IDSA Guidelines for Community-Acquired Pneumonia in Healthy Adults
Outpatient Treatment for Previously Healthy Adults Without Comorbidities
For healthy adults with community-acquired pneumonia and no significant underlying health conditions, the IDSA/ATS guidelines recommend amoxicillin 1 g orally three times daily for 5-7 days as first-line therapy. 1
Primary Treatment Options
Amoxicillin 1 g three times daily is the preferred first-line agent, providing excellent coverage against Streptococcus pneumoniae including drug-resistant strains, Haemophilus influenzae, and other common respiratory pathogens 2, 1
Doxycycline 100 mg twice daily serves as an acceptable alternative for patients who cannot tolerate amoxicillin, though this carries lower quality evidence 2, 1
Macrolides (azithromycin 500 mg day 1, then 250 mg daily for days 2-5; or clarithromycin 500 mg twice daily) should ONLY be used in areas where pneumococcal macrolide resistance is documented to be <25% 2, 1
Treatment Duration
Treat for a minimum of 5 days AND until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability 2, 1
Hospitalized Patients (Non-ICU)
For hospitalized patients without ICU-level severity, the IDSA recommends either β-lactam plus macrolide combination therapy OR respiratory fluoroquinolone monotherapy—both carry strong recommendations with high-quality evidence. 2, 1
Recommended Regimens
Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily (strong recommendation, level I evidence) 2, 1
Alternative β-lactams include cefotaxime 1-2 g IV every 8 hours or ampicillin-sulbactam 3 g IV every 6 hours, always combined with a macrolide 2
Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily) is equally effective 2, 1
For penicillin-allergic patients, use respiratory fluoroquinolone as the preferred alternative 2
Critical Timing
- Administer the first antibiotic dose in the emergency department immediately upon diagnosis—delayed administration beyond 8 hours increases 30-day mortality by 20-30% 2, 1
Transition to Oral Therapy
- Switch from IV to oral antibiotics when the patient is hemodynamically stable, clinically improving, able to take oral medications, and has normal GI function—typically by day 2-3 of hospitalization 2, 1
Severe CAP Requiring ICU Admission
Combination therapy is mandatory for all ICU patients—monotherapy is inadequate for severe disease. 2, 1
ICU Regimen
Ceftriaxone 2 g IV daily (or cefotaxime 1-2 g IV every 8 hours, or ampicillin-sulbactam 3 g IV every 6 hours) PLUS either azithromycin 500 mg IV daily OR respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 2, 3
For penicillin-allergic ICU patients, use respiratory fluoroquinolone PLUS aztreonam 2 g IV every 8 hours 2
Special Pathogen Coverage
Add antipseudomonal coverage ONLY when risk factors are present: structural lung disease, recent hospitalization with IV antibiotics within 90 days, or prior respiratory isolation of P. aeruginosa 2, 1
- Use antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin or levofloxacin PLUS aminoglycoside 2
Add MRSA coverage ONLY when risk factors are present: prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates 2, 1
- Add vancomycin 15 mg/kg IV every 8-12 hours or linezolid 600 mg IV every 12 hours 2
Diagnostic Testing
Obtain blood cultures and sputum Gram stain/culture before initiating antibiotics in ALL hospitalized patients to allow pathogen-directed therapy and de-escalation 2, 1
Chest radiograph is strongly recommended to confirm diagnosis in all suspected CAP patients 2, 4
Critical Pitfalls to Avoid
Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25%—this leads to treatment failure 2, 1
Never use macrolide monotherapy in hospitalized patients—it provides inadequate coverage for typical bacterial pathogens like S. pneumoniae 2, 1
Never delay antibiotic administration beyond 8 hours in hospitalized patients—this increases mortality 2, 1
Avoid indiscriminate fluoroquinolone use in uncomplicated outpatient CAP due to resistance concerns and serious adverse events 1
Do not automatically add broad-spectrum coverage for Pseudomonas or MRSA without documented risk factors 2, 1