A 62-year-old man with COPD and chronic bronchiectasis presents with acute exacerbation characterized by purulent sputum, fever, and dyspnea. Sputum culture grows Pseudomonas aeruginosa sensitive to all antipseudomonal agents. What is the drug of choice for this respiratory tract infection?

Explanation

## Drug of Choice for Pseudomonas aeruginosa Respiratory Infection **Key Point:** Pseudomonas aeruginosa respiratory infections, particularly in hospitalized or severely ill patients, require combination therapy with an antipseudomonal beta-lactam plus an aminoglycoside for synergy and to prevent resistance emergence. ### Rationale for Combination Therapy **High-Yield:** The gold standard for serious P. aeruginosa infections (respiratory, bloodstream, urinary in hospitalized patients) is **dual therapy**: an antipseudomonal beta-lactam (piperacillin-tazobactam, ceftazidime, or carbapenems like meropenem) PLUS an aminoglycoside (gentamicin, amikacin, or tobramycin). **Clinical Pearl:** Combination therapy achieves: - Synergistic bactericidal activity - Reduced risk of resistance emergence during therapy - Better outcomes in severe infections and immunocompromised hosts - Broader coverage of heterogeneous P. aeruginosa populations ### Comparison of Monotherapy Options (Why They Fall Short) | Agent | Role | Limitation in P. aeruginosa | | --- | --- | --- | | Ceftazidime | Antipseudomonal beta-lactam | Monotherapy insufficient for serious infections; resistance risk | | Piperacillin-tazobactam | Antipseudomonal beta-lactam + beta-lactamase inhibitor | Monotherapy insufficient for serious infections; resistance risk | | Fluoroquinolone (ciprofloxacin) | Oral/IV option, lung penetration | Monotherapy only for mild infections; high resistance rates; inferior outcomes in severe disease | | **Combination (beta-lactam + aminoglycoside)** | **Synergistic dual therapy** | **Gold standard for serious infections** | **Warning:** Do NOT use monotherapy with a single agent for serious P. aeruginosa infections in hospitalized or critically ill patients — this significantly increases resistance and treatment failure risk. ### Clinical Context This patient has: - Chronic lung disease (bronchiectasis) — high P. aeruginosa colonization risk - Acute exacerbation with systemic symptoms (fever, dyspnea) - Likely hospitalization-level severity These factors mandate combination therapy. **Mnemonic:** **PABA** = **P**seudo **A**lways needs **B**eta-lactam + **A**minoglycoside (for serious infections) [cite:KD Tripathi 8e Ch 58]