A 65-year-old man with known Chronic Obstructive Pulmonary Disease (COPD), classified as GOLD Stage D, presents with increased sputum purulence, increased sputum volume, and increased dyspnoea. His oxygen saturation is 91% on room air. He is haemodynamically stable. According to NICE guidelines, what is the most appropriate initial pharmacological management for this exacerbation in primary care?