What is the appropriate dosage of Zofran (ondansetron) for a 15-month-old child?

Ondansetron Dosing for a 15-Month-Old Child

For a 15-month-old child, ondansetron should be dosed at 0.15 mg/kg per dose (maximum 16 mg), administered orally, intravenously, or intramuscularly depending on the clinical scenario. 1

Weight-Based Dosing Calculation

• A typical 15-month-old weighs approximately 10-12 kg 1
• Using the standard pediatric dose of 0.15 mg/kg:
  • For a 10 kg child: 1.5 mg per dose
  • For a 12 kg child: 1.8 mg per dose 1
• The maximum single dose is 16 mg, though this ceiling is rarely relevant for toddlers 1

Route of Administration by Clinical Context

For Acute Gastroenteritis (Most Common Indication)

• Oral disintegrating tablet (ODT) is preferred for ease of administration in young children 2, 3
• Single dose of 0.15 mg/kg orally in the emergency department or clinic setting 3
• Onset of action occurs within 30 minutes of oral administration 4

For Food Protein-Induced Enterocolitis Syndrome (FPIES)

• Ondansetron is appropriate for children ≥6 months of age 5, 1
• For mild episodes: 0.15 mg/kg intramuscularly (maximum 16 mg) 5, 1
• For moderate-to-severe episodes: 0.15 mg/kg intravenously or intramuscularly (maximum 16 mg) 5, 1
• This 15-month-old meets the age requirement for safe use 5

For Chemotherapy-Induced Nausea/Vomiting

• 0.15 mg/kg IV 30 minutes before chemotherapy, then repeat at 4 and 8 hours after the first dose 1, 2
• Combining with dexamethasone significantly improves efficacy 1, 2

Critical Safety Considerations

Age-Specific Precautions

• Do not use in infants under 6 months of age for FPIES management due to limited safety data 5, 1
• At 15 months, this child is well above the minimum age threshold 5

QT Interval Prolongation

• Ondansetron can prolong the QT interval in a dose-dependent manner 1, 6
• The 0.15 mg/kg dose with 16 mg maximum provides an appropriate safety margin 1
• Use with special caution in children with underlying heart disease 5

Overdose Risk in Toddlers

• Severe toxicity has been reported in a 12-month-old who ingested 56-64 mg (seven to eight 8 mg tablets), resulting in seizures, obtundation, and serotonin syndrome 6
• Counsel caregivers to store ondansetron securely out of reach of toddlers, particularly the ODT formulation which may be mistaken for candy 6

Pharmacokinetic Considerations in Young Children

• Pediatric patients have increased clearance compared to adults, with a shorter half-life of approximately 2.5-3 hours 4, 7
• This faster metabolism supports the safety of standard weight-based dosing in toddlers 4
• Peak plasma concentrations occur 1 hour after oral administration 4

Common Pitfalls to Avoid

• Avoid repeat dosing within 4 hours unless specifically indicated for chemotherapy protocols 1
• Do not exceed the maximum single dose of 16 mg, even in larger toddlers 1
• Do not use routinely for simple viral gastroenteritis without evidence of dehydration or failed oral rehydration 3
• Recognize that ondansetron does not treat the underlying cause and should be part of comprehensive rehydration therapy 3

Expected Efficacy and Monitoring

• In gastroenteritis, ondansetron reduces vomiting episodes and improves oral rehydration success 2, 3
• Monitor for ongoing vomiting, adequate oral intake, and signs of dehydration after administration 3
• The dose range of 0.13-0.26 mg/kg shows similar efficacy, so precise weight-based calculation is less critical than ensuring the dose falls within this range 3

Tolerability Profile

• Generally well tolerated in young children 2, 7
• Most common adverse effects include headache (less relevant in toddlers who cannot report it), constipation, and diarrhea 2, 7
• Ondansetron does not cause extrapyramidal reactions, unlike metoclopramide, making it safer for pediatric use 7