Ondansetron Dosing for a 4-Year-Old, 25 kg Male
For this 4-year-old child weighing 25 kg, administer ondansetron 0.15 mg/kg per dose, which equals 3.75 mg (rounded to 4 mg in clinical practice), with a maximum single dose of 16 mg. 1
Weight-Based Dosing Calculation
- The standard pediatric dose is 0.15 mg/kg per dose for children ≥6 months of age 1, 2
- For a 25 kg child: 25 kg × 0.15 mg/kg = 3.75 mg per dose 1
- The maximum single dose is capped at 16 mg regardless of weight 1, 2
- This child is well below the maximum dose threshold 1
Route of Administration
Intravenous (IV) Route
- IV is preferred for severe symptoms (e.g., severe vomiting with dehydration, hypotension, or extreme lethargy) 1
- Administer 0.15 mg/kg (3.75 mg for this patient) IV 1
Intramuscular (IM) Route
- IM may be used when IV access is unavailable or delayed 1
- Same dose applies: 0.15 mg/kg (3.75 mg) IM 1
Oral Route
- Oral ondansetron at 0.1-0.15 mg/kg has demonstrated efficacy in pediatric patients 2, 3
- The injectable formulation can be given orally if needed 3
Dosing Frequency
- The dose can be repeated every 8 hours as clinically indicated 2, 4
- For chemotherapy-induced emesis, the typical regimen is three doses: 30 minutes before chemotherapy, then at 4 and 8 hours afterward 4
- In acute care settings without hepatic impairment, dosing can be repeated as needed 1
Important Safety Considerations
Cardiac Precautions
- Exercise special caution in children with underlying heart disease due to potential QT interval prolongation 1
- Monitor for arrhythmias in at-risk patients 1
Age Eligibility
- This 4-year-old patient meets the age requirement (≥6 months) for ondansetron use 1
Common Adverse Effects
- Mild to moderate headache, constipation, and diarrhea are most frequently reported 2
- In postoperative settings, wound problems, anxiety, drowsiness, and pyrexia may occur 2
- Serious adverse events are rare, with severe reactions occurring in <1% of pediatric patients 5
Clinical Context-Specific Dosing
The 0.15 mg/kg dose (3.75 mg for this 25 kg child) is appropriate across multiple clinical scenarios:
- Chemotherapy-induced nausea/vomiting: 0.15 mg/kg IV/IM 1, 2
- Postoperative nausea/vomiting: 0.15 mg/kg IV (though doses as low as 0.05 mg/kg have shown efficacy) 6
- Food protein-induced enterocolitis syndrome (FPIES): 0.15 mg/kg IV for severe symptoms or IM for moderate symptoms 1
Practical Dosing Note
While the calculated dose is 3.75 mg, rounding to 4 mg is clinically appropriate and safe given the wide therapeutic window and the fact that doses up to 0.45 mg/kg have been used in pediatric patients without significant adverse effects 3.