What is the recommended dose of metronidazole (Flagyl) for pediatric patients?

Metronidazole Dosing for Pediatric Patients

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

Standard Dosing by Clinical Scenario

General Infections (Anaerobic Coverage)

• For most anaerobic infections, use 30-40 mg/kg/day divided into three doses (every 8 hours), maximum 500 mg per dose 1
• Standard treatment duration is 10 days for most infections 1
• The FDA label specifies 35-50 mg/kg/24 hours divided into three doses for amebiasis 2

Skin and Soft Tissue Infections (Necrotizing Infections)

• For mixed necrotizing infections requiring anaerobic coverage, use 7.5 mg/kg/dose every 6 hours IV 3
• This is typically combined with cefotaxime (50 mg/kg/dose every 6 hours) or other broad-spectrum agents 3

Clostridium difficile Infection (CDI)

The dosing differs significantly based on severity:

Non-severe CDI:

• 7.5 mg/kg/dose three or four times daily (maximum 500 mg per dose) for 10 days 1, 4
• This applies to both initial episodes and first recurrence 4

Severe CDI:

• Oral vancomycin is preferred over metronidazole (strong recommendation) 4
• If metronidazole must be used: 10 mg/kg/dose three times daily IV (maximum 500 mg per dose) 1, 4

Fulminant CDI:

• Do not use metronidazole as monotherapy 5
• If used, give IV metronidazole 500 mg every 8 hours concurrently with high-dose oral vancomycin 5

Intra-abdominal Infections

• Use 30-40 mg/kg/day divided every 8 hours as part of combination therapy 1
• Should be combined with aminoglycosides, carbapenems, or advanced-generation cephalosporins 1

Inflammatory Bowel Disease (Perianal Crohn's Disease)

• 10-20 mg/kg/day in divided doses 1

Important Clinical Considerations

Dosing Frequency

• While traditional dosing is every 6-8 hours, recent pharmacokinetic data supports once-daily dosing (30 mg/kg/dose) for appendicitis, achieving adequate AUC/MIC ratios for Bacteroides fragilis with MIC ≤2 mcg/mL 6
• However, guideline-recommended dosing remains every 8 hours for most infections 3, 1

Maximum Doses

• Never exceed 500 mg per individual dose in pediatric patients 1, 4
• Total daily dose should not exceed 4 grams in a 24-hour period 2

Route of Administration

• Oral and IV dosing are generally equivalent in bioavailability 2
• For severe infections, start with IV therapy and transition to oral once clinically improving 7

Common Pitfalls to Avoid

• Do not use standard adult dosing (500 mg TID) in children—always calculate weight-based dosing 1
• Do not use metronidazole monotherapy for severe or fulminant CDI—vancomycin is superior 4, 5
• Do not exceed 500 mg per dose even in larger adolescents 1, 4
• For CDI, recognize that the dosing is LOWER (7.5 mg/kg/dose) than for other anaerobic infections (10-13 mg/kg/dose) 3, 4

Special Populations

• In hepatic impairment, reduce doses and monitor closely 2
• Metronidazole is well-tolerated in children with minimal side effects compared to adults 7
• Nausea, anorexia, and metallic taste may occur but are generally mild 8