Oral Metronidazole Dosing in Pediatric Patients
For most pediatric infections requiring metronidazole, use 30-40 mg/kg/day divided every 8 hours (maximum 500 mg per dose), but for Clostridium difficile infection specifically, use the lower dose of 7.5 mg/kg/dose three or four times daily (maximum 500 mg per dose). 1, 2
Standard Dosing by Clinical Indication
General Anaerobic Infections
- Administer 30-40 mg/kg/day divided into three doses (every 8 hours), with a maximum of 500 mg per dose 1
- For intra-abdominal infections requiring anaerobic coverage, use this standard 30-40 mg/kg/day dosing as part of combination therapy with aminoglycosides, carbapenems, or advanced-generation cephalosporins 1
- Standard treatment duration is 7-10 days for most infections 1, 2
Clostridium Difficile Infection (CDI)
- For non-severe CDI: 7.5 mg/kg/dose three or four times daily (maximum 500 mg per dose) for 10 days 1, 2, 3
- For severe CDI requiring IV therapy: 10 mg/kg/dose three times daily IV (maximum 500 mg per dose) 1
- Critical caveat: Metronidazole is no longer first-line for CDI—oral vancomycin or fidaxomicin are now preferred agents 3
- If no response within 5-7 days, switch to oral vancomycin 3
- For second or subsequent recurrences, use oral vancomycin instead of metronidazole 2
Crohn's Disease (Perianal Fistulizing Disease)
- Use 10-20 mg/kg/day in divided doses 1, 2
- This provides good short-term response and may bridge to immunosuppressive medications 1
Amebiasis
- 35-50 mg/kg/24 hours divided into three doses for 10 days 4
Age-Specific Dosing Considerations
Neonates (Requires Weight and Postnatal Age-Based Adjustment)
- Postnatal age ≤7 days and weight ≤2000 g: 7.5 mg/kg every 12 hours 1
- Postnatal age ≤7 days and weight >2000 g: 7.5-10 mg/kg every 12 hours 1
- Postnatal age >7 days and weight <1200 g: 7.5-10 mg/kg every 8-12 hours 1
- Postnatal age >7 days and weight >2000 g: 10 mg/kg every 8 hours 1
Infants and Children
- Standard dosing: 15-22.5 mg/kg/day divided every 8 hours 1
- Some patients may require up to 30 mg/kg/day divided every 8 hours based on serum levels 1
- Children ≥12 years: 200 mg to maximum 2000 mg per day 5
Children <12 Years
- 20-30 mg/kg body weight per day 5
Critical Safety Warnings
Neurotoxicity Risk
- Avoid prolonged or repeated courses due to risk of cumulative and potentially irreversible peripheral neuropathy 3
- In one study of pediatric Crohn's disease patients, 85% developed sensory peripheral neuropathy after 4-11 months of therapy 6
- Do not extend therapy beyond 14 days without compelling justification 3
- If doses >10 mg/kg/day are used chronically, monitor closely for neurologic symptoms 6
Special Populations
- Malnourished children: Reduce dose by 60% (to approximately 12 mg/kg/day) due to impaired drug clearance and risk of accumulation 7
- Severe hepatic disease: Use lower doses and monitor plasma levels closely 4
- Renal failure: No dosage adjustment needed for parent drug, but metabolites accumulate 4, 8
- Elderly patients: May require dose adjustment and serum level monitoring 4
Route of Administration Considerations
- Oral bioavailability approaches 100%, making oral and IV dosing equivalent 8
- Rectal and vaginal administration results in lower serum concentrations and should be avoided when therapeutic levels are needed 8
Important Clinical Pitfalls
- Recognize that CDI dosing (7.5 mg/kg/dose) is LOWER than dosing for other anaerobic infections (10-13 mg/kg/dose) 1
- Do not use metronidazole as monotherapy for complicated intra-abdominal infections—always combine with broader antimicrobial coverage 1
- Maximum single dose is 500 mg regardless of weight-based calculation 1, 2
- Maximum daily dose should not exceed 4 g in 24 hours 4