A 64-year-old woman presents to the emergency department with fever, productive cough, and pleuritic chest pain for 2 days. Vitals: temperature 101.8 F, blood pressure 128/74 mmHg, heart rate 104 per minute, respiratory rate 22 per minute, oxygen saturation 95 percent on room air. She has no comorbidities or recent antibiotic use. Chest radiograph shows a right lower lobe infiltrate. What is the most appropriate empiric outpatient antibiotic regimen?