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

This is a randomized, 12-week, double-blind, placebo-controlled, dose-ranging study in patients with IBS-C. Patients will undergo a Screening Period to determine eligibility. After completing a Screening Visit patients will undergo a 2-week Pre-Treatment assessment using the Interactive Voice Response System (IVRS) during which they will complete daily assessments of bowel movements (BMs), stool consistency (Bristol Stool Form Scale- BSFS), abdominal pain or abdominal discomfort and other symptoms associated with IBS-C. Data from the two-week IVRS Pre-treatment assessment are used to define the patient's baseline from which change will be determined. Patients who meet all entry criteria will be randomized to one of five treatment groups ( 0.3mg,1.0mg,3.0mg,9mg,or Placebo) on Day 1 of the Treatment Period. Patients will take an oral dose of study drug daily (QD) for 12 weeks and continue the daily IVRS diaries (BMs, abdominal pain, other symptoms). On Weeks 2, 4, 8, and 12, patients will return to the clinic to undergo safety and efficacy assessments. For 2 weeks after completing dosing, (i.e., Post-Treatment Period), patients will continue to complete daily IVRS diaries. Patients will then return to the clinical site for a final follow-up visit (End of Study Visit). The planned duration of participation in this study will be approximately 112 days from signing of informed consent through post-treatment or 145 days if 30 day washout of a prohibited concomitant medication or stabilization of a medical condition is required before Pre-Treatment (up to 148 days, with all windows considered).