Patient description: A 34 year old man comes to the clinic complaining of dizziness and severe diarrhea since yesterday. He has returned from an international trip few days ago and was living in a camp in Sudan for a month. He developed abdominal pain followed by bloating and nausea as well as loose bowel movements. Soon he was having profuse watery diarrhea without odor. The stool is watery and white but the patient has no fever. Blood pressure is 95/62 lying down and drops to 75/40 standing. The skin turgor has reduced. HR is 110 and he looks ill with dry mucosa. V. cholerae was seen in dark-field microscopy of a fresh stool specimen. The lab study is as bellow: Sodium 137 meq/L Potassium 2 meq/L Chloride 94meq/L CO2 15 meq/L Fecal leukocytes None seen Fecal occult blood Negative

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Irritable Bowel Syndrome Constipation Males or females >18 years of age Meet Rome III for IBS[2] Recurrent abdominal pain or discomfort at least 3 days per month in the last 3 months associated with 2 or more of the following: 1. Improvement with defecation 2. Onset associated with a change in frequency 3. Onset associated with a change in form (appearance) of stool *Criteria fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis Fulfill the Rome III stool consistency for IBS-C[2] Hard or lumpy stools for >25% of bowel movements Loose (mushy) or watery stools for <25% of bowel movements Capable of independently completing all requirements of the study including returning for required visits Able to provide written informed consent for study participation Willing to discontinue prohibited medications during study participation  Unable to understand or provide written informed consent Pregnant or nursing Patients with IBS-D, IBS-M or unsubtyped IBS by Rome III criteria[2] IBS with diarrhea (IBS-D) 1. Loose (mushy) or watery stools for >25% of bowel movements 2. Hard or lumpy stools for <25% of bowel movements Mixed IBS (IBS-M) 1. Hard or lumpy stools >25% of bowel movements 2. Loose (mushy) or watery stools for >25% of bowel movements Unsubtyped IBS 1. Insufficient abnormality of stool pattern to meet for IBS-C, IBS-D or IBS-M Documented allergy or intolerance to lubiprostone Failure of balloon expulsion test Inability to expel 50cc balloon within 1 minute Use of drugs known to affect gastrointestinal motility 1. Laxatives (stable doses of fiber taken for minimum of 4 weeks will be allowed) Osmotic laxatives: Magnesium hydroxide, Polyethylene glycol,Lactulose, Sorbitol Stimulant laxatives: Bisacodyl, Anthraquinones (senna), Misoprostol 2. Prokinetic agents: Metoclopramide, domperidone, erythromycin 3. Anti-diarrheal agents: Loperamide, Diphenoxylate, Bismuth 4. Anti-spasmotics: Dicyclomine, Hyoscyamine 5. Opioid, narcotic, opioid/narcotic-containing analgesics: Morphine, Hydrocodone, Codeine, Methadone, Propoxyphene 6. Probiotics 7. Systemic antibiotics within last 3 months 8. Recently initiated antidepressants (stable dose for >2 months for non-GI conditions will be allowed) 9. Benzodiazepines * Subjects taking prohibited medications will be required to stop these at the screening visit and remain off of them until completion of the study