What is the first line treatment for bacterial respiratory infections?

First-Line Treatment for Bacterial Respiratory Infections

For bacterial respiratory infections, amoxicillin is the first-line antibiotic for most patients, with amoxicillin-clavulanate reserved for those with recent antibiotic use, comorbidities, or moderate-to-severe disease. 1, 2

Upper Respiratory Tract Infections

Acute Bacterial Rhinosinusitis

• Amoxicillin-clavulanate (1.75-4 g/250 mg per day) is the preferred first-line agent for adults with mild disease who have not received antibiotics in the previous 4-6 weeks 1, 2
• Alternative first-line options include amoxicillin (1.5-4 g/day), cefpodoxime proxetil, cefuroxime axetil, or cefdinir 1
• For patients with β-lactam allergies, TMP/SMX, doxycycline, azithromycin, clarithromycin, or telithromycin may be used, but expect bacteriologic failure rates of 20-25% 1
• For adults with recent antibiotic use (within 4-6 weeks) or moderate disease, use respiratory fluoroquinolones (levofloxacin, moxifloxacin, gatifloxacin) or high-dose amoxicillin-clavulanate (4 g/250 mg per day) 1

Pediatric Acute Bacterial Rhinosinusitis

• High-dose amoxicillin-clavulanate (90 mg/6.4 mg per kg per day) is first-line for children with mild disease and no recent antibiotic use 1, 2
• Alternative options include high-dose amoxicillin (90 mg/kg per day), cefpodoxime proxetil, cefuroxime axetil, or cefdinir 1
• For β-lactam allergies, use TMP/SMX, azithromycin, clarithromycin, or erythromycin, acknowledging limited effectiveness with 20-25% bacterial failure rates 1

Acute Otitis Media

• Amoxicillin is the reference first-line antibiotic for acute otitis media 1, 2
• Amoxicillin-clavulanate or second-generation cephalosporins (cefuroxime) are alternatives when β-lactamase-producing organisms (H. influenzae, M. catarrhalis) are suspected 1
• Macrolides have reduced efficacy due to S. pneumoniae resistance rates and should be reserved for penicillin-allergic patients 1

Lower Respiratory Tract Infections

Acute Exacerbations of Chronic Bronchitis

The decision to treat depends on disease severity and clinical criteria:

• For simple chronic bronchitis (FEV1 >80%, no dyspnea): Immediate antibiotics are NOT recommended, even with fever present 1, 3
• For chronic obstructive bronchitis (FEV1 35-80%): Treat only if ≥2 of 3 Anthonisen criteria are present (increased sputum volume, increased sputum purulence, increased dyspnea) 1, 3
• For chronic respiratory insufficiency (FEV1 <35%, dyspnea at rest): Immediate antibiotic therapy is recommended 1, 3

First-line antibiotics for infrequent exacerbations (≤3 per year) with FEV1 ≥35%:

• Amoxicillin is the reference first-line agent 1, 3
• First-generation cephalosporins are alternatives 1, 3
• Macrolides, pristinamycin, or doxycycline for β-lactam allergies 1, 3
• Avoid cotrimoxazole due to inconsistent pneumococcal activity and poor benefit/risk ratio 1

Second-line antibiotics for frequent exacerbations (≥4 per year), FEV1 <35%, or first-line failure:

• Amoxicillin-clavulanate is the reference second-line agent 1, 3
• Second-generation (cefuroxime-axetil) or third-generation (cefpodoxime-proxetil, cefotiam-hexetil) oral cephalosporins 1, 3
• Respiratory fluoroquinolones (levofloxacin, moxifloxacin) 1, 3
• Do NOT use ciprofloxacin or ofloxacin (inadequate pneumococcal coverage) or cefixime (inactive against penicillin-resistant S. pneumoniae) 1, 3

Community-Acquired Pneumonia (Outpatient)

For previously healthy adults without recent antibiotic use:

• Amoxicillin is preferred first-line therapy in the UK and European guidelines 1
• Macrolides (azithromycin, clarithromycin) or doxycycline are first-line options in North American guidelines 1
• Respiratory fluoroquinolones (levofloxacin, moxifloxacin, gatifloxacin) are reserved for patients with comorbidities or recent antibiotic use 1

For patients with comorbidities (COPD, diabetes, heart disease) or recent antibiotic use:

• Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily, moxifloxacin 400 mg daily) 1, 4
• Combination therapy: High-dose amoxicillin or amoxicillin-clavulanate PLUS a macrolide 1

Target Pathogens and Resistance Considerations

All regimens must cover the primary respiratory pathogens:

• S. pneumoniae (including penicillin-resistant strains) 1, 3, 5
• H. influenzae (including β-lactamase producers) 1, 3, 5
• M. catarrhalis (β-lactamase producer) 1, 3, 5

Critical resistance patterns:

• Penicillin resistance in S. pneumoniae exceeds 20% in many regions and >50% in some Asian countries 5
• Macrolide resistance in S. pneumoniae reaches 70-80% in some Asian countries 5
• β-lactamase production occurs in 30-40% of H. influenzae isolates 1, 5
• Respiratory fluoroquinolones maintain >98% susceptibility against S. pneumoniae, including resistant strains 4, 6, 5

Reassessment and Treatment Failure

• Assess clinical response at 48-72 hours after initiating therapy 1, 2
• Fever should resolve within 24 hours for pneumococcal infections and 2-4 days for other bacterial etiologies 2
• If no improvement after 72 hours, switch to an alternative antibiotic class with broader coverage or consider complications 1, 2
• When switching antibiotics, consider the limitations of the initial agent's spectrum 1

Common Pitfalls to Avoid

• Do NOT use first-generation cephalosporins (cephalexin) for respiratory infections due to inadequate activity against penicillin-resistant S. pneumoniae 2
• Do NOT assume all cephalosporins are equivalent—second and third-generation agents have significantly better respiratory pathogen coverage 2
• Do NOT use ciprofloxacin or ofloxacin for respiratory infections (inadequate pneumococcal coverage); reserve ciprofloxacin for Pseudomonas infections 1, 3
• Do NOT prescribe antibiotics for acute bronchitis in otherwise healthy adults—most cases are viral and antibiotics provide no benefit 3
• Do NOT rely on purulent sputum alone as an indication for antibiotics—color change does not necessarily indicate bacterial infection 3
• Do NOT overuse respiratory fluoroquinolones for mild disease, as this promotes resistance in gut and respiratory organisms 1