What are the recommended antibiotics for treating lower respiratory infections, such as community-acquired pneumonia?

Recommended Antibiotics for Lower Respiratory Infections

For community-acquired pneumonia (CAP), first-line treatment should be amoxicillin 3 g/day orally for patients without risk factors, or macrolides for suspected atypical pathogens in adults under 40 years without underlying disease. 1

Treatment Algorithm Based on Setting and Severity

Outpatient Management

• First-line options:

  • Suspected pneumococcal origin (especially in adults >40 years):
    • Amoxicillin 3 g/day orally 1
  • Suspected atypical pathogens (adults <40 years without underlying disease):
    • Macrolides: Azithromycin 500 mg daily for 3 days or 500 mg on day 1 followed by 250 mg daily for 4 days 1, 2
    • Clarithromycin 250-500 mg twice daily for at least 5 days 1
  • Alternative option:
    • Telithromycin 1

• Duration: Minimum 7 days (except azithromycin and clarithromycin which have shorter courses) 2

• Assessment: Evaluate response at days 5-7 (improvement of symptoms) 1

Hospital Ward Management

• First-line options:

  • Second-generation cephalosporin (e.g., IV cefuroxime 750-1500 mg every 8 hours) 1
  • Third-generation cephalosporin (e.g., IV cefotaxime 1 g every 8 hours or IV ceftriaxone 1 g daily) 1
  • IV benzyl penicillin 1-4×10^6 units every 2-4 hours or IV amoxicillin 1 g every 6 hours 1
  • Macrolide (e.g., IV or oral erythromycin 1 g every 8 hours) 1

• Duration: 7-14 days depending on pathogen and clinical response 1, 2

• Assessment: Evaluate response at days 2-3 (fever, lack of progression of pulmonary infiltrates) 1

Intensive Care Unit Management

• Special considerations for pulmonary abscess/cavitated pneumonia or aspiration:
  • IV amoxicillin-clavulanate 2 g every 6 hours 1, 2
  • Second or third-generation cephalosporin plus either:
    • Second-generation quinolone (ofloxacin, ciprofloxacin) or
    • Macrolide (IV erythromycin 1 g every 6 hours) plus rifampicin (600 mg twice daily) with/without IV clindamycin (600 mg every 8 hours) 1

Pathogen-Specific Considerations

Streptococcus pneumoniae

• Amoxicillin remains the drug of choice, especially for penicillin-susceptible strains 1, 2
• For penicillin-resistant strains, consider higher doses of amoxicillin or respiratory fluoroquinolones 2

Atypical Pathogens (Mycoplasma, Chlamydia, Legionella)

• Macrolides are the preferred agents 1, 3
• Azithromycin has shown excellent efficacy against Mycoplasma pneumoniae (100% eradication) 4
• Legionella infections require 21 days of treatment 2

Haemophilus influenzae

• Amoxicillin-clavulanate for beta-lactamase producing strains 1, 2
• Azithromycin is effective against H. influenzae, including ampicillin-resistant strains 5

Important Considerations and Cautions

Azithromycin Safety Profile

• Well-tolerated with fewer side effects than comparator drugs (11.3% vs 31%) 4
• Monitor for QT prolongation in at-risk patients (known QT prolongation, history of torsades de pointes, congenital long QT syndrome, bradyarrhythmias, or uncompensated heart failure) 6
• Consider hepatotoxicity risk; discontinue immediately if signs of hepatitis occur 6

Treatment Failure

• If no improvement after 72 hours, consider alternative antibiotics 2
• For non-responding patients, consider additional investigations:
  • Fibreoptic bronchoscopy
  • Detection of pneumococcal and Legionella pneumophila antigens
  • Bronchoalveolar lavage if opportunistic agents are suspected 1

Clostridium difficile Risk

• All antibiotics carry risk of C. difficile-associated diarrhea
• Monitor for diarrhea during and up to two months after antibiotic use 6

Evidence Strength

The most recent guidelines from Praxis Medical Insights (2025) align with earlier recommendations from the European Respiratory Society and French guidelines, supporting the use of amoxicillin as first-line therapy for suspected pneumococcal infections and macrolides for atypical pathogens. Clinical trials have demonstrated that azithromycin is as effective as standard regimens with better tolerability 3, 4, 7, making it an excellent choice for appropriate patients.