How are antibiotics classified?

Antibiotic Classification Systems

Antibiotics are primarily classified using the World Health Organization's AWaRe framework, which categorizes them into Access, Watch, and Reserve groups based on their potential for developing antimicrobial resistance and their role in clinical practice. 1, 2

The AWaRe Classification System

Access Antibiotics (Green)

• First-line treatments for common infections
• Lower potential for developing resistance
• Should be widely available, affordable, and accessible
• Examples include:
  • Amoxicillin
  • Penicillins
  • Amoxicillin-clavulanate

Watch Antibiotics (Orange)

• Higher risk of antimicrobial resistance development
• More adverse events and toxicities
• Key targets for antimicrobial stewardship programs
• Include highest priority agents from the List of Critically Important Antimicrobials
• Examples include:
  • Fluoroquinolones
  • Carbapenems

Reserve Antibiotics (Red)

• Last-resort options
• Used only for specific patient populations when alternatives are inadequate
• Should be protected and prioritized in stewardship programs
• Used primarily for multidrug-resistant infections

Additional Classification Methods

By Chemical Structure

• Beta-lactams (share a common beta-lactam ring structure) 3, 4, 5
  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Monobactams
• Aminoglycosides
• Tetracyclines
• Macrolides
• Fluoroquinolones
• Glycopeptides

By Mechanism of Action

• Cell wall synthesis inhibitors (e.g., beta-lactams, vancomycin)
• Protein synthesis inhibitors (e.g., aminoglycosides, tetracyclines, macrolides)
• DNA/RNA synthesis inhibitors (e.g., fluoroquinolones)
• Metabolic pathway inhibitors (e.g., trimethoprim-sulfamethoxazole)

By Spectrum of Activity

• Narrow-spectrum: Target specific types of bacteria
• Broad-spectrum: Effective against a wide range of bacteria

Pharmacokinetic/Pharmacodynamic Classification

Antibiotics can also be classified based on their pharmacokinetic/pharmacodynamic (PK/PD) properties 1:

1. Concentration-dependent killing with post-antibiotic effect

   • Efficacy correlates with peak concentration to MIC ratio or AUC/MIC
   • Examples: Aminoglycosides, fluoroquinolones, daptomycin

2. Time-dependent killing with minimal post-antibiotic effect

   • Efficacy correlates with time above MIC
   • Examples: Beta-lactams (penicillins, cephalosporins)

3. Time-dependent killing with prolonged post-antibiotic effect

   • Efficacy correlates with AUC/MIC
   • Examples: Vancomycin, teicoplanin

Clinical Implications of Classification

• The classification system guides appropriate antibiotic selection
• First-choice antibiotics are typically narrow-spectrum agents with favorable risk-benefit ratios and low resistance levels
• Second-choice antibiotics are broader-spectrum with higher resistance rates or less favorable risk-benefit profiles
• Classification helps structure antimicrobial stewardship programs
• AWaRe classification facilitates monitoring of antibiotic consumption patterns

Penetration Characteristics

Different antibiotic classes have varying abilities to penetrate tissues and biofilms 1:

• Beta-lactams may have limited penetration into certain tissues like cardiac vegetations
• Lipophilic antibiotics generally have better tissue penetration
• Certain antibiotics have specialized penetration characteristics (e.g., CNS penetration)

Resistance Mechanisms Considerations

When classifying antibiotics, resistance mechanisms are important factors 1, 4:

• Beta-lactamase production (affects beta-lactam antibiotics)
• Target site modifications (e.g., PBP modifications affecting beta-lactams)
• Efflux pumps (affects multiple antibiotic classes)
• Decreased membrane permeability

Understanding these classification systems helps clinicians select appropriate antibiotics while promoting antimicrobial stewardship and minimizing resistance development.