What antibiotics are used to treat diarrhea caused by bacterial infections?

Antibiotic Selection for Bacterial Diarrhea

Azithromycin is the preferred first-line empiric antibiotic for bacterial diarrhea requiring treatment, particularly for dysentery (bloody diarrhea with fever) or severe febrile diarrhea, due to widespread fluoroquinolone resistance in Campylobacter and Shigella species. 1, 2

When to Use Antibiotics (and When NOT to)

Indications for empiric antibiotics:

• Dysentery (bloody diarrhea with fever and abdominal pain) presumed due to Shigella 1, 2
• Infants <3 months of age with suspected bacterial etiology 2
• Recent international travelers with fever ≥38.5°C and/or signs of sepsis 2
• Immunocompromised patients with severe illness and bloody diarrhea 2
• Suspected enteric fever with sepsis features 2

Absolute contraindications:

• NEVER use antibiotics for suspected STEC O157 or Shiga toxin 2-producing E. coli infections - this increases risk of hemolytic uremic syndrome 2, 3
• Asymptomatic contacts of patients with diarrhea should not receive antibiotics 2
• Mild, non-bloody, non-febrile watery diarrhea does not require antibiotics 3

First-Line Antibiotic: Azithromycin

Dosing regimens:

• Single 1000 mg dose (preferred for adherence) 1, 3
• Alternative: 500 mg daily for 3 days 1, 3

Why azithromycin is superior:

• Fluoroquinolone resistance in Campylobacter now exceeds 90% in Southeast Asia, India, and increasingly worldwide 1, 2, 3
• Azithromycin demonstrated superiority over levofloxacin in Thailand, reducing diarrhea duration by >32 hours 1
• Achieves 100% clinical and bacteriological cure rates for Campylobacter 3
• More effective than fluoroquinolones for Shigella infections 1
• Superior to ciprofloxacin for cholera, reducing diarrhea duration by >1 day 1, 2

Pathogen coverage:

• Campylobacter jejuni (first choice) 1
• Shigella species (first choice) 1
• Vibrio cholerae (first choice) 1, 2
• Salmonella species (when treatment indicated) 1

Second-Line Alternative: Fluoroquinolones

Use ciprofloxacin ONLY when:

• Azithromycin is unavailable 3
• Geographic region has documented low fluoroquinolone resistance 1, 3
• Non-dysenteric watery diarrhea in areas without high Campylobacter resistance 1

Dosing:

• Ciprofloxacin 750 mg single dose or 500 mg twice daily for 3 days 1
• Levofloxacin 500 mg daily for 3 days 1

Critical limitations:

• Fluoroquinolone resistance exceeds 90% for Campylobacter in many regions 1, 2
• Inferior outcomes for Shigella compared to azithromycin 1
• FDA warnings for serious adverse effects including tendon rupture, QT prolongation, and C. difficile infection 1, 3
• Should be avoided if ciprofloxacin MIC ≥0.12 μg/mL for Shigella even if reported as "susceptible" 1

Pathogen-Specific Recommendations

For Campylobacter infections:

• Azithromycin is first choice 1
• Ciprofloxacin only if susceptible (increasingly rare) 1

For Shigella infections:

• Azithromycin or ceftriaxone are first-line 1
• Ciprofloxacin or TMP-SMX only if susceptible 1
• Beta-lactams (ceftriaxone) more effective than fluoroquinolones when 90% Shigella confirmed 1, 2

For non-typhoidal Salmonella:

• Usually NOT indicated for uncomplicated infection 1
• Treat only if: neonates (<3 months), age >50 with atherosclerosis, immunosuppression, cardiac disease, or significant joint disease 1
• If treatment needed: ceftriaxone, ciprofloxacin (if susceptible), TMP-SMX (if susceptible), or amoxicillin (if susceptible) 1
• For bacteremia: ceftriaxone PLUS ciprofloxacin to avoid initial treatment failure 1

For Salmonella typhi (typhoid fever):

• Ceftriaxone or ciprofloxacin (first choice) 1
• Alternatives: ampicillin, TMP-SMX, or azithromycin 1

For Vibrio cholerae:

• Azithromycin (single dose) superior to ciprofloxacin 1, 2
• Doxycycline alternative 1, 2
• Reduces diarrhea duration by ~1.5 days and stool volume by 50% 1, 2

For Yersinia enterocolitica:

• TMP-SMX (first choice) 1
• Alternatives: fluoroquinolone, cefotaxime, or doxycycline 1
• For severe disease: third-generation cephalosporin plus gentamicin 1

Special Situation: Clostridium difficile Infection

This requires DIFFERENT antibiotics - do not use azithromycin or fluoroquinolones:

• Oral vancomycin 125 mg four times daily for 10 days (first choice) 1, 4
• Fidaxomicin 200 mg twice daily for 10 days (alternative, lower recurrence rates) 1
• Metronidazole 400-500 mg three times daily for 10 days (acceptable for non-severe CDI in children or adults who cannot obtain vancomycin/fidaxomicin) 1

Critical point: Parenteral vancomycin is NOT effective for CDI - must use oral formulation 4

Pediatric Considerations

For children requiring antibiotics:

• Third-generation cephalosporin for infants <3 months or those with neurologic involvement 2
• Azithromycin for other children, based on local susceptibility patterns 2
• Fluoroquinolones should be avoided in pediatric patients due to increased adverse events including joint/surrounding tissue effects 5

What NOT to Use

Avoid these antibiotics due to resistance:

• TMP-SMX (co-trimoxazole): Increasing resistance compromises efficacy 1, 3
• Ampicillin: Widespread resistance 3
• Erythromycin: Widespread bacterial resistance 3
• Tetracyclines (except doxycycline specifically for cholera) 3

Critical Pitfalls to Avoid

Geographic resistance patterns matter:

• Default to azithromycin in Southeast Asia regardless of severity due to >90% fluoroquinolone resistance 1, 2, 3
• Fluoroquinolones may still be reasonable in regions with documented low resistance 1

Drug interactions:

• Avoid aluminum or magnesium-containing antacids with azithromycin - they reduce absorption 3

Monitoring requirements:

• Obtain stool cultures before antibiotics when possible, though empiric therapy warranted in severe cases 3
• Reassess patients not responding within 48-72 hours for complications, resistance, or non-infectious causes 2, 3

Rehydration is paramount:

• Oral rehydration solution (50-90 mEq/L sodium) for mild-moderate dehydration 2, 3
• Intravenous fluids for severe dehydration, shock, altered mental status, or ileus 1, 2
• Antibiotics are adjunctive - rehydration is the cornerstone of all diarrhea management 1, 2, 3

Immunocompromised patients:

• Consider empiric antibacterial treatment even for less severe illness 3
• Monitor for systemic absorption if using oral vancomycin for CDI, especially with renal insufficiency or concomitant aminoglycoside use 4