What is the recommended dose of Zofran (ondansetron) for a 7-month-old patient weighing 7kg?

Ondansetron Dosing for a 7-Month-Old Infant Weighing 7kg

For a 7-month-old infant weighing 7kg, the recommended dose of ondansetron is 1.05 mg (calculated as 0.15 mg/kg), administered intravenously or intramuscularly, with a maximum single dose not to exceed 16 mg. 1

Weight-Based Dosing Calculation

• The standard pediatric dose for infants ≥6 months is 0.15 mg/kg per dose 1, 2
• For a 7kg infant: 7 kg × 0.15 mg/kg = 1.05 mg per dose
• This dose can be rounded to approximately 1 mg for practical administration 1

Age-Specific Safety Considerations

• Ondansetron is only recommended for infants ≥6 months of age due to limited safety and efficacy data in younger infants 1
• At 7 months of age, this patient meets the minimum age requirement for safe ondansetron use 1
• Use in infants <6 months should be avoided unless the clinical situation is judged critical 1

Route of Administration

• Intravenous route is preferred when IV access is already established, particularly in severe presentations requiring fluid resuscitation 1
• Intramuscular route is an acceptable alternative when IV access is difficult or delayed 1
• Oral formulations are available but IV/IM routes provide more reliable absorption in acutely ill infants 2

Clinical Indications in Infants

• Ondansetron is indicated for moderate to severe vomiting (>3 episodes) with associated lethargy, hypotonia, or ashen/cyanotic appearance 1
• May be considered for milder presentations (1-2 episodes of emesis without lethargy) in infants ≥6 months 1
• Commonly used for chemotherapy-induced nausea/vomiting, postoperative nausea/vomiting, and acute gastroenteritis in this age group 2

Monitoring and Follow-Up

• Monitor clinical response over 4-6 hours from the onset of symptoms 1
• Observe for resolution of vomiting and improvement in hydration status 1
• Watch for adverse effects including headache (though difficult to assess in infants), constipation, or diarrhea 2, 3

Important Safety Warnings

• Severe toxicity has been reported with ondansetron overdose in infants, including obtundation, seizures, QTc prolongation, and serotonin syndrome 4
• The therapeutic dose (0.15 mg/kg) has an excellent safety profile, but accidental ingestion of multiple tablets can cause life-threatening toxicity 4
• Transient elevations in liver transaminases may occur (6-8% of patients), though this is often related to concurrent chemotherapy rather than ondansetron itself 3
• Ondansetron does not cause extrapyramidal symptoms, unlike metoclopramide, making it safer for pediatric use 2, 3

Common Pitfalls to Avoid

• Do not exceed 0.15 mg/kg per dose in infants, as higher doses increase toxicity risk without improving efficacy 1, 2
• Avoid using ondansetron in infants <6 months unless absolutely necessary due to insufficient safety data 1
• Do not confuse the 0.15 mg/kg pediatric dose with adult fixed dosing (4-8 mg), which would result in overdosing in small infants 1
• Ensure proper storage of ondansetron tablets away from children, as accidental ingestion by toddlers can cause severe toxicity 4