Metronidazole Dosing for a 37 kg Male Patient
For a 37 kg male patient, administer metronidazole 500 mg IV every 8 hours (approximately 40 mg/kg/day total) for most serious infections requiring anaerobic coverage. 1
Standard Pediatric Dosing Framework
The recommended dose of metronidazole for pediatric patients is 30-40 mg/kg/day divided every 8 hours, with a maximum of 500 mg per dose. 1 For your 37 kg patient, this calculates to:
- Total daily dose: 1,110-1,480 mg/day (30-40 mg/kg/day × 37 kg)
- Per-dose amount: 370-493 mg every 8 hours
- Practical dosing: 500 mg IV every 8 hours (reaching the maximum per-dose limit) 1
This dosing applies to most infections requiring metronidazole including intra-abdominal infections, complicated skin/soft tissue infections, and anaerobic infections. 1
Condition-Specific Dosing Adjustments
For Clostridium difficile Infection (CDI)
If treating CDI specifically, use LOWER doses than for other anaerobic infections:
- Non-severe CDI: 7.5 mg/kg/dose three or four times daily (maximum 500 mg per dose) = approximately 278 mg every 6-8 hours 2, 1
- Severe CDI requiring IV therapy: 10 mg/kg/dose three times daily (maximum 500 mg per dose) = 370 mg every 8 hours 2, 1
For Mixed Necrotizing Infections
For severe necrotizing soft tissue infections requiring anaerobic coverage, use 7.5 mg/kg/dose every 6 hours IV (278 mg every 6 hours), typically combined with cefotaxime or other broad-spectrum agents. 1
Important Clinical Considerations
Duration of therapy: Standard treatment duration is 10 days for most infections. 1
Route of administration: Metronidazole has nearly 100% oral bioavailability, so IV and oral dosing are equivalent once the patient can tolerate oral intake. 3 However, for serious infections, initiate with IV therapy.
Once-daily dosing: While some centers use once-daily dosing (30 mg/kg as a single dose) for appendicitis based on pharmacokinetic data showing adequate AUC/MIC ratios, 4 the guideline-recommended dosing remains every 8 hours for most infections. 1 The traditional divided dosing (every 8 hours) is the safer, evidence-based approach for serious systemic infections.
Weight threshold: At 37 kg, this patient is approaching but has not reached the 40 kg threshold where adult dosing typically begins. 5 Continue with weight-based pediatric dosing rather than fixed adult doses.
Monitoring and Safety
Pharmacokinetic considerations: Children older than 4 years have pharmacokinetic parameters similar to adults, with adequate clearance and distribution. 3 Your patient should achieve therapeutic concentrations with standard dosing.
Renal adjustment: Minimal dose adjustment needed for renal impairment since metronidazole is primarily hepatically metabolized, though metabolites accumulate in renal failure. 3 Monitor for toxicity if significant renal dysfunction present.
Hepatic adjustment: Reduce dosing in severe liver dysfunction due to decreased metabolism. 3