What are the recommended antibiotics (Abx) for infectious colitis?

Recommended Antibiotics for Infectious Colitis

For infectious colitis, oral vancomycin 125 mg four times daily for 10 days is the first-line treatment for Clostridium difficile infection, while metronidazole 500 mg three times daily for 10 days is recommended for non-severe cases and azithromycin 1000 mg as a single dose is effective for empiric treatment of febrile dysenteric diarrhea caused by invasive bacterial enteropathogens. 1, 2, 3

Pathogen-Specific Treatment Recommendations

Clostridium difficile Colitis

• First-line therapy:

  • Non-severe cases: Oral metronidazole 500 mg three times daily for 10 days 2
  • Severe cases: Oral vancomycin 125 mg four times daily for 10 days 2, 1
  • Severity assessment based on: fever >38.5°C, hemodynamic instability, leukocytosis >15×10^9/L, creatinine rise >50% above baseline, or pseudomembranous colitis on endoscopy 2

• If oral therapy not possible:

  • Non-severe: IV metronidazole 500 mg three times daily for 10 days 2
  • Severe: IV metronidazole 500 mg three times daily for 10 days PLUS intracolonic vancomycin 500 mg in 100 mL normal saline every 4-12 hours and/or vancomycin 500 mg four times daily via nasogastric tube 2, 1

• For recurrent C. difficile infection:

  • Second recurrence: Vancomycin 125 mg four times daily for at least 10 days, consider taper/pulse strategy 2, 1
  • Fidaxomicin 200 mg twice daily for 10 days is an alternative option 1

Other Bacterial Enteropathogens

• For Shigella, Salmonella, and Campylobacter:
  • Empiric treatment: Azithromycin 1000 mg as a single dose 3
  • Adjust based on culture and sensitivity results

Staphylococcal Enterocolitis

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

Treatment Algorithm Based on Clinical Presentation

1. Assess severity of colitis:

   • Check for fever, rigors, hemodynamic instability, peritoneal signs, ileus, leukocytosis, creatinine elevation, lactate elevation 2
   • Obtain stool studies: C. difficile toxin testing, culture for bacterial pathogens, inflammatory markers (leukocytes, lactoferrin, calprotectin) 1, 3

2. Consider epidemiologic factors:

   • Recent antibiotic use (suggests C. difficile)
   • International travel (may suggest specific pathogens)
   • Shellfish consumption
   • Community vs. healthcare-associated 3, 5

3. Initial management:

   • Discontinue the inciting antibiotic if possible 1
   • Avoid antiperistaltic agents and opiates as they may mask symptoms and worsen disease 2, 1
   • Provide supportive care with fluid and electrolyte replacement

4. Pathogen-directed therapy:

   • C. difficile confirmed: Follow severity-based recommendations above
   • Shiga toxin-producing E. coli (STEC): Avoid antibiotics due to risk of hemolytic uremic syndrome 3
   • Other bacterial enteropathogens: Initiate pathogen-specific antimicrobial therapy 3, 5

Special Considerations

• Treatment response assessment: Expect decreased stool frequency and improved consistency within 3 days 2, 1

• Treatment failure: Absence of improvement after 3 days of appropriate therapy 2

• Surgical consultation: Consider early for patients with perforation, systemic inflammation not responding to antibiotics, toxic megacolon, or severe ileus 2, 1

• Risk factors for complications:

  • Age >65 years (monitor renal function during and after treatment) 4
  • Severe underlying disease
  • Continued use of antibiotics for non-C. difficile infections 1

• Monitoring for recurrence:

  • Watch for increased stool frequency and looser stools for up to 2 months after treatment 1
  • Recurrence rates of 5-50% have been reported 6

Common Pitfalls to Avoid

1. Inappropriate antibiotic selection: Using broad-spectrum antibiotics unnecessarily may increase risk of C. difficile recurrence 1

2. Failure to discontinue inciting antibiotics: When possible, stop the antibiotic that triggered the colitis 1

3. Overuse of vancomycin: Reserve for severe cases to prevent development of vancomycin-resistant organisms 7

4. Inadequate monitoring: Failure to assess treatment response within 3 days may delay recognition of treatment failure 2, 1

5. Missing STEC: When low-grade or no fever is present in a patient with acute dysentery, specifically request testing for E. coli O157:H7 and Shiga toxin 3