A 72-year-old man with moderate COPD presents with increased dyspnoea, sputum volume and purulent sputum over 3 days. He is afebrile, saturating 94 percent on room air, with mild wheeze on examination. He normally uses a long-acting muscarinic antagonist and a long-acting beta agonist inhaler, and has had one exacerbation in the last year. What is the most appropriate management for this exacerbation?