What antibiotic covers community-acquired pneumonia (CAP) and streptococcal (strep) infections?

Antibiotic Coverage for Community-Acquired Pneumonia and Streptococcal Infections

For community-acquired pneumonia (CAP) that also covers streptococcal infections, use amoxicillin 1 gram three times daily for healthy adults without comorbidities, or a β-lactam (amoxicillin-clavulanate, ceftriaxone, or cefotaxime) plus a macrolide (azithromycin or clarithromycin) for patients with comorbidities or requiring hospitalization. 1, 2

Outpatient Treatment Algorithm

For Previously Healthy Adults Without Comorbidities:

• First-line choice: Amoxicillin 1 gram orally three times daily 1, 2

  • This provides excellent coverage for Streptococcus pneumoniae (the most common CAP pathogen) and Streptococcus pyogenes (Group A Strep) 1, 2
  • Amoxicillin remains highly active against most streptococcal species, including penicillin-susceptible S. pneumoniae 1

• Alternative options:

  • Doxycycline 100 mg orally twice daily 1, 2
  • Macrolide monotherapy (azithromycin 500 mg day 1, then 250 mg daily days 2-5) only if local macrolide resistance is <25% 1, 2

For Adults With Comorbidities (Diabetes, Heart/Lung/Liver Disease, Recent Antibiotics):

Combination therapy is strongly recommended: 1

• High-dose amoxicillin-clavulanate 2000/125 mg twice daily PLUS azithromycin (500 mg day 1, then 250 mg daily) 1
  • Alternative β-lactams: ceftriaxone, cefpodoxime 200 mg twice daily, or cefuroxime 500 mg twice daily 1
  • Doxycycline 100 mg twice daily can substitute for the macrolide 1

OR

• Respiratory fluoroquinolone monotherapy: levofloxacin 750 mg daily or moxifloxacin 400 mg daily 1

Inpatient Non-ICU Treatment

Two equally effective options: 1

1. β-lactam PLUS macrolide combination:

   • Ceftriaxone 1-2 grams IV daily OR cefotaxime OR ampicillin-sulbactam 1
   • PLUS azithromycin 500 mg IV/PO daily OR clarithromycin 1

2. Respiratory fluoroquinolone monotherapy:

   • Levofloxacin 750 mg IV/PO daily OR moxifloxacin 400 mg IV/PO daily 1

Severe CAP (ICU Patients)

Mandatory combination therapy: 1

• β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS either:
  • Azithromycin 500 mg IV/PO daily 1
  • OR a respiratory fluoroquinolone (levofloxacin 750 mg or moxifloxacin 400 mg) 1

Special Consideration for Group A Streptococcus (S. pyogenes):

• If Streptococcus pyogenes pneumonia is suspected (post-influenza, fulminant presentation), add clindamycin 600 mg IV every 8 hours to the β-lactam 1, 3
• Clindamycin inhibits toxin production and is specifically recommended for toxic shock associated with Group A strep pneumonia 1, 3

Key Clinical Nuances

Why Amoxicillin Works Despite "Atypical" Coverage Concerns:

Multiple high-quality studies demonstrate that amoxicillin monotherapy achieves >90% clinical cure rates in CAP, despite lacking coverage for atypical pathogens like Mycoplasma and Chlamydophila 1, 4, 5. This suggests that atypical organisms may be less clinically significant than traditionally believed in immunocompetent outpatients, or that host immunity handles these pathogens adequately.

Resistance Considerations:

• Drug-resistant S. pneumoniae (DRSP): High-dose amoxicillin (1 gram three times daily) or amoxicillin-clavulanate (2000/125 mg twice daily) covers strains with penicillin MICs up to 4 mg/L 1, 4, 5
• Macrolide resistance: Ranges from 20-30% in many regions; avoid macrolide monotherapy if local resistance exceeds 25% 1, 2
• Recent antibiotic use (within 3 months): Select a different antibiotic class to reduce resistance risk 1

Common Pitfalls to Avoid:

1. Don't use first-generation cephalosporins (cephalexin) for CAP—they lack adequate coverage for S. pneumoniae with elevated penicillin MICs 1

2. Don't use ciprofloxacin for CAP—it has inadequate pneumococcal coverage; only levofloxacin (750 mg dose), moxifloxacin, or gemifloxacin are appropriate fluoroquinolones 1

3. Reserve fluoroquinolones for appropriate patients due to serious adverse effects including tendinopathy, peripheral neuropathy, and CNS effects 1, 2

4. For penicillin-allergic patients: Use a respiratory fluoroquinolone OR aztreonam plus a macrolide (if hospitalized) 1

Treatment Duration

• Standard CAP: 5-7 days for most cases 1, 2
• Severe CAP or specific pathogens: 10 days minimum 2, 6
• Legionella, Staphylococcus aureus, or gram-negative bacilli: 14-21 days 2, 6

Why Combination Therapy for Hospitalized Patients?

Combination therapy (β-lactam plus macrolide) for hospitalized CAP patients consistently demonstrates lower mortality compared to β-lactam monotherapy in large observational studies 1. The macrolide component provides coverage for atypical pathogens (Legionella, Mycoplasma) and may have immunomodulatory effects that improve outcomes 1.