Metronidazole Dosing for E. histolytica in a 27.5kg Child
For a 27.5kg child with E. histolytica infection, give 15 mL of metronidazole 125mg/5mL suspension three times daily for 5-10 days.
Dose Calculation
The FDA-approved pediatric dose for intestinal amebiasis is 35-50 mg/kg/day divided into three doses for 10 days 1. Using the standard dosing:
- Weight: 27.5 kg
- Dose range: 35-50 mg/kg/day
- Recommended dose: 40 mg/kg/day (middle of range) = 1,100 mg/day
- Divided into 3 doses: ~367 mg per dose (round to 375 mg for practical dosing)
Volume calculation with 125mg/5mL suspension:
- 375 mg ÷ 125 mg = 3 units of 5mL
- 15 mL per dose, three times daily
Alternatively, using the lower end (35 mg/kg/day = 962.5 mg/day ÷ 3 = ~320 mg per dose = 12.5-13 mL per dose) is acceptable for less severe cases 1.
Treatment Duration
The standard treatment duration is 10 days for intestinal amebiasis in children 1. The FDA label specifies 5-10 days for acute intestinal amebiasis, with 10 days being preferred for complete eradication 1. Research supports this duration, showing an 88% parasitic cure rate with 40 mg/kg/day for 10 days 2.
Clinical Considerations
Shorter courses (3-5 days) are inadequate: Studies demonstrate that rapid absorption and short treatment duration result in high failure rates (37-62% recurrence) 3, 4. The 10-day regimen is necessary to achieve adequate luminal concentrations 2.
Monitor for treatment failure: Verify cure with three stool samples taken on different days, 1-2 weeks after completing therapy 2. If cysts reappear, consider extending treatment or using an alternative agent 1.
Dosing in context: The IDSA guidelines for infectious diarrhea confirm E. histolytica as a treatable parasitic cause of persistent diarrhea, supporting the use of metronidazole as first-line therapy 5.
Common Pitfalls
Underdosing: Using adult fixed doses (500-750 mg TID) in children results in subtherapeutic levels. Always calculate weight-based dosing 1.
Premature discontinuation: Stopping at 3-5 days leads to treatment failure in over half of patients 3, 4.
Not confirming cure: Asymptomatic cyst passage can persist despite clinical improvement; post-treatment stool examination is essential 2, 3.