What are the differences in antibiotic regimens for Community-Acquired Pneumonia (CAP) versus Catheter-Related Bloodstream Infections (CRBSI)?

Antibiotic Regimens: CAP vs CRBSI

Fundamental Differences in Pathogen Coverage

Community-acquired pneumonia and catheter-related bloodstream infections require completely different antibiotic strategies because they target distinct pathogens, anatomic sites, and resistance patterns.

CAP: Respiratory Pathogens

CAP treatment targets respiratory pathogens including Streptococcus pneumoniae, atypical organisms (Mycoplasma, Chlamydia, Legionella), Haemophilus influenzae, and Moraxella catarrhalis 1. The empiric regimens prioritize coverage of these organisms based on severity and setting 1.

CRBSI: Bloodstream Pathogens

CRBSI requires coverage for skin flora and biofilm-forming organisms, primarily coagulase-negative staphylococci, Staphylococcus aureus (including MRSA), gram-negative bacilli, and Candida species. These pathogens originate from catheter colonization and require different antimicrobial approaches with consideration for catheter removal.

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CAP Treatment Algorithm by Severity

Outpatient CAP (No Comorbidities)

• First-line: Amoxicillin 1 g three times daily 1
• Alternative: Doxycycline 100 mg twice daily 1
• Macrolides (azithromycin 500 mg day 1, then 250 mg daily; clarithromycin 500 mg twice daily) only in areas where pneumococcal macrolide resistance is <25% 1

Outpatient CAP (With Comorbidities)

• Combination therapy: β-lactam (amoxicillin-clavulanate, cefpodoxime, or cefuroxime) plus macrolide or doxycycline 1
• Monotherapy alternative: Respiratory fluoroquinolone (levofloxacin 750 mg daily, moxifloxacin 400 mg daily) 1

Hospitalized CAP (Non-ICU)

• Preferred regimen: Ceftriaxone 1-2 g IV daily plus azithromycin 500 mg daily 1
• Alternative: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1
• Duration: Minimum 5-7 days once clinically stable 1

Severe CAP (ICU)

• Mandatory combination: β-lactam (ceftriaxone 2 g IV daily, cefotaxime 1-2 g IV every 8 hours, or ampicillin-sulbactam 3 g IV every 6 hours) plus either azithromycin 500 mg daily OR respiratory fluoroquinolone 1
• Add vancomycin 15 mg/kg IV every 8-12 hours if MRSA risk factors present (post-influenza pneumonia, cavitary infiltrates, prior MRSA) 1
• Add antipseudomonal coverage (piperacillin-tazobactam, cefepime, or carbapenem plus ciprofloxacin/levofloxacin) if Pseudomonas risk factors present 1

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CRBSI Treatment Algorithm

Empiric CRBSI Therapy (Pending Cultures)

While the provided evidence focuses on CAP, standard CRBSI management requires:

• Vancomycin (for MRSA and coagulase-negative staphylococci coverage) plus
• Gram-negative coverage (cefepime, piperacillin-tazobactam, or carbapenem depending on local resistance patterns and patient risk factors)
• Consider antifungal therapy (echinocandin) in high-risk patients with prolonged catheterization, TPN, or immunosuppression

Definitive CRBSI Therapy (Culture-Directed)

Treatment duration and catheter management depend on the identified organism:

• Coagulase-negative staphylococci: 5-7 days if catheter removed, 10-14 days if retained
• S. aureus: 14 days minimum (4-6 weeks if complicated bacteremia with metastatic foci)
• Gram-negative bacilli: 7-14 days depending on organism and catheter removal
• Candida species: 14 days after first negative blood culture and catheter removal

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Key Distinctions Between CAP and CRBSI Management

Pathogen Spectrum

• CAP: Predominantly respiratory pathogens requiring atypical coverage 1
• CRBSI: Skin flora and biofilm-forming organisms requiring anti-staphylococcal and anti-biofilm strategies

Source Control

• CAP: No removable source; relies entirely on antimicrobial therapy 1
• CRBSI: Catheter removal often essential for cure, particularly with S. aureus or Candida

Duration of Therapy

• CAP: 5-7 days for uncomplicated cases, 14-21 days for specific pathogens (Legionella, S. aureus, gram-negative bacilli) 1
• CRBSI: Varies by organism (5-7 days for coagulase-negative staphylococci to 4-6 weeks for complicated S. aureus bacteremia)

Combination Therapy Rationale

• CAP: Combination therapy targets both typical and atypical pathogens, with mortality benefit demonstrated for severe cases 2, 3
• CRBSI: Combination therapy used empirically for broad coverage pending cultures, then narrowed based on susceptibilities

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Critical Pitfalls to Avoid

CAP-Specific Pitfalls

• Never delay antibiotics beyond 8 hours in hospitalized CAP patients—this increases 30-day mortality by 20-30% 1
• Avoid macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25% 1
• Do not use first-generation cephalosporins for hospitalized CAP—they lack adequate coverage 2
• Obtain blood and sputum cultures before initiating antibiotics in all hospitalized patients 1

CRBSI-Specific Pitfalls

• Do not assume CRBSI is always catheter-related—obtain cultures from both catheter and peripheral sites
• Avoid inadequate duration for S. aureus bacteremia—minimum 14 days, with echocardiography to rule out endocarditis
• Do not retain catheters with S. aureus or Candida bloodstream infections—removal is essential for cure
• Consider biofilm-active agents (daptomycin, linezolid) for persistent bacteremia despite appropriate antibiotics