What are the recommended antibiotics for lower respiratory tract infections (LRTIs) with a suspected bacterial cause?

Recommended Antibiotics for Lower Respiratory Tract Infections

For outpatient LRTIs with suspected bacterial cause, amoxicillin or tetracycline are first-line antibiotics, with macrolides (azithromycin, clarithromycin) or fluoroquinolones (levofloxacin, moxifloxacin) reserved for penicillin allergy or high local resistance rates. 1

When to Prescribe Antibiotics

Not all LRTIs require antibiotics—many are viral and self-limiting. Prescribe antibiotics only when:

• Suspected or confirmed pneumonia (new focal chest signs, dyspnoea, tachypnoea, fever >4 days) 1
• COPD exacerbations with all three cardinal symptoms: increased dyspnoea, increased sputum volume, AND increased sputum purulence 1
• High-risk patients: age >75 years with fever, cardiac failure, insulin-dependent diabetes, or serious neurological disorder 1

Outpatient Antibiotic Selection Algorithm

First-Line Choices (Community-Managed LRTI)

For previously healthy adults without comorbidities:

• Amoxicillin (preferred first-line) 1, 2
• Tetracycline (alternative first-line) 1
• Duration: 5-7 days 1, 3

For patients with penicillin allergy:

• Newer macrolides: azithromycin, roxithromycin, or clarithromycin (only in areas with <25% pneumococcal macrolide resistance) 1, 3
• Doxycycline 100mg twice daily 1, 3

Second-Line Choices

When first-line agents fail or high local resistance exists:

• Amoxicillin-clavulanate (beta-lactam + beta-lactamase inhibitor) for areas with high beta-lactamase-producing H. influenzae 1
• Respiratory fluoroquinolones: levofloxacin or moxifloxacin (reserve for clinically relevant resistance to all first-choice agents) 1

Important caveat: Fluoroquinolones carry risks of tendinopathy, peripheral neuropathy, and CNS effects—use only when other options are unsuitable 3

Hospital-Managed LRTI (Non-Pneumonia)

For moderate COPD exacerbations or bronchitis requiring hospitalization:

• Beta-lactam: amoxicillin 500-1,000mg every 8 hours OR amoxicillin-clavulanate 1g every 8 hours 1
• Alternative: newer macrolides (azithromycin 500mg daily for 3 days, then 250mg daily for 5 days; OR clarithromycin 250-500mg every 12 hours) 1
• Second-generation fluoroquinolone: ciprofloxacin 500mg every 12 hours or ofloxacin 400mg every 12 hours 1
• Duration: minimum 7 days 1

Community-Acquired Pneumonia (CAP)

Outpatient CAP

For healthy adults:

• Amoxicillin 1g three times daily (most effective against S. pneumoniae, the most common pathogen) 3
• Alternatives: doxycycline 100mg twice daily or macrolides 3

For adults with comorbidities:

• Combination therapy: beta-lactam PLUS macrolide (e.g., amoxicillin-clavulanate + azithromycin) 3
• Monotherapy alternative: respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 3

Hospitalized CAP (Medical Ward)

• Second-generation cephalosporin: IV cefuroxime 750-1,500mg every 8 hours 1
• Third-generation cephalosporin: IV ceftriaxone 1g every 24 hours OR IV cefotaxime 1g every 8 hours 1
• Alternative: IV benzylpenicillin 1-4×10⁶ units every 2-4 hours OR IV amoxicillin 1g every 6 hours 1
• Macrolide addition: IV or oral erythromycin 1g every 8 hours 1

Severe CAP (ICU)

• Combination therapy: beta-lactam (cefotaxime, ceftriaxone, or ceftaroline) PLUS macrolide OR respiratory fluoroquinolone 3
• For suspected Pseudomonas: antipseudomonal beta-lactam PLUS ciprofloxacin or aminoglycoside PLUS macrolide 3

Special Situations

Suspected aspiration pneumonia or pulmonary abscess:

• Amoxicillin-clavulanate 2g IV every 6 hours 1, 3
• Alternative: clindamycin 600mg IV every 8 hours 1

Suspected Legionella pneumophila:

• Extended duration: 21 days of treatment 1, 4, 3
• Regimen: macrolide ± rifampicin 600mg every 12 hours 1

ESRD patients:

• Ceftriaxone requires no dose adjustment (minimal renal clearance) 4
• Amoxicillin requires dose adjustment in ESRD 4

Treatment Duration Summary

• Uncomplicated LRTI/bronchitis: 5-7 days 1, 3
• Community-acquired pneumonia: 5-7 days (minimum 5 days if clinically stable) 3
• Severe pneumonia: 10-14 days 4
• Legionella, Staphylococcus, or gram-negative enteric bacilli: 14-21 days 3

Monitoring Response

Patients should be instructed to:

• Expect clinical improvement within 3 days of starting antibiotics 1
• Return if fever persists >4 days, dyspnoea worsens, or no improvement by 3 days 1
• Understand that cough may persist beyond antibiotic course duration 1

For hospitalized patients:

• Assess response at day 2-3 and consider alternative diagnoses or complications if no improvement 1, 3

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for viral bronchitis in otherwise healthy adults—most LRTIs are self-limiting 1, 5
• Always cover Streptococcus pneumoniae when treating suspected bacterial LRTI 5
• Consider local resistance patterns when selecting antibiotics—macrolides should only be used where pneumococcal resistance is <25% 1, 3
• Avoid fluoroquinolones as first-line due to adverse effect profile and resistance concerns 3
• Do not use expectorants, mucolytics, antihistamines, or bronchodilators for acute LRTI in primary care 1