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

Inclusion Criteria:

• Male or female aged 18-75, inclusive

• Body Mass Index = 18-35 kg/m2, inclusive

• Meets modified Rome III criteria for irritable bowel syndrome with constipation whichincludes abdominal pain or discomfort for at least 3 days/month in the last 3 monthswith symptom onset for at least 6 months.

• Less than 3 CSBMs and less than 6 SBMs per week during the last 3 months.

• Hard or lumpy stools ≥ 25 % of defecations

• Patient has average abdominal pain intensity scores ≥ 3 (scale 0-10)for the combined 2week pre-treatment period

• Patient is willing to discontinue use of supplemental fiber, laxatives, prescriptionand nonprescription medications, herbal or dietary supplements intended to treatconstipation during the screening, pre-treatment, treatment and 2-week post-treatmentperiods

• Willing to maintain a stable diet during the study.

• Patients with hemorrhoids and/or diverticulosis (NOT diverticulitis) CAN be enteredinto the study.

Exclusion Criteria:

• Loose stool (mushy) or watery stool in the absence of any laxative or prohibitedmedicine for > 25% of BMs during the 3 months prior to screening visit OR during the 14 day pre-treatment period

• Patient has diarrhea-predominant or mixed ( diarrhea and constipation cycling ordiarrhea and normal cycling) IBS.

• Active peptic ulcer disease not adequately treated or not stable

• History of cathartic colon, laxative, enema abuse, or ischemic colitis.

• Fecal impaction within 3 months of screening

• Patient has had /has any: structural abnormality of the GI tract or gastric bypasssurgery, pelvic floor dysfunction, pseudo-obstruction, active infectious gastritis,diverticulitis, anal fissures or any disease or condition that can affect GI motilityor defecation or can be associated with abdominal pain

• Unexplained and clinically significant "alarm symptoms" including lower GI bleeding,iron-deficiency anemia, weight loss or systemic signs of infection or colitis.

• Major surgery within 60 days of screening.