A 52-year-old man with a 2-week history of persistent cough, low-grade fever (38.2°C), and malaise presents to the respiratory clinic. Chest X-ray shows bilateral interstitial infiltrates with a 'atypical' pattern. Sputum culture on standard media and blood cultures are negative. Serology shows a fourfold rise in antibody titre to Chlamydia pneumoniae between acute and convalescent sera. Which of the following is the most appropriate antimicrobial therapy?