6,500-fold selective in the targeting of the endothelin A receptor versus the endothelin B receptor.

Pulmonary arterial hypertension (PAH) is a condition that involves high blood pressure and structural changes in the walls of the pulmonary arteries, which are the blood vessels that connect the right side of the heart to the lungs. PAH causes shortness of breath, limits activity, and is eventually fatal unless treated successfully with heart/lung or lung transplantation. PAH is estimated to afflict approximately 100,000 to 200,000 people worldwide, many of whom are children and young women.

The most frequent adverse events that occurred in patients receiving Thelin, which were more common than in placebo-treated patients, were headache, edema, nausea, upper respiratory tract infection, dizziness, insomnia, nasopharyngitis, and nasal congestion. Because Thelin inhibits the metabolism of warfarin, a decreased dose of warfarin is needed when co- administered with Thelin.

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