Question

A $61$-year-old man comes to the primary care clinic reporting a 4-day history of productive cough, subjective fevers, and worsening shortness of breath. He has a past medical history of type 2 diabetes mellitus, opioid use disorder currently managed with maintenance methadone therapy, and major depressive disorder. His other medications include metformin and citalopram. He has no known drug allergies.

Vital signs show a temperature of $38.3^\circ\text{C}$ ($100.9^\circ\text{F}$), heart rate of $94/\text{min}$, blood pressure of $126/82\text{ mm Hg}$, respiratory rate of $20/\text{min}$, and oxygen saturation of $95\%$ on room air. Physical examination reveals bronchial breath sounds and crackles over the left lower lung field.

Laboratory evaluation shows a leukocyte count of $12,500/\text{mm}^3$. A comprehensive metabolic panel is within normal limits. A chest radiograph demonstrates a left lower lobe consolidation. An electrocardiogram obtained in the clinic shows normal sinus rhythm with a QTc interval of $520\text{ ms}$.

Which of the following is the most appropriate empiric pharmacologic intervention for this patient?