A 64-year-old male is evaluated in the hospital on day 4 of admission. He initially presen… — USMLE Step 2 CK

A 64-year-old male is evaluated in the hospital on day $4$ of admission. He initially presented with right upper quadrant abdominal pain, high-grade fevers, and profound fatigue. His past medical history is significant for type 2 diabetes mellitus. Upon admission, a computed tomography (CT) scan of the abdomen with intravenous contrast demonstrated a single, $5.5\text{ cm}$ , thick-walled, hypodense fluid collection in the right hepatic lobe. He was started on empiric intravenous piperacillin-tazobactam. A CT-guided percutaneous drain was subsequently placed, which yielded $40\text{ mL}$ of purulent material. Currently, his temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate is $82/\text{min}$ , and blood pressure is $128/84\text{ mmHg}$ . His leukocyte count has decreased from $18,200/\text{mm}^3$ on admission to $8,400/\text{mm}^3$ . Blood cultures drawn on admission are negative. The abscess fluid culture has finalized, demonstrating a pure growth of *Streptococcus anginosus*. Susceptibility testing reveals the organism is susceptible to penicillin, ceftriaxone, and clindamycin, but resistant to erythromycin. Which of the following is the most appropriate next step in pharmacotherapy?

Transition to intravenous ceftriaxoneAnswer
B
Continue intravenous piperacillin-tazobactam
C
Add oral metronidazole to the current regimen
D
Transition to oral ciprofloxacin and metronidazole
E
Discontinue all antibiotics and maintain percutaneous drainage

Answer

Transition to intravenous ceftriaxone

The correct answer is to transition to intravenous ceftriaxone. This patient has a pyogenic liver abscess that is responding well to initial management. While pyogenic liver abscesses are often polymicrobial (requiring empiric broad-spectrum coverage for enteric Gram-negatives and anaerobes), this patient's culture grew a pure isolate of *Streptococcus anginosus*. *S. anginosus* is a well-known cause of monomicrobial tissue abscesses, including hepatic abscesses. Because definitive culture and susceptibility data are now available, the standard of care—driven by principles of antimicrobial stewardship—is to de-escalate therapy. Continuing piperacillin-tazobactam is unnecessarily broad. Transitioning to a targeted, narrow-spectrum beta-lactam such as ceftriaxone or penicillin G effectively treats the infection while minimizing the risk of adverse effects and antimicrobial resistance.

Step-by-Step Solution

Assess the patient's current clinical status and primary diagnosis.

The patient is clinically improving from a pyogenic liver abscess, with normalized vitals and leukocyte counts following source control (drainage) and empiric antibiotics.

Establishing stability confirms that the current overall management strategy is effective and allows for safe adjustments to the pharmacotherapy regimen.

Analyze the finalized microbiology and susceptibility data.

The abscess is monomicrobial, caused by Streptococcus anginosus, which is susceptible to narrow-spectrum beta-lactams like penicillin and ceftriaxone.

Definitive culture data supersedes the need for broad-spectrum empiric coverage.

Apply the principles of antimicrobial stewardship.

The broad-spectrum agent (piperacillin-tazobactam) should be discontinued and replaced with a targeted, narrower-spectrum agent (ceftriaxone) that covers the identified isolate.

De-escalating therapy minimizes collateral damage to the host microbiome, reduces the risk of Clostridioides difficile infection, and prevents the development of antimicrobial resistance.

Key Concept

De-escalation of empiric broad-spectrum antibiotics to targeted, narrow-spectrum agents in pyogenic liver abscess once definitive culture and susceptibility data are available.

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