The Efficacy of AZD1722 in Constipation Predominant Irritable Bowel Syndrome (IBS-C)

Inclusion Criteria: * Females and males must agree to use appropriate methods of contraception or be sterile (with appropriate documentation) * Subject is ambulatory * Subject meets definition of IBS-C using Rome III Criteria for the Diagnosis of IBS with a history of \<5 SBMs per week * Subject meets Screening eligibility criteria (see below) * A colonoscopy based on AGA guidelines; every 10 years at ≥ 50 years old, or the occurrence of any warning signs (i.e., unexplained weight loss, non-hemorrhoid blood in stools) * Ability to communicate well with the Investigator and to comply with the requirements of the entire study, including an understanding of how to use the touch-tone telephone electronic diary. * Written informed consent and a willingness to participate in the study as it is described. * Daily access to a touch tone telephone. 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. * Use of medications that are known to affect stool consistency (Prohibited Medications), including fiber supplements, anti-diarrheals, cathartics, antacids, opiates, prokinetic drugs, laxatives, enemas, antibiotics within 4 weeks of enrollment, probiotics (including probiotic yogurt); or salt or electrolyte supplements containing sodium, potassium, chloride, or bicarbonate formulations during the seven days prior to treatment; unless specified as rescue medication, and used accordingly. * Clinical evidence of significant cardiovascular, respiratory, renal, hepatic, gastrointestinal, hematologic, neurologic, psychiatric or any disease that may interfere with the subject successfully completing the trial. * The subject has a history or current evidence of laxative abuse (in the clinical judgment of the physician). * Hepatic dysfunction (ALT \[SGPT\] or AST \[SGOT\] \>2.5 times the upper limit of normal) or renal impairment (serum creatinine \> 2mg/dL). * Any evidence of or treatment of malignancy (other than localized basal cell, squamous cell skin cancer or cancer in situ that has been resected) within the previous year. * Any surgery on the stomach, small intestine or colon, excluding appendectomy. * Pregnant or lactating women. * A major psychiatric disorder (DSM-III-R or DSM-IV) including major depression or other psychoses that has required hospitalization in the last 3 years. History of attempted suicide or uncontrolled bipolar disorder. Alcohol or substance abuse in the last year. * Participation in other clinical trials within 1 month prior to Day -14 (beginning of screening period). * If, in the opinion of the Investigator the subject is unable or unwilling to fulfill the requirements of the protocol or has a condition, which would render the results uninterpretable.