Ondansetron Dosing for a 10-Month-Old, 10 kg Infant
For a 10-month-old infant weighing 10 kg, administer 1.5 mg of ondansetron, which equals approximately 1.9 mL of the 4 mg/5 mL syrup formulation.
Weight-Based Calculation
- The standard pediatric dose of ondansetron is 0.15 mg/kg per dose with a maximum single dose of 16 mg 1, 2
- For a 10 kg infant: 0.15 mg/kg × 10 kg = 1.5 mg per dose 1
Volume Conversion for 4 mg/5 mL Syrup
- The concentration is 4 mg per 5 mL, which equals 0.8 mg/mL 1
- To deliver 1.5 mg: 1.5 mg ÷ 0.8 mg/mL = 1.875 mL (can round to 1.9 mL or 2 mL for practical administration) 2
Critical Age Restriction
- Ondansetron should only be used in infants ≥6 months of age due to limited safety and efficacy data in younger infants 1, 2
- At 10 months of age, this infant meets the minimum age requirement 1, 2
Route Selection Based on Clinical Context
- For mild symptoms (1-2 episodes of vomiting, no lethargy): Consider oral administration of 1.5 mg (approximately 2 mL of syrup) 2
- For moderate symptoms (>3 episodes with mild lethargy): Administer 0.15 mg/kg intramuscularly if oral route is not feasible 2
- For severe symptoms (>3 episodes with severe lethargy, hypotonia, or cyanosis): Administer 0.15 mg/kg intravenously if IV access is established 2
Safety Considerations
- QT interval prolongation: Ondansetron can prolong the QT interval in a dose-dependent manner 1, 2
- Avoid use in infants with congenital long QT syndrome, electrolyte abnormalities, or known cardiac conduction abnormalities without cardiology consultation 1, 2
- Special caution is warranted in children with congenital heart disease 2
Common Pitfalls to Avoid
- Do not exceed 16 mg as a single dose, regardless of weight-based calculation 2
- Do not use in infants <6 months old, as this is outside the approved age range 1, 2
- The dose can be rounded by up to 15% for practical home administration, so rounding 1.875 mL to 2 mL is acceptable 2