Ondansetron Dosing for a 5-Year-Old
For a 5-year-old child, ondansetron should be dosed at 0.15 mg/kg per dose (maximum 8 mg), with the specific weight-based dose depending on the child's weight and clinical indication. 1
Weight-Based Dosing Algorithm
A typical 5-year-old weighs approximately 15-23 kg. Based on this weight range, the following dosing applies:
The standard pediatric calculation of 0.15 mg/kg translates to approximately 2.25-3.45 mg for most 5-year-olds (15-23 kg range). 1
Route and Frequency by Clinical Context
For Chemotherapy-Induced Nausea/Vomiting
- First dose: 0.15 mg/kg IV or IM (maximum 16 mg) given 30 minutes before chemotherapy 1
- Subsequent doses: Repeat at 4 and 8 hours after the first dose 1
- Enhanced efficacy: Combining ondansetron with dexamethasone significantly improves antiemetic control for highly emetogenic chemotherapy 1, 3
For Postoperative Nausea/Vomiting
- Single dose: 0.1 mg/kg IV (for children weighing ≤40 kg) or 4 mg (for children weighing >40 kg) given immediately before or following anesthesia induction 4
- Timing: Administer over at least 30 seconds 4
For Acute Gastroenteritis with Vomiting
- Single oral dose: 0.15 mg/kg (maximum 8 mg) 5, 6
- Timing: Begin oral rehydration 15 minutes after ondansetron administration 5
- Evidence: A single dose reduces IV fluid requirements (p=0.015) and hospitalization rates (p=0.007) compared to placebo 5
Formulation Options
Oral Administration
- Oral disintegrating tablets (ODT): Preferred for children who have difficulty swallowing; dissolves on tongue without water 2
- Oral suspension: Available at 6 mg/mL concentration 1
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL 1
Parenteral Administration
- IV/IM: 0.15 mg/kg per dose (maximum 16 mg for chemotherapy; maximum 4 mg for postoperative use in children ≤40 kg) 1, 4
Critical Safety Considerations
QT prolongation risk: Ondansetron can prolong the QT interval in a dose-dependent manner; the 0.15 mg/kg dose with appropriate maximum limits provides an adequate safety margin. 1
Age restrictions: For food protein-induced enterocolitis syndrome (FPIES), ondansetron should only be used in children ≥6 months of age. 1
Diarrhea: In gastroenteritis patients, ondansetron may increase diarrhea episodes during the 48 hours following administration, though this does not typically require treatment modification. 5
Common Pitfalls to Avoid
- Underdosing: Do not use adult fixed doses (4 mg or 8 mg) without weight-based calculation in children under 40 kg 1, 2
- Delayed administration: For chemotherapy, the first dose must be given 30 minutes before chemotherapy begins, not after nausea develops 1
- Monotherapy in high-risk settings: For highly emetogenic chemotherapy, ondansetron alone is insufficient; add dexamethasone for optimal efficacy 1, 3
Pharmacokinetic Considerations
Children aged 4-18 years demonstrate higher ondansetron clearance compared to adults, resulting in a shorter half-life (2.5-3 hours vs. 3-3.5 hours in adults), which supports the dosing intervals recommended above. 4
No dosage adjustment is required for renal impairment in pediatric patients, as renal clearance contributes only 5% to overall drug elimination. 4