Metronidazole Dosing for a 5-Year-Old Child Weighing 20kg
For a 5-year-old child weighing 20kg, the recommended dose of metronidazole is 7.5 mg/kg/dose three or four times daily, which equals 150mg three or four times daily, with a maximum dose of 500mg per dose. 1
Dosing Guidelines Based on Indication
For Clostridium difficile Infection
- For non-severe initial episode: 7.5 mg/kg/dose three or four times daily for 10 days (150mg TID or QID) 1
- Maximum dose: 500mg three or four times daily 1
- Note that current guidelines now prefer vancomycin or fidaxomicin over metronidazole for C. difficile infections when available 2, 3
For Other Anaerobic Infections
- Standard pediatric dosing remains 7.5 mg/kg/dose three or four times daily 1
- Once-daily dosing (30 mg/kg/day) may be appropriate for certain indications like appendicitis based on pharmacokinetic studies 4
- Duration typically 7-10 days depending on clinical response and indication 5
Pharmacokinetic Considerations
- Metronidazole is well absorbed orally with excellent tissue distribution 6
- Half-life is 6-10 hours in adults but may differ in children 6
- Pediatric dosing cannot simply be scaled down from adult dosing using weight alone, as elimination does not change in direct proportion to weight 7
- For children 2 years and older (including our 5-year-old patient), pharmacokinetics are more similar to adults and differ primarily in size 7
Special Considerations
- Dosage adjustment may be necessary in malnourished children, with studies suggesting up to 60% reduction in daily dose 8
- Avoid prolonged or repeated courses due to risk of cumulative and potentially irreversible neurotoxicity 2, 3
- Monitor for common side effects including nausea, metallic taste, and gastrointestinal discomfort 6
- Drug interactions with alcohol, warfarin, and phenytoin have been reported 6
Administration Tips
- Can be given with food to minimize gastrointestinal side effects 6
- Ensure completion of the full course of therapy even if symptoms improve before completion 1
- For C. difficile infection, if the patient doesn't respond to metronidazole within 5-7 days, consider switching to oral vancomycin 1
Common Pitfalls to Avoid
- Underdosing in children by using simple mg/kg calculations from adult doses 7
- Continuing metronidazole beyond recommended duration, increasing risk of neurotoxicity 2, 3
- Failing to recognize when vancomycin would be more appropriate (e.g., in severe C. difficile infection) 1
- Not accounting for potential drug interactions, particularly with warfarin 6