What is the volume of metronidazole (antibiotic) suspension in milliliters (mL) to be administered every 8 hours to a child weighing 45 kilograms (kg)?

Metronidazole Dosing for a 45 kg Child

For a 45 kg child, the appropriate dose of metronidazole is 30 mg/kg/day divided every 8 hours, which equals 450 mg (15 ml of suspension) per dose given every 8 hours. 1

Dosage Calculation

• Metronidazole dosing for children is typically 30 mg/kg/day divided into three doses (every 8 hours) 1, 2
• For a 45 kg child: 45 kg × 30 mg/kg/day = 1,350 mg/day
• Divided into three doses: 1,350 mg ÷ 3 = 450 mg per dose every 8 hours 1

Formulation Considerations

• If using metronidazole suspension (which typically comes as 125 mg/5 ml or 250 mg/5 ml):
  • For 125 mg/5 ml concentration: 450 mg ÷ (125 mg/5 ml) = 18 ml per dose 2
  • For 250 mg/5 ml concentration: 450 mg ÷ (250 mg/5 ml) = 9 ml per dose 2
• Standard metronidazole suspension is often 125 mg/5 ml, so 15 ml (450 mg) would be administered every 8 hours 2

Evidence Supporting This Dosing

• The Infectious Diseases Society of America (IDSA) guidelines recommend metronidazole 500 mg orally three times per day (every 8 hours) for adults with non-severe Clostridium difficile infection 1
• For pediatric patients, the recommended dose is 30 mg/kg/day divided every 8 hours, which aligns with established practice for treating anaerobic infections 2
• Clinical studies have demonstrated good efficacy and safety of metronidazole at this dosage for treating anaerobic infections in children 2

Alternative Dosing Considerations

• Some recent research suggests that once-daily dosing of metronidazole (30 mg/kg once daily) may be effective for certain indications like appendicitis due to its long half-life and concentration-dependent killing 3
• However, for most infections requiring metronidazole, the standard every 8-hour dosing remains the recommended approach to ensure adequate drug concentrations throughout the treatment period 1, 2
• Some studies have explored every 12-hour dosing (twice daily) with similar clinical outcomes to every 8-hour dosing in adults, but this is not yet standard practice in pediatrics 4

Important Monitoring Considerations

• Monitor for potential side effects including nausea, metallic taste, and potential neurotoxicity with prolonged use 1
• The IDSA guidelines specifically warn to "avoid repeated or prolonged courses due to risk of cumulative and potentially irreversible neurotoxicity" 1
• For children with malnutrition, dose adjustments may be necessary as drug metabolism can be altered 5, 6