What antibiotics should be given to a patient with severe pneumonia and which organisms should be suspected?

Treatment of Severe Pneumonia: Suspected Organisms and Antibiotic Selection

For severe pneumonia, the recommended first-line therapy is an intravenous combination of a broad-spectrum β-lactamase stable antibiotic (co-amoxiclav, cefuroxime, or ceftriaxone) plus a macrolide (clarithromycin or erythromycin). 1

Suspected Organisms

The organisms suspected in severe pneumonia vary based on whether it is community-acquired or hospital-acquired:

Community-Acquired Severe Pneumonia

• Common pathogens:
  • Streptococcus pneumoniae (most common)
  • Haemophilus influenzae
  • Legionella pneumophila
  • Staphylococcus aureus (especially in post-viral pneumonia)
  • Gram-negative enteric bacilli (in elderly or those with comorbidities)

Hospital-Acquired/Ventilator-Associated Pneumonia

• Common pathogens:
  • Pseudomonas aeruginosa
  • Klebsiella pneumoniae
  • Acinetobacter species
  • Methicillin-resistant Staphylococcus aureus (MRSA)
  • Other multi-drug resistant organisms

Antibiotic Recommendations

First-line Treatment for Severe Community-Acquired Pneumonia:

• Intravenous combination therapy:
  • Broad-spectrum β-lactamase stable antibiotic (one of):
    • Co-amoxiclav
    • Cefuroxime (second-generation cephalosporin)
    • Ceftriaxone or cefotaxime (third-generation cephalosporins)
  • PLUS a macrolide:
    • Clarithromycin
    • Erythromycin 2, 1

Alternative Regimen (for penicillin/macrolide intolerance):

• Fluoroquinolone with enhanced pneumococcal activity (e.g., levofloxacin) plus intravenous benzylpenicillin 1

For Suspected Pseudomonas aeruginosa:

• Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, or carbapenem)
• PLUS either ciprofloxacin or an aminoglycoside 1, 3, 4

Duration of Treatment

• For severe microbiologically undefined pneumonia: 10 days
• For Legionella, staphylococcal, or Gram-negative enteric bacilli pneumonia: 14-21 days 2, 1

Management of Treatment Failure

If a patient fails to improve as expected:

1. Conduct a careful clinical review by an experienced clinician
2. Order further investigations (repeat chest radiograph, CRP, WBC, microbiological testing)
3. Consider changing antibiotics:
   • For those on combination therapy, consider changing to a fluoroquinolone with effective pneumococcal coverage
   • Consider adding rifampicin for severe pneumonia not responding to combination treatment 2

Special Considerations

• For nosocomial pneumonia, piperacillin-tazobactam (4.5g IV every 6 hours) is indicated for treatment of moderate to severe cases caused by beta-lactamase producing organisms 3
• When P. aeruginosa is isolated or suspected, continue aminoglycoside treatment in combination with appropriate β-lactam antibiotics 3, 4
• Adjust dosing in patients with renal impairment 3

Common Pitfalls to Avoid

1. Delayed initiation of antibiotics - Start treatment immediately after diagnosis for severe pneumonia
2. Inadequate spectrum coverage - Ensure coverage of likely pathogens based on clinical setting
3. Failure to reassess - Review antibiotic therapy within 24-48 hours and adjust based on clinical response and culture results
4. Prolonged IV therapy - Switch to oral therapy once clinical improvement occurs and temperature has been normal for 24 hours
5. Inappropriate monotherapy - Use combination therapy for severe pneumonia to ensure adequate coverage

Remember that early, appropriate antibiotic therapy significantly reduces mortality in severe pneumonia cases. The choice of empiric antibiotics should be guided by local resistance patterns and individual risk factors.