Right lower lobe pneumonia with air bronchograms on chest x-ray

A 68-year-old man with type 2 diabetes and COPD presents with 4 days of high-grade fever, rigors, productive cough with rusty sputum, right-sided pleuritic chest pain, and dyspnea. Vital signs: T 39.4°C, HR 118, BP 96/58 mmHg, RR 28, SpO₂ 88% on room air. Examination reveals bronchial breath sounds, increased vocal resonance, and crackles in the right lower zone. Frontal chest X-ray shows dense homogeneous consolidation in the right lower zone with preserved lucent branching air bronchograms (marked **A**), obscured right hemidiaphragm, and preserved right heart border. Blood cultures grow Streptococcus pneumoniae. Which of the following is the most appropriate initial antibiotic regimen for this patient with severe community-acquired pneumonia?