The most appropriate initial antimicrobial therapy for this patient?

A 12-year-old boy with cystic fibrosis presents to the emergency department with a 3- day history of severe coughing, which is productive of a yellow-greenish purulent sputum. He had fever and chills at home. He also complains of chest congestion and chest pain that is worse with coughing. On physical examination, his temperature is 39.6 C (103.2 F), blood pressure is 98/68 mm Hg, pulse is 102/min, and respirations are 24/min. He is noted to be lethargic. He has rales on the left lower lung field on auscultation, and chest radiography shows an infiltrate in the left lower lobe. Which of the following is the most appropriate initial antimicrobial therapy for this patient?

(A) Amoxicillin-clavulanate and gentamicin

(B) Azithromycin and ceftriaxone

© Ceftazidime and tobramycin

(D) Levofloxacin and metronidazole

(E) Trimethoprim-sulfamethoxazole and vancomycin