A Double-Blind, Active-Controlled, Long-Term Safety Extension Study of Optimized Doses of Darusentan in Subjects With Resistant Hypertension Despite Receiving Combination Therapy With Three or More Antihypertensive Drugs, Including a Diuretic, as Compared to Guanfacine (Protocol DAR-312-E)

This is a double-blind, active-controlled, long-term study of a new experimental drug called darusentan. Darusentan in not currently approved by the United States Food and Drug Administration (FDA), which means that a doctor cannot prescribe this drug. The purpose of this study is to evaluate the long-term safety of darusentan (optimized dose) as compared to an active control, administered orally.