community-acquired pneumonia
Contents
Severity-stratified empiric therapy. CURB-65 guides site of care. Ward admission: β-lactam + macrolide (or respiratory fluoroquinolone monotherapy). ICU: β-lactam + macrolide always — never fluoroquinolone monotherapy. β-lactam monotherapy is non-inferior for non-severe CAP (CAP-START (2015)). Minimum 5 days; can stop at 3 days if clinically stable (PTC (2021)).
- first-line: ceftriaxone 2 g IV daily + azithromycin 500 mg PO/IV daily
- alternative first-line: ampicillin 2 g IV q6h + azithromycin (or doxycycline 100 mg PO BID)
- if penicillin/cephalosporin allergy: levofloxacin 750 mg PO/IV daily (or moxifloxacin 400 mg PO daily)
- if aspiration risk: amoxicillin-clavulanate 1.2 g IV q8h — routine anaerobic cover not recommended for simple aspiration
- if ICU admission: ceftriaxone 2 g IV daily + azithromycin 500 mg IV daily (never fluoroquinolone monotherapy)
- if ICU + pseudomonal risk factors: piperacillin-tazobactam 4.5 g IV q6h + azithromycin 500 mg IV daily (or levofloxacin 750 mg IV daily)
- step down to PO when: afebrile ≥48 h, tolerating oral intake, improving clinically
- duration: minimum 5 days — afebrile ≥48 h + no more than 1 sign of clinical instability before stopping
Empiric choices reflect Canadian resistance patterns and ATS/IDSA 2019 guidelines. Always check your institution’s local antibiogram — macrolide resistance in S. pneumoniae varies significantly between centres.
severity assessment
CURB-65
| criterion | points |
|---|---|
| Confusion (AMT ≤8 or new disorientation) | 1 |
| Urea >7 mmol/L | 1 |
| Respiratory rate ≥30/min | 1 |
| Blood pressure: SBP <90 or DBP ≤60 mmHg | 1 |
| age ≥65 | 1 |
| score | disposition |
|---|---|
| 0–1 | outpatient (mortality <3%) |
| 2 | short-stay / ward admission |
| 3–5 | ward or ICU (mortality 15–40%) |
ATS/IDSA major criteria for direct ICU: invasive mechanical ventilation or vasopressors. Minor criteria (≥3 → ICU): RR ≥30, PaO₂/FiO₂ ≤250, multilobar infiltrates, confusion, uraemia, leucopaenia, thrombocytopaenia, hypothermia, hypotension requiring fluids.
empiric therapy by setting
outpatient — no comorbidities
- amoxicillin 1 g PO TID × 5 days
- alternative: doxycycline 100 mg PO BID × 5 days
- azithromycin 500 mg day 1 → 250 mg days 2–5 only if local pneumococcal macrolide resistance <25%
outpatient — with comorbidities
Comorbidities = chronic heart, lung, liver, or renal disease; diabetes; alcoholism; malignancy; asplenia.
- amoxicillin-clavulanate 875/125 mg PO BID (or cefuroxime 500 mg PO BID) + azithromycin or doxycycline
- or respiratory fluoroquinolone monotherapy: levofloxacin 750 mg PO daily or moxifloxacin 400 mg PO daily
inpatient — ward (non-severe)
- ceftriaxone 2 g IV daily + azithromycin 500 mg PO/IV daily
- or ampicillin 2 g IV q6h + azithromycin/doxycycline
- or respiratory fluoroquinolone monotherapy
β-lactam monotherapy (without macrolide) is non-inferior for non-severe CAP — CAP-START (2015) showed no difference in 90-day mortality. Consider if macrolide contraindicated (QTc prolongation, drug interactions).
inpatient — ICU
- ceftriaxone 2 g IV daily + azithromycin 500 mg IV daily — always combination therapy
- never fluoroquinolone monotherapy in ICU
- if pseudomonal risk (structural lung disease, prior Pseudomonas isolation, recurrent courses of antibiotics): piperacillin-tazobactam 4.5 g IV q6h or cefepime 2 g IV q8h or meropenem 1 g IV q8h + anti-pseudomonal fluoroquinolone or aminoglycoside
- if MRSA risk (prior MRSA, recent influenza, cavitary infiltrate, empyema): add vancomycin or linezolid — de-escalate promptly if cultures negative
penicillin allergy pathway
| allergy history | approach |
|---|---|
| GI upset, non-immune side effects | not a true allergy — use cephalosporins freely |
| distant mild rash (>10 years ago) | cephalosporin cross-reactivity <2% — ceftriaxone generally safe |
| confirmed anaphylaxis / severe reaction | respiratory fluoroquinolone (levofloxacin 750 mg or moxifloxacin 400 mg) |
| severe allergy + ICU | levofloxacin 750 mg IV + aztreonam 2 g IV q8h |
duration
| setting | standard | short-course evidence |
|---|---|---|
| outpatient | 5 days | — |
| ward (non-severe) | 5 days minimum | 3 days if stable at 72 h — PTC (2021): non-inferior to 8 days |
| ICU / severe | 7 days | no short-course data for severe CAP |
| empyema / abscess | 2–6 weeks | guided by drainage and imaging response |
Clinical stability criteria (all must be met before stopping): temperature <37.8°C, HR <100, RR <24, SBP ≥90, SpO₂ ≥90% on room air, tolerating PO, normal mental status.
adjunctive corticosteroids
CAPE COD (2023): hydrocortisone 200 mg/day IV × 4 days then taper (8 days total) in severe CAP (PSI class ≥IV or CURB-65 ≥3) reduced 28-day mortality (NNT ~14). Excluded immunocompromised, influenza, and aspiration.
Not indicated for non-severe CAP. Watch for hyperglycaemia, superinfection, and GI bleeding.
when to broaden
- no improvement by 48–72 h → repeat cultures, CT chest (abscess? empyema? alternative diagnosis?)
- parapneumonic effusion >1 cm → diagnostic thoracentesis (pH, glucose, LDH, gram stain, culture)
- complicated parapneumonic effusion or empyema → chest tube drainage + extended antibiotics
traps
- sputum culture is low-yield in CAP and not recommended routinely for outpatients or non-severe inpatients — obtain only if MRSA/pseudomonal risk or failure to improve
- do not cover anaerobes for aspiration pneumonia unless lung abscess or empyema — Ott (2019) showed no benefit of routine anaerobic cover
- procalcitonin <0.25 µg/L suggests viral aetiology but does not safely exclude bacterial CAP in the acutely ill — use clinical judgement
- Legionella urinary antigen detects only serogroup 1 (~70% of cases) — send if epidemiological risk (travel, water exposure, outbreak) and consider empiric macrolide cover
- do not switch to fluoroquinolone solely because a patient has a penicillin “allergy” documented as GI upset — assess the allergy properly
- CURB-65 underestimates severity in young patients — use clinical judgement and ATS/IDSA minor criteria alongside