What is the recommended dose of Zofran (ondansetron) for a 16 lb infant?

Ondansetron Dosing for a 16 lb Infant

For a 16 lb (7.3 kg) infant who is at least 6 months old, the recommended ondansetron dose is 1.1 mg (calculated as 0.15 mg/kg), administered intramuscularly or intravenously depending on clinical severity, with a maximum single dose of 16 mg. 1, 2, 3

Critical Age Restriction

• Ondansetron should ONLY be used in infants ≥6 months of age due to extremely limited safety and efficacy data in younger infants. 1, 2, 3
• If this 16 lb infant is younger than 6 months, ondansetron is not recommended unless the clinical situation is judged critical. 1, 3

Weight-Based Calculation

• The standard pediatric dose is 0.15 mg/kg per dose. 1, 2, 3
• For a 16 lb infant (7.3 kg): 7.3 kg × 0.15 mg/kg = 1.1 mg per dose. 1, 2
• This dose is well below the maximum of 16 mg per dose. 1, 2, 3

Route Selection Based on Clinical Severity

For Mild Presentations (1-2 episodes of emesis, no lethargy)

• Consider 0.15 mg/kg intramuscular (1.1 mg for this infant) if age ≥6 months. 1
• Attempt oral rehydration first; ondansetron may be considered but is not always necessary. 1

For Moderate Presentations (>3 episodes of emesis with mild lethargy)

• Administer 0.15 mg/kg intramuscular (1.1 mg for this infant). 1
• Consider IV access for fluid resuscitation (20 mL/kg normal saline bolus). 1

For Severe Presentations (>3 episodes of emesis with severe lethargy, hypotonia, or cyanosis)

• Administer 0.15 mg/kg intravenous (1.1 mg for this infant) if IV access is established. 1
• If IV access is delayed, give 0.15 mg/kg intramuscular immediately. 1
• Prioritize rapid fluid resuscitation with 20 mL/kg normal saline bolus. 1

Clinical Context Considerations

Food Protein-Induced Enterocolitis Syndrome (FPIES)

• This is the primary pediatric indication where specific age-based dosing guidelines exist for ondansetron. 1, 3
• The dose remains 0.15 mg/kg regardless of severity, but route and adjunctive therapy differ. 1

Acute Gastroenteritis

• A single oral dose of ondansetron has been shown to reduce recurrent vomiting, need for IV fluids, and hospital admissions in children with acute gastroenteritis. 4
• While this represents "off-label/on-evidence" use, the same weight-based dosing (0.15 mg/kg) applies. 4

Critical Safety Warnings

• QT interval prolongation: Ondansetron can prolong the QT interval in a dose-dependent manner. 1, 2
• Special caution is warranted in infants with congenital heart disease or electrolyte abnormalities. 1, 2
• Do NOT use in infants with congenital long QT syndrome. 2

Monitoring Requirements

• Monitor the infant for 4-6 hours from onset of reaction to assess response. 1, 3
• Observe for resolution of vomiting and improvement in clinical status. 1
• If symptoms persist or worsen despite ondansetron, transfer to emergency department or intensive care unit. 1

Common Pitfall to Avoid

• Never assume all infants can receive ondansetron—always verify the infant is ≥6 months old before administration. 1, 3
• The 16 mg maximum dose applies to all pediatric patients, but for this 7.3 kg infant, the calculated dose of 1.1 mg is far below this ceiling. 1, 2