What antibiotics can I give to a patient with a community-acquired infection?

Antibiotics for Community-Acquired Infections

For previously healthy adults with community-acquired pneumonia, start with amoxicillin 1 gram three times daily as first-line therapy, as it provides the most effective coverage against Streptococcus pneumoniae, the most common pathogen. 1

Treatment Algorithm Based on Patient Characteristics

Healthy Adults Without Comorbidities

• Amoxicillin 1 gram three times daily is the preferred first-line agent with strong recommendation and moderate quality evidence 1
• Alternative options include:
  • Doxycycline 100 mg twice daily (conditional recommendation, low quality evidence) 1
  • Macrolides (azithromycin 500 mg daily for 3 days or 500 mg day 1 then 250 mg daily for 5 days; clarithromycin 250-500 mg twice daily) 2, 1
  • Erythromycin 1 gram three times daily 2

Adults With Comorbidities

• Combination therapy is recommended: beta-lactam (amoxicillin-clavulanate 1 gram three times daily) plus a macrolide 1
• Alternative: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) 1
• Reserve fluoroquinolones for patients with comorbidities or when other options cannot be used due to risks of tendinopathy, peripheral neuropathy, and CNS effects 1, 3

Recent Antibiotic Exposure

• Choose a different antibiotic class than recently used to reduce resistance risk 1
• If recent beta-lactam use: switch to macrolide or fluoroquinolone
• If recent macrolide use: switch to beta-lactam or fluoroquinolone

Special Clinical Scenarios

Suspected Aspiration Pneumonia

• Amoxicillin-clavulanate (1 gram three times daily plus clavulanate 125 mg three times daily) 1
• Alternative: Clindamycin 300 mg four times daily 2, 1

Penicillin Allergy

• Macrolides (azithromycin or clarithromycin) as first choice 2
• Doxycycline 100 mg twice daily as alternative 2, 1
• Respiratory fluoroquinolones if macrolides contraindicated 1

Suspected Atypical Pathogens (Mycoplasma, Chlamydia, Legionella)

• Macrolides (azithromycin 500 mg daily or clarithromycin 250-500 mg twice daily) 1
• Alternative: Doxycycline 100 mg twice daily 2, 1
• Alternative: Respiratory fluoroquinolone 1

Inpatient Treatment (Non-ICU)

• Beta-lactam plus macrolide combination: ceftriaxone 1 gram daily or cefotaxime 1 gram every 8 hours plus azithromycin or clarithromycin 1
• Alternative: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) 1
• Benzyl penicillin 1-4 million units every 2-4 hours or amoxicillin 1 gram every 6 hours in areas with low beta-lactamase-producing Haemophilus influenzae 2

Severe CAP (ICU Patients)

• Beta-lactam (ceftriaxone, cefotaxime, or ceftaroline) plus either macrolide or respiratory fluoroquinolone 1
• If Pseudomonas concern: Antipseudomonal beta-lactam (piperacillin-tazobactam 4.5 grams every 6 hours) plus ciprofloxacin 400 mg twice daily or aminoglycoside plus macrolide 1

Treatment Duration

• Standard duration: 5-7 days for most antibiotics in community-acquired infections 1
• Extended treatment (14-21 days) for suspected Legionella, staphylococcal, or gram-negative enteric bacilli pneumonia 1
• Assess clinical response at day 2-3 for hospitalized patients or day 5-7 for outpatients 2, 1

Critical Pitfalls to Avoid

Azithromycin Contraindications

• Do not use azithromycin in patients with known QT prolongation, torsades de pointes history, congenital long QT syndrome, or those on QT-prolonging drugs 3
• Avoid in patients with uncorrected hypokalemia, hypomagnesemia, or clinically significant bradycardia 3
• Not appropriate for moderate-to-severe pneumonia requiring hospitalization, bacteremia, cystic fibrosis, nosocomial infections, or immunocompromised patients 3

Fluoroquinolone Cautions

• Reserve for patients with true contraindications to beta-lactams and macrolides due to serious adverse effects including tendinopathy, peripheral neuropathy, and CNS effects 1, 3
• Elderly patients are more susceptible to QT interval prolongation with these agents 3

Aminoglycosides

• Avoid aminoglycosides for pleural infections as they have poor pleural space penetration and are inactive in acidic pleural fluid 2

Resistance Considerations

• Amoxicillin-clavulanate maintains activity against beta-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis while providing enhanced coverage for penicillin-resistant Streptococcus pneumoniae 4, 5
• Third-generation oral cephalosporins (cefixime, cefdinir) are alternatives for beta-lactamase-producing pathogens when amoxicillin-clavulanate cannot be used 6