What antibiotic would be started for a patient with a suspected severe infection?

Empiric Antibiotic Selection for Severe Infections

For a patient with suspected severe infection, meropenem is the recommended first-line empiric antibiotic therapy due to its broad spectrum of activity against most pathogens and effectiveness in septic shock. 1

Selection Algorithm Based on Infection Severity and Risk Factors

For Septic Shock/Severe Infection:

• First choice: Meropenem 1g IV every 8 hours 1, 2

  • Provides coverage against most gram-negative bacteria (including Pseudomonas), gram-positive bacteria, and anaerobes
  • Preferred for severe infections and septic shock 2

• Add vancomycin 15-20 mg/kg IV every 8-12 hours if MRSA is suspected or patient has risk factors 1:

  • Prior IV antibiotics within 90 days
  • Known MRSA colonization
  • Healthcare-associated infection
  • High local MRSA prevalence (>20%)

For Moderate Infections Without Septic Shock:

• First choice: Piperacillin-tazobactam 4.5g IV every 6 hours 1
  • Excellent broad-spectrum coverage without overuse of carbapenems

For Community-Acquired Infections Without Risk Factors:

• First choice: Ceftriaxone 1-2g IV daily 3, 4
  • Effective against most community-acquired pathogens
  • Once-daily dosing advantage

Important Considerations for Antibiotic Selection

Risk Factors for Resistant Organisms:

• Previous antibiotic exposure within 3 months 1
• Hospitalization in past 12 months 1
• Nursing facility residence with indwelling devices 1
• Known colonization with resistant organisms 1
• Local epidemiology with high resistance rates 1

Infection Site Considerations:

• Pneumonia: Add macrolide or respiratory fluoroquinolone for atypical coverage 1
• Intra-abdominal infection: Ensure anaerobic coverage with metronidazole if using cephalosporins 1
• Skin/soft tissue: Add specific MRSA coverage if risk factors present 1

De-escalation Strategy

• Obtain appropriate cultures before starting antibiotics if possible (without delaying treatment) 1
• Reassess antibiotic regimen within 48-72 hours based on culture results 1, 2
• De-escalate to narrower spectrum antibiotics once pathogen and susceptibilities are known 1, 2
• Avoid prolonged broad-spectrum therapy when unnecessary 1, 5

Common Pitfalls to Avoid

• Delayed antibiotic administration: Each hour of delay in appropriate antibiotic therapy increases mortality in septic shock 1
• Inadequate empiric coverage: Associated with 19% higher mortality in sepsis 5
• Unnecessarily broad coverage: Also associated with 22% higher mortality 5
• Fluoroquinolone overuse: Avoid empiric use in areas with >10% resistance rates 2
• Failure to consider local resistance patterns: Local antibiograms should guide empiric therapy 1

Special Considerations

• For patients with penicillin allergy: Consider aztreonam plus metronidazole plus an agent for gram-positive coverage 1
• For immunocompromised patients: Consider broader empiric coverage including antifungals if appropriate 1
• For healthcare-associated infections: Carbapenems are superior to third-generation cephalosporins due to increasing resistance 1

Remember that the first dose of antibiotics should be administered within one hour of recognition of sepsis or septic shock to improve outcomes 1. The initial empiric regimen can and should be narrowed once culture results are available.