A 52-year-old man from Delhi presents with a 5-day history of fever, productive cough with purulent sputum, and dyspnea. Chest X-ray shows bilateral interstitial infiltrates with a reticular pattern. Blood cultures are sterile. Sputum Gram stain shows scanty gram-negative cocci. PCR for Chlamydia pneumoniae is positive. The patient is allergic to penicillins. What is the most appropriate next step in management?