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): 5.0-55.0,  Secretory Diarrhea Approximately 170 adult (male and female) patients must be enrolled to ensure that 96 patients (48 active and 48 placebo) are evaluable in Part A. In Part B, approximately 156 pediatric patients will be enrolled to ensure that 120 pediatric patients (60 active and 60 placebo) are evaluable for the analysis of 24 hour stool output, the primary outcome measure. PART A ***Inclusion Criteria*** A patient will be considered eligible for participation in the study if the following are satisfied on admission (Day 1) to the Dhaka Hospital of icddr,b Adults aged 18 years to 55 years Duration of illness: History of acute watery diarrhea of less than 24 hours' duration without fever or visible blood in feces Clinical signs and symptoms of severe dehydration (>10% loss of body weight based on rehydration weight) Stool RDT and/or stool DF microscopy demonstrating presence of V. cholerae Must have a purging rate greater than/equal to 20 mL/kg (5 mL/kg/h) during the initial 4 to 6-hour screening/observation period, and signs of clinical dehydration must be corrected Written informed consent for participation in the study (see Section 6.1.2 for details of the consent process) Negative urine pregnancy test for all female patients  *** A patient with any of the following at screening for study enrollment will not qualify for the study Received antidiarrheal medication (eg, loperamide, diphenoxylate) within 7 days before screening Abnormal ECG findings, with the exception of sinus tachycardia, premature atrial contractions, or ECG intervals within normal limits for sinus rate Use of drugs metabolized predominantly via CYP2C9 within 7 days before screening (see Section 5.7) Concomitant infection requiring antimicrobial therapy other than the study drug that may interfere with the evaluation of either the efficacy or safety of the study drug Patients unwilling or unable to take part in this study or refusing to sign informed consent (patients who participate on the basis of proxy consent will be re-consented at the end of the screening/observation period; those refusing consent at that time will be excluded from further study participation) Patients previously enrolled in this or any other investigational study within the past 30 days PART B ***Inclusion Criteria*** A patient will be considered eligible for participation in the study if the following are satisfied on admission (Day 1) to the Clinical Research Ward (CRW) of Dhaka Hospital Pediatric population aged ≥ 5 years to < 18 years of age Duration of illness: History of acute watery diarrhea of less than 24 hours' duration without fever or visible blood in feces