An 18-month-old girl is brought in with a 3-day history of frequently passing loose stools.

This child has acute viral gastroenteritis with mild dehydration. She remains alert, active, and continues to produce urine, indicating mild volume depletion. According to MCCQE objectives and pediatric guidelines, the first-line management of mild to moderate dehydration due to gastroenteritis is oral rehydration therapy (ORT) using a commercially prepared oral rehydration solution (ORS). ORS contains the appropriate balance of glucose and electrolytes to promote sodium and water absorption via the sodium-glucose cotransporter in the intestine. Antidiarrheal agents such as loperamide are contraindicated in young children due to risk of adverse effects and limited benefit. Withholding food until diarrhea resolves is unnecessary; early refeeding with an age-appropriate diet is recommended once rehydration begins. Apple juice and chicken broth do not provide the correct electrolyte composition and may worsen diarrhea due to high osmolarity. Routine lactose restriction is not indicated unless persistent symptoms suggest secondary lactose intolerance. Early ORT reduces the need for intravenous fluids and hospital admission.