What are the first-line and second-line antibiotic treatments for common bacterial infections?

First-Line and Second-Line Antibiotic Treatments for Common Bacterial Infections

First-line antibiotics for common bacterial infections should be selected from the WHO Access group, which includes narrow-spectrum agents with favorable risk-benefit ratios and lower resistance potential, while second-line options typically come from the Watch group for specific indications or when resistance is suspected. 1

WHO AWaRe Framework for Antibiotic Selection

The WHO has developed a framework that categorizes antibiotics into three groups to guide appropriate use:

Access Group (First-Line Options)

• These antibiotics should be widely available, affordable, and of assured quality 1
• They have good clinical activity against commonly susceptible bacteria with lower resistance potential 1
• Examples include amoxicillin, ampicillin, benzylpenicillin, gentamicin, and cloxacillin 1
• These are typically recommended as empiric first-choice treatment options for common infections 1

Watch Group (Often Second-Line Options)

• These antibiotics have greater concerns regarding toxicity and potential for developing antimicrobial resistance 1
• They should be targets of antimicrobial stewardship programs 1
• Examples include fluoroquinolones, carbapenems, and third-generation cephalosporins like cefotaxime and ceftriaxone 1
• They are often associated with more adverse events, toxicities, and higher costs 1

Reserve Group (Last-Resort Options)

• These should only be used when other alternatives are inadequate or have failed 1
• They are effective against multidrug-resistant organisms 1
• Their use should be protected and prioritized in stewardship programs 1

Specific Recommendations for Common Infections

Sepsis

First-choice options:

• Amoxicillin + gentamicin (both Access group) 1
• Ampicillin + gentamicin (both Access group) 1
• Benzylpenicillin + gentamicin (both Access group) 1

Second-choice options:

• Amikacin + cloxacillin (both Access group) 1
• Cefotaxime (Watch group) 1
• Ceftriaxone (Watch group) 1

Skin and Soft Tissue Infections

First-choice options:

• For impetigo: Dicloxacillin, cefalexin, clindamycin 1
• For non-purulent infections: Benzylpenicillin, phenoxymethylpenicillin, cloxacillin 1

Second-choice options:

• For MRSA infections: Vancomycin, linezolid, daptomycin 1
• For diabetic wound moderate-severe infections: Levofloxacin, ceftriaxone, ampicillin-sulbactam 1

Respiratory Tract Infections

First-choice options:

• Community-acquired pneumonia: Amoxicillin or amoxicillin-clavulanate 2
• Acute exacerbations of chronic bronchitis: Amoxicillin or amoxicillin-clavulanate 2

Second-choice options:

• Community-acquired pneumonia: Levofloxacin, clarithromycin, or ceftriaxone 3
• Acute sinusitis: Levofloxacin 500mg once daily for 10-14 days 3

Clinical Considerations for Antibiotic Selection

Key Principles for Empiric Therapy

• Initial empiric therapy with appropriate antibiotics is critical as delayed effective treatment increases mortality 4
• "Getting it right up front" with appropriate broad-spectrum coverage followed by de-escalation once culture results are available improves outcomes 4
• Consider local resistance patterns when selecting empiric therapy 5

Important Caveats

• Inappropriate initial empirical therapy is associated with increased mortality, morbidity, and length of hospital stay 4
• Beta-lactam resistance is increasing, particularly through beta-lactamase production in common pathogens like H. influenzae and M. catarrhalis 2
• Fluoroquinolone resistance in S. pneumoniae remains relatively low (<1% for levofloxacin in the US) but varies by region 3
• Single-cell pathogen diagnostics are emerging as tools to enable more precise antibiotic selection and reduce broad-spectrum use 5

Mechanism-Based Selection

• Beta-lactams (penicillins, cephalosporins) target cell wall synthesis and remain effective for many common infections 6
• Glycopeptides (vancomycin) retain high activity against staphylococci but face resistance among enterococci 6
• Polymyxins are increasingly used for multidrug-resistant Gram-negative infections 6
• Daptomycin targets both membrane function and peptidoglycan synthesis, making it effective for staphylococcal infections 6

Algorithm for Antibiotic Selection

1. Identify the likely infection site and suspected pathogens
2. Start with Access group antibiotics as first-line therapy unless:
   • Local resistance patterns suggest they would be ineffective 1
   • Patient has risk factors for resistant organisms 1
   • Infection is severe or life-threatening 1
3. Consider Watch group antibiotics as second-line options when:
   • First-line therapy has failed 1
   • Patient has documented allergies to first-line agents 1
   • Specific pathogens with known resistance are suspected 1
4. Reserve group antibiotics should only be used when documented multidrug resistance is present 1
5. De-escalate to narrower spectrum therapy once culture results are available 4