A 55-year-old man presents with 3 days of fever, productive cough with green sputum and pleuritic chest pain. He is a non-smoker with no significant comorbidities. Observations: temperature 38.3 °C, blood pressure 130/80 mmHg, heart rate 96 beats/min, respiratory rate 20 breaths/min, oxygen saturation 97% on air. Chest examination reveals localised crackles in the right lower zone. He is well enough to be managed as an outpatient. According to Australian antibiotic guidelines, what is the most appropriate empiric treatment?