A 35-year-old otherwise healthy woman presents with 3 days of fever, productive cough and pleuritic chest pain. Vital signs: temperature 38.4 °C, respiratory rate 22 breaths/min, blood pressure 118/70 mmHg, oxygen saturation 96% on room air. CURB-65 score is 0. She can tolerate oral medications and prefers home treatment. According to Australian community-acquired pneumonia guidance, which is the most appropriate first-line antibiotic?