What is the recommended dose of metronidazole (Flagyl) for a 3-year-old patient weighing 11kg?

Metronidazole Dosing for a 3-Year-Old Weighing 11kg

For this 3-year-old child weighing 11kg, administer metronidazole at 7.5-10 mg/kg per dose every 8 hours (approximately 82.5-110 mg per dose, three times daily), with the specific dose depending on the indication and severity of infection. 1

Standard Dosing Framework

The dosing varies significantly based on the clinical indication:

For Most Anaerobic Infections (Intra-abdominal, Soft Tissue)

• Use 30-40 mg/kg/day divided every 8 hours, which translates to approximately 10-13.3 mg/kg per dose (110-146 mg per dose for this 11kg child), with a maximum of 500 mg per dose 1
• The Infectious Diseases Society of America recommends this higher dosing range for standard anaerobic coverage 1
• For severe infections, use the higher end of this range (closer to 40 mg/kg/day) 1

For Clostridium difficile Infection (CDI)

• For non-severe CDI: Use 7.5 mg/kg per dose, 3-4 times daily (approximately 82.5 mg per dose for this 11kg child) 2, 3
• For severe CDI requiring IV therapy: Use 10 mg/kg per dose, three times daily (approximately 110 mg per dose) 1
• Critical caveat: Metronidazole is no longer first-line for CDI; vancomycin or fidaxomicin are strongly preferred 2, 3

For Mixed Necrotizing Infections

• Use 7.5 mg/kg per dose every 6 hours IV (approximately 82.5 mg per dose, four times daily), typically combined with broad-spectrum agents like cefotaxime 1

Practical Dosing Calculation for This Patient

For an 11kg child:

• Standard anaerobic infections: 110-146 mg per dose every 8 hours (330-440 mg/day total)
• Non-severe CDI: 82.5 mg per dose, 3-4 times daily (247.5-330 mg/day total)
• Severe infections requiring q6h dosing: 82.5 mg per dose every 6 hours (330 mg/day total)

Critical Safety Considerations

• Avoid prolonged or repeated courses due to risk of cumulative and potentially irreversible neurotoxicity 2, 3
• Do not extend therapy beyond 14 days without compelling justification 3
• Monitor for peripheral neuropathy, especially with prolonged use 2
• Standard treatment duration is 10 days for most infections 1, 2

Important Clinical Pitfalls

• Recognize that CDI dosing (7.5 mg/kg/dose) is LOWER than standard anaerobic infection dosing (10-13 mg/kg/dose) 1
• For CDI, if no response within 5-7 days, switch to oral vancomycin rather than continuing metronidazole 3
• No dosage adjustment needed for renal dysfunction 3
• Common side effects include nausea, metallic taste, and gastrointestinal discomfort 3