What is the best antibiotic for respiratory infections?

Best Antibiotic for Respiratory Infections

For respiratory infections, amoxicillin remains the reference first-line antibiotic treatment for most cases, particularly for pneumococcal pneumonia in both adults and children. 1

Selection Based on Type of Respiratory Infection

Acute Bronchitis

• Immediate antibiotic therapy is generally not recommended for simple acute bronchitis in otherwise healthy adults, as most cases are viral in origin 1
• Antibiotic therapy should only be initiated if fever (>38.5°C) persists for more than 3 days 2, 1
• When antibiotics are indicated for bronchitis:
  • In children under 3 years: beta-lactams (amoxicillin, amoxicillin-clavulanate, cefuroxime-axetil, or cefpodoxime-proxetil) 2
  • In patients above 3 years: macrolides are preferred 2
  • Treatment duration should be 5-8 days 2, 1

Community-Acquired Pneumonia

• For adults without risk factors:
  • Amoxicillin (3 g/day) is the reference treatment for pneumococcal pneumonia 2, 1
  • Alternative first-line options include macrolides, doxycycline, or pristinamycin 2
• For children:
  • Under 3 years: amoxicillin 80-100 mg/kg/day in three daily doses 2, 1
  • Over 3 years: amoxicillin if pneumococcal infection is suspected; macrolides if atypical pathogens are suspected 2
• Treatment duration: 7-14 days for adults, 5-10 days for children 2, 1

Exacerbations of Chronic Bronchitis

• For patients with infrequent exacerbations and FEV1 >35%: amoxicillin remains the reference treatment 2, 1
• For patients with chronic obstructive bronchitis (FEV1 between 35-80%): immediate antibiotic therapy only if at least two of the three Anthonisen criteria are present (increased sputum volume, increased sputum purulence, increased dyspnea) 2, 1
• For patients with risk factors or suspected atypical pathogens: amoxicillin-clavulanate, parenteral 2nd or 3rd generation cephalosporins, or respiratory fluoroquinolones 2

Antibiotic Options Based on Suspected Pathogens

For Streptococcus pneumoniae

• First-line: Amoxicillin (high-dose) 2, 1
• Alternatives: Macrolides (azithromycin, clarithromycin), doxycycline 2, 3

For Haemophilus influenzae

• First-line: Amoxicillin-clavulanate 2
• Alternatives: Cefuroxime, cefpodoxime, azithromycin 2, 4

For Atypical Pathogens (Mycoplasma, Chlamydia, Legionella)

• First-line: Macrolides (azithromycin, clarithromycin) 1, 5
• Alternatives: Doxycycline, respiratory fluoroquinolones 2, 3

Advantages of Specific Antibiotics

Amoxicillin

• Reference treatment for pneumococcal infections 2, 1
• Good tissue penetration and excellent activity against S. pneumoniae 2
• Cost-effective option with established safety profile 1

Azithromycin

• Once-daily dosing for 3-5 days (shorter treatment duration) 4, 6
• Better tolerated than erythromycin with fewer gastrointestinal side effects 5, 6
• Higher tissue and intracellular concentrations that persist for several days 7
• Broader spectrum including activity against H. influenzae and atypical pathogens 4, 5

Doxycycline

• Effective against respiratory pathogens including Mycoplasma pneumoniae and Chlamydia 3
• Twice-daily oral dosing 2, 3
• Alternative for patients with penicillin allergies 1, 3

Common Pitfalls and Caveats

• Avoid treating all bronchitis cases with antibiotics when most are viral in origin 1
• Avoid using fluoroquinolones as first-line therapy when narrower-spectrum antibiotics would be appropriate 1
• Avoid antibiotics with poor activity against S. pneumoniae (such as ciprofloxacin or cefixime) for respiratory infections 1
• Be aware of increasing macrolide resistance in S. pneumoniae, group A streptococci, and H. influenzae 5
• Therapeutic efficacy should be assessed within 48-72 hours after initiating treatment; treatment should not be changed within this period unless clinical worsening occurs 2, 1