Ondansetron Dosing for a 20-Month-Old Weighing 13.5 kg

For a 20-month-old child weighing 13.5 kg, the recommended ondansetron dose is 0.15 mg/kg, which equals approximately 2 mg per dose. 1

Weight-Based Dosing Calculation

At 13.5 kg, this child falls below the 15 kg threshold used in most pediatric dosing guidelines 1
Using the standard 0.15 mg/kg/dose recommendation: 13.5 kg × 0.15 mg/kg = 2.025 mg (round to 2 mg) 1
The maximum single dose should not exceed 16 mg 1

Ondansetron is recommended for infants ≥6 months of age, and at 20 months, this child is well within the safe age range 1
For infants <6 months, ondansetron should only be used if the situation is judged critical due to limited safety and efficacy data 1

Ondansetron is most commonly used in pediatrics for:
- Chemotherapy-induced nausea and vomiting: Multiple 0.15 mg/kg IV doses have shown efficacy, with 70-72% of children experiencing ≤2 emetic episodes 2
- Postoperative nausea and vomiting: 0.1-0.15 mg/kg IV has proven significantly superior to placebo and other antiemetics 2
- Acute gastroenteritis with vomiting: Reduces emesis during oral rehydration and lowers rates of IV fluid administration and hospital admission 3
- Food Protein-Induced Enterocolitis Syndrome (FPIES): 0.15 mg/kg/dose for moderate to severe reactions 1

Oral route: Bioavailability is approximately 60%, with peak plasma concentrations at 1 hour after administration 4, 5
Intravenous route: Preferred when IV access is already established, particularly in severe presentations requiring fluid resuscitation 1
Intramuscular route: Preferred when IV access is difficult or delayed 1
Ondansetron should be administered at least 30 minutes before chemotherapy when used prophylactically 6

Standard dosing: 0.15 mg/kg per dose, which can be repeated every 8 hours as needed 4, 2
For chemotherapy-induced emesis, the typical regimen is three doses on the day of chemotherapy (30 minutes before, then 4 and 8 hours afterward) 4
For gastroenteritis, additional doses every 8 hours may be given after discharge 3

Common adverse effects include headache (most frequent), constipation, and diarrhea 2, 5
Ondansetron is notably free of extrapyramidal side effects, unlike metoclopramide or prochlorperazine 5
In gastroenteritis patients, ondansetron may increase episodes of diarrhea during the 48-hour follow-up period 3
Monitor for response over 4-6 hours from onset of treatment 1
Ondansetron is generally well tolerated and rarely necessitates treatment withdrawal 2

Elimination half-life: Approximately 3.5 hours in healthy volunteers, but shorter in pediatric patients due to increased clearance 4, 5
Hepatic metabolism accounts for 95% of clearance; <5% is excreted unchanged in urine 5
No dosage adjustment needed based on age alone in children ≥6 months 1

Do not underdose: The 0.15 mg/kg dose has been validated in multiple studies and should not be reduced arbitrarily 1, 2
Avoid use in infants <6 months unless the clinical situation is critical 1
Do not rely on ondansetron alone for delayed chemotherapy-induced emesis, as efficacy for delayed symptoms has not been well established 4
Consider combination with dexamethasone in chemotherapy settings, as this significantly improves antiemetic efficacy 2