Ondansetron Dosing for 43 kg Patient
For a 43 kg pediatric patient, administer ondansetron 0.15 mg/kg per dose, which equals 6.45 mg (can be rounded to 6 mg for practical administration using available formulations), with a maximum single dose of 16 mg. 1, 2
Weight-Based Calculation
- 43 kg × 0.15 mg/kg = 6.45 mg per dose 1, 2
- This dose is well below the maximum single dose of 16 mg 2, 3
- Practical rounding to 6 mg or 8 mg (depending on available formulations) is acceptable 1
Route of Administration
Intravenous route:
- 0.15 mg/kg (6.45 mg for 43 kg patient) administered over at least 30 seconds 3
- For severe presentations with persistent vomiting or inability to tolerate oral intake 2
Intramuscular route:
- 0.15 mg/kg (6.45 mg for 43 kg patient) 2
- Alternative when IV access is difficult but patient requires parenteral therapy 2
Oral route:
- 0.15 mg/kg (6.45 mg for 43 kg patient) 1
- Appropriate for mild to moderate presentations where oral intake is feasible 1
- Oral disintegrating tablets may improve tolerability in vomiting patients 4
Clinical Context Considerations
For acute gastroenteritis with vomiting:
- Single dose of ondansetron 0.15 mg/kg is recommended for children >4 years old 1
- Reduces need for IV rehydration by 56% (RR 0.44) 5
- Reduces hospitalization rates by 51% (RR 0.49) 5
- Increases vomiting cessation within 8 hours by 41% (RR 1.41) 5
For food protein-induced enterocolitis syndrome (FPIES):
- Ondansetron 0.15 mg/kg (maximum 16 mg) for moderate to severe presentations 2
- Administer intramuscularly if age ≥6 months and IV access not yet established 2
- Consider IV ondansetron for severe presentations with hypotension or shock 2
For chemotherapy-induced nausea/vomiting:
- 0.15 mg/kg per dose for three doses (before chemotherapy, then 4 and 8 hours after) 6, 7
- Alternative single high-dose regimen: 0.6 mg/kg (maximum 32 mg) has shown equivalent efficacy 8
- For 43 kg patient: either 6.45 mg × 3 doses OR single 25.8 mg dose (can round to 24-32 mg) 8
For postoperative nausea/vomiting:
- Single dose of 0.1-0.15 mg/kg (4.3-6.45 mg for 43 kg patient) 6
- Since patient weighs >40 kg, can use adult dose of 4 mg 3
Dose-Response Evidence
- No significant dose-response relationship exists within the range of 0.13-0.26 mg/kg 4
- Higher doses (up to 0.26 mg/kg) do not provide superior efficacy compared to 0.15 mg/kg 4
- Higher doses also do not increase side effects within this range 4
- This supports using the standard 0.15 mg/kg dose rather than escalating 4
Timing and Repeat Dosing
For acute gastroenteritis:
- Single dose is typically sufficient 5
- May repeat every 8-12 hours if vomiting recurs, though evidence for repeat dosing is limited 1
For chemotherapy:
- Three-dose regimen: 30 minutes before chemotherapy, then 4 and 8 hours after 6, 7
- Alternative: single high dose before chemotherapy 8
For FPIES:
- May repeat every 10-15 minutes in severe cases if initial dose ineffective 2
Safety Considerations
Common adverse effects:
- Headache (most frequent) 3, 6
- Constipation 3, 6
- Diarrhea (may increase frequency, but does not worsen outcomes) 1, 3
Serious but rare adverse effects:
- QT prolongation (monitor ECG if risk factors present) 3
- Serotonin syndrome (if combined with other serotonergic drugs) 3
- Hypersensitivity reactions including anaphylaxis (rare) 3
Contraindications and cautions:
- Avoid in patients with congenital long QT syndrome 3
- Use caution with other QT-prolonging medications 3
- Avoid if bloody diarrhea or high fever suggests inflammatory/invasive diarrhea 1
Practical Administration Tips
- For oral disintegrating tablets: Place on tongue, allow to dissolve, no water needed 4
- For IV administration: Infuse over at least 30 seconds to 2-5 minutes 3
- For IM administration: Use when IV access difficult but parenteral route needed 2
- Available formulations: 4 mg and 8 mg tablets/ODT; 2 mg/mL injection 3
- For 43 kg patient: Use 4 mg + 2 mg = 6 mg, or round to 8 mg (single 8 mg tablet) for practical administration 1