What antibiotics are used to treat infectious colitis?

Antibiotics for Infectious Colitis

For infectious colitis, oral vancomycin 125 mg four times daily for 10 days or fidaxomicin 200 mg twice daily for 10 days are the preferred first-line treatments for C. difficile infection, which is the most common cause of infectious colitis. 1

Determining the Cause of Infectious Colitis

The selection of antibiotics depends on identifying the specific pathogen:

1. C. difficile colitis - Most common nosocomial cause of infectious colitis

   • Diagnosed through stool tests for C. difficile toxin
   • Often associated with prior antibiotic use
   • May present with pseudomembranous colitis in severe cases

2. Other bacterial pathogens

   • Shigella, Salmonella, Campylobacter, E. coli (STEC)
   • Diagnosed through stool culture or PCR testing
   • Treatment varies by pathogen

Treatment Algorithm for C. difficile Colitis

Non-severe C. difficile Infection

• First-line (mild-moderate cases with limited access to vancomycin/fidaxomicin):
  • Oral metronidazole 500 mg three times daily for 10 days 2, 1
  • Note: Metronidazole should be limited to initial episodes of mild-moderate disease only 2

Severe C. difficile Infection

• Defined by: WBC ≥15,000 cells/mL or serum creatinine >1.5 mg/dL 1
• First-line:
  • Oral vancomycin 125 mg four times daily for 10 days OR
  • Fidaxomicin 200 mg twice daily for 10 days 1

Fulminant C. difficile Infection

• Defined by: Hypotension, shock, ileus, or megacolon 1
• Treatment:
  • Oral vancomycin 500 mg four times daily PLUS
  • IV metronidazole 500 mg every 8 hours
  • If ileus present: Add rectal vancomycin 500 mg in 100 mL normal saline every 6 hours 1

Important Considerations

• Discontinue the inciting antibiotic as soon as possible to reduce recurrence risk 2, 1
• Avoid prolonged or repeated courses of metronidazole due to risk of cumulative and potentially irreversible neurotoxicity 2
• Monitor for treatment response during the first 5-6 days; consider changing to vancomycin if deterioration occurs 1
• Infection control measures are essential:
  • Hand hygiene with soap and water (alcohol-based sanitizers are less effective against C. difficile spores)
  • Contact precautions and isolation
  • Thorough environmental cleaning 1

Treatment of Recurrent C. difficile Infection

• First recurrence:

  • If metronidazole was used initially: Vancomycin 125 mg four times daily for 10 days
  • If standard regimen was used initially: Consider tapered/pulsed vancomycin regimen or fidaxomicin 1

• Multiple recurrences:

  • Tapered/pulsed vancomycin regimen
  • Fidaxomicin 200 mg twice daily for 10 days
  • Consider bezlotoxumab as adjunctive therapy
  • Fecal microbiota transplantation for patients who have failed appropriate antibiotic treatments 1

Treatment of Other Causes of Infectious Colitis

For non-C. difficile infectious colitis (Shigella, Salmonella, Campylobacter):

• Azithromycin 1000 mg single dose can be used empirically for febrile dysenteric diarrhea 3
• Pathogen-specific therapy should be initiated once laboratory diagnosis is confirmed 3

Cautions and Monitoring

• Patients >65 years should be monitored for renal function during and after vancomycin treatment 1, 4
• Vancomycin capsules are for oral use only and not systemically absorbed when used for C. difficile colitis 4
• Monitor for recurrence for up to 2 months after treatment 1