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 ceftriaxone 1-2g IV daily plus azithromycin 500mg daily; for severe ICU pneumonia, use a β-lactam (ceftriaxone or cefotaxime) plus a macrolide (azithromycin or clarithromycin), or add antipseudomonal coverage if risk factors are present. 1, 2, 3

Outpatient Treatment Algorithm

Previously healthy adults without comorbidities:

• Amoxicillin 1g every 8 hours is first-line therapy 1, 2
• Alternative: Doxycycline 100mg twice daily (first dose 200mg for rapid serum levels) 2
• For patients over 40 years or with comorbidities: Use amoxicillin 3g/day OR a respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 4

Patients with comorbidities or recent antibiotic use:

• Respiratory fluoroquinolone monotherapy (levofloxacin or moxifloxacin) OR β-lactam plus macrolide combination 1, 2
• Critical pitfall: Avoid using the same antibiotic class if the patient received antibiotics in the past 3 months due to resistance risk 2

Hospitalized Non-ICU Patients

Standard regimen (preferred):

• Ceftriaxone 1-2g IV daily PLUS azithromycin 500mg IV daily 1, 4, 3
• Alternative: Cefotaxime 1-2g IV every 8 hours plus azithromycin 4

Alternative monotherapy:

• Respiratory fluoroquinolone alone (levofloxacin 750mg IV daily or moxifloxacin 400mg IV daily) 1, 2

Critical timing requirement:

• Administer first antibiotic dose while still in the emergency department, ideally within 4 hours of presentation 4
• Delays beyond 8 hours increase 30-day mortality by 20-30% 4

Route considerations:

• Most patients can be treated with oral antibiotics if no contraindications exist 5
• When oral therapy is contraindicated, use IV ampicillin or benzylpenicillin plus erythromycin or clarithromycin 5

Severe CAP/ICU Treatment

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 a non-antipseudomonal cephalosporin 1, 2

Patients WITH Pseudomonas risk factors (cystic fibrosis, bronchiectasis, recent hospitalization, recent broad-spectrum antibiotics):

• Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS either ciprofloxacin OR macrolide plus aminoglycoside 1, 2, 6

MRSA coverage:

• Add vancomycin or linezolid when community-acquired MRSA is suspected (prior MRSA infection, recent hospitalization, recent antibiotic use, or IV drug use) 2

Duration of Therapy

Minimum duration:

• 5 days minimum for most patients 1, 2
• Patient must be afebrile for 48-72 hours and have no more than one sign of clinical instability before discontinuing 1, 2

Extended duration (14-21 days):

• Legionella, staphylococcal, or Gram-negative enteric bacilli pneumonia 5, 1
• Severe microbiologically undefined pneumonia 5

General recommendation:

• Treatment should generally not exceed 8 days in a responding patient 1, 2
• Short-course regimens (≤7 days) are as effective as extended courses for mild-to-moderate pneumonia 7

Switch to Oral Therapy

Criteria for IV-to-oral switch:

• Hemodynamically stable, clinically improving, able to take oral medications, and normal GI function 4
• Up to half of hospitalized patients are eligible for switch by hospital Day 3 5
• Can safely switch even with positive blood cultures (except S. aureus, which requires longer IV therapy) 5

Sequential vs. step-down therapy:

• Sequential therapy (same drug levels): Doxycycline, linezolid, fluoroquinolones 5
• Step-down therapy (lower oral levels): β-lactams, macrolides—both approaches are clinically effective 5

Common Pitfalls to Avoid

Fluoroquinolone misuse:

• Ciprofloxacin alone is inadequate for pneumococcal coverage—only levofloxacin 750mg and moxifloxacin have sufficient activity 4
• Reserve fluoroquinolones for β-lactam allergies or specific indications to prevent resistance 2
• FDA warnings exist for increasing adverse events with fluoroquinolones 2, 8

Macrolide resistance:

• S. pneumoniae resistance to macrolides ranges 30-40% and often co-exists with β-lactam resistance 4
• Never use azithromycin or macrolides as single agents for hospitalized patients 4

Inadequate atypical coverage:

• Ensure coverage for Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila 2
• While no mortality benefit exists for empirical atypical coverage, clinical success is significantly higher when atypicals are covered, especially for Legionella 4

Failure to reassess:

• Do not change antibiotics within the first 72 hours unless marked clinical deterioration or bacteriologic data necessitate change 5
• For patients failing to improve, conduct careful review of clinical history, examination, and investigations; consider repeat chest radiograph, CRP, white cell count, and further microbiological testing 5, 2