What is the recommended approach for choosing antibiotics in different systems?

Antibiotic Selection Across Different Body Systems

Use the WHO AWaRe framework as your primary guide: start with Access group antibiotics (narrow-spectrum agents like amoxicillin, ampicillin, benzylpenicillin) as first-line therapy for most common infections, escalate to Watch group antibiotics (fluoroquinolones, third-generation cephalosporins, carbapenems) only when resistance is documented or suspected, and reserve Reserve group antibiotics exclusively for confirmed multidrug-resistant organisms. 1, 2

Core Selection Principles

Prioritize narrow-spectrum antibiotics with favorable risk-benefit ratios over broad-spectrum agents whenever clinically appropriate. 1 The guiding principles for antibiotic selection are:

• Resistance prevention: Privilege narrow-spectrum antibiotics and employ fluoroquinolone- and carbapenem-sparing strategies unless evidence demonstrates superiority of these agents for specific infections 1

• Clinical efficacy considerations: Evaluate time to symptom resolution, complication rates including mortality, and specific drug toxicity including both short- and long-term adverse effects 1

• Practical feasibility: Prefer oral formulations when possible, especially for pediatric patients, and select agents allowing hospital-to-primary care transitions with shorter treatment durations 1

The AWaRe Classification System

The WHO categorizes antibiotics into three groups using a traffic-light approach: 1, 2

Access Group (Green Light)

• Characteristics: Good activity against commonly susceptible bacteria, lower resistance potential, should be widely available in all healthcare facilities 1, 2
• Examples: Amoxicillin, ampicillin, benzylpenicillin, gentamicin, cloxacillin, cefalexin 2
• Clinical application: These are first-choice empiric treatment options for common infections 2

Watch Group (Orange Light)

• Characteristics: Higher risk of selecting resistant bacteria, more adverse events and toxicities, higher cost, require antimicrobial stewardship monitoring 1, 2
• Examples: Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin), carbapenems, third-generation cephalosporins (cefotaxime, ceftriaxone, ceftazidime) 1, 2
• Clinical application: Second-choice options when first-line agents fail or when higher resistance rates are documented 1

Reserve Group (Red Light)

• Characteristics: Last-resort options for confirmed or suspected multidrug-resistant organisms, major targets for stewardship programs 1, 2
• Clinical application: Use only when other alternatives are inadequate or have failed, with documented multidrug resistance 2

System-Specific Antibiotic Selection

Sepsis

• First-choice Access group combinations: Amoxicillin + gentamicin, ampicillin + gentamicin, or benzylpenicillin + gentamicin 2
• Rationale: These narrow-spectrum combinations provide adequate gram-positive and gram-negative coverage while minimizing resistance selection 2

Skin and Soft Tissue Infections

• Non-purulent infections: Benzylpenicillin, phenoxymethylpenicillin, or cloxacillin as first-choice Access group agents 2
• Impetigo: Dicloxacillin, cefalexin, or clindamycin 2
• Key consideration: These narrow-spectrum agents target common gram-positive pathogens (Staphylococcus aureus, Streptococcus pyogenes) without unnecessary broad coverage 2

Respiratory Tract Infections

• First-line approach: Access group antibiotics unless local resistance patterns demonstrate ineffectiveness 2
• Common pitfall: Avoid routine use of fluoroquinolones or broad-spectrum cephalosporins in otherwise healthy patients without comorbidities 3
• Evidence note: From 2008-2019, broad-spectrum antibiotic use for outpatient community-acquired pneumonia decreased from 45% to 19% in otherwise healthy patients, reflecting improved stewardship 3

Gastrointestinal Infections (Bacterial Diarrhea)

• Traveler's diarrhea: Azithromycin (single dose) shows superior efficacy over ciprofloxacin with reduced clinical failure rates 1
• Important caveat: Increasing Bacteroides fragilis resistance to fluoroquinolones necessitates combination with metronidazole when these agents are used 1

Intra-Abdominal Infections

For community-acquired mild-to-moderate infections: 1

• Narrow-spectrum options: Ampicillin/sulbactam, cefazolin or cefuroxime + metronidazole, ticarcillin/clavulanate, ertapenem
• Critical consideration: Review local E. coli susceptibility before using ampicillin-based regimens due to increasing resistance 1

For high-severity or healthcare-associated infections: 1

• Broader coverage required: Piperacillin/tazobactam, imipenem/cilastatin, meropenem, or third/fourth-generation cephalosporins + metronidazole
• Rationale: More resistant flora including Pseudomonas aeruginosa, Enterobacter species, MRSA, and Candida require broader empiric coverage 1

Algorithmic Approach to Selection

1. Identify infection site and likely pathogens based on clinical presentation 2, 4

2. Assess patient risk factors: 1, 4

   • Recent hospitalization or frequent healthcare exposure
   • Recent antibiotic use
   • Immunosuppression
   • Severity of illness using validated scoring systems

3. Start with Access group antibiotics for community-acquired infections in otherwise healthy patients 2

4. Escalate to Watch group when: 1, 2

   • Patient has significant comorbidities (diabetes, chronic heart/liver/renal disease)
   • Healthcare-associated infection suspected
   • High local resistance rates documented
   • Severe illness requiring broader coverage

5. Obtain cultures before initiating therapy when feasible, then de-escalate based on susceptibility results 4

6. Transition from IV to oral once clinical stability achieved, preferably using narrow-spectrum oral agents even after broad-spectrum IV therapy 5

Critical Pitfalls to Avoid

• Overuse of fluoroquinolones: Despite convenience, these Watch group agents drive resistance and should be reserved for specific indications 1, 3

• Prolonged treatment durations: Ten-day courses remain common but shorter durations are often adequate; prefer antibiotics allowing brief treatment courses 1, 3

• Ignoring local resistance patterns: In vitro susceptibility testing has limitations, but local antibiograms should guide empiric choices 1, 6

• Failure to de-escalate: Once pathogens and susceptibilities are known, narrow-spectrum antibiotics are preferable to continued broad-spectrum coverage 1, 5

• Using broad-spectrum agents in low-risk patients: Otherwise healthy outpatients with community-acquired infections rarely require Watch group antibiotics 3

Special Considerations

When microbiological diagnosis is unavailable: Clinical stability after broad-spectrum IV therapy allows safe transition to narrow-spectrum oral antibiotics in healthcare-associated pneumonia 5

Bacteroides fragilis coverage: Substantial resistance exists to clindamycin, cefotetan, cefoxitin, and quinolones; these should not be used alone when B. fragilis is likely 1

Inadequate empiric therapy consequences: Seriously ill patients with suspected infection require comprehensive workup and immediate broad-spectrum coverage, as inadequate initial therapy increases mortality 4