Decision support only — doses are eTG-aligned for Australian adults with normal renal function, but local hospital protocols and antibiograms vary (and severe-CAP regimens differ between sites). Severity assessment and the penicillin-allergy label drive the choice as much as the doses. Always check renal function, weight, allergy, and local guidance. Verify all doses.
1 Community-acquired pneumonia — by severity (eTG)
Low severityoutpatient
Well, no severity features (CORB 0–1).
Amoxicillin 1 g PO tds (5 days). Add doxycycline 100 mg PO bd if comorbidity, atypical suspected, or not improving. Allergy → doxycycline or clarithromycin alone.
Moderate severityward
Needs admission, not ICU.
Benzylpenicillin 1.2 g IV q6h + doxycycline 100 mg PO bd (or azithromycin 500 mg IV/PO daily). Step down to amoxicillin 1 g PO tds + doxycycline when improving.
High severityICU / IRVS
SMART-COP ≥3 / needs respiratory or vasopressor support.
Ceftriaxone 2 g IV daily + azithromycin 500 mg IV daily. Severe penicillin allergy → moxifloxacin 400 mg IV daily (± azithromycin). Some sites use benzylpenicillin + gentamicin + azithromycin.
Tropical / severeNorthern Australia
Severe CAP in the wet-season tropics or melioidosis risk.
Cover Burkholderia pseudomallei (melioidosis) & Acinetobacter: meropenem 1 g IV q8h + azithromycin 500 mg IV daily (± gentamicin per local advice).
Assess severity with the Australian tools (CORB / SMART-COP), not just CURB-65 — SMART-COP predicts the need for intensive respiratory/vasopressor support. Doxycycline is preferred over a macrolide when an atypical agent is needed (fewer interactions, less C. difficile). Treat for 5 days if clinically stable.
2 Hospital-acquired pneumonia — by resistance risk (eTG)
Low Pseudomonas riskearly, no MDR risk
HAP without risk factors for resistant organisms.
Ceftriaxone 2 g IV daily (monotherapy). Cefotaxime is an alternative.
↑ Pseudomonas / MDR riskor severe
Recent broad-spectrum abx, prolonged stay, colonisation, structural lung disease, immunosuppression.
Piperacillin-tazobactam 4.5 g IV q6h (extended 3h infusion) or cefepime 2 g IV q8h; meropenem 1 g IV q8h if MDR Gram-negative risk.
MRSA riskadd cover
Known colonisation, prior MRSA, correctional-facility residence, high local prevalence.
Add vancomycin 15–20 mg/kg IV q8–12h (level-guided; loading dose if severe) — or linezolid.
Review at 48hdon't set-and-forget
Cultures back, trajectory clearer.
Reassess the diagnosis; de-escalate to cultures; stop if HAP/VAP isn't supported. Usual course 7 days.
HAP = pneumonia ≥48h after admission; VAP = ≥48h after intubation. The 2025 eTG stratifies by Pseudomonas risk and emphasises reviewing the diagnosis at 48h rather than reflexively continuing broad therapy. A 7-day course is non-inferior to longer for most.
3 Severity, site of care & duration
Australian severity tools
- CORBConfusion, O₂ sat ≤90%, RR ≥30, BP (SBP <90 / DBP ≤60). ≥2 → severe.
- SMART-COPWeighted score predicting need for intensive respiratory/vasopressor support; ≥3 → high risk.
- CURB-65Familiar internationally; eTG prefers CORB/SMART-COP + clinical red flags.
- SiteSeverity + social factors decide outpatient vs ward vs ICU — not the score alone.
Duration & the switch
- CAP5 days if stable — afebrile, improving, stable obs. Longer only for complications/unusual organisms.
- HAP/VAP7 days for most; review at 48h.
- IV→oralSwitch when improving, haemodynamically stable, and tolerating oral.
- De-escalateNarrow to culture results at 48–72h; stop atypical cover if excluded.
4 Pathogens, adjuncts & the traps
Bugs & adjuncts
- TypicalPneumococcus, H. influenzae, Moraxella.
- AtypicalMycoplasma, Chlamydophila, Legionella (more in severe) — doxycycline/macrolide.
- InfluenzaIn season → add oseltamivir; droplet precautions.
- SteroidsHydrocortisone in severe CAP reduces mortality CAPE COD — not in non-severe disease.
Don't miss
- EffusionParapneumonic effusion/empyema → tap it; pH <7.2 or pus → drain (see pleural sheet).
- Not resolvingReconsider TB, malignancy, abscess, wrong organism, or the wrong diagnosis.
- HostImmunocompromise → think PJP, fungi; tropical → don't under-treat melioidosis.
- AllergyMost "penicillin allergy" labels are not true allergy — delabelling widens safer, narrower options.
Sources.
Therapeutic Guidelines (eTG) — Antibiotic: community-acquired & hospital-acquired pneumonia (Australian empirical regimens & doses; CORB/SMART-COP severity; tropical/melioidosis cover; March 2025 update — ceftriaxone 2 g preferred, VAP stratified by Pseudomonas risk, review at 48h). ATS/IDSA CAP 2019 + 2025 update; ERS/ESICM 2023 severe CAP; ATS/IDSA HAP/VAP 2016.
Key evidence: CAPE COD (hydrocortisone reduces mortality in severe CAP); short-course (5-day CAP / 7-day HAP) non-inferiority trials; doxycycline-vs-macrolide non-inferiority.
Caveats: regimens are eTG-aligned but local protocols vary — several Australian hospitals use benzylpenicillin + gentamicin + azithromycin for severe CAP. Doses assume normal renal function and adult weight — adjust for CrCl (esp. vancomycin, meropenem, oseltamivir). Tropical/Northern-Australia therapy differs by melioidosis & Acinetobacter risk. Verify everything against eTG and your antimicrobial-stewardship team. Companion to the respiratory set (bronchiectasis, pleural disease).