A 58-year-old man is evaluated in the hospital on day 4 of admission for a pyogenic liver … — USMLE Step 2 CK

A $58$ -year-old man is evaluated in the hospital on day $4$ of admission for a pyogenic liver abscess. He initially presented with a $1$ -week history of right upper quadrant pain, high-grade fever, and chills. On admission, computed tomography of the abdomen revealed a $5.5$ -cm fluid collection in the right hepatic lobe. He underwent prompt percutaneous catheter drainage and was empirically started on intravenous piperacillin-tazobactam.

Over the past $48$ hours, his clinical condition has markedly improved. He is currently tolerating a regular diet and has been afebrile for two days. Current vital signs are:
Temperature: $37.1^\circ C$ ( $98.8^\circ F$ )
Blood pressure: $128/78$ mmHg
Pulse: $76/min$
Respirations: $14/min$

Laboratory results today show a leukocyte count of $8,500/\mu L$ , down from $18,200/\mu L$ on admission. The percutaneous drain is currently putting out $10$ mL of serosanguinous fluid daily.

The abscess fluid culture from day $1$ has finalized and is growing *Streptococcus anginosus*. Susceptibility testing results are as follows:

Antimicrobial Agent	Susceptibility
Ampicillin	Susceptible
Ceftriaxone	Susceptible
Ciprofloxacin	Resistant
Piperacillin-tazobactam	Susceptible
Vancomycin	Susceptible

Which of the following is the most appropriate next step in the pharmacologic management of this patient?

Transition to oral amoxicillinAnswer
B
Continue intravenous piperacillin-tazobactam
C
Transition to oral ciprofloxacin and metronidazole
D
Add intravenous vancomycin
E
Discontinue all antimicrobial therapy

Answer

The most appropriate next step is to transition the patient to oral amoxicillin.

This patient has a pyogenic liver abscess that has been successfully managed with percutaneous catheter drainage (source control) and initial empiric intravenous antibiotics. He is now clinically stable, afebrile for

48

hours, and tolerating a regular diet. These milestones fulfill the clinical criteria for transitioning from intravenous to oral antimicrobial therapy. The abscess fluid culture has identified a monomicrobial infection with *Streptococcus anginosus*, which susceptibility testing confirms is sensitive to ampicillin. Oral amoxicillin provides excellent oral bioavailability, effectively targets the isolated organism, and represents the ideal narrow-spectrum agent. Transitioning to oral amoxicillin aligns directly with core antibiotic stewardship principles by de-escalating therapy to the narrowest effective spectrum, allowing for safe hospital discharge while completing the required

4

6

week total antibiotic course.

Step-by-Step Solution

Assess the patient's clinical trajectory and criteria for step-down therapy.

The patient is afebrile, tolerating an oral diet, and has a normalized leukocyte count, indicating clinical stability and adequate source control.

Clinical stability dictates the safe timing for transition from intravenous to oral antimicrobial therapy.

Analyze the culture and susceptibility data.

The abscess fluid grew *Streptococcus anginosus*, which is susceptible to ampicillin but resistant to ciprofloxacin.

Definitive therapy must be tailored to the specific causative organism and its unique susceptibility profile.

Apply principles of antibiotic stewardship to modify the pharmacotherapy.

De-escalate from the broad-spectrum empiric regimen (piperacillin-tazobactam) to a targeted, highly bioavailable narrow-spectrum oral agent (amoxicillin).

Narrow-spectrum targeted therapy effectively eradicates the infection while minimizing the risk of multi-drug resistance and collateral damage to the host microbiome.

Key Concept

In a clinically stable patient with a drained pyogenic liver abscess, broad-spectrum intravenous antibiotics should be de-escalated to targeted, narrow-spectrum oral therapy based on specific culture and susceptibility data.

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