In children aged 3 months to 10 years who present to the Pediatric Emergency Department (PED) with recent, significant vomiting and moderate dehydration, is treatment with Ondansetron Orally Disintegrating Tablet (ODT) better tolerated than treatment with Ondansetron Oral Solution (OS)? Our hypothesis is that children who receive Ondansetron ODT will have 10% less vomiting within 15 minutes of administration than those receiving Ondansetron OS.

Vomiting related to viral gastroenteritis is the most common presentation to the Alberta Children's Hospital Pediatric Emergency Department. Recently, a clinical pathway was implemented to improve the care and flow of patients with vomiting and/or diarrhea through the department. Administration of an antiemetic, Ondansetron, is an integral part of improving the hydration status of children managed by the pathway. However it is not know whether Oral Solution or Oral Disintegrating Tablets are better tolerated in children who have active vomiting. The investigators aim to show that children receiving Oral Disintegrating Tablets have less vomiting immediately after medication administration than children receiving Oral Solution. By demonstrating this improved tolerability the investigators will provide health care providers the stimulus for implementing Ondansetron Oral Disintegrating Tablets into their practice for children with active vomiting.

Inclusion Criteria:

• Children aged 3 months to 10 years with recent,
• significant vomiting and moderate dehydration who are managed according to the Alberta Health Services (Calgary and Area) Acute Childhood Vomiting & Diarrhea Pathway.
• The following definitions are used to determine inclusion according to the pathway: Recent, significant vomiting - Vomiting at least 6 episodes in the past 6 hours and at least once in the past hour; Moderate dehydration (Gorelick Score 2) - Two of the following: capillary refill time greater than 2 seconds, absence of tears, dry mucous membranes, ill general appearance.

Exclusion Criteria:

• Children who are excluded from the Alberta Health Services (Calgary and Area) Acute Childhood Vomiting & Diarrhea Pathway.
• These criteria include: Vomiting or Diarrhea for greater than 7 days, Localized abdominal pain, Chronic medical conditions affecting major organ systems (Ex, diabetes, PKU, immunodeficiency), Likely GI Obstruction (abdominal distension, bilious vomiting, absent bowel sounds), Weight less than 8kg. Children who have received anti-emetics at home will not be excluded but will be tracked.

Alberta Children's Hospital Emergency department, all patients presenting with acute gastroenteritis