What antibiotics are effective against Streptococcus pneumoniae (strep pneumonia), Haemophilus influenzae (H. flu), and Moraxella catarrhalis infections?

Antibiotics for Treating Strep Pneumonia, H. Influenzae, and Moraxella Catarrhalis

Respiratory fluoroquinolones (levofloxacin, moxifloxacin, or gatifloxacin) are the most effective antibiotics for treating infections caused by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis due to their excellent coverage against all three pathogens. 1, 2

First-Line Treatment Options

For Outpatient Treatment:

• Respiratory fluoroquinolones (levofloxacin 750mg daily or moxifloxacin 400mg daily)

  • Provide >90% coverage against all three pathogens 1
  • FDA-approved for community-acquired pneumonia caused by these organisms 2
  • Particularly effective for multi-drug resistant S. pneumoniae 1

• High-dose amoxicillin-clavulanate (875mg/125mg twice daily)

  • Excellent coverage for H. influenzae (including β-lactamase producers) and M. catarrhalis 1, 3
  • Good coverage for S. pneumoniae (90-92%) 1

For Hospitalized Patients:

• Ceftriaxone (1-2g IV daily) 1
  • Excellent activity against all three pathogens
  • Can be used as initial parenteral therapy before transitioning to oral options

Second-Line Options

• Cefuroxime axetil (500mg twice daily)

  • Active against H. influenzae and moderately active against S. pneumoniae and M. catarrhalis 1
  • Better option than first-generation cephalosporins 3

• Doxycycline (100mg twice daily)

  • Good option for patients with non-type I penicillin allergies 1
  • Active against approximately 90% of S. pneumoniae strains 1

Pathogen-Specific Considerations

For S. pneumoniae:

• Respiratory fluoroquinolones have >99% activity 1
• High-dose amoxicillin or amoxicillin-clavulanate (95-97% activity) 1
• Ceftriaxone (95-97% activity) 1

For H. influenzae:

• 30-35% produce β-lactamase, making them resistant to ampicillin 3, 4
• Best options: respiratory fluoroquinolones, ceftriaxone, cefixime, or high-dose amoxicillin-clavulanate (95-100% activity) 1, 5

For M. catarrhalis:

• 90% produce β-lactamase 4

• Best options: respiratory fluoroquinolones, cefixime, amoxicillin-clavulanate (100% activity) 1, 5

Treatment Algorithm

1. For healthy outpatients with no risk factors:

   • High-dose amoxicillin-clavulanate OR
   • Respiratory fluoroquinolone (if penicillin allergic)

2. For patients with comorbidities or recent antibiotic use:

   • Respiratory fluoroquinolone OR
   • Ceftriaxone (if hospitalized)

3. For severe infections requiring hospitalization:

   • Ceftriaxone 1-2g IV daily plus a macrolide 1
   • OR respiratory fluoroquinolone IV 1

Important Considerations

• Resistance patterns: Local resistance patterns should guide therapy, especially for S. pneumoniae
• β-lactamase production: High rates in H. influenzae (33-35%) and M. catarrhalis (>90%) necessitate β-lactamase-stable agents 4, 6
• Fluoroquinolone concerns: Despite excellent coverage, there are concerns about overuse leading to resistance development 1
• Duration of therapy: 5-7 days for respiratory fluoroquinolones; 7-10 days for other agents 3

Common Pitfalls to Avoid

1. Using standard-dose amoxicillin alone - Ineffective against β-lactamase-producing H. influenzae and M. catarrhalis
2. Using macrolides as monotherapy - Increasing resistance in S. pneumoniae and poor activity against H. influenzae
3. Using TMP-SMX - High resistance rates among all three pathogens (only 40-70% susceptibility) 1
4. Using first-generation cephalosporins - Poor activity against H. influenzae and M. catarrhalis 3

By selecting an appropriate antibiotic with activity against all three pathogens, you can effectively treat infections while minimizing the risk of treatment failure due to resistance.