Ondansetron Dosing for a 36kg, 12-Year-Old Child
For a 12-year-old child weighing 36kg, administer ondansetron 0.15 mg/kg per dose, which equals 5.4 mg (can be rounded to 4 mg for practical administration using available tablet strengths), with a maximum single dose of 16 mg. 1, 2
Weight-Based Dosing Algorithm
- For children weighing >23-40 kg: The standard dose is 0.15 mg/kg per dose 1, 2
- For your 36kg patient: This calculates to 5.4 mg per dose 1, 2
- Practical rounding: The dose can be rounded by up to 15% for practical administration, so 4 mg (one standard tablet) is acceptable and commonly used 1, 2
- Alternative: If using the weight-based dosing table, children >23-40 kg receive 60 mg twice daily for treatment courses, but for single-dose antiemetic use, 4 mg is standard 1, 2
Route-Specific Administration
- Oral route: 0.15 mg/kg/dose (4-6 mg for this patient), available as oral disintegrating tablets (ODT) or regular tablets 1, 2
- Intravenous (IV) route: 0.15 mg/kg/dose (5.4 mg for this patient), maximum 16 mg single dose 1
- Intramuscular (IM) route: 0.15 mg/kg/dose (5.4 mg for this patient), maximum 16 mg single dose 1
Dosing Frequency
- Single dose: Most commonly used for acute nausea/vomiting 1, 2
- Repeat dosing: Can be repeated every 8 hours as needed 2
- Maximum daily dose: Do not exceed 16 mg per single dose regardless of weight-based calculation 1
Clinical Context Considerations
- For acute gastroenteritis with moderate symptoms (>3 episodes of vomiting with mild lethargy): Administer ondansetron 0.15 mg/kg IM or oral 1
- For postoperative nausea/vomiting: 0.1-0.15 mg/kg IV is effective 3, 4
- For chemotherapy-induced nausea: Multiple doses of 0.15 mg/kg may be used 3, 5
Safety Considerations and Contraindications
- Age restriction: Only use in children ≥6 months of age 1
- Cardiac concerns: Exercise special caution in children with heart disease due to potential QT interval prolongation 1
- Avoid in: Children with known cardiac conduction abnormalities without cardiology consultation 1
Common Pitfalls to Avoid
- Do not exceed 16 mg as a single dose, even if weight-based calculation suggests higher 1
- Do not use in infants <6 months old, as safety data are insufficient 1
- Monitor for diarrhea: Ondansetron may increase diarrhea episodes in gastroenteritis patients 6
- Watch for headache: The most common adverse effect, though generally mild 3, 4
Practical Administration Tips
- Oral disintegrating tablets (ODT) are preferred for children who may have difficulty swallowing or ongoing nausea 2, 3
- Administer 15 minutes before oral rehydration in gastroenteritis cases 6
- Can be given without regard to meals, though administration with food may improve tolerability 3
Expected Efficacy
- In gastroenteritis: Reduces median vomiting episodes to 0 during ED observation, decreases IV fluid requirements, and lowers admission rates 6
- In postoperative setting: Superior to placebo, droperidol, and metoclopramide for preventing emesis 3
- Onset of action: Peaks 1 hour after oral dose with half-life of 3.5 hours 4