Annotations only — chart still shows the full chemistry of each drug.
1. Clinical Syndrome
Pneumonia acquired outside the hospital or healthcare facility — fever, cough, dyspnea, sputum production, plus consolidation on imaging. Excludes patients hospitalized within 90 days, residents of long-term care, recent IV antibiotics — those raise concern for HAP-like pathogens.
2. Pathogens
Consider the patient: Age & comorbidities (COPD, alcohol use, heart failure, immunosuppression), prior antibiotics within 90 days (raises MRSA/Pseudomonas risk), recent influenza (S. aureus superinfection), aspiration risk, vaccination status (PCV20).
Consider the case: Severity (CURB-65, PSI), microbiologic data (sputum culture, blood cultures, urinary antigens, MRSA nasal PCR, respiratory viral panel).
Common
- Streptococcus pneumoniae
Most common bacterial cause.
- Haemophilus influenzae
Common in COPD / smokers; ~25–30% β-lactamase-positive.
- Staphylococcus aureus (MSSA)
Post-influenza superinfection; cavitary disease.
- Streptococcus pneumoniae
- Atypical
- Mycoplasma pneumoniae
"Walking pneumonia" — young adults; covered by macrolide / doxy / respiratory FQ.
- Mycoplasma pneumoniae
Less common
- Moraxella catarrhalis
COPD exacerbation; ALWAYS β-lactamase-positive — use amox-clav or different class.
- Klebsiella pneumoniae
Alcohol use disorder, aspiration.
- Staphylococcus aureus (MRSA)
Risk factors → empiric coverage.
- Pseudomonas aeruginosa
Structural lung disease, recent IV abx.
- Moraxella catarrhalis
- Atypical
- Legionella pneumophila
Severe CAP; classic GI symptoms + hyponatremia + transaminitis. Send urine antigen in hospitalized CAP.
- Chlamydia pneumoniae (Chlamydophila pneumoniae)
Mild pneumonia ± pharyngitis in young adults; covered by atypical agents.
- Legionella pneumophila
3. Empiric Therapy
| Tier | First choice | Alternatives | Duration | Comments |
|---|---|---|---|---|
| Outpatient — no comorbidities |
|
| 5 days (afebrile ≥48h, clinically stable) | No comorbidities, no recent abx, no MRSA/Pseudo risk. |
| Outpatient — with comorbidities |
|
| 5 days | Comorbidities (chronic heart, lung, liver, renal disease; DM; alcohol use; malignancy; asplenia). |
| Admitted to ward |
|
| 5 days minimum (afebrile + stable) | Standard ward admission. Switch to PO once clinically stable + tolerating PO. |
| Admitted to ICU |
|
| 5–7 days | All ICU CAP gets atypical coverage. Escalate per coverage triggers. |
Add coverage if:
- Prior IV antibiotics within 90 days
- Prior MRSA respiratory colonization
- Cavitary pneumonia
- Recent hospitalization
- Recent influenza (S. aureus superinfection risk)
Add:
- 15–20 mg/kg · q8–12h · IV
Or linezolid 600 mg IV/PO q12h.
- 600 mg · q12h · IV
De-escalate if MRSA nasal PCR negative — high NPV in pneumonia.
- Prior IV antibiotics within 90 days
- Prior Pseudomonas respiratory colonization
- Structural lung disease (bronchiectasis, severe COPD)
Add:
- 4.5 g · q8h (extended infusion) · IV
Or cefepime 2 g IV q8h.
- 2 g · q8h · IV
Replaces ceftriaxone in the base regimen.
4. Directed Therapy
Once cultures back, narrow:
- S. pneumoniae (PCN-S): amoxicillin 1 g PO TID or PCN G
- MSSA: cefazolin 2 g IV q8h
- MRSA: continue vancomycin (target AUC 400–600) or linezolid
- Atypical (Mycoplasma, Legionella, Chlamydia): azithromycin or doxycycline
- Influenza positive: add oseltamivir; continue antibacterial if bacterial co-infection suspected
De-escalate empiric MRSA/Pseudomonas coverage at 48 h if cultures negative and clinical improvement.
5. Monitoring
Resolution: afebrile within 48–72 h, decreasing oxygen requirement, improving WBC. Repeat imaging at 6–8 weeks if smoker / age ≥50 to evaluate for underlying malignancy.
Toxicity: vanco level + Cr (if used), QTc on macrolide + fluoroquinolone, C. diff if persistent diarrhea.
Pearls
Most CAP courses are now 5 days if clinically stable + afebrile ≥48 h (IDSA/ATS 2019). Don't extend just because of minor lab abnormalities.