What are the uses of antibiotics in treating bacterial infections?

Uses of Antibiotics in Treating Bacterial Infections

Antibiotics should be reserved exclusively for proven or strongly suspected bacterial infections, with selection guided by infection site, severity, local resistance patterns, and patient risk factors—not prescribed empirically for viral illnesses or self-limiting conditions. 1

Core Principles of Antibiotic Use

When Antibiotics Are Indicated

• Serious bacterial infections requiring immediate treatment include septic shock, organ dysfunction, severe community-acquired pneumonia (PSI IV-V), bacterial meningitis, and complicated intra-abdominal infections with peritonitis 1, 2
• Moderate-severity community infections such as perforated appendicitis, acute bacterial rhinosinusitis with persistent symptoms >10 days or worsening after initial improvement, and pyelonephritis warrant antibiotic therapy 1
• Skin and soft tissue infections including cellulitis, erysipelas, necrotizing fasciitis, and impetigo caused by streptococci or staphylococci require antibacterial treatment 1, 3
• Bone and joint infections, bacterial endocarditis, and febrile neutropenia represent high-mortality conditions where antibiotics are life-saving 1, 4

When Antibiotics Should Be Withheld

• Acute bronchitis in healthy adults is predominantly viral (75% reduction in antibiotic use without worsening outcomes when withheld) 5, 2, 6
• Uncomplicated diverticulitis in immunocompetent patients does not require antibiotics (strong recommendation, moderate certainty) 2
• Lower respiratory tract infections without pneumonia on chest imaging should not receive antibiotics 2
• Otitis media is self-limiting in most cases; antibiotics contribute minimally to resolution but substantially to resistance 1

Infection-Specific Antibiotic Selection

Intra-Abdominal Infections

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

• Single agents: ertapenem, moxifloxacin, tigecycline, cefoxitin, or ticarcillin-clavulanate
• Combination therapy: metronidazole plus cefazolin, cefuroxime, ceftriaxone, cefotaxime, levofloxacin, or ciprofloxacin
• Coverage must include enteric gram-negative aerobes, gram-positive streptococci, and anaerobes for distal small bowel/colon-derived infections 1

For high-risk or severe infections: 1

• Carbapenems (imipenem-cilastatin, meropenem, doripenem) or piperacillin-tazobactam as single agents
• Combination: cefepime, ceftazidime, ciprofloxacin, or levofloxacin, each with metronidazole
• Duration: 3-5 days after adequate source control is sufficient; extending beyond 5-7 days without clinical improvement warrants investigation for uncontrolled infection source, not automatic continuation 1

Acute Bacterial Rhinosinusitis

For adults with moderate disease: 1

• First-choice (90-92% efficacy): respiratory fluoroquinolones (levofloxacin, moxifloxacin), ceftriaxone, or high-dose amoxicillin-clavulanate (4g/250mg daily)
• Second-choice (83-88% efficacy): high-dose amoxicillin (4g/day), cefpodoxime, cefuroxime, cefdinir, or TMP-SMX
• Avoid macrolides/azalides (77-81% efficacy) unless resistance patterns favor them 1

For pediatric patients: 1

• First-choice (91-92% efficacy): ceftriaxone or high-dose amoxicillin-clavulanate (90mg/6.4mg per kg daily)
• Second-choice (82-87% efficacy): high-dose amoxicillin (90mg/kg daily), cefpodoxime, cefdinir, or TMP-SMX

Urinary Tract Infections

For uncomplicated cystitis: 5

• First-line: trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days
• Alternative: nitrofurantoin for 5 days
• Avoid amoxicillin alone due to high E. coli resistance rates 5
• Avoid fluoroquinolones as first-line given serious adverse effects (tendon, nerve, CNS toxicity) unless resistance precludes safer options 5

For pyelonephritis or complicated UTI: 5, 6

• Fluoroquinolones (levofloxacin 500-750mg daily) may be justified when benefits outweigh risks
• Single-dose or short-course therapy appropriate only for acute bacterial cystitis due to E. coli in women 6

Respiratory Infections

For community-acquired pneumonia (severe): 1, 2

• Immediate empiric antibiotics after obtaining blood/sputum cultures
• Coverage based on local resistance patterns and patient risk factors

For COPD exacerbations: 5, 2

• Antibiotics warranted only when all three criteria present: increased dyspnea, increased sputum production, and sputum purulence
• Limit treatment to 5 days duration 5
• Withholding antibiotics in non-severe exacerbations reduces use by 34-44% without increased mortality 2

Methicillin-Resistant Staphylococcal Infections

Vancomycin indications: 4

• Serious/severe MRSA infections including endocarditis, septicemia, bone infections, lower respiratory tract infections, skin/soft tissue infections
• Penicillin-allergic patients or those failing other drugs
• Effective alone or with aminoglycoside for S. viridans/S. bovis endocarditis; requires aminoglycoside combination for enterococcal endocarditis 4

Daptomycin alternative: 7

• For MRSA infections when vancomycin contraindicated or ineffective
• Monitor for myopathy, rhabdomyolysis, and eosinophilic pneumonia 7

AWaRe Classification Framework

Access Group (First-Line, Widely Available)

• These antibiotics include amoxicillin, amoxicillin-clavulanate, cefazolin, ceftriaxone, metronidazole, and TMP-SMX for empiric first- or second-choice treatment of common infections 1
• Should be affordable, available in appropriate formulations, and of assured quality 1

Watch Group (Stewardship Targets)

• Fluoroquinolones and carbapenems have greater toxicity concerns and resistance potential; use only when Access group inadequate 1
• Includes highest priority critically important antimicrobials requiring monitoring programs 1
• May be first-choice for specific indications (e.g., severe intra-abdominal infections) but second-choice for others 1

Reserve Group (Last-Resort Options)

• Reserved for multidrug-resistant organisms when all other options have failed or are inadequate 1
• Should be protected through strict stewardship to preserve effectiveness 1

Critical Stewardship Principles

Culture and Susceptibility Testing

• Routine cultures optional for lower-risk community-acquired infections but valuable for detecting resistance patterns 1
• Mandatory cultures for higher-risk patients, health care-associated infections, prior antibiotic exposure, and when local resistance exceeds 10-20% for common isolates 1
• Anaerobic cultures unnecessary if empiric anaerobic coverage provided 1
• Gram stains help identify yeast in health care-associated infections but have no proven value for routine community-acquired infections 1

Duration Optimization

• Short-course therapy (3-5 days) after adequate source control is standard for complicated intra-abdominal infections 1
• Single doses equivalent to multiple doses for uncomplicated appendicitis/cholecystitis with adequate source control 1
• Extending beyond 5-7 days without improvement indicates need for diagnostic investigation, not automatic continuation 1

Resistance Mitigation

• Recent antibiotic use is the major risk factor for resistant pathogens; other factors include age and daycare attendance 1
• Fluoroquinolone resistance in E. coli requires reviewing local susceptibility profiles before prescribing 1
• Inappropriate use for self-limiting infections (e.g., otitis media, viral bronchitis) is a major contributor to resistance 1, 8

Common Pitfalls to Avoid

• Do not prescribe antibiotics for acute bronchitis without clear bacterial signs (purulent sputum, fever, leukocytosis) 5, 2
• Do not use fluoroquinolones routinely as first-line therapy given FDA warnings about tendon rupture, peripheral neuropathy, CNS effects, and aortic complications 5
• Do not continue antibiotics beyond 5 days in stable patients without reassessing for uncontrolled infection source 1, 5
• Do not use broad-spectrum agents (piperacillin-tazobactam, carbapenems) for mild community-acquired infections when narrow-spectrum options suffice 1
• Do not prescribe antibiotics for viral infections including COVID-19 without high clinical suspicion of bacterial co-infection 2

Special Considerations

Bacteriostatic vs. Bactericidal Distinction

• Clinical outcomes are equivalent between bacteriostatic and bactericidal agents for pneumonia, skin/soft tissue infections, and intra-abdominal infections 9
• This classification is clinically irrelevant for most infections; no conclusion can be drawn for meningitis, endocarditis, or neutropenia due to lack of studies 9

Combination Therapy

• Aminoglycoside combinations required for enterococcal endocarditis with vancomycin 4
• Rifampin, aminoglycosides, or both used with vancomycin for early-onset prosthetic valve endocarditis 4
• Metronidazole combinations necessary when primary agent lacks anaerobic coverage 1