What are the recommended antibiotics for treating pneumonia?

Recommended Antibiotics for Pneumonia

Community-Acquired Pneumonia (CAP) - Outpatient Treatment

For outpatients without comorbidities, amoxicillin 1g three times daily is the preferred first-line agent, with macrolides (azithromycin or clarithromycin) or doxycycline as alternatives for penicillin-allergic patients. 1

• Amoxicillin monotherapy is appropriate when local pneumococcal resistance to macrolides is <25% 1
• Macrolide alternatives include azithromycin 500mg on day 1 then 250mg daily, or clarithromycin 500mg twice daily 1
• Doxycycline 100mg twice daily provides another option for penicillin-allergic patients 1

Outpatients with Comorbidities

For patients with chronic heart, lung, liver, or renal disease, diabetes, alcoholism, malignancy, or asplenia, combination therapy with amoxicillin/clavulanate plus a macrolide OR monotherapy with a respiratory fluoroquinolone is recommended. 1

• Combination regimens: Amoxicillin/clavulanate 875mg/125mg twice daily PLUS azithromycin or doxycycline 1
• Fluoroquinolone monotherapy: Levofloxacin 750mg daily, moxifloxacin 400mg daily, or gemifloxacin 320mg daily 1
• Alternative beta-lactams include cefpodoxime 200mg twice daily or cefuroxime 500mg twice daily 1

Community-Acquired Pneumonia - Hospitalized Patients (Non-Severe)

Combined oral therapy with amoxicillin and a macrolide (erythromycin or clarithromycin) is the preferred regimen for hospitalized patients with non-severe CAP. 1

• Most hospitalized patients can be adequately treated with oral antibiotics rather than IV formulations 1
• When oral treatment is contraindicated, use IV ampicillin or benzylpenicillin plus IV erythromycin or clarithromycin 1
• Respiratory fluoroquinolones (levofloxacin only agent licensed in UK per 2001 guidelines) provide an alternative for penicillin/macrolide intolerance or concerns about Clostridium difficile 1

Critical Pitfall to Avoid

Amoxicillin monotherapy should only be considered for patients previously untreated in the community or those admitted for non-clinical reasons (elderly, socially isolated) who would otherwise be treated outpatient 1. The decision to use monotherapy versus combination therapy should be reviewed within the first 24 hours of admission 1.

Severe Community-Acquired Pneumonia (ICU-Level)

Patients with severe pneumonia require immediate parenteral antibiotics with an IV beta-lactam combined with a macrolide. 1

• IV combination therapy should be initiated immediately after diagnosis 1
• The 2001 BTS guidelines recommend IV cephalosporin or penicillin plus IV macrolide 1
• More recent evidence supports ceftriaxone 2g IV daily plus azithromycin 500mg as highly effective combination therapy 2, 3

Hospital-Acquired and Ventilator-Associated Pneumonia

Piperacillin-tazobactam 4.5g IV every 6 hours is the recommended first-line backbone agent for hospital-acquired and ventilator-associated pneumonia, with additional agents added based on mortality and MRSA risk factors. 4, 5, 6

Risk Stratification Framework

High mortality risk factors include: 4, 5

• Need for ventilatory support due to pneumonia
• Septic shock at presentation
• ARDS preceding VAP
• Acute renal replacement therapy prior to VAP onset

MRSA risk factors include: 4, 5

• Prior IV antibiotic use within 90 days
• Treatment in unit where >20% of S. aureus isolates are methicillin-resistant
• Unknown MRSA prevalence
• Prior detection of MRSA by culture or screening

Treatment Algorithm by Risk Category

Low mortality risk, no MRSA risk factors: 4

• Monotherapy with piperacillin-tazobactam 4.5g IV q6h, cefepime 2g IV q8h, levofloxacin 750mg IV daily, or imipenem 500mg IV q6h

Low mortality risk WITH MRSA risk factors: 4

• Dual therapy: Base regimen PLUS vancomycin 15mg/kg IV q8-12h (target trough 15-20mg/mL) or linezolid 600mg IV q12h

High mortality risk or recent IV antibiotics: 4, 5

• Triple therapy required:
  • Primary antipseudomonal agent: Piperacillin-tazobactam 4.5g IV q6h (preferred) 5
  • Second antipseudomonal agent: Ciprofloxacin 400mg IV q8h, levofloxacin 750mg IV daily, OR aminoglycoside (amikacin 15-20mg/kg IV daily, gentamicin 5-7mg/kg IV daily, or tobramycin 5-7mg/kg IV daily) 4, 5
  • MRSA coverage (if risk factors present): Vancomycin or linezolid 4, 5

Ventilator-Associated Pneumonia Specific Recommendations

For patients on mechanical ventilation with possible aspiration pneumonia, piperacillin-tazobactam 4.5g IV q6h plus an aminoglycoside (for P. aeruginosa coverage) is recommended, with MRSA coverage added based on risk factors. 4, 6

• The FDA label specifically indicates piperacillin-tazobactam for nosocomial pneumonia caused by P. aeruginosa should be treated in combination with an aminoglycoside 6
• Treatment duration is typically 7-14 days 6
• Continue aminoglycoside therapy in patients from whom P. aeruginosa is isolated 6

Critical Dosing and Administration Details

• All IV antibiotics should be infused over 30 minutes to optimize pharmacokinetics 5, 6
• For nosocomial pneumonia, the higher dose of piperacillin-tazobactam (4.5g vs 3.375g) is required 6
• Piperacillin-tazobactam and aminoglycosides must be reconstituted, diluted, and administered separately (co-administration via Y-site possible under certain conditions) 6

Renal Dosing Adjustments

For patients with creatinine clearance ≤40 mL/min, dosing must be reduced: 6

• CrCl 20-40 mL/min: Piperacillin-tazobactam 3.375g IV q6h for nosocomial pneumonia
• CrCl <20 mL/min: Piperacillin-tazobactam 2.25g IV q6h for nosocomial pneumonia
• Hemodialysis: 2.25g IV q8h plus 0.75g after each dialysis session

Aspiration Pneumonia

Piperacillin-tazobactam 4.5g IV every 6 hours is the first-line antibiotic for aspiration pneumonia, providing necessary anaerobic coverage inherent to this condition. 4

• The same risk stratification and treatment algorithm applies as for hospital-acquired pneumonia 4
• Piperacillin-tazobactam demonstrated superior effectiveness against gram-positive infections and faster improvement in temperature and WBC count compared to imipenem/cilastatin 4
• Treatment duration is typically 5-7 days if patient is afebrile for 48 hours and reaches clinical stability 4

Critical Pitfalls to Avoid

Never use aztreonam as monotherapy - it lacks gram-positive activity and requires addition of MRSA coverage (vancomycin or linezolid) 4, 5

Avoid aminoglycoside monotherapy - lower clinical response rates compared to other regimens 5

Do not use fluoroquinolones as first-line community agents - reserve for selected hospitalized patients to minimize resistance development 1

Never delay antibiotics in severe pneumonia - parenteral antibiotics should be administered immediately after diagnosis 1

De-escalation Strategy

Once culture results return, narrow antibiotic spectrum based on susceptibilities to reduce C. difficile risk, adverse effects, and resistance development. 5

• If MRSA was covered empirically but not isolated, discontinue vancomycin or linezolid 5
• For confirmed MSSA, narrow to oxacillin, nafcillin, or cefazolin (preferred over broader agents) 7
• Obtain appropriate cultures before initiating antibiotics and consider local antimicrobial resistance patterns 4