How should antibiotics be used to treat bacterial infections?

Appropriate Use of Antibiotics for Treating Bacterial Infections

Antibiotics should be prescribed based on the specific infection type, suspected pathogens, local resistance patterns, and patient factors, with the narrowest effective spectrum for the shortest appropriate duration to reduce antimicrobial resistance and adverse effects.

Antibiotic Selection Principles

Classification Framework

The WHO classifies antibiotics into three categories according to the AWaRe framework 1:

• Access (first-line): Lower resistance potential (e.g., amoxicillin, penicillins)
• Watch: Higher resistance risk (e.g., fluoroquinolones, carbapenems)
• Reserve: Last-resort options for multidrug-resistant infections

Key Selection Factors

1. Infection site and suspected pathogens
2. Local antibiotic resistance patterns
3. Patient-specific factors (allergies, comorbidities, pregnancy)
4. Narrowest effective spectrum to minimize collateral damage
5. Appropriate duration - shorter courses when evidence supports

Infection-Specific Recommendations

Respiratory Tract Infections

Community-Acquired Pneumonia

• First-line: Amoxicillin 3 g/day for healthy adults 2
• Alternatives for higher risk patients: Amoxicillin-clavulanate, parenteral 2nd/3rd generation cephalosporin, or fluoroquinolone active against S. pneumoniae 2
• Duration: 5-7 days for clinically stable patients 2

Pediatric Pneumonia

• Children <3 years: Amoxicillin 80-100 mg/kg/day in three daily doses 2
• Children >3 years:
  • Suspected pneumococcal: Amoxicillin
  • Suspected atypical (Mycoplasma/Chlamydia): Macrolides 2

Acute Bronchiolitis

• Generally no antibiotics needed (primarily viral) 2
• Consider antibiotics only with:
  • Persistent high fever (>38.5°C for >3 days)
  • Confirmed bacterial superinfection 2

Urinary Tract Infections

Uncomplicated Cystitis in Women

• First-line options:
  • Nitrofurantoin for 5 days
  • Trimethoprim-sulfamethoxazole (TMP-SMZ) for 3 days
  • Fosfomycin as single dose 2

Uncomplicated Pyelonephritis

• First-line options:
  • Fluoroquinolones for 5-7 days
  • TMP-SMZ for 14 days (based on susceptibility) 2

Skin and Soft Tissue Infections

Nonpurulent Cellulitis

• Duration: 5-6 day course of antibiotics active against streptococci 2
• Close follow-up required, especially for patients able to self-monitor

Sepsis and Bloodstream Infections

Neonatal Sepsis

• First-line combinations 2:
  • Amoxicillin + gentamicin
  • Ampicillin + gentamicin
  • Benzylpenicillin + gentamicin

Adult Sepsis

• Initial empiric therapy should cover the most likely pathogens based on infection source and local resistance patterns 2
• De-escalation should occur when culture results become available 2

Neutropenic Fever

• High-risk patients: Intravenous broad-spectrum antibiotics 2
• Low-risk patients:
  • Oral therapy: Ciprofloxacin plus amoxicillin-clavulanate 2
  • Note: Don't use fluoroquinolones if patient was on fluoroquinolone prophylaxis 2

Duration of Therapy

General Principles

• Documented infections: Continue antibiotics at least until resolution of neutropenia (ANC >500 cells/mm³) or longer if clinically necessary 2
• Unexplained fever: Continue initial regimen until clear signs of marrow recovery 2

Specific Recommendations

• Community-acquired pneumonia: 5-7 days for clinically stable patients 2
• Uncomplicated cystitis: 3-5 days depending on antibiotic choice 2
• Nonpurulent cellulitis: 5-6 days 2

Special Considerations

Antimicrobial Stewardship

• Avoid extended use of cephalosporins in settings with high ESBL-producing Enterobacteriaceae 2
• Limit fluoroquinolone use due to selective pressure for ESBLs and MRSA 2
• Consider carbapenem-sparing treatments in settings with high carbapenem-resistant K. pneumoniae 2

Microbiological Sampling

• Always obtain specimens before starting antibiotics in:
  • Healthcare-associated infections
  • Community-acquired infections with risk for resistant pathogens
  • Critically ill patients 2

Monitoring and Reassessment

• Reassess when culture results available for potential de-escalation 2
• Monitor for antibiotic-associated complications, which occur in approximately 17% of patients receiving broad-spectrum antibiotics 3

Common Pitfalls to Avoid

1. Excessive duration: 30% of outpatient antibiotics are unnecessary or continued too long 2
2. Default 10-day courses: Many infections can be treated with shorter courses with similar outcomes and fewer adverse events 2
3. Broad-spectrum overuse: In a study of 600 patients treated for suspected sepsis, 79.1% received antibiotics that were overly broad in retrospect 3
4. Neglecting local resistance patterns: Treatment should be guided by local epidemiology 2
5. Failure to de-escalate: Antibiotics should be narrowed when culture results become available 2

By following these evidence-based recommendations, clinicians can optimize antibiotic therapy to effectively treat infections while minimizing the risks of antimicrobial resistance and adverse effects.