What is the appropriate dosage of metronidazole (antibiotic/antiprotozoal medication) for a pediatric patient?

Metronidazole Dosing for Pediatric Patients

For most pediatric infections requiring metronidazole, use 30-40 mg/kg/day divided every 8 hours (maximum 500 mg per dose) for 7-10 days. 1, 2

Standard Dosing by Clinical Indication

Anaerobic Bacterial Infections (Most Common)

• Dose: 30-40 mg/kg/day divided every 8 hours 1
• Maximum single dose: 500 mg 1, 2
• Duration: 7-10 days for most infections 1, 3
• For severe infections (bone/joint, lower respiratory tract, endocardium): may require longer treatment 4

Intra-Abdominal Infections

• Dose: 30-40 mg/kg/day divided every 8 hours 1
• Must be combined with aminoglycosides, carbapenems, or advanced-generation cephalosporins 1
• Maximum 500 mg per dose 1

Clostridium difficile Infection (CDI)

Non-severe CDI:

• Dose: 7.5 mg/kg/dose three or four times daily 2, 3
• Maximum 500 mg per dose 2, 3
• Duration: 10 days 2, 3
• Note: This is LOWER dosing than other anaerobic infections 1

Severe or Fulminant CDI:

• Oral vancomycin is preferred over metronidazole (strong recommendation) 2
• If metronidazole used: 10 mg/kg/dose IV three times daily (maximum 500 mg per dose) 2, 3
• May be added to oral vancomycin in critically ill patients 3

Recurrent CDI:

• First recurrence: same dosing as initial episode (7.5 mg/kg/dose 3-4 times daily) 2
• Second or subsequent recurrences: oral vancomycin preferred over metronidazole 2

Perianal Crohn's Disease

• Dose: 10-20 mg/kg/day in divided doses 5, 1
• Often combined with ciprofloxacin (20 mg/kg/day) 5
• Good short-term response; may bridge to immunosuppressive medications 5

Amebiasis

• Acute intestinal amebiasis: 35-50 mg/kg/day divided into three doses for 10 days 4
• Amebic liver abscess: same dosing 4

Mixed Necrotizing Infections

• Dose: 7.5 mg/kg/dose every 6 hours IV 1
• Typically combined with cefotaxime (50 mg/kg/dose every 6 hours) or other broad-spectrum agents 1

Critical Dosing Distinctions

The dosing varies significantly by indication—this is a common pitfall:

• Most anaerobic infections: 30-40 mg/kg/day divided every 8 hours (10-13 mg/kg/dose) 1
• Non-severe CDI: 7.5 mg/kg/dose 3-4 times daily (22.5-30 mg/kg/day total) 1, 2
• Severe CDI (IV): 10 mg/kg/dose three times daily 2
• Amebiasis: 35-50 mg/kg/day 4

Route of Administration

• Oral route is preferred when possible 2, 3
• For CDI specifically, oral administration achieves high intraluminal concentrations 3
• IV administration reserved for severe infections or when oral route not feasible 1, 4

Important Safety Considerations

• Maximum single dose: 500 mg regardless of weight-based calculations 1, 2, 3
• Maximum daily dose: 4 grams in 24 hours 4
• Pharmacokinetics in children similar to adults at equal weight-related doses 6
• Once-daily dosing (30 mg/kg) achieves adequate AUC/MIC ratios for appendicitis but is not yet standard practice 7

Special Populations

Hepatic impairment:

• Doses below usual recommendations should be administered cautiously 4
• Close monitoring of plasma levels and toxicity recommended 4

Renal impairment:

• Dose reduction not specifically required in anuric patients 4
• Accumulated metabolites rapidly removed by dialysis 4

Common Pitfalls to Avoid

1. Do not use the same dose for all indications—CDI requires lower per-dose amounts than other anaerobic infections 1
2. Do not exceed 500 mg per dose even if weight-based calculations suggest higher amounts 1, 2, 3
3. Do not use metronidazole monotherapy for intra-abdominal infections—always combine with agents covering aerobic gram-negatives 1
4. Do not use metronidazole as first-line for severe CDI—vancomycin is superior 2