What are the first-line and second-line antibiotic treatments for respiratory tract infections of bacterial origin?

First-Line and Second-Line Antibiotics for Bacterial Respiratory Tract Infections

For bacterial respiratory tract infections, first-line treatment is aminopenicillins (particularly amoxicillin or amoxicillin-clavulanate), while second-line options include macrolides, respiratory fluoroquinolones, tetracyclines, or cephalosporins depending on suspected pathogens and patient factors. 1

First-Line Antibiotic Therapy

Upper Respiratory Tract Infections

• First-line: Amoxicillin (1.5-4g/day for adults, 80-100 mg/kg/day for children) 2, 1
• For suspected β-lactamase producers: Amoxicillin-clavulanate 2, 1
• Duration: 5-7 days for most infections 2

Lower Respiratory Tract Infections

• First-line: Aminopenicillin (amoxicillin) or aminopenicillin with β-lactamase inhibitor (amoxicillin-clavulanate) 2, 1
• Dosage:
  • Adults: 1.5-4g/day divided in 2-3 doses 1
  • Children <30kg: 80-100 mg/kg/day in three daily doses 1
• Duration: 5-7 days for most infections 2

Second-Line Antibiotic Therapy

When to Use Second-Line Therapy

• Failure of first-line therapy after 72 hours 2
• Penicillin allergy 2, 1
• High frequency of β-lactamase-producing H. influenzae in the area 2
• Chronic lung disease 2
• Suspected atypical pathogens (Mycoplasma, Chlamydia, Legionella) 2, 1

Second-Line Options

1. Macrolides (azithromycin, clarithromycin) 2, 1

   • Particularly for atypical pathogens
   • Azithromycin: 3-5 day course 3, 4

2. Respiratory Fluoroquinolones 2, 5

   • Levofloxacin, moxifloxacin
   • Reserved for more severe cases or when first-line treatments fail 1
   • Effective against S. pneumoniae, H. influenzae, and atypical pathogens 5

3. Tetracyclines (doxycycline) 2, 6

   • Effective for respiratory infections caused by Mycoplasma pneumoniae 6
   • Alternative for penicillin-allergic patients 1

4. Cephalosporins 2

   • Oral options: cefuroxime-axetil, cefpodoxime-proxetil 2
   • For non-anaphylactic penicillin allergy 1

Pathogen-Specific Considerations

Streptococcus pneumoniae

• First-line: Amoxicillin (high-dose) 2, 1
• Second-line: Respiratory fluoroquinolones, macrolides 2

Haemophilus influenzae

• First-line: Amoxicillin-clavulanate 2, 1
• Second-line: Cephalosporins, fluoroquinolones 2

Atypical Pathogens (Mycoplasma, Chlamydia, Legionella)

• First-line: Macrolides 2, 1
• Second-line: Doxycycline, fluoroquinolones 2, 6

Treatment Algorithm

1. Assess severity and likely pathogens:

   • Mild-moderate community-acquired infection → Aminopenicillin
   • Severe infection or risk factors → Broader coverage

2. First-line therapy:

   • Start with amoxicillin or amoxicillin-clavulanate
   • Evaluate response within 72 hours 2

3. If no improvement after 72 hours:

   • Switch to appropriate second-line agent based on suspected pathogen 2
   • Consider diagnostic testing if not done initially

4. For penicillin-allergic patients:

   • Non-anaphylactic: Cephalosporins
   • Anaphylactic: Macrolides, doxycycline, or fluoroquinolones 1

Special Considerations

• Avoid macrolides as first-line when possible due to increasing resistance rates 1
• Reserve fluoroquinolones for treatment failures or more severe infections to prevent resistance development 1
• Duration of therapy has been trending shorter: 5-7 days for most infections is sufficient 2, 4
• Reassess therapy if symptoms worsen or fail to improve after 72 hours 2

Common Pitfalls to Avoid

1. Overuse of antibiotics for viral infections - Most upper respiratory infections are viral and do not require antibiotics 1

2. Using fluoroquinolones as first-line therapy - This should be avoided to prevent development of resistance 1

3. Inadequate dosing of amoxicillin - Higher doses (80-100 mg/kg/day for children, 1.5-4g/day for adults) are needed for resistant S. pneumoniae 1

4. Failing to reassess after 72 hours - Treatment should be reevaluated if no improvement is seen 2

5. Not considering local resistance patterns - Local antibiogram data should guide empiric therapy choices 2