Ondansetron Dosing for a 2-Year-Old Child
For a 2-year-old child, ondansetron should be dosed at 0.15 mg/kg as a single oral dose, with weight-based adjustments: children ≤15 kg receive a maximum of 4 mg, while those >15 kg can receive higher doses based on weight categories. 1, 2
Weight-Based Dosing Algorithm
The dosing depends on the child's weight:
- For children ≤15 kg (most 2-year-olds fall in this category): Administer 0.15 mg/kg orally as a single dose, typically resulting in 2-4 mg 1, 2
- For children >15-23 kg: 0.15 mg/kg, typically 4 mg 1
- Intravenous dosing (if oral route not feasible): 0.1-0.15 mg/kg IV 1
Clinical Context and Indications
Ondansetron is most effective for:
- Acute gastroenteritis with vomiting: A single 0.15 mg/kg oral dose reduces the need for IV rehydration by over 50% compared to placebo 2
- Chemotherapy-induced nausea/vomiting: Multiple doses of 5 mg/m² or 0.15 mg/kg IV/oral can be given 1
- Postoperative nausea/vomiting: 0.1-0.15 mg/kg IV is effective 1
Practical Administration Tips
- Timing: Administer after failure of initial oral rehydration in gastroenteritis 2
- Formulation: Oral dosing is preferred when the child can tolerate it; ondansetron dissolving tablets work well in young children 1
- Single dose efficacy: One dose is often sufficient for acute gastroenteritis, avoiding unnecessary repeated dosing 2
Safety Profile
Ondansetron is well-tolerated in children as young as 3 months:
- Most common side effects are mild headache, constipation, or diarrhea 1
- No extrapyramidal reactions occur (unlike metoclopramide) 3
- No sedation, which is advantageous for assessment and discharge planning 4, 1
- No dosage adjustment needed for renal impairment 5
Common Pitfalls to Avoid
- Do not underdose: Studies show even doses as low as 2 mg/m²/day are effective, but 0.15 mg/kg is the evidence-based standard 4, 1
- Do not use domperidone instead: Domperidone showed no benefit over placebo for gastroenteritis-related vomiting in children 2
- Avoid repeated dosing without reassessment: A single dose is typically sufficient for acute gastroenteritis; if vomiting persists, investigate other causes 2