Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Irritable Bowel Syndrome Adult male or female, aged ≥18 and ≤75 years old Subject/ legal representative is able to understand and sign informed consent form Have abdominal pain severity defined as weekly average of "worst abdominal pain in past 24 hours" score of ≥ 3.0 on a 0 to 10 point scale during the second week of the Baseline phase Have IBS-D according to Rome III and ≥25% of stools on the BSS rated as 6 or 7 during the Baseline phase Not pregnant, lactating, or breastfeeding If a female of childbearing potential, the subject must agree to remain abstinent or practice two medically acceptable forms of contraception during the screening, baseline, treatment, and withdrawal periods. Acceptable forms of contraception oral contraception, intrauterine devices, implantable devices, and barrier methods. If a barrier method is chosen, a double barrier is required Discontinue all medications used to treat IBS symptoms (prescription and non-prescription) and prescription analgesics at least two (2) weeks prior to the start of the baseline period until after the final study visit. (Final study visit occurs two (2) weeks after the last dose of study medication.) Acetaminophen may be used as a rescue medication as long as it is carefully documented on the Case Report Form (CRF). Fiber supplements are permitted if they are taken at the same frequency and amount throughout the study and were taken during the four (4) weeks prior to the Baseline phase. This must be documented in the source document file and the CRF Willing and able to comply with all study-related procedures, including not incorporating significant changes in diet  Positive for fecal ova and parasites (O&P) or Clostridium difficile (ELISA) or other bacterial pathogens (standard stool culture) during the Screening phase Taking medication for the treatment of IBS during the baseline phase (other than acetaminophen) Taking any treatment for IBS including any of the following classes of medications within 2 weeks prior to baseline visit (Visit 2), or at any point during the study Antispasmodic or anticholinergic agents Combination products including atropine, hyoscyamine, phenobarbital, and/or scopolamine Antidepressants (such as monoamine oxidase inhibitors [MAOI], selective serotonin reuptake inhibitors [SSRIs], and tricyclic antidepressants), to but not limited to the following Combination products including pheniramine, phenyltoloxamine, or pyrilamine Laxatives Opioids/narcotic analgesics Phenothiazines antipsychotics and anti-emetics