A 45-year-old previously healthy man presents to his GP with a 3-day history of fever, productive cough and pleuritic chest pain. He is febrile at 38.5°C, respiratory rate 20 breaths/min, oxygen saturation 96% on room air and blood pressure 125/75 mmHg. Chest auscultation reveals right basal crackles. He is able to take oral medications and has no significant comorbidities. What is the most appropriate empirical oral antibiotic?