What antibiotics are effective for treating lung infections?

Antibiotics for Lung Infections

For community-acquired pneumonia, use amoxicillin or amoxicillin-clavulanate as first-line therapy for outpatients, and add a macrolide (azithromycin or clarithromycin) or use a respiratory fluoroquinolone (levofloxacin or moxifloxacin) for hospitalized patients. 1

Outpatient Treatment (Community-Acquired Pneumonia)

First-line options:

• Amoxicillin 500-1000 mg every 8 hours for 7-10 days 1
• Amoxicillin-clavulanate 1 g every 8 hours orally in areas with high beta-lactamase-producing H. influenzae 1
• Macrolides (azithromycin 500 mg day 1, then 250 mg daily for 4 days OR clarithromycin 250-500 mg every 12 hours for at least 5 days) for atypical pathogens (Mycoplasma, Chlamydophila, Legionella) 1

Alternative options:

• Doxycycline 100 mg every 12 hours in areas with low pneumococcal resistance 1
• Respiratory fluoroquinolones (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) 1

Hospitalized Patients (Medical Ward)

Recommended regimens:

• Second-generation cephalosporin (cefuroxime 750-1500 mg IV every 8 hours) OR third-generation cephalosporin (ceftriaxone 1-2 g IV every 12-24 hours or cefotaxime 1-2 g IV every 8 hours) 1
• Add a macrolide (azithromycin or clarithromycin) to beta-lactam therapy for broader coverage including atypical pathogens 1
• Alternatively, use respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV/PO daily or moxifloxacin 400 mg IV/PO daily) 1, 2

For aspiration pneumonia or lung abscess:

• Amoxicillin-clavulanate 1.2 g IV every 6-8 hours 1

Intensive Care Unit (Severe Pneumonia)

Without Pseudomonas risk:

• Third-generation cephalosporin (ceftriaxone or cefotaxime) PLUS macrolide (azithromycin preferred) 1
• OR respiratory fluoroquinolone (levofloxacin 750 mg or moxifloxacin 400 mg) ± cephalosporin 1

With Pseudomonas risk factors (recent hospitalization, frequent antibiotics in last 3 months, severe COPD with FEV1 <30%, oral steroids >10 mg prednisone daily):

• Antipseudomonal beta-lactam (ceftazidime 2 g IV every 8 hours, cefepime 2 g IV every 8 hours, piperacillin-tazobactam 4.5 g IV every 6 hours, or meropenem 1 g IV every 8 hours) 1
• PLUS ciprofloxacin 400 mg IV every 8 hours 1
• OR PLUS macrolide + aminoglycoside (gentamicin 5-7 mg/kg IV daily, tobramycin 5-7 mg/kg IV daily, or amikacin 15-20 mg/kg IV daily) 1

Hospital-Acquired Pneumonia (Non-Ventilator)

Low mortality risk, no MRSA factors:

• Piperacillin-tazobactam 4.5 g IV every 6 hours 1
• OR cefepime 2 g IV every 8 hours 1
• OR levofloxacin 750 mg IV daily 1, 2
• OR meropenem 1 g IV every 8 hours or imipenem 500 mg IV every 6 hours 1

High mortality risk OR recent IV antibiotics (last 90 days):

• Two antipseudomonal agents (avoid combining two beta-lactams): one from above list PLUS aminoglycoside or ciprofloxacin 1
• PLUS vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) OR linezolid 600 mg IV every 12 hours for MRSA coverage 1

Pathogen-Specific Coverage

For Streptococcus pneumoniae (penicillin MIC <2):

• Penicillin G, amoxicillin, or amoxicillin-clavulanate preferred 1
• Alternatives: ceftriaxone, cefotaxime, levofloxacin, moxifloxacin 1

For atypical pathogens (Mycoplasma, Chlamydophila):

• Doxycycline 100 mg every 12 hours for 7-14 days (preferred for Mycoplasma) 1
• Azithromycin 500 mg day 1, then 250 mg daily for 4 days (preferred for Chlamydophila) 1
• Alternatives: levofloxacin 750 mg daily or moxifloxacin 400 mg daily 1

For Legionella:

• Levofloxacin 750 mg IV/PO daily (preferred) 1
• OR moxifloxacin 400 mg IV/PO daily 1
• Alternative: azithromycin 1000 mg IV day 1, then 500 mg IV/PO daily 1
• Duration: 21 days for Legionella or S. aureus pneumonia 1

For MRSA:

• Vancomycin 15 mg/kg IV every 8-12 hours (with rifampicin) 1
• OR linezolid 600 mg IV/PO every 12 hours 1

Treatment Duration

• 5-7 days for uncomplicated community-acquired pneumonia in responding patients 1
• 7-10 days for classical bacterial pneumonia 1
• 10-14 days for Mycoplasma or Chlamydophila 1
• 21 days for Legionella, S. aureus, or severe pneumonia 1
• Generally not exceeding 8 days in responding patients; biomarkers like procalcitonin may guide shorter duration 1

Chronic Bronchitis Exacerbation

Antibiotics indicated when:

• Severe COPD with exacerbation 1
• OR at least 2 of 3 Anthonisen criteria: increased dyspnea, increased sputum volume, increased sputum purulence 1

First-line (infrequent exacerbations, FEV1 >35%):

• Amoxicillin 1
• Alternatives: macrolides, doxycycline, first-generation cephalosporins 1

Second-line (frequent exacerbations ≥4/year, FEV1 <35%):

• Amoxicillin-clavulanate (preferred) 1
• Alternatives: cefuroxime-axetil, respiratory fluoroquinolones (levofloxacin, moxifloxacin) 1

Key Clinical Pitfalls

Avoid these common errors:

• Do not use ciprofloxacin alone for pneumococcal pneumonia—it has inadequate activity 1
• Do not use cefixime for pneumococcal infections with decreased penicillin susceptibility 1
• Reserve ciprofloxacin for Pseudomonas infections 1
• Switch from IV to oral when fever resolves and patient is clinically stable (temperature ≤37.8°C, heart rate ≤100, respiratory rate ≤24, systolic BP ≥90 mmHg, oxygen saturation ≥90%) 1
• Assess response at 2-3 days; fever should resolve within this timeframe 1