What is the recommended dose of Flagyl (metronidazole) for treating intraabdominal infections?

Metronidazole Dosing for Intraabdominal Infections

For intraabdominal infections, the recommended dose of metronidazole is 500 mg intravenously every 8 hours. 1

Dosing Guidelines Based on Administration Route

Intravenous Administration

• The FDA-approved loading dose for IV metronidazole is 15 mg/kg infused over one hour (approximately 1 g for a 70-kg adult) 2
• Maintenance dose is 7.5 mg/kg infused over one hour every 6 hours (approximately 500 mg for a 70-kg adult) 2
• For intraabdominal infections specifically, the Infectious Diseases Society of America (IDSA) recommends 500 mg every 8 hours 1
• Duration of therapy is typically 7-10 days, though may be limited to 4-7 days if adequate source control is achieved 1

Special Considerations

• Patients with severe hepatic disease metabolize metronidazole more slowly, requiring lower doses and close monitoring of plasma levels 2
• In elderly patients, pharmacokinetics may be altered, necessitating serum level monitoring for dose adjustment 2
• For patients with continuous nasogastric aspiration, be aware that sufficient metronidazole may be removed to reduce serum levels 2

Combination Therapy for Intraabdominal Infections

• Metronidazole is typically used in combination with other antibiotics to provide adequate coverage against both aerobic and anaerobic pathogens 1, 3
• Common combinations include:
  • Metronidazole + cefepime (2 g IV every 12 hours) 4
  • Metronidazole + cefuroxime (1.5 g IV every 8 hours) 5
  • Metronidazole + cefotaxime (1-2 g IV every 6-8 hours) 6
  • Metronidazole + gentamicin (5-7 mg/kg IV every 24 hours) 7

Special Clinical Scenarios

Fulminant Clostridium difficile Infection

• For fulminant C. difficile infection with ileus, intravenously administered metronidazole (500 mg every 8 hours) should be used in addition to oral or rectal vancomycin 1
• This is particularly important when ileus may impair delivery of oral vancomycin to the colon 1

Surgical Prophylaxis

• For surgical prophylaxis in contaminated or potentially contaminated colorectal surgery: 2
  • 15 mg/kg infused over 30-60 minutes and completed approximately one hour before surgery
  • Followed by 7.5 mg/kg infused over 30-60 minutes at 6 and 12 hours after the initial dose

Safety Considerations

• Prolonged or repeated courses of metronidazole should be avoided due to the risk of cumulative and potentially irreversible neurotoxicity 8
• Monitor for adverse effects, with the most common being nausea and diarrhea 3
• IV administration should be by slow intravenous drip infusion only, either continuous or intermittent 2
• Do not use equipment containing aluminum for administration 2

Clinical Efficacy

• Metronidazole in combination with appropriate aerobic coverage has demonstrated high clinical cure rates (88-97%) in multiple clinical trials for intraabdominal infections 3, 6, 4, 5
• Metronidazole provides essential coverage against anaerobic pathogens commonly found in intraabdominal infections 1