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), with specific dose adjustments based on infection severity and type. 1
Standard Dosing by Clinical Indication
General Anaerobic Infections
- Administer 30-40 mg/kg/day divided every 8 hours (given three times daily) with a maximum of 500 mg per dose for most anaerobic infections including intra-abdominal infections. 1
- This dosing achieves adequate serum concentrations (peak 15-30 mcg/mL, trough 4-11.6 mcg/mL) and provides 93% coverage against anaerobic isolates. 2
- For severe mixed necrotizing infections requiring anaerobic coverage, use 7.5 mg/kg/dose every 6 hours IV (four times daily), typically combined with broad-spectrum agents like cefotaxime. 1
Clostridium difficile Infection (CDI)
Note: CDI requires LOWER dosing than other anaerobic infections. 1
- For non-severe CDI (initial episode or first recurrence): Use 7.5 mg/kg/dose three or four times daily for 10 days (maximum 500 mg per dose). 3, 4
- For severe or fulminant CDI: Oral vancomycin is strongly preferred over metronidazole. 3
- If metronidazole must be used in severe CDI, administer 10 mg/kg/dose IV three times daily (maximum 500 mg per dose) as adjunctive therapy to oral vancomycin. 3, 4
- For second or subsequent recurrences, oral vancomycin is recommended over metronidazole. 3
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
- Higher doses within the recommended range may be warranted for severe infections. 1
Crohn's Disease (Perianal Disease)
- Administer 10-20 mg/kg/day in divided doses. 1
Route of Administration Considerations
- Oral metronidazole is preferred over IV for CDI because it achieves high intraluminal concentrations where the infection occurs. 4
- IV administration may be necessary for severe systemic infections or when oral route is not feasible. 1
- Both oral (40-50 mg/kg/day) and IV (30 mg/kg/day) routes have been used safely, with oral dosing slightly higher to account for absorption. 2
Duration of Therapy
- Standard duration for most infections is 10 days. 1, 4
- For serious anaerobic infections like intracranial abscess or chronic sinusitis, treatment may extend to 14-52 days (average 26 days). 2
Special Populations
Premature Neonates
- Dosing in premature infants should be based on postmenstrual age rather than postnatal age alone, as clearance correlates with postmenstrual age. 5
- Population clearance is calculated as 0.038 L/h/kg × (postmenstrual age/30). 5
- Published dosing recommendations for premature infants vary significantly and may result in subtherapeutic concentrations; postmenstrual age-based dosing is recommended. 6
Malnourished Children
- Severely malnourished children require a 60% dose reduction to 12 mg/kg/day (instead of the standard 30 mg/kg/day) due to significantly impaired biotransformation. 7
- Standard dosing in malnourished children would result in drug accumulation and increased risk of adverse effects. 7
Emerging Evidence on Once-Daily Dosing
- Recent pharmacokinetic data in children aged 4-17 years with appendicitis suggests that 30 mg/kg once daily achieves adequate AUC/MIC ratios (≥70) for Bacteroides fragilis with MIC ≤2 mcg/mL in 96-100% of patients. 8
- This is based on metronidazole's long half-life, concentration-dependent killing, and 3-hour post-antibiotic effect. 8
- However, this once-daily approach is not yet reflected in major guidelines and should be considered investigational for most indications. 8
Critical Dosing Distinctions
The most common prescribing error is using the same dose for all indications. Remember:
- CDI = 7.5 mg/kg/dose (LOWER dose, 3-4 times daily) 1, 3
- Most other anaerobic infections = 10-13 mg/kg/dose (HIGHER dose, every 8 hours) 1
- Maximum single dose = 500 mg regardless of indication 1, 3, 4