What is the recommended dose of metronidazole for a 3-year-old child weighing 11 kg?

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

For a 3-year-old child weighing 11 kg, the recommended intravenous metronidazole dose is 30-40 mg/kg/day divided every 8 hours, which equals 110-147 mg per dose (330-440 mg total daily dose), with a maximum of 500 mg per individual dose. 1, 2

Standard Dosing Calculation

• The Infectious Diseases Society of America recommends 30-40 mg/kg/day divided every 8 hours for most pediatric infections requiring metronidazole. 1

• For an 11 kg child, this translates to:

  • Total daily dose: 330-440 mg/day
  • Individual dose: 110-147 mg every 8 hours 1, 2

• The maximum single dose should not exceed 500 mg, which is well above the calculated dose for this child. 2

Dosing Adjustments by Clinical Indication

The specific dose within the 30-40 mg/kg/day range depends on the type and severity of infection:

For Intra-Abdominal Infections

• Use 30-40 mg/kg/day divided every 8 hours (110-147 mg per dose for 11 kg child) as part of combination therapy with aminoglycosides, carbapenems, or advanced-generation cephalosporins. 1, 2

For Clostridium difficile Infection (CDI)

• For non-severe CDI: Use 7.5 mg/kg/dose three or four times daily (approximately 82.5 mg per dose for 11 kg child), maximum 500 mg per dose. 1, 3
• For severe CDI requiring IV therapy: Use 10 mg/kg/dose three times daily (110 mg per dose for 11 kg child), maximum 500 mg per dose. 1, 3
• Note: Oral vancomycin is preferred over metronidazole for severe or fulminant CDI. 4, 3

For Mixed Necrotizing Infections

• Use 7.5 mg/kg/dose every 6 hours IV (82.5 mg per dose for 11 kg child), typically combined with cefotaxime or other broad-spectrum agents. 1

Duration of Therapy

• The standard duration for most infections is 10 days. 1, 3

Critical Considerations and Pitfalls

Important dosing distinctions to avoid errors:

• CDI requires LOWER dosing (7.5 mg/kg/dose) compared to other anaerobic infections (10-13 mg/kg/dose or 30-40 mg/kg/day divided). 1

• In children with severe malnutrition and hepatic involvement, reduce the dose by 60% to approximately 12 mg/kg/day, as hepatic dysfunction significantly prolongs metronidazole half-life. 2

• Avoid repeated or prolonged courses due to risk of cumulative and potentially irreversible neurotoxicity. 4

Route of Administration

• Intravenous metronidazole is appropriate for severe infections, hospitalized patients, or when oral administration is not feasible. 1, 3

• Transition to oral therapy (40-50 mg/kg/day) can occur once the patient demonstrates clinical improvement and can tolerate oral medications. 5