• The primary objective of this trial is to compare the dose-ranging pharmacodynamic effects of orally administered placebo, and 100 and 1000 ug qd of MD-1100 Acetate on gastrointestinal transit in patients with C-IBS.

• The secondary objectives of this trial are:

  1. To compare the dose ranging pharmacodynamic effects of placebo, and 100 and 1000 ug MD-1100 Acetate once daily on time to first bowel movement after first drug intake.
  2. To describe and summarize the effects of placebo, and 100 and 1000 ug MD-1100 Acetate once daily on stool frequency, stool consistency, ease of passage and sensation of incomplete evacuation during the Treatment Period relative to Baseline.

Using a double-blind, randomized, placebo-controlled, parallel group study design, the effects of placebo and two different doses of orally administered MD-1100 Acetate on gastric emptying, small bowel transit and total colonic transit will be compared and evaluated in patients with C-IBS.

After eligibility is confirmed, the patient will return for baseline measurement of colonic transit to ensure that the transit profile is not greater than the mean transit profile of healthy controls in order to avoid a ceiling effect. A patient must have a geometric center of ≤2.65 at 24 hours, or ≤3.0 at 24 hours and ≤3.9 at 48 hours in order to be randomized to a 5-day Treatment Period of study medication. Eligible patients will receive oral study medication for 5 days during which colonic transit will be measured.

Approximately 36 (n=36) patients will be randomized to one of three different treatment groups: placebo (n=12), 100 ug MD-1100 (n=12), or 1000 ug MD-1100 (n=12). All dosing of study medication will be supervised at the Mayo Clinic.

Patients will complete a daily Stool Diary to record bowel habits for 5 consecutive days during the Pretreatment Period and then for the 5 consecutive days of the Treatment PeriodPhysical examinations, vital signs, electrocardiograms, and clinical laboratory tests will be performed throughout the study and adverse events will be recorded for safety evaluation.

Inclusion Criteria:

• Patient agrees to use a medically accepted, double-barrier form of contraception (e.g., IUD and condom) during participation;
• No evidence of pelvic floor dysfunction and the completion of a negative digital rectal exam prior to the first dose of study medication;
• Absence of an evacuation disorder as defined per protocol;
• Patients must meet ROME II Criteria for C-IBS;
• The patient's Baseline Colonic Transit Test must show a geometric center (GC) ≤ 2.65 at 24 hours, or ≤ 3.0 at 24 hours and ≤ 3.9 at 48 hours.

Exclusion Criteria:

• History of clinically-significant manifestations of any major system organ class;
• History of inflammatory bowel disease or gastric ulcers;
• Significant GI surgery within 6 months;
• Clinically-significant prolonged diarrhea within 60 days;
• Special dietary habit and/or an intense physical workout program within 4 weeks;
• Certain drug hypersensitivities
• History of alcoholism or drug addiction within 12 months;
• Receipt of an investigational drug during the study or within 30 days;
• Use of any prescription medication or OTC, non-prescription medications disallowed by the protocol within 7 days.