What is the recommended pediatric dose of ondansetron (Zofran) for children ≥ 4 kg?

Ondansetron Pediatric Dosing

The recommended pediatric dose of ondansetron for children ≥4 kg is 0.15 mg/kg per dose (maximum 16 mg per single dose), administered intravenously, intramuscularly, or orally depending on clinical context. 1, 2

Weight-Based Calculation

• Calculate the dose precisely as 0.15 mg/kg without rounding beyond the exact calculation, as ondansetron has a narrow therapeutic window. 2
• For practical examples: a 10 kg child receives 1.5 mg, a 20 kg child receives 3 mg, a 30 kg child receives 4.5 mg, and a 40 kg child receives 6 mg per dose. 1
• The absolute maximum is 16 mg per single administration, regardless of weight (reached at approximately 107 kg). 1, 2

Age-Specific Restrictions

• Ondansetron should only be used in infants ≥6 months of age due to limited safety and efficacy data in younger infants. 1, 2
• For infants 6 months to 2 years weighing ≥4 kg, the same 0.15 mg/kg dosing applies. 1
• Standard weight-based dosing (0.15 mg/kg, maximum 16 mg) applies to children 2-12 years and adolescents. 2

Route of Administration by Clinical Context

Chemotherapy-Induced Nausea/Vomiting

• High-emetic-risk chemotherapy: Administer 0.15 mg/kg IV (maximum 16 mg) 30 minutes before chemotherapy, then repeat at 4 and 8 hours after the first dose, combined with dexamethasone and aprepitant for optimal efficacy. 1, 2, 3
• Moderate-emetic-risk chemotherapy: Use ondansetron 0.15 mg/kg combined with dexamethasone as a two-drug regimen. 1, 2
• Low-emetic-risk chemotherapy: Ondansetron monotherapy at 0.15 mg/kg is sufficient. 2
• The addition of dexamethasone significantly improves antiemetic efficacy compared to ondansetron alone. 1, 4

Postoperative Nausea/Vomiting

• Children weighing ≤40 kg: Administer 0.1 mg/kg IV over at least 30 seconds immediately before or following anesthesia induction. 3
• Children weighing >40 kg: Administer 4 mg IV over at least 30 seconds. 3
• For infants 1-24 months undergoing routine surgery, a single 0.1 mg/kg IV dose within 5 minutes following induction is effective. 3

Acute Gastroenteritis

• Children >4 years: Administer 0.15 mg/kg orally (maximum 8 mg for oral administration) for persistent vomiting. 1, 5
• Begin with reduced osmolarity oral rehydration solution as first-line therapy; ondansetron facilitates oral rehydration by reducing vomiting. 5

Food Protein-Induced Enterocolitis Syndrome (FPIES)

• Mild episodes (infants ≥6 months): 0.15 mg/kg IM (maximum 16 mg). 1
• Moderate-to-severe episodes (infants ≥6 months): 0.15 mg/kg IV or IM (maximum 16 mg). 1

Oral Administration Considerations

• Ondansetron oral suspension is available at 6 mg/mL concentration. 1, 2
• For a 3 mg dose, administer 0.5 mL of suspension. 2
• May be given without regard to meals, though co-administration with food can improve gastrointestinal tolerability. 1, 2

Dosing Frequency

• For chemotherapy: Three doses on day 1 (pre-chemotherapy, then at 4 and 8 hours), followed by oral dosing for at least 3 days after the last day of chemotherapy. 3, 6
• For acute vomiting: Single-dose therapy is often sufficient, though ondansetron can be administered every 8 hours if needed, with maximum daily doses typically limited to 2-3 doses in 24 hours. 1
• Repeat dosing caveat: In postoperative settings, administering a second 4 mg IV dose does not provide additional control if the first dose was ineffective. 3

Critical Safety Considerations

• QT prolongation: Ondansetron can prolong the QT interval in a dose-dependent manner; the 0.15 mg/kg dose with 16 mg maximum provides an appropriate safety margin. 1
• Avoid in specific populations: Do not use in children with congenital long QT syndrome, electrolyte abnormalities (hypokalemia, hypomagnesemia), or concurrent QT-prolonging medications. 1
• Special caution in infants with heart disease: Exercise heightened vigilance when administering to infants with underlying cardiac conditions. 1
• Contraindication in inflammatory diarrhea: Avoid ondansetron if the child has bloody diarrhea or high fever suggesting invasive/inflammatory diarrhea. 5

Common Pitfalls to Avoid

• Do not round doses excessively: Calculate precisely to 0.15 mg/kg to avoid under- or overdosing. 1, 2
• Do not confuse maximum doses: The 16 mg maximum applies to IV/IM routes; oral administration has an 8 mg maximum per single dose for practical purposes in younger children. 1
• Do not use in infants <6 months: Limited safety data exists for this age group. 1, 2
• Do not rely on ondansetron alone for high-emetic-risk chemotherapy: Combination with dexamethasone and aprepitant is significantly more effective. 1, 2
• Recognize increased diarrhea as a side effect: Ondansetron may increase diarrhea frequency in gastroenteritis, but this does not worsen clinical outcomes. 5