Ondansetron Dosing for a 12 kg Infant
For a 12 kg infant, administer ondansetron 0.15 mg/kg per dose, which equals 1.8 mg (can be rounded to 2 mg for practical administration), with a maximum single dose of 16 mg. 1
Route-Specific Dosing
Intravenous (IV) Administration
- Dose: 0.15 mg/kg/dose (1.8 mg for a 12 kg infant) 2, 1
- Maximum single dose: 16 mg 2, 1
- This is the preferred route for severe symptoms requiring immediate intervention 2
Intramuscular (IM) Administration
- Dose: 0.15 mg/kg/dose (1.8 mg for a 12 kg infant) 2, 1
- Maximum single dose: 16 mg 2, 1
- Use when IV access is difficult or delayed 2
Oral Administration
- Dose: 0.1 mg/kg for oral disintegrating formulation 3
- For a 12 kg infant, this equals 1.2 mg
- Oral route is appropriate for mild-to-moderate symptoms in outpatient settings 4
Age Restrictions and Safety
Ondansetron should only be used in infants ≥6 months of age. 2, 1 This is a critical safety threshold established by the American Academy of Allergy, Asthma, and Immunology. 2
Important Safety Considerations
- Special caution is warranted in children with heart disease due to potential QT interval prolongation 1
- Monitor for cardiac effects, particularly if the infant has underlying cardiac conditions 1
- The dose range of 0.13-0.26 mg/kg has been shown to be safe without increased side effects at higher doses within this range 5
Clinical Context-Specific Dosing
For Acute Gastroenteritis
- Mild symptoms (1-2 episodes of vomiting, no lethargy): Consider ondansetron 0.15 mg/kg IM if age ≥6 months 2
- Moderate symptoms (>3 episodes of vomiting with mild lethargy): Administer ondansetron 0.15 mg/kg IM 2
- Severe symptoms (>3 episodes with severe lethargy, hypotonia, or cyanosis): Administer ondansetron 0.15 mg/kg IV; if IV access is difficult, use IM route 2
For Chemotherapy-Induced Nausea/Vomiting
- Standard dosing: 0.15 mg/kg IV for three doses (30 minutes before chemotherapy, then 4 and 8 hours afterward) 6
- Loading doses of 16 mg/m² (maximum 24 mg) have been shown to be safe in pediatric oncology patients 7
For Postoperative Nausea/Vomiting
- Dose: 0.075-0.15 mg/kg IV administered before or during surgery 3
- Single dose is typically sufficient for prophylaxis 3
Practical Administration Tips
- Rounding for ease of administration: The dose can be rounded by up to 15% for practical home administration 8
- For a 12 kg infant receiving 1.8 mg, rounding to 2 mg is acceptable and practical 8
- Oral disintegrating tablets dissolve rapidly and do not require water, making administration easier in vomiting children 4
Common Pitfalls to Avoid
- Do not use in infants <6 months old – this is outside the approved age range and safety data are insufficient 2, 1
- Do not exceed 16 mg as a single dose regardless of weight-based calculation 2, 1
- Avoid in children with known cardiac conduction abnormalities without cardiology consultation 1
- Do not assume higher doses are more effective – research shows no additional benefit beyond 0.15 mg/kg within the therapeutic range 5
Efficacy Data
- A single oral dose of ondansetron decreased continued vomiting within the first 4 hours from 42.9% to 19.5% (54.5% reduction) in children with acute gastroenteritis 4
- Number needed to treat: 4 children to prevent one case of continued vomiting 4
- The medication is cost-effective, reducing total mean costs by 31.2% compared to care without ondansetron 4