What antibiotics are used to treat a bacterial stomach bug?

Antibiotics for Bacterial Stomach Infections

For bacterial gastroenteritis, the recommended first-line treatment is azithromycin, which is effective against most common enteric pathogens and can be given as a single 500 mg dose for acute watery diarrhea or 1000 mg for dysentery. Alternative options include fluoroquinolones such as ciprofloxacin or levofloxacin, though increasing resistance limits their effectiveness 1, 2.

Treatment Approach Based on Clinical Presentation

Mild-to-Moderate Community-Acquired Infection

• Azithromycin: 500 mg once daily for 3 days for watery diarrhea; single 1000 mg dose for dysentery 1, 2
• Ciprofloxacin: 500 mg twice daily for 3 days (if local E. coli resistance is <10%) 1
• Metronidazole + Ceftriaxone: For suspected anaerobic involvement 1

Severe Infection or Healthcare-Associated Infection

• Piperacillin/Tazobactam: 4.5 g IV every 6 hours 1, 3
• Meropenem: 1 g IV every 8 hours 1
• Imipenem/Cilastatin: 1 g IV every 8 hours 1

Pathogen-Specific Treatment

Helicobacter pylori Infection

For H. pylori-positive peptic ulcer disease, the recommended regimens are:

1. Standard Triple Therapy (first-line if low clarithromycin resistance) 1:

   • PPI standard dose twice daily
   • Clarithromycin 500 mg twice daily
   • Amoxicillin 1000 mg twice daily (or Metronidazole 500 mg twice daily)
   • Duration: 14 days

2. Sequential Therapy (if high clarithromycin resistance) 1:

   • Days 1-5: PPI + Amoxicillin 1000 mg twice daily
   • Days 6-10: PPI + Clarithromycin 500 mg twice daily + Metronidazole 500 mg twice daily

3. Second-line Therapy (if first-line fails) 1:

   • PPI standard dose twice daily
   • Levofloxacin 500 mg once daily (or 250 mg twice daily)
   • Amoxicillin 1000 mg twice daily
   • Duration: 10 days

Traveler's Diarrhea

• Azithromycin: Single 500 mg dose (preferred due to lower resistance) 2
• Rifaximin: 200 mg three times daily for 3 days (only for non-invasive diarrhea) 2

Important Considerations

When to Use Antibiotics

Antibiotics are NOT recommended for:

• Most cases of acute watery diarrhea in immunocompetent adults 1
• Suspected viral gastroenteritis
• STEC O157 infections (may increase risk of hemolytic uremic syndrome) 1

Antibiotics ARE recommended for:

• Dysentery (bloody diarrhea with fever and abdominal pain) 1
• Severe illness with signs of systemic infection
• Immunocompromised patients 1
• Infants <3 months with suspected bacterial infection 1
• Travelers with fever ≥38.5°C and signs of sepsis 1

Duration of Therapy

• For most uncomplicated infections: 3-5 days 1, 2
• For complicated intra-abdominal infections with adequate source control: 4-7 days 3
• Continue until resolution of clinical signs (normalization of temperature, WBC count, return of normal GI function) 1

Pitfalls to Avoid

1. Using fluoroquinolones in areas with high resistance rates (>10% resistance among E. coli) 1
2. Prescribing antibiotics for viral gastroenteritis
3. Using antibiotics for STEC O157 infections, which may increase risk of hemolytic uremic syndrome 1
4. Prolonging antibiotic therapy beyond 7 days without clear indication (increases risk of C. difficile infection) 3
5. Failing to consider antimicrobial resistance patterns in your local area 1

By following these evidence-based recommendations, you can effectively treat bacterial stomach infections while minimizing antibiotic resistance and adverse effects.