What is the initial treatment for pneumonia?

Initial Treatment for Pneumonia

For outpatients without comorbidities, start with amoxicillin 1g every 8 hours; for hospitalized non-ICU patients, use a β-lactam (ceftriaxone 1-2g IV daily) plus a macrolide (azithromycin 500mg IV daily); for severe ICU pneumonia, use an antipseudomonal β-lactam plus either a respiratory fluoroquinolone or a macrolide plus aminoglycoside. 1, 2, 3

Treatment Algorithm by Clinical Setting

Outpatient Treatment (Mild CAP)

Previously healthy adults under 40 years:

• First-line: Amoxicillin 1g every 8 hours orally 1, 2
• Alternative: Doxycycline 100mg twice daily (200mg first dose) 2
• For atypical pathogen coverage: Macrolide monotherapy (azithromycin 500mg Day 1, then 250mg Days 2-5) is acceptable in younger patients without comorbidities 2, 3

Adults ≥40 years or with comorbidities:

• Preferred: Amoxicillin 3g/day orally OR respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 2, 3
• Alternative: β-lactam plus macrolide combination 1, 2
• Comorbidities include COPD, diabetes, heart/liver/renal disease, malignancy, or recent antibiotic use within 3 months 1, 2

Hospitalized Non-ICU Patients (Moderate CAP)

Standard regimen:

• Ceftriaxone 1-2g IV every 24 hours PLUS azithromycin 500mg IV daily 1, 2, 3, 4
• Alternative β-lactams: Cefotaxime 1-2g IV every 8 hours, ampicillin, or co-amoxiclav 5

Alternative monotherapy:

• Respiratory fluoroquinolone alone: Levofloxacin 750mg IV daily OR moxifloxacin 400mg IV daily 1, 2, 3
• Reserve fluoroquinolones for β-lactam allergies or when C. difficile risk is high 5, 2

Critical timing consideration:

• Administer first antibiotic dose in the Emergency Department, ideally within 4 hours of presentation 3
• Delays beyond 8 hours increase 30-day mortality by 20-30% 3

Severe CAP/ICU Patients

Without Pseudomonas risk factors:

• β-lactam (ceftriaxone, cefotaxime, or cefuroxime) PLUS macrolide (clarithromycin or azithromycin) 5, 1, 2
• Alternative: Respiratory fluoroquinolone (levofloxacin or moxifloxacin) with or without β-lactam 1, 2

With Pseudomonas risk factors:

• Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin OR aminoglycoside (gentamicin, tobramycin, amikacin) plus azithromycin 1, 2
• Pseudomonas risk factors: structural lung disease (bronchiectasis, cystic fibrosis), recent hospitalization, recent broad-spectrum antibiotics, or immunosuppression 1, 2

MRSA coverage:

• Add vancomycin or linezolid when MRSA suspected (prior MRSA infection, recent hospitalization, IV drug use, or necrotizing pneumonia on imaging) 2

Route and Duration of Therapy

Parenteral to oral switch criteria:

• Patient hemodynamically stable, clinically improving, afebrile for 24 hours, able to take oral medications, and normal GI function 5, 2
• Up to 50% of hospitalized patients meet criteria by Day 3 5
• Sequential therapy (same drug IV to PO) or step-down therapy (different drug class) both effective 5

Treatment duration:

• Minimum 5 days with patient afebrile for 48-72 hours and no more than one clinical instability sign 1, 2, 3
• Uncomplicated S. pneumoniae: 7-10 days typically sufficient 2
• Legionella, Staphylococcus, or Gram-negative bacilli: Extend to 14-21 days 5, 1, 2
• Most patients should not exceed 8 days if responding appropriately 1, 2

Critical Pitfalls to Avoid

Inadequate pneumococcal coverage:

• Ciprofloxacin alone is inadequate for pneumococcal CAP 3
• Only levofloxacin 750mg and moxifloxacin have sufficient pneumococcal activity 3
• Macrolide monotherapy inappropriate for hospitalized patients due to 30-40% pneumococcal resistance 2, 3

Inappropriate patient selection for oral therapy:

• Do NOT use oral antibiotics for patients with: moderate-to-severe illness, cystic fibrosis, nosocomial acquisition, known/suspected bacteremia, requiring hospitalization, elderly/debilitated, immunodeficiency, or functional asplenia 6

Premature antibiotic changes:

• Do not change antibiotics within first 72 hours unless marked clinical deterioration or definitive microbiological data necessitate change 5
• Radiographic worsening without clinical deterioration is common and expected in first 24-48 hours 5

Fluoroquinolone overuse:

• Reserve for specific indications to prevent resistance development 2
• Consider QT prolongation risk in elderly, those with cardiac disease, electrolyte abnormalities, or on QT-prolonging medications 6

Special Pathogen Considerations

Legionella species:

• Levofloxacin, moxifloxacin, or azithromycin (preferred macrolide) with or without rifampin 1
• Extend treatment to 14-21 days 5, 1

Atypical pathogens (Mycoplasma, Chlamydophila):

• Macrolides, doxycycline, or respiratory fluoroquinolones provide coverage 1
• Combination therapy with β-lactam plus macrolide ensures coverage when etiology uncertain 1, 2, 4

Viral pneumonia:

• Test all patients for COVID-19 and influenza when community prevalence exists 4
• Positive viral testing may affect need for antibacterial therapy and infection control measures 4

Monitoring and Reassessment

Failure to improve by Day 3:

• Conduct careful review by experienced clinician of history, examination, prescription chart, and all investigations 5
• Obtain repeat chest radiograph, CRP, white cell count, and additional microbiological specimens 5, 2
• Consider complications: empyema, lung abscess, resistant organisms, alternative diagnoses, or drug fever 5

Clinical stability criteria before discharge:

• Temperature ≤37.8°C, heart rate ≤100 bpm, respiratory rate ≤24/min, systolic BP ≥90 mmHg, oxygen saturation ≥90% on room air, ability to maintain oral intake, normal mental status 5, 1

Follow-up:

• Arrange clinical review at 6 weeks with chest radiograph for persistent symptoms, abnormal physical signs, or high malignancy risk (smokers >50 years) 5