A 60-year-old male underwent subtotal gastrectomy for gastric cancer. On postoperative day 3, he developed high fever, chills, cough with small amounts of purulent sputum, and left lower chest pain. Chest X-ray showed left lower lobe pneumonia with abscess formation. Sputum cultures repeatedly grew Staphylococcus aureus, with drug sensitivity testing showing resistance to oxacillin. Which of the following antibiotic choices is inappropriate?