What is the appropriate dosage of Zofran (ondansetron) for a 5-year-old experiencing vomiting?

Ondansetron Dosing for a 5-Year-Old with Vomiting

For a 5-year-old child with vomiting from acute gastroenteritis, administer ondansetron 0.15 mg/kg orally (maximum 4 mg) as a single dose to facilitate oral rehydration. 1

Weight-Based Dosing

• Oral route: 0.15-0.2 mg/kg per dose, with a maximum single dose of 4 mg 1, 2
• Intramuscular/Intravenous route: 0.15 mg/kg per dose, with a maximum of 16 mg per dose (reserved for moderate-to-severe presentations or when oral route fails) 3
• The American Academy of Pediatrics specifically recommends weight-based dosing for pediatric patients with persistent vomiting due to ondansetron's efficacy and favorable side effect profile 1

Clinical Context and Indications

Ondansetron is indicated when:

• Persistent vomiting impedes oral rehydration therapy 1, 2
• The child is unable to tolerate oral fluids due to ongoing emesis 2, 4
• Vomiting is limiting the effectiveness of standard oral rehydration therapy 5, 6

The Infectious Diseases Society of America specifically recommends ondansetron as an antiemetic to facilitate oral rehydration in children >4 years of age with acute gastroenteritis associated with vomiting 1

Evidence of Efficacy

• A single oral dose of ondansetron significantly reduces failure of oral rehydration therapy (31% vs 62% with placebo, p<0.001) 5
• Children receiving ondansetron consume significantly more oral rehydration solution (645 mL vs 554 mL, mean difference 91 mL) 5
• Ondansetron reduces vomiting episodes during both the first 8 hours (RR: 0.33) and the subsequent 24 hours (RR: 0.15) 7
• The number needed to treat is 2, meaning for every 2 children treated, one additional child will have successful oral rehydration 7

Critical Safety Considerations

Cardiac precautions: Special caution is warranted in children with underlying heart disease due to ondansetron's potential to prolong the QT interval 3, 1

Age restriction: Ondansetron should only be used in children ≥6 months of age for acute gastroenteritis management 3

Not a replacement for hydration: Antiemetic treatment should not replace appropriate fluid and electrolyte therapy, which remains the mainstay of treatment for gastroenteritis 1

Administration Approach

• Give ondansetron before starting oral rehydration therapy to maximize effectiveness 5
• A single dose is typically sufficient for acute gastroenteritis 5, 6
• Ensure adequate hydration is provided alongside or immediately after ondansetron administration 1
• The oral route is preferred when the child can tolerate it 2

Common Pitfalls to Avoid

• Do not delay hydration: Ondansetron should facilitate, not replace, oral rehydration efforts 1
• Do not use routinely: Reserve for cases where vomiting truly impedes oral intake, not for every episode of gastroenteritis 2, 4
• Do not give multiple doses reflexively: Most evidence supports single-dose administration for acute gastroenteritis 5, 6
• Screen for cardiac history: Always ask about congenital heart disease or arrhythmias before administration 3, 1