What is the recommended dosage of Ondansetron (Ondansetron HCl) for a 6-year-old patient weighing approximately 20 kg?

Ondansetron Dosing for a 6-Year-Old Child

For a 6-year-old child weighing approximately 20 kg, administer ondansetron 0.15 mg/kg, which equals 3 mg per dose, with an absolute maximum single dose of 16 mg. 1, 2

Weight-Based Dosing Calculation

• The standard pediatric dose is 0.15 mg/kg per administration 1, 2, 3
• For a 20 kg child: 0.15 mg/kg × 20 kg = 3 mg per dose 2
• This dosing applies regardless of route (IV, IM, or oral) 2, 3

Route-Specific Administration

Intravenous (IV) Administration

• Administer 3 mg (0.15 mg/kg) IV over 2-5 minutes 3
• Maximum single dose: 16 mg 1, 2, 3

Intramuscular (IM) Administration

• Use the same dose as IV: 3 mg (0.15 mg/kg) IM when IV access is difficult 2, 3
• IM route is an acceptable alternative with equivalent dosing 2, 3

Oral Administration

• Oral dosing follows the same 0.15 mg/kg calculation = 3 mg 4
• Oral bioavailability is 59%, but the recommended dose remains unchanged 5, 6

Clinical Context and Frequency

For Postoperative Nausea/Vomiting

• Single dose of 0.15 mg/kg (3 mg) is typically sufficient 3

For Chemotherapy-Induced Nausea/Vomiting

• Administer 0.15 mg/kg every 4 hours for three doses (30 minutes before chemotherapy, then at 4 and 8 hours) 3, 5
• Consider adding dexamethasone for enhanced efficacy, as combination therapy significantly improves antiemetic control compared to ondansetron alone 1, 3, 4

For Acute Gastroenteritis

• Single oral dose of 0.1-0.15 mg/kg (2-3 mg) effectively reduces vomiting 7
• One dose decreased continued vomiting from 42.9% to 19.5% within 4 hours 7

Critical Safety Considerations

• Exercise special caution in children with cardiac disease or known heart conditions due to potential QT interval prolongation 1, 2, 3
• Monitor for cardiac effects if the child has any underlying heart disease 2
• Ondansetron is generally well tolerated in pediatric patients, with headache, constipation, and diarrhea being the most common mild adverse events 4

Common Pitfalls to Avoid

• Never exceed 16 mg as a single dose, regardless of calculated weight-based dosing 1, 2, 3
• Do not confuse the 0.15 mg/kg pediatric dose with adult fixed dosing regimens 8
• Pediatric patients have increased clearance (half-life 2.5 hours) compared to adults, but this does not require dose adjustment beyond standard weight-based calculation 6
• The 32 mg single-dose regimen mentioned in some adult guidelines should not be extrapolated to pediatric patients 5