Ondansetron IM Dosing for 31-lb (14-kg) Patient
For a 31-lb (14-kg) patient, administer ondansetron 0.15 mg/kg intramuscularly, which equals 2.1 mg (typically rounded to 2 mg in clinical practice). This weight-based dosing is supported by FDA labeling and provides equivalent systemic exposure to intravenous administration 1.
Dosing Calculation and Administration
- Weight-based dose: 0.15 mg/kg × 14 kg = 2.1 mg IM
- Practical rounding: Most clinicians would administer 2 mg given available concentrations
- Bioequivalence: The FDA label confirms that IM and IV ondansetron at 4 mg doses produce equivalent systemic exposure (AUC), with IM achieving peak concentrations at 41 minutes versus 10 minutes for IV 1
Age-Specific Considerations
If this patient is younger than 6 months, consider dose reduction:
- Infants 1-4 months: Clearance is reduced by 53-76% compared to older children 2
- Recommended adjustment: Use 0.1 mg/kg instead of 0.15 mg/kg for infants under 6 months to achieve similar exposure as older children 2
- Close monitoring: Required for patients under 4 months due to immature drug clearance mechanisms 2
Clinical Context
The 0.15 mg/kg IM dose is established for:
- Chemotherapy-induced nausea/vomiting: Standard three-dose regimen (0.15 mg/kg × 3 doses) 1
- Procedural sedation: Single 0.1 mg/kg IM dose effectively reduces ketamine-associated vomiting (12.5% vs 21.5% in controls) 3
- Acute gastroenteritis: Single 0.2 mg/kg dose (oral or IM) for vomiting control, though IM offers no advantage over oral route 4
Important Caveats
- Maximum single dose: While not explicitly stated in pediatric labeling, adult dosing typically caps at 16 mg
- QT prolongation risk: Higher doses (>8 mg IV) cause clinically significant QTc prolongation; the 2 mg dose for this patient carries minimal cardiac risk 1
- Radiation therapy dosing: Guidelines recommend 8 mg or 0.15 mg/kg IV for moderate-to-high emetogenic risk, applicable across age groups 5
The 0.15 mg/kg IM dose (2 mg for this 14-kg patient) represents the FDA-approved standard that balances efficacy with safety, providing antiemetic coverage equivalent to IV administration without the need for vascular access.