What antibiotics are recommended for a patient with a respiratory infection, considering factors such as severity, suspected cause, medical history, and age?

Antibiotic Selection for Respiratory Infections

For community-acquired lower respiratory tract infections, amoxicillin or amoxicillin-clavulanate should be the first-line antibiotic choice, with macrolides (azithromycin or clarithromycin) reserved for atypical pathogen coverage or penicillin allergy. 1

Community-Acquired Pneumonia (CAP)

Non-Severe CAP (Outpatient/Medical Ward)

• First-line options include:

  • Amoxicillin 500-1000 mg every 8 hours orally 1
  • Amoxicillin-clavulanate 875/125 mg every 12 hours or 500/125 mg every 8 hours 2, 3
  • Beta-lactam PLUS macrolide (erythromycin 1g every 8 hours, azithromycin 500 mg day 1 then 250 mg daily, or clarithromycin 250-500 mg every 12 hours) 1

• Duration: 7-10 days for uncomplicated bacterial CAP 1

• Extended duration: 10-14 days for Mycoplasma pneumoniae or Chlamydophila pneumoniae; 21 days for Legionella pneumophila or Staphylococcus aureus 1

Severe CAP (ICU Admission)

• Recommended regimen: Third-generation cephalosporin (cefotaxime 1g IV every 8 hours or ceftriaxone 1g IV every 24 hours) PLUS macrolide 1
• Alternative: Third-generation cephalosporin PLUS respiratory fluoroquinolone (levofloxacin or moxifloxacin) 1

Pseudomonas Risk Factors Present

• Use: Anti-pseudomonal cephalosporin OR acylureidopenicillin/beta-lactamase inhibitor PLUS ciprofloxacin 1
• Alternative: Carbapenem PLUS ciprofloxacin 1

COPD Exacerbations

Mild COPD Exacerbation

• Antibiotics indicated when ≥2 of 3 Anthonisen criteria present: increased sputum purulence, increased sputum volume, increased dyspnoea 1
• First-line: Amoxicillin 500-1000 mg every 8 hours OR tetracyclines (doxycycline 100 mg every 12 hours) 1
• Alternatives: Amoxicillin-clavulanate, macrolides, levofloxacin, or moxifloxacin 1

Moderate/Severe COPD Exacerbation

• Preferred: Amoxicillin-clavulanate (co-amoxiclav) 1
• Alternatives: Levofloxacin or moxifloxacin 1

COPD with Pseudomonas Risk

• Use: Ciprofloxacin 500 mg every 12 hours orally 1

Treatment Duration

• Standard: At least 7 days (except clarithromycin and azithromycin which have shorter courses) 1
• Legionella suspected: 21 days 1

Bronchiectasis

Acute Exacerbations

• No Pseudomonas risk: Amoxicillin-clavulanate, levofloxacin, or moxifloxacin 1
• Pseudomonas risk factors: Ciprofloxacin 1

Frequent Exacerbations (≥3 per year)

• If Pseudomonas aeruginosa isolated: Long-term inhaled anti-pseudomonal antibiotic OR long-term macrolide 1
• If other potentially pathogenic microorganisms: Long-term macrolides OR long-term oral/inhaled targeted antibiotic 1
• If no pathogen identified: Long-term macrolides (azithromycin 250 mg three times weekly as pragmatic starting dose) 1

Upper Respiratory Tract Infections

Acute Bacterial Rhinosinusitis

• Indications for antibiotics: Symptoms persisting >10 days without improvement, severe symptoms (fever >39°C with purulent discharge/facial pain ≥3 days), or "double sickening" pattern 4
• First-line: Amoxicillin-clavulanate 875/125 mg every 12 hours or 500/125 mg every 8 hours for 7-10 days 2, 4
• Alternatives: Doxycycline or respiratory fluoroquinolone (levofloxacin/moxifloxacin) 4

Streptococcal Pharyngitis

• First-line: Amoxicillin for 10 days 4
• Alternative: Azithromycin (if penicillin allergy) 4

Pediatric Considerations

Acute Otitis Media (Children <3 years)

• High-dose amoxicillin-clavulanate: 80-100 mg/kg/day (amoxicillin component) divided into three doses for 10 days 2, 3
• Maximum daily dose: 3 g/day 4

Community-Acquired Pneumonia (Children)

• First-line: Amoxicillin-clavulanate 80-100 mg/kg/day (amoxicillin component) in three divided doses 2
• Children >3 years: Consider adding macrolide for atypical pathogen coverage 2

Monitoring and Response Assessment

Expected Response Timeline

• Fever resolution: Within 2-3 days of antibiotic initiation 1
• Clinical reassessment: If no improvement by 48-72 hours, consider alternative diagnosis, resistant pathogen, or complications 1, 2, 4

Route Switching

• IV to oral transition: When fever resolves and clinical condition stabilizes 1

Critical Pitfalls to Avoid

• Do not use first-generation cephalosporins (cephalexin) for respiratory infections due to inadequate activity against penicillin-resistant S. pneumoniae 4
• Do not substitute two 250/125 mg tablets for one 500/125 mg tablet of amoxicillin-clavulanate—they contain different clavulanate ratios 3
• Do not use fluoroquinolones inactive against pneumococci (ofloxacin, ciprofloxacin) or cefixime for pneumococcal infections 4
• Avoid macrolide monotherapy in areas with high pneumococcal macrolide resistance rates 1
• Consider local resistance patterns when selecting empiric therapy—national guidelines may not reflect regional antibiotic susceptibility 1