Ondansetron Dosing for a 9-Year-Old Child
For a 9-year-old child, ondansetron should be dosed at 0.15 mg/kg (maximum 16 mg) per dose, with the specific route and frequency depending on the clinical indication. 1
Weight-Based Dosing Strategy
The standard pediatric dosing is 0.15 mg/kg per dose with a maximum single dose of 16 mg. 1 For a typical 9-year-old weighing approximately 25-40 kg, this translates to:
- 25 kg child: 3.75 mg per dose
- 30 kg child: 4.5 mg per dose
- 35 kg child: 5.25 mg per dose
- 40 kg child: 6 mg per dose
Route and Frequency by Clinical Context
For Chemotherapy-Induced Nausea/Vomiting
Highly emetogenic chemotherapy: Administer 0.15 mg/kg IV or IM (maximum 16 mg) 30 minutes before chemotherapy, then repeat at 4 and 8 hours after the first dose. 1 For children receiving highly emetogenic chemotherapy, combining ondansetron with dexamethasone significantly improves efficacy. 1
Moderately emetogenic chemotherapy: Use a 5-HT3 receptor antagonist (ondansetron or granisetron) combined with dexamethasone. 1 The FDA label supports oral dosing of 4 mg three times daily for children under 12 years, which showed similar efficacy to 8 mg three times daily in adolescents 12-18 years. 2
For Acute Gastroenteritis/Vomiting
Single oral dose: 0.15 mg/kg (maximum 16 mg) is effective for reducing vomiting episodes and decreasing the need for IV rehydration and hospitalization. 3 Research demonstrates that doses ranging from 0.13-0.26 mg/kg show similar efficacy without increased side effects, supporting the 0.15 mg/kg standard. 4
For Food Protein-Induced Enterocolitis Syndrome (FPIES)
Age restriction applies: Ondansetron should only be used in children ≥6 months of age. 1
- Mild episodes: Consider 0.15 mg/kg IM (maximum 16 mg) 1
- Moderate-to-severe episodes: Administer 0.15 mg/kg IV or IM (maximum 16 mg) 1
For Postoperative Nausea/Vomiting
Prophylactic dosing: 0.1-0.15 mg/kg IV (maximum 16 mg) administered before or during anesthesia induction is significantly more effective than placebo, droperidol, or metoclopramide. 5
Practical Formulation Considerations
Oral disintegrating tablets are available in 4 mg and 8 mg strengths, making them practical for children who have difficulty swallowing pills. 2 Round doses to the nearest available tablet strength for ease of administration:
- For calculated doses of 3-5 mg: use 4 mg tablet
- For calculated doses of 6-10 mg: use 8 mg tablet
- For doses >10 mg: use combination of tablets not exceeding 16 mg maximum
Critical Safety Considerations
QTc prolongation: Ondansetron can prolong the QT interval in a dose-dependent manner. 2 The 32 mg single IV dose previously used in adults is no longer recommended due to this risk. 2 The pediatric dose of 0.15 mg/kg with a 16 mg maximum provides an appropriate safety margin.
Age restriction: Do not use ondansetron in infants under 6 months of age for FPIES management. 1 However, research in gastroenteritis has included children as young as 6 months with demonstrated safety. 3
Diarrhea: Ondansetron may increase diarrhea episodes in children with gastroenteritis, though this does not outweigh the benefits of reduced vomiting and decreased need for IV therapy. 3
No dosage adjustment needed for renal impairment or based on age alone. 2
Common Pitfalls to Avoid
Avoid exceeding 16 mg per dose even in larger/older children, as this increases the risk of QTc prolongation without additional efficacy benefit. 1, 2
Do not use the adult 32 mg single-dose regimen in pediatric patients. 2
For severe FPIES reactions, do not delay IV access and fluid resuscitation while attempting to administer ondansetron—give IM if IV access is difficult. 1
Recognize that ondansetron alone may be insufficient for highly emetogenic chemotherapy; combination with dexamethasone or aprepitant significantly improves outcomes. 1