A 72-year-old man with COPD and increased cough, purulent sputum and dyspnoea for 3 days presents to the ED. He is afebrile, RR 24/min, SpO₂ 91% on room air, and has no signs of pneumonia. This is his second moderate exacerbation this year. What is the most appropriate pharmacologic management in addition to inhaled bronchodilators and oxygen?