What is the recommended antibiotic for bacterial gastroenteritis?

Recommended Antibiotic for Bacterial Gastroenteritis

Azithromycin is the first-line antibiotic for bacterial gastroenteritis when treatment is indicated, particularly for dysentery (bloody diarrhea) or severe cases with fever. 1, 2

When Antibiotics Are Actually Needed

Most gastroenteritis is viral and does not require antibiotics. 2 Antibiotic treatment should be reserved for:

• Dysentery (bloody diarrhea with fever) - Strong indication 1
• Severe watery diarrhea with high fever (>38.5°C) suggesting invasive bacterial disease 1
• Immunocompromised patients with moderate-to-severe symptoms 1
• Specific high-risk groups: infants <3 months, adults >50 years with atherosclerosis, patients with valvular heart disease or prosthetic vascular materials 1

First-Line Treatment: Azithromycin

Dosing:

• Adults: 500 mg once daily for 3 days OR 1 gram single dose 1, 2, 3
• Children: 10 mg/kg once daily for 3 days (maximum 500 mg/day) 1, 4

Why azithromycin is preferred:

• Superior efficacy against fluoroquinolone-resistant Campylobacter (>90% resistance rates in many regions) 1
• Effective against Shigella, Salmonella, enteroinvasive E. coli, Aeromonas, and Yersinia 1, 5
• Better tolerated than fluoroquinolones with fewer serious adverse effects 1
• No risk of C. difficile infection or tendon rupture (unlike fluoroquinolones) 1
• Single-dose regimen improves compliance 1, 2

Common side effects: Nausea (3%), vomiting (<1%), diarrhea (5.9%) - can be reduced by splitting the 1-gram dose over the first day 1, 3

Pathogen-Specific Recommendations

Campylobacter

• First choice: Azithromycin 500 mg daily × 3 days 1
• Alternative: Ciprofloxacin 500 mg twice daily × 3 days (only if local resistance <10%) 1

Shigella

• First choice: Azithromycin 500 mg daily × 3 days OR 1 gram single dose 1
• Alternative: Ceftriaxone 2 grams IV daily (if azithromycin unavailable) 1
• Avoid fluoroquinolones if ciprofloxacin MIC ≥0.12 μg/mL, even if reported as "susceptible" 1

Non-typhoidal Salmonella

• Usually no antibiotics needed for uncomplicated gastroenteritis (prolongs carrier state) 1
• Treat if: Age <3 months, >50 years with vascular disease, immunocompromised, or invasive disease 1
• If treating: Ceftriaxone 2 grams IV daily OR ciprofloxacin 500 mg twice daily × 5-7 days (if susceptible) 1

Vibrio cholerae

• First choice: Azithromycin 1 gram single dose 1
• Alternative: Doxycycline 300 mg single dose 1

Yersinia enterocolitica

• First choice: Trimethoprim-sulfamethoxazole 160/800 mg twice daily × 5 days 1
• Alternative: Ciprofloxacin 500 mg twice daily × 5 days 1

Second-Line Options (When Azithromycin Cannot Be Used)

Ciprofloxacin

• Dosing: 500 mg twice daily × 3 days OR 750 mg single dose 1
• Use only if: Local Campylobacter fluoroquinolone resistance <10% AND patient has no risk factors for resistant organisms 1
• Major concerns: Widespread resistance in Campylobacter (>90% in Thailand, increasing globally), C. difficile risk, tendon rupture risk, QT prolongation 1

Rifaximin

• Dosing: 200 mg three times daily × 3 days 1
• Use only for: Non-invasive watery diarrhea (traveler's diarrhea from E. coli) 1
• Do NOT use for: Dysentery, fever, or suspected invasive pathogens (Campylobacter, Shigella, Salmonella) - failure rate up to 50% 1

Trimethoprim-Sulfamethoxazole

• Dosing: 160/800 mg twice daily × 3-5 days 1, 6
• Limited use due to: Widespread resistance in Shigella and Salmonella 1
• Consider for: Yersinia infections or when azithromycin/fluoroquinolones contraindicated 1

Critical Pitfalls to Avoid

1. Do not use fluoroquinolones empirically for dysentery - Resistance rates in Campylobacter and Shigella make them unreliable first-line agents 1

2. Do not use rifaximin for bloody diarrhea or fever - It fails in 50% of invasive infections 1

3. Do not treat uncomplicated non-typhoidal Salmonella gastroenteritis - Antibiotics prolong fecal shedding without clinical benefit 1

4. Do not rely on "susceptible" fluoroquinolone reports for Shigella if ciprofloxacin MIC ≥0.12 μg/mL - Clinical failures occur despite laboratory susceptibility 1

5. Always provide rehydration therapy - Antibiotics are adjunctive; fluid replacement is the cornerstone of treatment 2

Special Populations

Pregnant women: Azithromycin is safe; avoid doxycycline and fluoroquinolones 7, 2

Children: Azithromycin 10 mg/kg daily × 3 days; avoid fluoroquinolones in children <18 years due to cartilage toxicity 1, 4

Immunocompromised: Consider longer treatment courses (5-7 days) and broader coverage; may need ceftriaxone for severe disease 1, 2