Metronidazole Dosing for an 8-Year-Old Weighing 30 kg
For this 30 kg child, administer metronidazole 225-300 mg orally every 8 hours (7.5-10 mg/kg/dose), with a maximum of 500 mg per dose, depending on the specific infection being treated. 1, 2
Standard Dosing by Clinical Indication
For Most Anaerobic Infections (Including Intra-Abdominal Infections)
- Administer 7.5 mg/kg/dose every 8 hours (approximately 225 mg per dose for this 30 kg child) 1, 3
- This translates to 22.5-30 mg/kg/day total daily dose divided into three doses 1
- Standard duration is 7-10 days for most infections 1, 2
For Clostridium difficile Infection (CDI)
- For non-severe CDI: Use 7.5 mg/kg/dose three or four times daily (225 mg per dose for this child), maximum 500 mg per dose 2, 4
- Duration is 10 days 2, 4
- Important caveat: Current guidelines now prefer oral vancomycin or fidaxomicin over metronidazole for CDI due to concerns about neurotoxicity and treatment failure 4
- If no response within 5-7 days, switch to oral vancomycin 4
For Severe Infections Requiring IV Therapy
- Administer 10 mg/kg/dose IV every 8 hours (300 mg per dose for this child), maximum 500 mg per dose 2
- This higher dose is reserved for severe or fulminant infections 2
For Amebiasis (Intestinal or Hepatic)
- Use 35-50 mg/kg/day divided into three doses (approximately 350-500 mg per dose for this child) 3
- Duration is 10 days 3
Practical Administration Details
- Oral formulation: Can be given without regard to meals, though administration with food may improve gastrointestinal tolerability 3
- No renal adjustment needed: Metronidazole pharmacokinetics are unaffected by renal failure 4
- Maximum single dose: Never exceed 500 mg per dose regardless of weight-based calculation 1, 2
Critical Safety Warnings
- Avoid prolonged courses: Do not extend therapy beyond 14 days without compelling justification due to risk of cumulative and potentially irreversible neurotoxicity 4
- Monitor for side effects: Common adverse effects include nausea, metallic taste, and gastrointestinal discomfort 4
- Complete the full course: Even if symptoms improve before completion 4
Key Clinical Pitfall
The most common dosing error is using the higher 10 mg/kg/dose for all infections, when 7.5 mg/kg/dose is appropriate for most anaerobic infections and CDI. 1, 2 Reserve the 10 mg/kg/dose for severe infections requiring IV therapy or specific indications like perianal Crohn's disease.