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Difficulty: HardGastroenterology and Hepatology

A 58-year-old man with a history of diet-controlled type 2 diabetes mellitus is evaluated in the hospital on day 3 of admission. He initially presented with progressive left lower quadrant abdominal pain, nausea, and low-grade fever. Computed tomography of the abdomen and pelvis demonstrated inflammation of the sigmoid colon with surrounding fat stranding, consistent with acute uncomplicated diverticulitis. He was admitted and started on empiric intravenous piperacillin-tazobactam. Currently, his temperature is 37.1°C (98.8°F), his abdominal pain has largely resolved, and he is tolerating a regular diet. Blood cultures drawn on admission have grown *Escherichia coli* and *Bacteroides fragilis*. Susceptibility testing reveals that both isolates are susceptible to amoxicillin-clavulanate, ertapenem, and piperacillin-tazobactam. The *E. coli* isolate demonstrates high-level resistance to ciprofloxacin and levofloxacin. Based on these findings, which of the following is the most appropriate next step in pharmacotherapy?

  1. Transition to oral amoxicillin-clavulanateAnswer
  2. B
    Transition to oral ciprofloxacin and metronidazole
  3. C
    Continue intravenous piperacillin-tazobactam
  4. D
    Transition to oral cephalexin and metronidazole
  5. E
    Add intravenous vancomycin to the current regimen

Answer

The most appropriate next step is to transition the patient to oral amoxicillin-clavulanate.
The correct answer utilizes optimal antimicrobial stewardship principles. The patient has met the clinical criteria for IV-to-PO conversion (afebrile, tolerating diet, hemodynamically stable). The culture data definitively rules out the use of a fluoroquinolone-based regimen due to resistance. Amoxicillin-clavulanate is available in an oral formulation, covers both the isolated Gram-negative and anaerobic bacteria, and is explicitly listed as susceptible on the panel. Transitioning to this drug allows for safe, effective outpatient completion of therapy.

Step-by-Step Solution

1
Assess the patient's current clinical trajectory.
The patient is afebrile, his pain has resolved, and he is tolerating oral intake.
These are the criteria for transitioning from intravenous to oral antibiotics and preparing for hospital discharge.
2
Analyze the microbiologic and susceptibility data provided.
Cultures show *E. coli* and *B. fragilis*. The *E. coli* is resistant to fluoroquinolones but susceptible to amoxicillin-clavulanate.
Antimicrobial therapy must be de-escalated and targeted based on objective susceptibility profiles to prevent resistance.
3
Select the narrowest, most effective oral regimen.
Oral amoxicillin-clavulanate covers both organisms effectively based on the lab data.
It acts as a potent, single-agent oral therapy, replacing the need for a broad-spectrum intravenous drug or a multi-drug regimen.

Key Concept

In patients recovering from intra-abdominal infections (like diverticulitis), prompt transition to narrow-spectrum oral antibiotics guided by specific culture and susceptibility data is essential for effective antimicrobial stewardship.
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Topics

Gastroenterology and Hepatology

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