BEKINDA (Ondansetron 24 mg Bimodal Release Tablets) for Vomiting Due to Presumed Acute Gastroenteritis or Gastritis

Inclusion Criteria: * Patients must have vomited at least twice in the 4 hours preceding signing informed consent. A vomiting episode is defined as an episode of forceful expulsion of stomach contents. Retching if a patient has already emptied his or her gastric contents is also considered vomiting episode. A distinct episode is characterized by a clear break in vomiting activity of at least 5 minutes * Emesis must have been nonbloody (streaks of blood presumed due to force of retching are allowed) * All patients (and a parent or guardian for patients \<age 18) must sign informed consent. Exclusion Criteria: * Severe dehydration. Severe dehydration is defined as two or more of the following criteria in the presence of decreased intake and increased output due to vomiting or diarrhea: Absent or severely decreased urine output; weak pulse and/or low blood pressure; parched mucous membranes; lethargy, confusion, delirium or loss of consciousness * Signs and symptoms severe enough to require immediate parenteral hydration and/or parenteral antiemetic medication * Temperature\>39.0 * Likely etiologies for acute vomiting and diarrhea other than acute infectious or toxic gastroenteritis or gastritis. This includes signs of an acute abdomen, which may require surgical intervention * Chemically-induced gastroenteritis, e.g., from alcohol, other drugs of abuse or other irritant chemicals * Use within 24 hours of study entry of specific medication for treatment of nausea and/or vomiting, e.g., 5-HT3 antagonists or phenothiazines, or receipt of any IV fluid for any reason. Nonspecific gastrointestinal remedies, such as antacids, proton pump inhibitors and homeopathic remedies, are permitted. * Congestive heart failure, bradyarrhythmia (baseline pulse\<55/min), known long QT syndrome * Patient who have known QTc prolongation \> 450 msec, noted on prior or screening ECG, or who are taking medication known to cause QT prolongation. Note: for current list of medications known to cause QT prolongation see: https://www.crediblemeds.org/healthcare-providers/drug-list/ Use list showing drugs with known risk TdP. * Known underlying disease which could affect assessment of hydration or modify outcome of treatment, e.g., renal failure, diabetes mellitus, liver disease, alcoholism. Patients with type 2 diet-controlled diabetes mellitus whose baseline blood glucose is \<200 may be entered into the study * Abdominal surgery within the past 3 months * History of bariatric surgery or bowel obstruction at any time * Hypersensitivity or other known intolerance to ondansetron or other 5-HT3 antagonists * Patient has taken apomorphine within 24 hours of screening * Patient has previously participated in this study * Patient has participated in another interventional clinical trial, for any indication, in the past 30 days * For women of childbearing potential: documented or possible pregnancy.