What is the recommended dose of Metronidazole (Flagyl) intravenous (IV) for pediatric patients?

Metronidazole IV Dosing for Pediatric Patients

The recommended intravenous dose of metronidazole for pediatric patients is 30-40 mg/kg/day divided every 8 hours, with a maximum of 500 mg per dose. 1, 2

Standard Dosing Regimen

For most pediatric infections requiring anaerobic coverage, administer 30-40 mg/kg/day divided into three doses (every 8 hours), not exceeding 500 mg per individual dose. 1, 2

• This dosing applies to children beyond the neonatal period and is the guideline-recommended regimen from the Infectious Diseases Society of America for complicated intra-abdominal infections 1
• The typical duration of therapy is 10 days for most infections 2

Neonatal Dosing (Age and Weight-Specific)

Neonates require significantly different dosing based on postnatal age and weight due to immature drug elimination pathways 2, 3:

• Postnatal age ≤7 days and weight ≤2000 g: 7.5 mg/kg every 12 hours 2
• Postnatal age ≤7 days and weight >2000 g: 7.5-10 mg/kg every 12 hours 2
• Postnatal age >7 days and weight <1200 g: 7.5-10 mg/kg every 8-12 hours 2
• Postnatal age >7 days and weight >2000 g: 10 mg/kg every 8 hours 2

Condition-Specific Dosing Variations

Complicated Intra-Abdominal Infections

• Use 30-40 mg/kg/day divided every 8 hours as part of combination therapy with aminoglycosides, carbapenems, or advanced-generation cephalosporins 1, 2
• For severe infections with undrained abscesses, maximize dosing within the recommended range (closer to 40 mg/kg/day) 1

Clostridium difficile Infection (CDI)

Critical dosing difference: CDI requires LOWER doses than other anaerobic infections 2:

• Non-severe CDI: 7.5 mg/kg/dose three or four times daily (maximum 500 mg per dose) for 10 days 2
• Severe CDI requiring IV therapy: 10 mg/kg/dose three times daily (maximum 500 mg per dose) 2

Necrotizing Infections with Anaerobic Coverage

• Use 7.5 mg/kg/dose every 6 hours IV, typically combined with cefotaxime (50 mg/kg/dose every 6 hours) or other broad-spectrum agents 2

Perianal Crohn's Disease

• Use 10-20 mg/kg/day in divided doses 2

Important Clinical Considerations

Dosing Frequency

Recent pharmacokinetic data demonstrates that once-daily dosing (30 mg/kg/dose) achieves adequate AUC/MIC ratios for Bacteroides fragilis with MIC ≤2 mcg/mL in pediatric appendicitis patients 4. However, the established guideline recommendation remains every 8 hours dosing for most infections 1, 2, and this should be followed in standard practice until further evidence supports widespread adoption of once-daily dosing.

Special Populations

• Malnourished children: Require dose reduction to approximately 12 mg/kg/day (60% reduction from standard dosing) due to impaired drug clearance 5
• Monitor for drug accumulation in severely malnourished patients as biotransformation is significantly affected 5

Maximum Dose Limits

• Individual doses should not exceed 500 mg regardless of calculated weight-based dose 2
• This ceiling prevents excessive drug exposure while maintaining therapeutic efficacy 2

Common Pitfalls to Avoid

• Do not simply scale adult doses by weight alone - this results in underdosing in infants/children and overdosing in neonates due to differences in drug elimination that are not proportional to weight 3
• Do not use the same dose for CDI as for other anaerobic infections - CDI requires lower dosing (7.5 mg/kg/dose vs 10-13 mg/kg/dose) 2
• Do not forget the 500 mg per dose maximum - even in larger adolescents, individual doses should be capped 2