What antibiotic is recommended for an otherwise healthy adult with mild to moderate bacterial diarrhea?

Antibiotic Treatment for Bacterial Diarrhea

For otherwise healthy adults with mild to moderate bacterial diarrhea, empiric antibiotic therapy is generally NOT recommended unless specific high-risk features are present. 1

When Antibiotics Are NOT Indicated

Most cases of acute watery diarrhea in immunocompetent adults without recent international travel should NOT receive empiric antibiotics. 1 The rationale includes:

• Self-limited disease course (typically resolves within 5 days) 2
• Risk of promoting antimicrobial resistance 1
• Potential for adverse drug effects without clear benefit 1

When Antibiotics ARE Indicated

Empiric antibiotic therapy should be initiated in the following specific scenarios:

For Bloody Diarrhea (Dysentery)

Treat empirically if the patient has: 1

• Fever documented in a medical setting PLUS abdominal pain PLUS bloody diarrhea with bacillary dysentery features (frequent scant bloody stools, fever, cramps, tenesmus) presumed to be Shigella
• Recent international travel with body temperature ≥38.5°C and/or signs of sepsis
• Immunocompromised status with severe illness and bloody diarrhea

For Watery Diarrhea

Exceptions where treatment may be considered: 1

• Immunocompromised patients
• Ill-appearing young infants
• Clinical features of sepsis or suspected enteric fever

Recommended Antibiotic Regimens

First-Line Choice: Azithromycin

Azithromycin is the preferred first-line antibiotic for bacterial diarrhea in most clinical scenarios: 1, 2

• Acute watery diarrhea: 500 mg single dose 2
• Febrile diarrhea/dysentery: 1,000 mg single dose 2
• Pediatric dosing: Azithromycin is recommended for children based on local susceptibility patterns and travel history 1

Advantages of azithromycin include:

• Effective against Campylobacter species, including ciprofloxacin-resistant strains 3
• Superior bacteriologic clearance compared to fluoroquinolones in areas with quinolone resistance 3
• Single-dose convenience for most presentations 2

Alternative: Fluoroquinolones (With Important Caveats)

Ciprofloxacin or levofloxacin may be used depending on local susceptibility patterns and travel history: 1, 4

• Ciprofloxacin: 500 mg every 12 hours for 5-7 days (FDA-approved dosing) 4, or 750 mg single dose for acute watery diarrhea 2
• Levofloxacin: 500 mg once daily for 3 days 2

Critical limitations of fluoroquinolones:

• Increasing resistance among Campylobacter species, particularly in Southeast Asia 2, 3
• Should NOT be used unless hospital surveys indicate ≥90% susceptibility of E. coli to quinolones 1
• Less effective than azithromycin for Campylobacter infections in areas with fluoroquinolone resistance 3

Third-Line: Rifaximin (Limited Indications)

Rifaximin 200 mg three times daily for 3 days is an option ONLY for: 2

• Non-invasive acute watery diarrhea
• Should NOT be used with fever, bloody stools, or signs of invasive illness 2

Critical Contraindications

AVOID antibiotics in the following situations:

• STEC O157 and other Shiga toxin 2-producing E. coli: Antibiotics should be avoided due to risk of hemolytic uremic syndrome 1
• Persistent watery diarrhea ≥14 days: Empiric treatment should be avoided; consider non-infectious causes 1

Adjunctive Therapy

Loperamide can be combined with antibiotics in appropriate cases: 1, 2

• May be given to immunocompetent adults with acute watery diarrhea 1
• Further reduces gastrointestinal symptoms and duration of illness when combined with antibiotics 2
• Contraindications: Children <18 years, suspected toxic megacolon, inflammatory diarrhea, or fever 1

Geographic Considerations

Antibiotic selection must account for regional resistance patterns: 2

• Southeast Asia (especially Thailand): High rates of fluoroquinolone-resistant Campylobacter; azithromycin preferred 3
• Latin America/Caribbean: Variable resistance patterns; both azithromycin and fluoroquinolones may be effective 5, 6
• Local susceptibility data should guide empiric choices when available 1

Common Pitfalls to Avoid

• Do not use trimethoprim-sulfamethoxazole empirically: Increasing resistance among common pathogens compromises efficacy 1, 5
• Do not use ampicillin-sulbactam: High rates of resistance among community-acquired E. coli 1
• Do not give fluoroquinolones to children: Third-generation cephalosporins preferred for infants <3 months or those with neurologic involvement 1
• Do not forget rehydration: Antibiotics are NOT a substitute for fluid and electrolyte therapy, which remains the cornerstone of management 1, 7