A 26-Wk Study to Assess Safety & Efficacy of Tenapanor for T/t of Chronic Idiopathic Constipation in Adults

This study consists of a 2-week Screening period, followed by a 26-week randomized treatment period (RTP), and a 4-week treatment-free Safety Follow-up period. After obtaining study informed consent from patients, the 2-week Screening period starts. Patients will be fully assessed for eligibility into the study. The assessments will include evaluation of inclusion/exclusion criteria, including medical histories, physical examination, vital signs, 12-lead electrocardiogram (ECG), and clinical laboratory tests. Patients will also self-report, on information about the status of their constipation symptoms and severity via an electronic diary (eDiary). Patient compliance with the eDiary will be monitored to determine eligibility at the end of screening. Eligible patients will be randomized (Visit 2) to receive tenapanor 5 mg BID (twice a day), 25 mg BID, 50 mg BID, or placebo for 26 consecutive weeks as the double-blind RTP. During this period, patients will continue recording daily assessments of constipation symptoms and weekly assessments of constipation severity in the eDiary. Patients will have return visits every two to six weeks at Weeks 2, 4, 8, 12, 16, 20 and 26(Visit 3-9) to undergo safety assessments. Upon completion of the 26-week RTP, patients will be monitored for AEs (adverse events) during the 4-week treatment-free Safety Follow-up period and complete the Follow-up visit (Visit 10) at the end of this period to undergo safety assessments.