Pneumonia USMLE Step 1 Practice Question

A 28-year-old previously healthy woman presents to the emergency department with a 3-day history of fever, productive cough, and sharp pleuritic chest pain. She reports mild dyspnea on exertion. Vital signs: temperature 39.2°C, heart rate 118/min, respiratory rate 22/min, blood pressure 128/76 mmHg, oxygen saturation 88% on room air. Physical examination reveals decreased breath sounds and dullness to percussion over the right lower lobe. Chest X-ray shows a right lower lobe consolidation without pleural effusion. Laboratory studies: WBC 14,500/μL, procalcitonin 2.8 ng/mL. She denies recent antibiotic exposure, intravenous drug use, and immunosuppression. Blood cultures have been obtained and are pending. Which of the following is the most appropriate initial empiric antibiotic regimen for this patient's community-acquired pneumonia?