What are the antibiotics of choice for bacterial colitis?

Antibiotic Treatment for Bacterial Colitis

First-Line Antibiotic Selection Based on Colitis Type

For C. difficile colitis, which represents the most common bacterial colitis requiring antibiotics, use oral metronidazole 500 mg three times daily for 10 days in non-severe disease, or oral vancomycin 125 mg four times daily for 10 days in severe disease. 1, 2

Non-Severe C. difficile Colitis

• Oral metronidazole 500 mg three times daily for 10 days is the first-line treatment 1, 2, 3
• Non-severe disease is defined by stool frequency <4 times daily, white blood cell count <15 × 10⁹/L, and absence of severe colitis signs 3
• In clearly antibiotic-induced cases, consider stopping the inciting antibiotic and observing for 48 hours, but monitor closely for deterioration 1

Severe C. difficile Colitis

• Oral vancomycin 125 mg four times daily for 10 days is the first-line treatment 1, 2, 3
• Severe disease indicators include marked leukocytosis (>15 × 10⁹/L), decreased albumin (<30 g/L), elevated creatinine (≥133 μM or ≥1.5 times baseline), fever, rigors, hemodynamic instability, or signs of peritonitis/ileus 1, 3
• Metronidazole is strongly discouraged in severe or life-threatening disease 1
• Consider increasing vancomycin to 500 mg four times daily in very severe cases 1
• Fidaxomicin 200 mg twice daily for 10 days is an alternative, though evidence for life-threatening disease is lacking 1

Recurrent C. difficile Colitis

• Oral vancomycin 125 mg four times daily for at least 10 days followed by either pulse or taper strategy 1, 2, 3
• Fidaxomicin 200 mg twice daily for 10 days is an alternative with lower recurrence rates (except in PCR ribotype 027) 1, 3
• For multiple recurrences unresponsive to antibiotics, fecal transplantation combined with oral antibiotics is strongly recommended 1

When Oral Therapy is Impossible

• Intravenous metronidazole 500 mg three times daily PLUS vancomycin 500 mg in 100 mL normal saline four times daily by nasogastric tube or intracolonic retention enema 1, 2
• Intravenous tigecycline 50 mg twice daily for 14 days can be considered as salvage therapy, though with marginal strength of recommendation 1

Other Bacterial Colitis (Non-C. difficile)

For bacterial colitis caused by Campylobacter, Salmonella, Shigella, E. coli, or Yersinia species, antibiotics are reserved for high-risk patients and complicated disease, as many infections are self-limiting 4. The evidence does not provide specific first-line antibiotic recommendations for these pathogens in the colitis setting, though fluoroquinolones and other agents are used based on local resistance patterns 3.

Critical Management Principles

Medications to Avoid

• Avoid antiperistaltic agents and opiates entirely in C. difficile infection, as these worsen outcomes 1, 2, 3
• Discontinue the inciting antibiotic immediately if possible 1, 2, 3

Surgical Intervention Criteria

• Consider colectomy for: perforation of the colon, toxic megacolon, acute abdomen, severe ileus, or systemic inflammation with deteriorating clinical condition not responding to antibiotics 1, 2, 3
• Operate before serum lactate exceeds 5.0 mmol/L 1, 2

Special Considerations for Inflammatory Bowel Disease

• For ulcerative colitis, no antibiotic regimen is generally recommended, even in acute severe disease 2
• Limited evidence suggests antibiotics may provide modest benefit in ulcerative colitis, though data is sparse 5, 6
• For Crohn's disease with colonic involvement, antibiotics (ciprofloxacin, metronidazole, or combination) may have modest effects 5

Common Pitfalls

• Using metronidazole in severe C. difficile colitis leads to treatment failure 1
• Delaying surgical intervention until lactate exceeds 5.0 mmol/L increases mortality 1, 2
• Continuing antiperistaltic agents or opiates can precipitate toxic megacolon 1, 2
• Failing to recognize that amoxicillin-clavulanate itself can cause C. difficile-associated diarrhea 7