What antibiotics are used to treat colitis?

Antibiotic Treatment for Colitis

The choice of antibiotic for colitis depends entirely on the etiology: for C. difficile colitis, use oral vancomycin 125 mg four times daily for severe disease or oral metronidazole 500 mg three times daily for non-severe disease; for ulcerative colitis and Crohn's disease, antibiotics are generally not recommended as primary therapy. 1, 2

C. difficile Colitis: The Primary Indication

Severity Assessment Determines Treatment Choice

First, assess disease severity to guide antibiotic selection:

• Non-severe disease is characterized by stool frequency <4 times daily, white blood cell count <15 × 10⁹/L, and absence of severe colitis signs 2
• Severe disease includes fever, rigors, hemodynamic instability, signs of peritonitis or ileus, marked leukocytosis, and elevated serum creatinine or lactate 1, 2

First-Line Antibiotic Regimens

For non-severe C. difficile colitis:

• Oral metronidazole 500 mg three times daily for 10 days 1, 2
• This remains the standard first-line therapy for mild-to-moderate disease 1

For severe C. difficile colitis:

• Oral vancomycin 125 mg four times daily for 10 days 1, 2, 3
• Vancomycin is FDA-approved specifically for C. difficile-associated diarrhea at this dose 3
• Critical caveat: Oral vancomycin must be used—parenteral vancomycin is not effective for C. difficile colitis 3

If oral therapy is impossible in severe disease:

• IV metronidazole 500 mg three times daily PLUS intracolonic vancomycin 500 mg in 100 mL normal saline every 4-12 hours and/or vancomycin 500 mg four times daily by nasogastric tube 1

Recurrent C. difficile Colitis

For second and subsequent recurrences:

• Oral vancomycin 125 mg four times daily for at least 10 days, with consideration of a taper/pulse strategy 1, 2
• Alternative: Fidaxomicin 200 mg twice daily for 10 days 1, 2
• Alternative: Teicoplanin 100 mg twice daily (if available) 1, 2

Critical Management Principles for C. difficile Colitis

Beyond antibiotics, several management steps are essential:

• Discontinue the inciting antibiotic immediately if the colitis was clearly induced by antibiotic use, particularly in mild cases 1
• Avoid antiperistaltic agents and opiates entirely as these can worsen outcomes and precipitate toxic megacolon 1, 2
• Monitor renal function in patients >65 years of age during and after treatment, as nephrotoxicity risk is increased with oral vancomycin 3
• Consider surgical intervention (colectomy) for perforation of the colon, toxic megacolon, severe ileus, or systemic inflammation with deteriorating clinical condition not responding to antibiotics 1, 2
• Operate before serum lactate exceeds 5.0 mmol/L 1

Inflammatory Bowel Disease (Ulcerative Colitis and Crohn's Disease)

For ulcerative colitis, no antibiotic regimen is generally recommended, including for acute severe disease. 1

This recommendation is supported by high-certainty evidence showing no difference between antibiotics and placebo in achieving clinical remission 4. While some older research suggested modest benefits, the most recent Cochrane systematic review (2022) found that antibiotics result in no difference in failure to achieve clinical remission (RR 0.88,95% CI 0.74 to 1.06) 4.

For Crohn's disease:

• Antibiotics may have a modest effect in decreasing disease activity, particularly in patients with colonic involvement 5
• Ciprofloxacin, metronidazole, or their combination are most commonly used for suppurative complications such as abscesses and fistulas 5
• Rifaximin has shown promising results in some studies 5, 6
• However, data remain limited and inconsistent, with no strong recommendation for routine use in luminal disease 6

Staphylococcal Enterocolitis

For staphylococcal enterocolitis (including methicillin-resistant strains):

• Total daily dosage is 500 mg to 2 g of oral vancomycin administered in 3 or 4 divided doses for 7 to 10 days 3
• This is an FDA-approved indication for oral vancomycin 3

Common Pitfalls to Avoid

• Do not use IV vancomycin for C. difficile colitis—it is ineffective because vancomycin is poorly absorbed orally and does not reach therapeutic levels in the colon when given parenterally 3
• Do not use oral vancomycin for systemic infections—it is not absorbed and will not treat infections outside the GI tract 3
• Be aware of potential systemic absorption in patients with inflammatory disorders of the intestinal mucosa, which may lead to nephrotoxicity and ototoxicity 3
• Avoid prolonged or recurrent antibiotic courses in inflammatory bowel disease due to significant side effects, C. difficile infection risk, and increasing antibiotic resistance 5