Sequential antimicrobial therapy, also known as intravenous to oral antimicrobial switching, should be considered in patients who have an intact and functioning gastrointestinal tract and whose clinical status is improving. This patient meets criteria for changing from intravenous ceftriaxone to an oral antimicrobial agent to complete the course of treatment for Escherichia coli pyelonephritis. When making a parenteral-to-oral antimicrobial switch, the bioavailability of the oral antimicrobial option is important and depends on the infection being treated. In patients with bacteremia, an agent with excellent bioavailability should be used (quinolones, trimethoprim-sulfamethoxazole, metronidazole, clindamycin, linezolid). Trimethoprim-sulfamethoxazole has excellent bioavailability, so it is the oral antimicrobial agent of choice.

Oral ciprofloxacin would be an option for this patient rather than intravenous. However, ciprofloxacin has a broader spectrum of activity than trimethoprim-sulfamethoxazole, so it would not be preferred. The most focused, narrowest-spectrum agent possible is preferred when an antimicrobial agent is prescribed.

Nitrofurantoin is used for acute, uncomplicated urinary tract infections. It is not adequate treatment for pyelonephritis, with or without bacteremia, because active levels are achieved only in the urine and not in the kidney parenchyma.