What is the first‑line antibiotic regimen for a healthy adult with community‑acquired pneumonia presenting with radiographic consolidation?

First-Line Antibiotic for Adult with Pneumonic Consolidation

For a healthy adult with community-acquired pneumonia presenting with radiographic consolidation, amoxicillin 1 g orally three times daily for 5–7 days is the first-line antibiotic of choice. 1

Rationale for Amoxicillin as First-Line

• Amoxicillin retains activity against 90–95% of Streptococcus pneumoniae isolates, including many penicillin-resistant strains, making it the most effective oral agent for the predominant bacterial pathogen in CAP. 1
• The American Thoracic Society and Infectious Diseases Society of America provide a strong recommendation with moderate-quality evidence for amoxicillin as preferred first-line therapy in previously healthy adults without comorbidities. 1, 2
• Amoxicillin demonstrates superior pneumococcal coverage compared with oral cephalosporins and has an excellent safety profile at high doses. 1, 2

Alternative First-Line Options

• Doxycycline 100 mg orally twice daily for 5–7 days is an acceptable alternative when amoxicillin is contraindicated, providing coverage of both typical bacterial pathogens and atypical organisms (Mycoplasma, Chlamydophila, Legionella). 1, 2
• Doxycycline carries a conditional recommendation with lower-quality evidence compared to amoxicillin. 1

When Macrolides Can Be Used

• Macrolide monotherapy (azithromycin or clarithromycin) should only be used when local pneumococcal macrolide resistance is documented to be <25%. 1, 2
• In most U.S. regions, macrolide resistance among S. pneumoniae is 20–30%, making macrolide monotherapy unsafe as first-line therapy. 1
• Breakthrough pneumococcal bacteremia occurs significantly more frequently with macrolide-resistant strains when macrolides are used alone. 1

Treatment Duration and Monitoring

• Treat for a minimum of 5 days and continue until the patient is afebrile for 48–72 hours with no more than one sign of clinical instability; typical duration for uncomplicated CAP is 5–7 days. 1, 2
• Clinical review at 48 hours (or sooner if symptoms worsen) is mandatory to assess symptom resolution, oral intake, and treatment response. 1

Criteria for Treatment Failure Requiring Escalation

• No clinical improvement by day 2–3 warrants adding or substituting a macrolide to provide atypical pathogen coverage. 1, 2
• Development of respiratory distress (respiratory rate >30/min, oxygen saturation <92%), inability to tolerate oral antibiotics, or new complications such as pleural effusion mandate hospital referral. 1
• If combination therapy (β-lactam + macrolide) fails, switch to a respiratory fluoroquinolone (levofloxacin 750 mg daily or moxifloxacin 400 mg daily). 1, 2

When Combination Therapy Is Required (Patients with Comorbidities)

• Adults with comorbidities (COPD, diabetes, chronic heart/lung/liver/renal disease, alcoholism, malignancy, immunosuppression) require combination therapy with amoxicillin-clavulanate 875/125 mg twice daily plus azithromycin (500 mg day 1, then 250 mg daily for 5–7 days). 1, 2
• Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) is an alternative for patients with comorbidities, particularly those with β-lactam allergy. 1, 2

Critical Pitfalls to Avoid

• Never use oral cephalosporins (cefuroxime, cefpodoxime) as first-line agents because they have inferior in-vitro activity against S. pneumoniae, lack atypical coverage, and are more costly without demonstrated clinical superiority. 1
• Avoid indiscriminate fluoroquinolone use in uncomplicated outpatient CAP due to FDA warnings about serious adverse events (tendon rupture, peripheral neuropathy, aortic dissection) and rising resistance. 1
• Do not extend therapy beyond 7 days in responding patients without specific indications (e.g., Legionella, Staphylococcus aureus, gram-negative enteric bacilli), as longer courses increase antimicrobial resistance risk. 1

Hospitalization Criteria

• Admit patients with a CURB-65 score ≥2 or any of the following: respiratory rate ≥30/min, oxygen saturation <90% on room air, systolic blood pressure <90 mmHg, altered mental status, multilobar infiltrates, or inability to maintain oral intake. 1