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Difficulty: EasyInfectious Diseases

During morning rounds, a 30-year-old nulligravid patient is evaluated for discharge planning. She was admitted to the general medical ward 48 hours ago for acute pyelonephritis and was started on empiric intravenous ceftriaxone. She has shown rapid clinical improvement; she is now afebrile, her right-sided costovertebral angle tenderness has completely resolved, and she is eating a regular diet without nausea. The urine culture collected at admission grew >100,000>100,000 CFU/mL of *Escherichia coli*. The susceptibility report is as follows:

AntimicrobialInterpretation
CephalexinSusceptible
CiprofloxacinSusceptible
NitrofurantoinSusceptible
Trimethoprim-sulfamethoxazoleResistant

Based on principles of antimicrobial stewardship, which of the following is the most appropriate next step in pharmacological management?

  1. Transition to oral cephalexinAnswer
  2. B
    Transition to oral ciprofloxacin
  3. C
    Transition to oral nitrofurantoin
  4. D
    Transition to oral trimethoprim-sulfamethoxazole
  5. E
    Continue intravenous ceftriaxone via outpatient parenteral therapy

Answer

Transition to oral cephalexin
This patient presented with acute pyelonephritis and has rapidly improved on empiric intravenous antibiotics. Because she is afebrile, clinically stable, and tolerating an oral diet, she is an excellent candidate for step-down therapy to oral antibiotics. According to the principles of antimicrobial stewardship, definitive therapy should utilize the narrowest-spectrum agent that is effective and has appropriate tissue penetration for the site of infection. Cephalexin, a first-generation cephalosporin, perfectly fits these criteria: it provides targeted coverage against the susceptible E. coli isolate and achieves excellent concentrations in the renal parenchyma.

Step-by-Step Solution

1
Evaluate the patient's clinical trajectory and current stability.
The patient is afebrile, her pain has resolved, and she tolerates oral intake, indicating readiness for transition from intravenous to oral antibiotics.
Intravenous to oral step-down therapy reduces hospital length of stay and avoids line-associated complications in clinically stable patients.
2
Analyze the urine culture susceptibility report.
The pathogen is susceptible to cephalexin, ciprofloxacin, and nitrofurantoin, but resistant to trimethoprim-sulfamethoxazole.
Guiding definitive therapy based on culture results ensures eradication while minimizing resistance.
3
Select the most appropriate oral agent based on site of infection and antimicrobial stewardship principles.
Cephalexin is selected because it is a narrow-spectrum oral agent with excellent renal tissue penetration.
Nitrofurantoin cannot be used for upper urinary tract infections, and ciprofloxacin is overly broad when a first-generation cephalosporin is effective.

Key Concept

In patients with acute pyelonephritis who demonstrate clinical improvement and tolerate oral intake, intravenous antibiotics should be transitioned to the narrowest-spectrum effective oral agent based on culture susceptibility.
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Infectious Diseases

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