A 48-year-old woman with a 6-week history of nasal obstruction, postnasal drip, and recurrent episodes of purulent rhinorrhea is diagnosed with chronic rhinosinusitis unresponsive to saline irrigation and intranasal corticosteroids. Culture of sinus secretions grows *Pseudomonas aeruginosa* and *Staphylococcus aureus*. What is the drug of choice for this case?

Explanation

## Treatment of Chronic Rhinosinusitis with *Pseudomonas aeruginosa* **Key Point:** When culture of sinus secretions documents *Pseudomonas aeruginosa*, **ciprofloxacin** is the drug of choice among oral agents, as it is the only widely available oral fluoroquinolone with reliable anti-pseudomonal activity. ### Why Ciprofloxacin Is the Correct Choice | Feature | Ciprofloxacin | Moxifloxacin | Cefixime | TMP-SMX | |---------|---------------|-------------|----------|----------| | **P. aeruginosa coverage** | **Good (DOC oral)** | **Poor/None** | Poor | Poor | | **S. aureus coverage** | Good (MSSA) | Excellent | Moderate | Moderate | | **Oral bioavailability** | ~70% | ~90% | ~50% | Good | | **Anti-pseudomonal activity** | **Yes** | **No** | No | No | **High-Yield:** Moxifloxacin is a **respiratory fluoroquinolone** with excellent gram-positive and anaerobic coverage, but it has **negligible activity against *Pseudomonas aeruginosa***. This is a well-established pharmacological fact (KD Tripathi 8e, Ch 49; Mandell's Principles of Infectious Diseases). Using moxifloxacin when *Pseudomonas* is the documented pathogen would represent a significant therapeutic error. ### Why Other Options Are Incorrect - **Moxifloxacin (A):** Despite excellent sinus penetration and broad-spectrum activity, moxifloxacin lacks meaningful anti-pseudomonal activity and should NOT be used when *P. aeruginosa* is documented. - **Cefixime (C):** A third-generation oral cephalosporin with poor *Pseudomonas* coverage; not appropriate here. - **TMP-SMX (D):** No reliable activity against *Pseudomonas aeruginosa*; not appropriate. ### Clinical Context **Chronic sinusitis with culture-documented *Pseudomonas aeruginosa*:** Ciprofloxacin 500–750 mg twice daily orally for 14–21 days is the standard oral agent of choice. For severe or refractory cases, IV anti-pseudomonal β-lactams (piperacillin-tazobactam, ceftazidime) may be required. **Clinical Pearl:** Among all oral antibiotics, ciprofloxacin is uniquely positioned as the drug of choice for *Pseudomonas aeruginosa* infections. Moxifloxacin and levofloxacin (respiratory fluoroquinolones) are preferred for pneumococcal/atypical coverage but must never be relied upon for *Pseudomonas* coverage. [cite: KD Tripathi Essentials of Medical Pharmacology 8e Ch 49; Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases 9e]