What is the recommended dose of metronidazole (antibiotic) for a 2-year-old child?

Metronidazole Dosing for a 2-Year-Old Child

For a 2-year-old child, metronidazole should be dosed at 7.5 mg/kg per dose given 3-4 times daily (maximum 500 mg per dose) for most common indications including Clostridium difficile infection, or 20-30 mg/kg/day divided into doses for parasitic infections.

Indication-Specific Dosing

For Clostridium difficile Infection (Most Common Pediatric Use)

• Oral metronidazole: 7.5 mg/kg per dose given 3-4 times daily for 10 days 1
• Maximum dose: 500 mg per dose (whether given 3 or 4 times daily) 1
• This is the recommended regimen for initial episodes of non-severe CDI in children 1

For severe or fulminant CDI, intravenous metronidazole at 10 mg/kg per dose three times daily (maximum 500 mg per dose) may be added to oral vancomycin in critically ill patients 1

For Anaerobic Infections

• Intravenous: 30 mg/kg/day divided into doses 2
• Oral: 40-50 mg/kg/day divided into doses 2
• Treatment duration typically ranges from 14-52 days depending on infection severity and location 2

For Parasitic Infections (Giardiasis)

• 15 mg/kg/day divided into three doses for 7 days 3
• Alternative general pediatric dosing: 20-30 mg/kg/day for children under 12 years 4

Practical Calculation Example

For a typical 2-year-old weighing approximately 12-13 kg:

• CDI dosing: 7.5 mg/kg × 12 kg = 90 mg per dose, given 3-4 times daily 1
• Anaerobic infection (IV): 30 mg/kg/day × 12 kg = 360 mg/day, divided appropriately 2

Important Clinical Considerations

Route of Administration

• Oral metronidazole is preferred for CDI as it achieves high intraluminal concentrations 1
• Intravenous route is reserved for severe/fulminant cases when oral administration is not feasible or when treating systemic anaerobic infections 1, 2

Common Pitfalls to Avoid

• Do not use metronidazole as first-line for severe CDI: Vancomycin is superior for severe disease in children 1
• Do not exceed maximum doses: The 500 mg per dose maximum should be respected even if weight-based calculations suggest higher doses 1
• Monitor for side effects: Nausea (4.9%), anorexia (6%), and metallic taste (24%) are common in children 3

Duration Considerations

• Most infections require 7-10 days of therapy 1, 3
• Serious anaerobic infections may require extended courses averaging 26 days 2
• Recent pharmacokinetic data supports once-daily dosing (30 mg/kg) for appendicitis in older children, though this is not yet standard for toddlers 5

When to Choose Alternative Agents

• For recurrent CDI (second or subsequent episode), vancomycin in tapered/pulsed regimens is preferred over metronidazole 1
• For severe CDI, oral vancomycin (10 mg/kg per dose four times daily, maximum 500 mg) is strongly recommended over metronidazole 1