Community-Acquired Pneumonia (CAP) Treatment Dosing in Hospital
For hospitalized patients with CAP, use a β-lactam plus macrolide combination OR respiratory fluoroquinolone monotherapy, with specific dosing based on severity and risk factors. 1
Non-ICU Hospitalized Patients
Patients WITH Comorbidities or Risk Factors for Drug-Resistant Streptococcus pneumoniae (DRSP)
Combination therapy (preferred):
- β-lactam PLUS macrolide:
- Ceftriaxone 1-2g IV daily PLUS azithromycin 500mg IV/PO daily 1, 2
- OR ampicillin-sulbactam PLUS macrolide (for aspiration risk or nursing home residents) 1
- Macrolide options: azithromycin 500mg on day 1, then 250mg daily OR clarithromycin 500mg twice daily 1
- Doxycycline 100mg twice daily can substitute for macrolides if allergic 1
Monotherapy alternative:
- Respiratory fluoroquinolone:
The 2019 ATS/IDSA guidelines provide strong evidence (moderate quality) supporting both combination therapy and fluoroquinolone monotherapy as equally effective options 1. The combination approach ensures coverage of both typical and atypical pathogens, while fluoroquinolone monotherapy offers convenience with broad spectrum coverage 1.
Patients WITHOUT Comorbidities or DRSP Risk Factors
- Azithromycin monotherapy: 500mg IV daily for 2-5 days, then 500mg PO daily 1
- However, few hospitalized patients truly fall into this low-risk category 1
ICU Patients (Severe CAP)
WITHOUT Pseudomonas Risk Factors
Mandatory combination therapy:
- β-lactam active against DRSP PLUS either azithromycin OR fluoroquinolone:
Erythromycin is NOT recommended for severe CAP due to administration difficulties and poor tolerance 1. The combination approach is essential because fluoroquinolone monotherapy efficacy in severe CAP remains uncertain, with limited ICU patient data 1.
WITH Pseudomonas Risk Factors
Dual antipseudomonal coverage required:
- Antipseudomonal β-lactam PLUS antipseudomonal fluoroquinolone:
- Cefepime, piperacillin-tazobactam, imipenem, OR meropenem PLUS ciprofloxacin 400mg IV every 8 hours 1
OR antipseudomonal β-lactam PLUS aminoglycoside PLUS azithromycin/fluoroquinolone:
- Provides coverage for DRSP, Legionella, and Pseudomonas 1
For β-lactam allergic patients with Pseudomonas risk:
- Aztreonam PLUS aminoglycoside PLUS antipneumococcal fluoroquinolone 1
Critical Dosing Considerations
Avoid antipseudomonal β-lactams when Pseudomonas is NOT suspected (cefepime, piperacillin-tazobactam, imipenem, meropenem should not be primary therapy without risk factors) 1. This prevents unnecessary broad-spectrum exposure and resistance development.
IV to Oral Transition
Switch criteria:
- Hemodynamically stable and clinically improving 2
- After 1-2 days of appropriate clinical response 1
- Use same agent or same drug class when switching 1
- For patients on IV β-lactam/macrolide combination, switching to macrolide alone is safe if no DRSP or gram-negative pathogens isolated 1
Duration of Therapy
Minimum 5 days of treatment with the following criteria met before discontinuation 1, 2:
Longer duration required for:
- Initial ineffective therapy 1
- Bacteremic S. aureus pneumonia (endocarditis risk) 1
- Meningitis or endocarditis complications 1
- Legionella: 10-14 days (14+ days if immunosuppressed) 1
- Mycoplasma/Chlamydophila: 10-14 days 1
The 2007 IDSA/ATS guidelines established 5 days as the minimal effective duration based on high-dose levofloxacin 750mg studies showing superior early defervescence compared to standard dosing 1. Traditional 7-10 day courses are no longer necessary for uncomplicated cases 1.
Special Populations
Aspiration risk or nursing home residents:
- Add anaerobic coverage: ampicillin-sulbactam, amoxicillin-clavulanate, OR high-dose ampicillin 1
- If lung abscess documented: add clindamycin or metronidazole 1
Augmented renal clearance (critically ill):
- Extend ceftobiprole infusion time to 4 hours to optimize drug exposure 3