A 26-Week Study to Evaluate the Efficacy and Safety of Tenapanor in IBS-C

Inclusion Criteria: * Males or females aged 18 to 75 years, inclusive * Females must be of non-childbearing potential; If of child-bearing potential, must have negative pregnancy test and confirm the use of one of the appropriate means of contraception * Males must agree to use appropriate methods of barrier contraception or have documented surgical sterilization * Subject meets definition of IBS-C using Rome III Criteria for the Diagnosis of IBS * A colonoscopy based on AGA guidelines; every 10 years at ≥50 years old Exclusion Criteria: * Functional diarrhea as defined by Rome III criteria * IBS with diarrhea (IBS-D), mixed IBS (IBS-M), or unsubtyped IBS as defined by Rome III criteria * Diagnosis or treatment of any clinically symptomatic biochemical or structural abnormality of the GI tract within 6 months prior to screening, or active disease within 6 months prior to screening; including but not limited to cancer, inflammatory bowel disease, diverticulitis, duodenal ulcer, erosive esophagitis, gastric ulcer, pancreatitis (within 12 months of screening), cholelithiasis, amyloidosis, ileus, non-controlled GERD, gastrointestinal obstruction or carcinoid syndrome. * Potential CNS cause of constipation (e.g., Parkinson's disease, spinal cord injury, or multiple sclerosis) * Subject has a history or current evidence of laxative abuse (in the clinical judgment of physician) * Hepatic dysfunction (ALT \[SGPT\] or AST \[SGOT\] \>2.5 times the upper limit of normal) or renal imp…