Question

A $62$-year-old man with a history of alcohol-associated cirrhosis and hepatic encephalopathy is evaluated on hospital day $4$. He was initially admitted for fever, worsening confusion, and diffuse abdominal pain. On admission, diagnostic paracentesis revealed an ascitic fluid absolute neutrophil count of $750/\text{mm}^3$, consistent with spontaneous bacterial peritonitis (SBP). Because the patient had been hospitalized three weeks prior for a variceal bleed, empiric therapy was initiated with intravenous piperacillin-tazobactam, and he was given intravenous albumin. Today, his temperature is $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), blood pressure is $112/68\text{ mm Hg}$, and pulse is $78/\text{min}$. He is alert, oriented, and reports that his abdominal pain has completely resolved. Ascitic fluid cultures drawn on admission have grown *Escherichia coli*. Susceptibility testing demonstrates that the organism is susceptible to ceftriaxone, cefotaxime, ciprofloxacin, and piperacillin-tazobactam; it is resistant to ampicillin. Which of the following is the most appropriate next step in the pharmacologic management of this patient's infection?