The Plecanatide Irritable Bowel Syndrome With Constipation Safety and Efficacy Study (IBS-C)

This study in patients with IBS-C is a randomized, double-blind, placebo-controlled, parallel-group clinical trial with 12 weeks of study drug therapy.

Inclusion Criteria: •Adult patients between the ages of 18 and 85 years (inclusive) with a diagnosis of IBS based on ROME III diagnostic criteria and meeting criteria for diagnosis of the constipation predominant subtype - IBS-C Exclusion Criteria: * Refusal or inability to sign informed consent for the trial * Refusal or inability to complete daily Episodic (real-time) BM / RM calls, End of Day daily Calls, and/or complete electronic questionnaires * BMI \> 35 or \< 18 * Women of child bearing potential who refuse to use an acceptable method of birth control for the duration of the trial * Women who are pregnant or lactating * Diagnosis of IBS-D or IBS-M * Organic or obstructive disease of the small or large intestine * Use of laxatives other than the study-supplied rescue medication (Dulcolax®, bisacodyl) * Use of a prohibited concomitant medication within the time frame prior to screening outlined in the study protocol for that medication * Unstable medical illness * Bilirubin \> 3X ULN in the absence of a conjugation defect * Any laboratory value \> 3X ULN unless discussed and approved by the study Medical Monitor