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Difficulty: HardInfectious Diseases

During bedside rounds on the medical ward, the care team evaluates a 28-year-old woman who is currently on her third day of hospitalization for acute pyelonephritis. At the time of admission, she reported right-sided flank pain, nausea, and subjective fevers, prompting the initiation of empiric intravenous ceftriaxone. Her symptoms have now completely resolved, and she has been tolerating a regular diet since yesterday evening. Vital signs are temperature 37.1°C (98.8°F), blood pressure 118/76 mm Hg, pulse 78/min, and respirations 14/min. The urine culture collected on admission has finalized, demonstrating >105> 10^5 CFU/mL of *Escherichia coli*. Antimicrobial susceptibility testing indicates that the isolate is resistant to ampicillin and ciprofloxacin, but is susceptible to ceftriaxone, trimethoprim-sulfamethoxazole, nitrofurantoin, and meropenem. Which of the following is the most appropriate next step in management?

  1. Transition to oral trimethoprim-sulfamethoxazoleAnswer
  2. B
    Transition to oral nitrofurantoin
  3. C
    Continue intravenous ceftriaxone to complete a 10-day course
  4. D
    Transition to oral ciprofloxacin
  5. E
    Transition to intravenous meropenem

Answer

Transition to oral trimethoprim-sulfamethoxazole
The correct action is to transition the patient to oral trimethoprim-sulfamethoxazole. The patient's clinical improvement (resolution of fever and pain, ability to tolerate oral intake) indicates she is ready for intravenous-to-oral step-down therapy. Among the susceptible options, trimethoprim-sulfamethoxazole is the optimal choice as it possesses high oral bioavailability and achieves excellent therapeutic concentrations within the renal parenchyma to successfully treat acute pyelonephritis.

Step-by-Step Solution

1
Assess the patient's clinical trajectory and readiness for step-down therapy.
The patient is afebrile, her flank pain has resolved, and she is tolerating a regular diet.
Clinical stability dictates the timing for transitioning from intravenous to oral antimicrobial therapy to facilitate hospital discharge and reduce catheter-related risks.
2
Analyze the antimicrobial susceptibility profile of the isolated pathogen.
The E. coli isolate is susceptible to ceftriaxone, trimethoprim-sulfamethoxazole, and nitrofurantoin, but resistant to ampicillin and ciprofloxacin.
Targeted oral therapy must be guided by in vitro susceptibility to ensure successful eradication of the infection.
3
Select the most appropriate oral agent that achieves therapeutic concentrations in the affected tissue.
Oral trimethoprim-sulfamethoxazole is chosen over nitrofurantoin.
Trimethoprim-sulfamethoxazole penetrates the renal parenchyma effectively. Nitrofurantoin only concentrates in the bladder and is inadequate for upper urinary tract infections like pyelonephritis.

Key Concept

Intravenous to oral antimicrobial transition in pyelonephritis and the pharmacokinetic limitations of nitrofurantoin.
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Topics

Infectious Diseases

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