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Difficulty: MediumInfectious Diseases

A 35-year-old woman is evaluated in the hospital on day 3 of admission for acute pyelonephritis. She originally presented to the emergency department with a 2-day history of fever, chills, right-sided flank pain, and intractable vomiting. At that time, she was febrile to 39.2°C (102.6°F) and hypotensive. After initial fluid resuscitation, she was empirically started on intravenous vancomycin and piperacillin-tazobactam. Today, her temperature is 37.1°C (98.8°F), blood pressure is 120/78 mm Hg, and pulse is 82/min. Her flank pain has significantly improved, but she continues to experience severe nausea and vomits immediately after attempting to drink any liquids. Blood and urine cultures from admission are now growing *Proteus mirabilis*. Susceptibility testing shows the isolate is intrinsically resistant to nitrofurantoin but susceptible to ampicillin, ceftriaxone, piperacillin-tazobactam, and ciprofloxacin. Which of the following is the most appropriate next step in pharmacotherapy?

  1. A
    Discontinue current antibiotics and initiate oral ciprofloxacin
  2. B
    Discontinue vancomycin and continue intravenous piperacillin-tazobactam
  3. Discontinue current antibiotics and initiate intravenous ceftriaxoneAnswer
  4. D
    Continue intravenous vancomycin and piperacillin-tazobactam
  5. E
    Discontinue piperacillin-tazobactam and continue intravenous vancomycin

Answer

Discontinue current antibiotics and initiate intravenous ceftriaxone
The patient has an uncomplicated *Proteus mirabilis* bacteremia and pyelonephritis that is susceptible to narrow-spectrum agents. According to antimicrobial stewardship guidelines, empiric broad-spectrum therapy (vancomycin and piperacillin-tazobactam) should be de-escalated to the narrowest effective therapy once culture and susceptibility results are known. Intravenous ceftriaxone is highly effective for susceptible Enterobacteriaceae and significantly narrows the spectrum compared to piperacillin-tazobactam. Furthermore, while the patient is hemodynamically stable and afebrile, her intractable vomiting strictly contraindicates the use of oral antibiotics, as gastrointestinal absorption cannot be guaranteed. Therefore, targeted intravenous therapy is required.

Step-by-Step Solution

1
Analyze the culture and susceptibility data.
The patient has a confirmed *Proteus mirabilis* infection that is susceptible to narrow-spectrum beta-lactams (e.g., ceftriaxone, ampicillin).
Identifying the specific pathogen allows for the transition from broad empiric therapy to targeted therapy.
2
Assess the patient's current clinical stability and route of administration feasibility.
The patient is afebrile and hemodynamically stable, which normally prompts a switch to oral therapy. However, she has intractable vomiting.
An intact, functioning gastrointestinal tract is a strict prerequisite for transitioning from intravenous to oral antibiotics.
3
Select the optimal definitive antibiotic regimen.
Intravenous ceftriaxone is selected as the next step in management.
Ceftriaxone provides the necessary targeted, narrow-spectrum Gram-negative coverage while utilizing the mandatory intravenous route, aligning with both infection control and antimicrobial stewardship principles.

Key Concept

Antimicrobial stewardship dictates de-escalating broad-spectrum empiric therapy to the narrowest effective agent based on culture data, while maintaining the intravenous route if the patient has gastrointestinal impairment (e.g., vomiting) that prevents reliable oral absorption.
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Topics

Infectious Diseases

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