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Difficulty: MediumInfectious Diseases

A 62-year-old woman is evaluated in the hospital on hospital day 3. She was initially admitted with fever, chills, severe right flank pain, and dysuria. On admission, her temperature was 39.1°C (102.4°F), heart rate was 112/min, and blood pressure was 105/65 mmHg. Physical examination revealed pronounced right costovertebral angle tenderness. Laboratory studies showed a leukocyte count of 16,500/mm³. Due to a history of an extended-spectrum beta-lactamase (ESBL)-producing *Escherichia coli* urinary tract infection two years ago, she was empirically started on intravenous meropenem. Today, her temperature is 37.1°C (98.8°F), her flank pain has significantly improved, and she is tolerating a regular diet. Blood and urine cultures obtained on admission both grow *Escherichia coli*. Susceptibility testing indicates the isolate is resistant to ampicillin, but susceptible to ceftriaxone, trimethoprim-sulfamethoxazole, ciprofloxacin, and meropenem. Which of the following is the most appropriate next step in management?

  1. Transition to oral trimethoprim-sulfamethoxazoleAnswer
  2. B
    Continue intravenous meropenem
  3. C
    Transition to oral nitrofurantoin
  4. D
    Switch to intravenous ceftriaxone
  5. E
    Transition to oral amoxicillin

Answer

The most appropriate next step in management is to transition the patient to oral trimethoprim-sulfamethoxazole.
The correct answer is to transition the patient to oral trimethoprim-sulfamethoxazole. This patient was appropriately started on empiric intravenous meropenem due to her history of an ESBL-producing organism. However, current cultures demonstrate a non-ESBL *Escherichia coli* strain. Because she has shown significant clinical improvement—being afebrile for at least 24 hours, having resolving symptoms, and tolerating oral intake—she meets the criteria for stepping down from intravenous to oral therapy. Trimethoprim-sulfamethoxazole is highly bioavailable, achieves excellent concentrations in the renal parenchyma, and is a narrower-spectrum agent, making it the ideal choice to complete her treatment course and facilitate hospital discharge.

Step-by-Step Solution

1
Assess the patient's clinical trajectory and current status.
The patient with acute pyelonephritis and bacteremia has shown clear clinical improvement; she is now afebrile, experiencing less pain, and successfully tolerating oral intake.
Clinical stability dictates whether a patient can be safely transitioned from intravenous to oral therapy.
2
Evaluate the microbiology and susceptibility data.
Cultures grew E. coli susceptible to ceftriaxone, TMP-SMX, and ciprofloxacin, indicating that the current infection is not caused by an ESBL-producing strain.
Objective culture data allows for the de-escalation of empiric broad-spectrum coverage to targeted therapy.
3
Select the optimal targeted antimicrobial agent.
Oral trimethoprim-sulfamethoxazole is selected because it is narrow-spectrum, highly bioavailable, and achieves excellent concentrations in the renal parenchyma.
Antimicrobial stewardship requires utilizing the narrowest effective agent via the least invasive route to minimize resistance, reduce side effects, and facilitate hospital discharge.

Key Concept

In patients with acute pyelonephritis who are clinically stable and tolerating oral intake, empiric intravenous antibiotics should be de-escalated to a targeted, highly bioavailable oral agent (such as trimethoprim-sulfamethoxazole or a fluoroquinolone) based on culture susceptibilities.
Estimated Time:1m 15s
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Infectious Diseases

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