A 58-year-old man with chronic obstructive pulmonary disease presents to the emergency department with a 3-day history of fever (38.9°C), productive cough with rust-colored sputum, and pleuritic chest pain. He reports recent hospitalization for acute exacerbation of COPD. On examination, he has consolidation on the left lower lobe with dullness to percussion. Chest X-ray confirms left lower lobe pneumonia. Blood cultures grow Gram-positive diplococci that are optochin-sensitive and bile-soluble. The organism is resistant to penicillin (MIC 2 µg/mL). What is the most appropriate empiric antibiotic therapy for this patient?