Pathophysiology
Clinical meaning
The clinician prescribes outpatient CAP antibiotics based on patient comorbidity status and local resistance patterns. For previously healthy adults without recent antibiotic use, amoxicillin 1g TID is first-line (Canadian guidelines). For patients with comorbidities (COPD, diabetes, CKD, alcoholism, immunosuppression) or recent antibiotic use within 3 months, amoxicillin-clavulanate 875/125 BID plus a macrolide (azithromycin) or a respiratory fluoroquinolone (moxifloxacin, levofloxacin) as monotherapy are recommended. Duration of therapy is typically 5-7 days, guided by clinical response and procalcitonin levels. The clinician must consider drug allergies (cross-reactivity between penicillins and cephalosporins is < 2% with 3rd/4th generation), drug interactions (macrolides and QT prolongation, fluoroquinolones and warfarin), and patient factors (pregnancy, renal function, age).