What is the recommended dose of Metronidazole (antibiotic/antiprotozoal medication) for a 28kg pediatric patient with unknown renal function and no known allergies?

Metronidazole Dosing for a 28kg Pediatric Patient

For a 28kg pediatric patient, administer metronidazole 210-280 mg (7.5-10 mg/kg) every 8 hours for most anaerobic infections, with a maximum of 500 mg per dose. 1, 2

Standard Dosing by Clinical Indication

Most Anaerobic Infections (Intra-abdominal, Soft Tissue, Aspiration Pneumonia)

• Administer 7.5-10 mg/kg/dose every 8 hours (210-280 mg per dose for this 28kg patient) 1, 3
• The total daily dose ranges from 22.5-30 mg/kg/day (630-840 mg/day for this patient) 1
• Maximum single dose is 500 mg, which this patient will not exceed 1, 2
• Standard treatment duration is 7-10 days 1, 4

Clostridium difficile Infection (CDI)

• For non-severe CDI: Use 7.5 mg/kg/dose (210 mg) three or four times daily for 10 days 1, 2
• Note that CDI dosing is LOWER than other anaerobic infections 1
• For severe CDI requiring IV therapy: 10 mg/kg/dose (280 mg) three times daily 1
• Important caveat: Current guidelines prefer vancomycin or fidaxomicin over metronidazole for CDI when available due to concerns about neurotoxicity and treatment failure 4

Perianal Fistulizing Crohn's Disease

• Administer 10-20 mg/kg/day in divided doses (280-560 mg/day for this patient) 1

Route of Administration

• Oral bioavailability approaches 100%, so oral and IV dosing are equivalent 5
• IV administration is typically reserved for severe infections or when oral route is not feasible 3
• The FDA label confirms adult oral dosing of 7.5 mg/kg every 6 hours (approximately 500 mg for a 70kg adult), which translates to the pediatric dosing above 3

Critical Safety Considerations

• Avoid prolonged or repeated courses beyond 14 days due to risk of cumulative and potentially irreversible neurotoxicity 4, 2
• No dosage adjustment needed for renal dysfunction, as metronidazole pharmacokinetics are unaffected by renal failure 4
• Monitor for common side effects including nausea, metallic taste, and gastrointestinal discomfort 4

Practical Calculation for This 28kg Patient

For standard anaerobic infections:

• Low end: 7.5 mg/kg × 28kg = 210 mg every 8 hours
• High end: 10 mg/kg × 28kg = 280 mg every 8 hours
• Most commonly prescribed: 250 mg every 8 hours (8.9 mg/kg/dose, well within guideline range)

For CDI:

• 7.5 mg/kg × 28kg = 210 mg three to four times daily (every 6-8 hours)