Ondansetron Dosing for 7-Month-Old Infant (8.4 kg)
For a 7-month-old infant weighing 8.4 kg, ondansetron should be dosed at 0.15 mg/kg intramuscularly or intravenously, which equals 1.26 mg (approximately 1.3 mg), with a maximum dose of 16 mg. 1
Evidence-Based Dosing Recommendation
The most relevant and high-quality guideline evidence comes from the 2017 international consensus on Food Protein-Induced Enterocolitis Syndrome (FPIES), which provides specific ondansetron dosing for infants ≥6 months of age 1:
- Dose: 0.15 mg/kg/dose 1
- Route: Intramuscular or intravenous 1
- Maximum: 16 mg/dose 1
- For this 8.4 kg infant: 8.4 kg × 0.15 mg/kg = 1.26 mg (round to 1.3 mg)
Age-Specific Considerations
Critical caveat: Ondansetron is only recommended for infants ≥6 months of age 1. At 7 months, this infant meets the minimum age requirement. The guideline explicitly states this age restriction for safety reasons, as there is limited data in younger infants 1.
Clinical Context for Use
Ondansetron at this dose is indicated for 1:
- Moderate FPIES reactions (>3 episodes of emesis with mild lethargy)
- Severe FPIES reactions (>3 episodes of emesis with severe lethargy, hypotonia, or ashen/cyanotic appearance)
- Can be considered for mild reactions in infants ≥6 months (1-2 episodes of emesis, no lethargy)
Route Selection
- Intramuscular route is preferred when IV access is difficult or delayed 1
- Intravenous route should be used when IV access is already established, particularly in severe presentations requiring fluid resuscitation 1
Important Safety Points
- Do not use in infants <6 months old unless the situation is judged critical, due to extremely limited safety and efficacy data 1
- Monitor for response over 4-6 hours from onset of reaction 1
- Ondansetron may cause mild sedation, though this is generally well-tolerated 2, 3
- The drug has a half-life of approximately 3.5 hours, which is slightly shorter in children compared to adults 3, 4
Common Pitfall to Avoid
Do not confuse this dosing with the influenza antiviral dosing tables found in multiple pediatric guidelines 1—those are completely unrelated to ondansetron (Zofran) dosing and pertain to oseltamivir, zanamivir, and other antivirals.