What antibiotics are used to treat infectious colitis?

Antibiotics for Infectious Colitis

For infectious colitis, metronidazole is the first-line antibiotic for Clostridioides difficile infection (CDI), while specific antibiotic choices for other causes should be guided by the identified pathogen. 1, 2

Clostridioides difficile Infection (CDI)

First-line Treatment

• Non-severe CDI:

  • Metronidazole 500 mg orally three times daily for 10 days 1
  • Consider stopping the inciting antibiotic if possible 1, 2

• Severe CDI (WBC >15,000 cells/mL OR serum creatinine >1.5 mg/dL):

  • Vancomycin 125 mg orally four times daily for 10 days 1, 2, 3

• Fulminant CDI (hypotension, shock, ileus, megacolon):

  • Vancomycin 500 mg orally four times daily PLUS
  • Metronidazole 500 mg IV every 8 hours 2
  • If oral therapy impossible: Metronidazole 500 mg IV three times daily PLUS intracolonic vancomycin 500 mg in 100 mL saline every 4-12 hours 1

Recurrent CDI

• First recurrence: Same as initial episode based on severity 1
• Second or later recurrences: Vancomycin in tapered/pulsed regimen 1, 2:
  • 125 mg four times daily for 10-14 days
  • 125 mg twice daily for 7 days
  • 125 mg once daily for 7 days
  • 125 mg every 2-3 days for 2-8 weeks

Other Infectious Causes of Colitis

Bacterial Pathogens

• Salmonella, Shigella, Campylobacter, E. coli:

  • Ciprofloxacin 500 mg twice daily for 5-7 days (if susceptible) 4
  • Alternative: Azithromycin 500 mg daily for 3 days

• Staphylococcal enterocolitis:

  • Vancomycin 125-250 mg orally four times daily for 7-10 days 3
  • Total daily dosage: 500 mg to 2 g administered orally in 3-4 divided doses

Special Populations

• Pediatric patients:

  • For CDI: 40 mg/kg/day of vancomycin in 3-4 divided doses (max 2g/day) 2, 3
  • For metronidazole: 30 mg/kg/day divided into three doses (max 500 mg/dose)

• Patients with β-lactam allergy:

  • For gram-positive infections: Consider macrolides, cotrimoxazole, or glycopeptides based on the specific pathogen 1

Diagnostic Approach

1. Obtain stool samples for:

   • C. difficile toxin assay (if antibiotic exposure or healthcare setting)
   • Bacterial culture and sensitivity
   • Multiplex PCR for common enteric pathogens 4

2. Consider sigmoidoscopy or colonoscopy for:

   • Patients with severe symptoms
   • When pseudomembranous colitis is suspected
   • Cases not responding to empiric therapy 2

Treatment Pearls and Pitfalls

Pearls

• Discontinue the inciting antibiotic whenever possible 1, 2
• Avoid antiperistaltic agents and opiates in infectious colitis 1
• Handwashing with soap and water (not alcohol-based sanitizers) is essential for preventing C. difficile spread 2

Pitfalls

• Antibiotics with highest risk for causing CDI include clindamycin, fluoroquinolones, and cephalosporins 2
• Even vancomycin and metronidazole can cause CDI when used parenterally 5
• Oral vancomycin is poorly absorbed and should not be used for systemic infections 3
• Metronidazole has decreased efficacy against C. difficile compared to vancomycin and has higher risk of neurotoxicity 2

Monitoring and Follow-up

• Monitor stool frequency, consistency, and systemic symptoms
• Treatment response: Decreased stool frequency and improved consistency after 3 days 1
• Consider surgical consultation for toxic megacolon, perforation, or severe disease not responding to antibiotics 1, 2

Remember that the choice of antibiotic should be guided by the identified pathogen, local resistance patterns, and patient factors such as severity of illness and comorbidities.