What is the appropriate ondansetron (Zofran) dose for a child, including weight‑based dosing, route (intravenous, intramuscular, oral), maximum single and daily limits, and age considerations for indications such as chemotherapy, postoperative nausea, or gastroenteritis?

Pediatric Ondansetron Dosing

The standard pediatric ondansetron dose is 0.15 mg/kg per dose (maximum 16 mg per dose), with route and frequency determined by clinical indication—chemotherapy, postoperative nausea, or gastroenteritis. 1

Weight-Based Dosing Algorithm

Use 0.15 mg/kg per dose as the universal starting point across all indications. 1 This translates to practical dosing as follows:

• 15 kg child: 2.25 mg per dose 1
• 20 kg child: 3 mg per dose 1
• 25 kg child: 3.75 mg per dose 1
• 30 kg child: 4.5 mg per dose 1
• 40 kg child: 6 mg per dose 1
• >40 kg: 6-8 mg per dose (approaching adult dosing) 1

Maximum single dose is 16 mg regardless of weight. 1

Route and Frequency by Clinical Context

Chemotherapy-Induced Nausea and Vomiting

For highly emetogenic chemotherapy, administer 0.15 mg/kg IV (maximum 16 mg) 30 minutes before chemotherapy, then repeat at 4 hours and 8 hours after the first dose. 1 The American Society of Clinical Oncology strongly recommends combining ondansetron with dexamethasone and aprepitant for optimal efficacy in this setting. 1

For moderate-emetic-risk chemotherapy, use ondansetron 0.15 mg/kg combined with dexamethasone as a two-drug regimen. 1 This combination significantly improves antiemetic efficacy compared to ondansetron alone. 1, 2

For low-emetic-risk chemotherapy, ondansetron monotherapy at 0.15 mg/kg is sufficient. 1

Postoperative Nausea and Vomiting

Administer 0.1 mg/kg IV (can use up to 0.15 mg/kg) as a single dose during anesthesia for procedures with high PONV risk (tonsillectomy, strabismus repair). 3 Research demonstrates that 50 mcg/kg (0.05 mg/kg) IV is as effective as higher doses, but guideline recommendations support 0.1-0.15 mg/kg for consistency. 3

Combining ondansetron with dexamethasone is significantly more effective than ondansetron alone in the postoperative setting. 2

Acute Gastroenteritis

For children >4 years with acute gastroenteritis and vomiting, administer 0.15 mg/kg orally (maximum 8 mg for oral route) as a single dose. 4 The Infectious Diseases Society of America recommends this specifically for children over 4 years of age. 4

Practical oral dosing for gastroenteritis:

• Use oral disintegrating tablets when available for ease of administration 4
• Oral suspension concentration is 6 mg/mL 1
• A dose-response study found no superiority of doses above 0.13 mg/kg in the gastroenteritis setting 5

Follow ondansetron with reduced osmolarity oral rehydration solution (ORS) at 5 mL/minute initially, then maintenance fluids. 4

Food Protein-Induced Enterocolitis Syndrome (FPIES)

For infants ≥6 months with FPIES:

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

The dose remains 0.15 mg/kg regardless of severity; only the route and adjunctive therapy differ. 1

Critical Age Restrictions

Do NOT use ondansetron in infants <6 months of age except in critical situations, due to limited safety and efficacy data. 1 The American Academy of Pediatrics specifically advises against routine use in this age group. 1

For infants 6-12 months, the weight-based dose of 0.15 mg/kg applies (e.g., 1.1 mg for a 7.3 kg infant). 1

Maximum Dose Limits

Single dose maximum: 16 mg 1

Daily maximum varies by indication:

• Chemotherapy: Up to 3 doses (at 0,4, and 8 hours) = 48 mg maximum daily 1
• Postoperative: Single dose only 3
• Gastroenteritis: Single dose only 4

Route-Specific Considerations

IV/IM administration:

• Preferred for chemotherapy and severe vomiting 1
• Administer IV over 15 minutes to minimize QT prolongation risk 1
• IM route acceptable for FPIES when IV access not established 1

Oral administration:

• Preferred for gastroenteritis and less severe presentations 4
• Oral disintegrating tablets dissolve without water 4
• Can be given without regard to meals, though administration with food may improve GI tolerability 6

Critical Safety Warnings

QT Prolongation Risk:

• Ondansetron prolongs the QT interval in a dose-dependent manner 1
• The 0.15 mg/kg dose with 16 mg maximum provides an appropriate safety margin 1
• Avoid in children with congenital long QT syndrome or electrolyte abnormalities 1
• Special caution warranted in infants with congenital heart disease 1

Gastroenteritis-Specific Cautions:

• Ondansetron may increase diarrhea frequency, but this does not worsen outcomes 4
• Avoid if bloody diarrhea or high fever suggests inflammatory/invasive diarrhea 4
• Monitor for 4-6 hours after administration to assess response 1

Common Pitfalls to Avoid

Do not withhold solid food for 24 hours after ondansetron in gastroenteritis—early feeding improves outcomes. 4

Do not use the BRAT diet during acute gastroenteritis—return to normal age-appropriate diet once rehydrated. 4

Do not combine with antimotility agents (loperamide) in children <18 years with acute diarrhea. 4

Do not exceed 8 mg per single oral dose in the gastroenteritis setting, even though the IV maximum is 16 mg. 1

For chemotherapy, do not use ondansetron as monotherapy for highly emetogenic regimens—always combine with dexamethasone. 1