A 55-year-old male with poorly differentiated squamous cell carcinoma of the right upper lung develops leukopenia (WBC count <0.5×10⁹/L, neutrophils <0.5×10⁹/L) after chemotherapy. He has had cough and high fever for 3 days. X-ray examination shows shrinkage of the right upper lung mass and dense consolidation in the right mid-lower lung fields. Which of the following empiric antibiotic therapies is inappropriate before obtaining microbiological results?