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Mechanistic Deep Dive
Pseudomonas Pathogenicity
- Biofilm formation
- Quorum sensing
- Type III secretion system
- Efflux pumps + porin downregulation
- Multidrug resistance challenge
Carbapenemase Production
- KPC (most common in US/Europe)
- NDM (Asian/Indian subcontinent)
- OXA-48 (Middle East, Europe)
- VIM, IMP
- Distinct enzymatic mechanisms
- Influences antibiotic choice
MRSA + USA300/USA400
- Genetic background
- PVL toxin (necrotizing pneumonia, severe)
- mecA gene
- Vanc + linezolid first-line
Recent Trials & Updates
ASPECT-NP (2019) â Ceftolozane-Tazobactam
- HAP/VAP including Pseudomonas
- Non-inferior to meropenem
- Approved for HAP/VAP
APEKS-NP (2020) â Cefiderocol
- HAP/VAP
- Increased mortality signal in critically ill
- Reserved for MDR Gram-negative
CREDIBLE-CR (2020) â Cefiderocol vs Best Available for CRE
- Higher mortality in cefiderocol arm (Acinetobacter-driven)
- Reserve usage
Procalcitonin Studies
- Multiple RCTs
- â Antibiotic duration without harm
- VAP/HAP applicable
Linezolid vs Vancomycin
- ZEPHyR study: equivalent for MRSA pneumonia
- Linezolid possibly slight benefit in MRSA pneumonia (lung penetration)
- Cost + thrombocytopenia considerations
Inhaled Antibiotics for VAP
- Tobramycin, colistin, amikacin
- Adjunctive in severe / MDR
- Mixed evidence (IASIS, INHALE)
High-Yield Specialist Points
Daptomycin in Pneumonia
- AVOID â inactivated by pulmonary surfactant
- Use vancomycin or linezolid instead
Vancomycin Pharmacokinetics
- AUC/MIC target: 400-600 (newer)
- Trough 15-20 ÎŒg/mL (older)
- Loading dose 25-30 mg/kg
- Maintenance based on renal function
MRSA Pneumonia Pathology
- Often necrotizing
- Cavitation
- PVL-producing strains
- Severe + multilobar
Linezolid + Serotonin Syndrome
- Reversible MAO inhibitor
- Caution with SSRIs, MAOIs
- Watch for serotonin syndrome
Inhaled Tobramycin / Colistin
- Adjunct for MDR Pseudomonas / Acinetobacter VAP
- Reduces resistance development
- Mixed efficacy evidence
Carbapenem Choices
- Ertapenem: NOT anti-Pseudomonas (unique)
- Imipenem-cilastatin: anti-Pseudomonas; lower seizure threshold
- Meropenem: anti-Pseudomonas; better tolerated
- Doripenem: rare use now (DORI-10 mortality concern)
ESBL vs CRE vs Carbapenemase
- ESBL: carbapenem-susceptible; treat with meropenem
- CRE: carbapenem-resistant; ceftaz-avibactam, meropenem-vaborbactam
- Carbapenemase types: KPC, NDM, OXA-48
- Specific enzymes affect choice
Aspergillus in Critically Ill
- Invasive pulmonary aspergillosis (IPA) in ICU
- CAPA (COVID-associated) + IAPA (influenza-associated)
- Bronchoscopy + galactomannan
- Voriconazole / isavuconazole
COVID-19 VAP
- Increased risk
- Prolonged ventilation, steroids, immunomodulators
- Standard empiric + consider Aspergillus
- Microbiologic confirmation important
Drug Allergy Considerations
- Penicillin allergy: cross-reactivity with cephalosporins low (< 5% with 3rd-gen)
- Carbapenems: < 1% cross-reactivity
- Aztreonam: no cross-reactivity (monobactam)
- Severe IgE-mediated: avoid β-lactams entirely
Multidrug-Resistant Pseudomonas
- Limited options
- Ceftolozane-tazo, ceftazidime-avibactam, cefiderocol
- Tobramycin + meropenem combo
- Consult ID
Pearls
- HAP/VAP: ⥠48 h after admission / intubation
- HCAP RETIRED (2016)
- MDR risk factors: recent IV abx, septic shock, ARDS, prolonged hosp, MRSA/Pseudo colonization
- Empiric: anti-Pseudo β-lactam + MRSA cover (vanc / linezolid)
- High MDR risk: double anti-Pseudo
- Duration: 7 days for most (PneumA)
- Daptomycin NOT for pneumonia (surfactant inactivates)
- Vancomycin trough: 15-20 (or AUC 400-600)
- Modern anti-MDR: ceftaz-avibactam, meropenem-vaborbactam, cefiderocol
- VAP prevention bundle: HOB 30-45°, SAT/SBT, oral care, subglottic suction