What is the recommended pediatric dose of ondansetron (Zofran) based on weight and age for vomiting or nausea, including maximum single and daily doses and adjustments for chemotherapy, postoperative or gastroenteritis-related vomiting, hepatic impairment, and QT‑interval monitoring?

Ondansetron (Zofran) Pediatric Dosing

The standard pediatric dose of ondansetron is 0.15 mg/kg per dose (maximum 16 mg per single dose) administered IV, IM, or orally, with route and frequency determined by clinical indication. 1, 2

Weight-Based Dosing Calculation

• For children ≥6 months: Calculate 0.15 mg/kg per dose, with an absolute maximum of 16 mg per single dose 1, 2
• Practical examples by weight:
  • 10 kg child: 1.5 mg per dose 1
  • 20 kg child: 3 mg per dose 1
  • 30 kg child: 4.5 mg per dose 1
  • 40 kg child: 6 mg per dose 1
  • ≥107 kg: Maximum 16 mg per dose (do not exceed) 1

Route-Specific Administration

Oral Dosing

• Oral suspension concentration: 6 mg/mL 2
• Can be given without regard to meals, though food may improve GI tolerability 3
• Maximum single oral dose: 8 mg for routine gastroenteritis (16 mg for chemotherapy contexts) 4

IV/IM Dosing

• Same weight-based calculation: 0.15 mg/kg (maximum 16 mg) 1, 2
• Peak effect: 3 minutes for IV administration 5

Clinical Context-Specific Protocols

Chemotherapy-Induced Nausea/Vomiting

High-emetic-risk chemotherapy (cisplatin, high-dose cyclophosphamide):

• Three-drug regimen: Ondansetron 0.15 mg/kg IV + dexamethasone + aprepitant 1, 4
• Timing: Administer 30 minutes before chemotherapy, then repeat at 4 and 8 hours after first dose 1
• This combination is significantly more effective than ondansetron alone 2, 6

Moderate-emetic-risk chemotherapy (carboplatin, doxorubicin):

• Two-drug regimen: Ondansetron 0.15 mg/kg IV + dexamethasone 1, 4
• Dexamethasone addition significantly improves efficacy compared to ondansetron monotherapy 2, 6

Low-emetic-risk chemotherapy:

• Ondansetron monotherapy: 0.15 mg/kg per dose is sufficient 2, 4

Acute Gastroenteritis

• Age restriction: Only use in children ≥6 months 1, 4
• Recommended for children >4 years with vomiting to facilitate oral rehydration 2, 4
• Single dose is often sufficient: 0.15 mg/kg IM or oral (maximum 8 mg for oral route in gastroenteritis) 4, 7
• Can repeat every 8 hours if needed, though typically limited to 2-3 doses in 24 hours 2
• Must ensure adequate hydration alongside ondansetron administration 4
• Efficacy data: 41% higher chance of vomiting cessation within 8 hours compared to placebo, with 56% reduction in IV hydration needs 2

Food Protein-Induced Enterocolitis Syndrome (FPIES)

• Mild episodes: 0.15 mg/kg IM (maximum 16 mg) for children ≥6 months 1
• Moderate-to-severe episodes: 0.15 mg/kg IV or IM (maximum 16 mg) 1
• Monitor for 4-6 hours from onset to assess response 1

Postoperative Nausea/Vomiting

• Single prophylactic dose: 0.15 mg/kg IV (maximum 16 mg) given at induction or end of surgery 6
• Ondansetron is superior to droperidol and metoclopramide for PONV prevention 6

Radiation-Induced Nausea/Vomiting

• Dosing: 8 mg oral or 0.15 mg/kg IV once daily before radiation therapy 1, 2
• Continue daily on treatment days 2

Critical Age Restrictions

• Infants <6 months: Do NOT use ondansetron except in critical situations due to limited safety data 1, 4
• Infants 6 months to 12 months: Safe to use at standard weight-based dosing (0.15 mg/kg) 1, 2
• Children ≥2 years: Standard weight-based dosing applies across all indications 2

Maximum Dosing Limits

• Single dose maximum: 16 mg per dose (never exceed, regardless of weight) 1, 2, 4
• Oral maximum for gastroenteritis: 8 mg per single dose 4
• Daily maximum: Typically 2-3 doses in 24 hours for acute conditions 2
• Severe hepatic impairment: Do not exceed 8 mg total daily dose 4

QT Interval Prolongation Considerations

Ondansetron can prolong the QT interval in a dose-dependent manner, but recent pediatric studies show minimal clinical significance at standard doses. 1, 4

Risk Stratification

• Obtain baseline ECG if: Known cardiac disease, congenital long QT syndrome, or electrolyte abnormalities 1, 4
• Monitor electrolytes: Particularly potassium and magnesium, as abnormalities increase QT prolongation risk 4
• Avoid in: Children with congenital long QT syndrome or uncorrected electrolyte abnormalities 1

Reassuring Safety Data

• Recent ED studies show: 0.15 mg/kg IV ondansetron did not cause clinically significant QTc prolongation in children with gastroenteritis 8, 5
• Mean QTc change: 0.4 milliseconds (not clinically significant) 8
• The 16 mg maximum provides an appropriate safety margin 1

Drug Interactions

• Avoid concurrent use with other QT-prolonging medications (certain antibiotics, antiarrhythmics) 2

Comparative Efficacy

Ondansetron should be first-line antiemetic over metoclopramide or domperidone due to superior efficacy and safety profile. 4, 6

• Ondansetron vs. metoclopramide: Significantly more effective with fewer extrapyramidal side effects 4, 6
• Ondansetron vs. domperidone: 95% cessation of vomiting at 24 hours vs. 85% (statistically significant) 7
• Metoclopramide should NOT be first-line due to high incidence of dystonic reactions in children 4

Common Pitfalls to Avoid

• Do not exceed 16 mg single dose even in adolescents or large children—this is an absolute maximum 4
• Do not use in infants <6 months unless situation is truly critical 1, 4
• Do not use ondansetron as substitute for appropriate fluid resuscitation in gastroenteritis 2, 4
• Do not round ondansetron doses beyond precise calculation—this medication requires exact weight-based dosing 3
• Do not use for multiple consecutive days without reassessing the underlying cause of vomiting 4

Adverse Effects Profile

• Generally well-tolerated with rare treatment discontinuation 6
• Most common: Mild-to-moderate headache, constipation, diarrhea 6, 9
• Postoperative patients: Wound problems, anxiety, drowsiness, pyrexia 6
• Serious adverse effects are rare at standard pediatric doses 6, 8, 5