Metronidazole Dosing for a 41-kg Pediatric Patient
For a 41-kg child, administer metronidazole 15 mL (375 mg) of the 125 mg/5 mL syrup three times daily for most anaerobic infections, or 20 mL (500 mg) three times daily for severe infections.
Standard Pediatric Dosing Framework
The appropriate dose depends on the specific indication, but general pediatric dosing principles apply:
For Most Anaerobic Infections
- Standard dose: 30-40 mg/kg/day divided into 3-4 doses 1, 2
- For a 41-kg child: 30 mg/kg/day = 1,230 mg/day ÷ 3 doses = 410 mg per dose (approximately 16 mL of syrup three times daily) 1
- Practical dosing: Round to 15 mL (375 mg) three times daily for ease of administration 2
For Severe Anaerobic Infections
- Higher dosing of 40-50 mg/kg/day may be used orally 2
- For a 41-kg child: 40 mg/kg/day = 1,640 mg/day ÷ 3 doses = 547 mg per dose (approximately 22 mL three times daily)
- Practical dosing: Round to 20 mL (500 mg) three times daily 2
For Specific Indications
Giardiasis:
- 15 mg/kg/day divided into three doses for 5-7 days 3, 4
- For 41 kg: 615 mg/day ÷ 3 = 205 mg per dose = 8 mL three times daily 3
C. difficile Infection (if vancomycin/fidaxomicin unavailable):
- 7.5 mg/kg/dose three to four times daily for 10 days, maximum 500 mg per dose 4
- For 41 kg: 7.5 × 41 = 308 mg per dose = 12 mL three to four times daily 4
- Important caveat: Metronidazole is no longer first-line for C. difficile; vancomycin or fidaxomicin are strongly preferred 3, 4
Dosing Frequency Considerations
Recent pharmacokinetic data suggests once-daily dosing (30 mg/kg) achieves adequate drug exposure for appendicitis and anaerobic infections 5. However, traditional three-times-daily dosing remains the guideline-recommended approach for most indications 4, 1, 2.
Critical Safety Warnings
- Avoid prolonged courses beyond 14 days due to cumulative and potentially irreversible neurotoxicity 3, 4
- Monitor for neurological symptoms during treatment 6
- Advise caregivers to avoid alcohol-containing products during treatment and for 24 hours after completion 3
Duration of Therapy
- Most anaerobic infections: 7-10 days 4, 2
- Giardiasis: 5-7 days 3
- C. difficile infection: 10 days 4
- Serious infections (abscess, pneumonia): 14-52 days depending on clinical response 2
Common Pitfalls to Avoid
- Do not use metronidazole as first-line for C. difficile infection when vancomycin or fidaxomicin are available, as cure rates are significantly inferior (76% vs 97% in severe disease) 3
- Do not underdose: Children over 12 years and weighing >40 kg can receive adult dosing of 500 mg three times daily 1
- Do not forget luminal therapy: For amoebic infections, always follow metronidazole with a luminal amoebicide to prevent relapse 6