Safety and Efficacy Study of Sitaxentan Sodium (Thelin™) in Patients With Pulmonary Arterial Hypertension

Inclusion Criteria: * Have a current diagnosis of symptomatic PAH classified by one of the following: 1. primary pulmonary hypertension (PPH) - also known as idiopathic pulmonary arterial hypertension (IPAH); 2. PAH associated with connective tissue diseases; 3. PAH associated with one of the following congenital heart defects: 1. repaired ASD, VSD or PDA greater than one year post-operative 2. un-repaired secundum ASD (with resting oxygen saturation greater than 88 percent in room air measured by oximeter) * World Health Organization (WHO) functional class II, III, IV * Greater than 12 and less than 75 years of age * Women of childbearing potential must be using two forms of medically acceptable contraception (at least one barrier method) * Have a cardiac catheterization within 6 months before study entry that shows the following values: 1. mean pulmonary artery pressure (PAPm) greater than 25 mmHg (at rest), 2. pulmonary capillary wedge pressure (PCWP) or left ventricular-end diastolic pressure less than 15 mmHg, and 3. pulmonary vascular resistance (PVR) greater than 3 mmHg/L/min. Exclusion Criteria: * Portal hypertension or chronic liver disease * ALT or AST levels greater than 1.5 times the upper limit of normal at the Screening Visit * Contraindication to treatment with an endothelin receptor antagonist * Recent history of abusing alcohol or illicit drugs * Chronic renal insufficiency * Pregnant or breastfeeding * Atrial septostomy within 30 days before study entry * Previous failure on bosentan because of safety concerns of the lack of clinical response