Empirical Antimicrobial Selection for Suspected Infections
For suspected infections requiring empirical antimicrobial therapy, use broad-spectrum antibiotics based on infection site, severity, and risk factors for resistant organisms, with vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem as the preferred regimen for severe infections. 1
Empirical Antimicrobial Selection by Infection Site
Intra-abdominal Infections
- For mild-moderate community-acquired infections: Ceftriaxone plus metronidazole or ciprofloxacin plus metronidazole 1
- For severe community-acquired or healthcare-associated infections: Piperacillin-tazobactam, imipenem-cilastatin, meropenem, or doripenem as single-agent therapy 1, 2
- For healthcare-associated infections with risk of resistant organisms: Add vancomycin to cover MRSA 1
- Consider antifungal therapy (fluconazole for C. albicans or echinocandin for non-albicans species) in critically ill patients if Candida is suspected 1
Skin and Soft Tissue Infections
- For mild-moderate community-acquired infections: Cefazolin, cephalexin, or SMX-TMP 1
- For severe infections or necrotizing fasciitis: Vancomycin or linezolid plus piperacillin-tazobactam, ampicillin-sulbactam, or a carbapenem 1
- For documented group A streptococcal necrotizing fasciitis: Penicillin plus clindamycin 1
- For pyomyositis: Vancomycin initially, with addition of gram-negative coverage in immunocompromised patients or after trauma 1
Pneumonia
- For community-acquired pneumonia: Ceftriaxone or cefotaxime plus a macrolide 1
- For healthcare-associated pneumonia: Piperacillin-tazobactam or ceftazidime plus levofloxacin 1
- For suspected MRSA pneumonia: Add vancomycin or linezolid 1
Factors Affecting Antimicrobial Selection
Infection Source and Likely Pathogens
- Gastrointestinal/genitourinary source: Cover for enteric gram-negatives and anaerobes with piperacillin-tazobactam or ceftriaxone plus metronidazole 1
- Skin/soft tissue source: Cover for Staphylococcus and Streptococcus species with vancomycin or linezolid 1
- Respiratory source: Cover for common respiratory pathogens with a respiratory fluoroquinolone or beta-lactam plus macrolide 1
Infection Severity
- For sepsis or septic shock: Use broad-spectrum agents immediately (vancomycin plus piperacillin-tazobactam or a carbapenem) 1, 3
- For necrotizing infections: Urgent surgical consultation plus broad-spectrum antibiotics (vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem) 1
Risk Factors for Resistant Organisms
- Healthcare-associated infection: Cover for MRSA and resistant gram-negatives 1
- Recent antibiotic exposure: Increased risk of resistant organisms 4
- Immunocompromised status: Broader coverage including antipseudomonal agents and consideration of antifungals 1
De-escalation Strategy
- Obtain appropriate cultures before starting antibiotics whenever possible 4, 5
- Re-evaluate antimicrobial therapy after 48-72 hours based on clinical response and culture results 5
- Narrow spectrum when pathogens are identified (de-escalation) 5
- Discontinue unnecessary antimicrobials to reduce risk of resistance development 3
Common Pitfalls and Caveats
- Inadequate initial empiric therapy is associated with increased mortality in severe infections 3
- Unnecessarily broad empiric antibiotics are also associated with higher mortality and increased risk of resistance 3
- Daptomycin should not be used for pneumonia as it is inactivated by pulmonary surfactant 6
- Fluoroquinolones have increasing resistance rates, particularly for E. coli, and should be used with caution 1
- Prolonged broad-spectrum therapy increases the risk of Clostridioides difficile infection and antimicrobial resistance 4