Empiric Antibiotic Selection: Site-Based Algorithms

Empiric antibiotic therapy is the initiation of antimicrobial treatment before the causative pathogen is identified, guided by the most likely organisms for a given infection site, local resistance patterns (antibiogram), infection severity, and patient-specific factors. The NP must understand that each anatomical site has a predictable microbiological 'ecosystem' that drives empiric selection. Community-acquired pneumonia (CAP): typical pathogens include Streptococcus pneumoniae (most common), Haemophilus influenzae, and Moraxella catarrhalis; atypical pathogens include Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila. Outpatient CAP is treated with amoxicillin (first-line for typical coverage) plus a macrolide (azithromycin for atypical coverage), or respiratory fluoroquinolone monotherapy (levofloxacin or moxifloxacin) for penicillin-allergic patients or those with comorbidities. Inpatient non-ICU CAP uses a beta-lactam (ceftriaxone or ampicillin-sulbactam) plus macrolide, or respiratory fluoroquinolone alone. ICU CAP requires a beta-lactam PLUS either macrolide or fluoroquinolone; add anti-pseudomonal coverage (piperacillin-tazobactam, cefepime, or meropenem) if risk factors for Pseudomonas exist (structural lung disease, COPD with frequent antibiotics, immunosuppression). Urinary tract infections: uncomplicated cystitis is treated with nitrofurantoin (first-line) or trimethoprim-sulfamethoxazole (if local resistance <20%); fluoroquinolones are reserved for complicated UTI or pyelonephritis. Intra-abdominal infections...