Intravenous Metronidazole Dosing for a 1-Year-Old Child
For a healthy 1-year-old child requiring intravenous metronidazole, administer 30-40 mg/kg/day divided every 8 hours (approximately 10-13 mg/kg per dose every 8 hours), with a maximum of 500 mg per individual dose. 1
Standard Dosing Algorithm
The dosing varies based on the specific infection being treated:
For Most Anaerobic Infections (Intra-abdominal, Soft Tissue)
- Dose: 30-40 mg/kg/day divided every 8 hours 1
- Per-dose calculation: Approximately 10-13 mg/kg every 8 hours
- Maximum per dose: 500 mg 1, 2
- Duration: Typically 7-10 days 2
For Clostridium difficile Infection
The dosing is lower than for other anaerobic infections 1:
- Non-severe CDI: 7.5 mg/kg per dose given 3-4 times daily orally (maximum 500 mg per dose) for 10 days 2
- Severe/fulminant CDI: 10 mg/kg per dose three times daily IV (maximum 500 mg per dose), combined with oral vancomycin 2
Important caveat: Oral metronidazole is strongly preferred over IV for CDI because it achieves high intraluminal concentrations where the infection occurs 2. IV metronidazole for CDI should only be used in fulminant cases with ileus when oral administration is not feasible 3.
Age-Specific Considerations for 1-Year-Olds
At 1 year of age, the child is well beyond the neonatal period where metronidazole clearance is significantly reduced 1. The Infectious Diseases Society of America confirms that infants and children require 15-22.5 mg/kg/day divided every 8 hours, with some patients requiring up to 30 mg/kg/day based on severity 1.
Key pharmacokinetic point: Children older than 4 years have pharmacokinetics similar to adults, but infants (including 1-year-olds) still have somewhat prolonged elimination half-lives compared to older children 4. However, the standard every-8-hour dosing interval is appropriate and well-validated 1, 5.
Clinical Dosing Example
For a 10 kg 1-year-old with an intra-abdominal infection:
- Total daily dose: 300-400 mg/day (30-40 mg/kg/day)
- Per-dose amount: 100-133 mg every 8 hours
- Practical dosing: 100-125 mg IV every 8 hours
Critical Safety Considerations
- Never exceed 500 mg per individual dose, regardless of weight-based calculations 1, 2
- Avoid prolonged or repeated courses due to cumulative and potentially irreversible neurotoxicity risk 3
- Monitor for neurotoxicity if treatment extends beyond 10 days 3
- The FDA label confirms metronidazole achieves excellent tissue penetration, including into the CNS, with approximately 20% protein binding 6
Evidence Quality Note
Recent high-quality evidence from the 2025 SCAMP trial demonstrated that metronidazole dosing at 15 mg/kg loading dose followed by 7.5 mg/kg maintenance doses (with age-adjusted intervals) achieved therapeutic success in infants with complicated intra-abdominal infections, with nearly 100% of pharmacodynamic targets met and no significant safety signals 5. This supports the guideline-recommended dosing ranges for this age group.