A 64-year-old man is evaluated in the hospital on day 3 of admission. He was initially adm… — USMLE Step 2 CK

A 64-year-old man is evaluated in the hospital on day 3 of admission. He was initially admitted with fever, confusion, and abdominal pain. His medical history includes hepatitis C virus-related cirrhosis complicated by ascites. Three weeks ago, he was hospitalized for an acute variceal hemorrhage treated with endoscopic band ligation. Upon this admission, a diagnostic paracentesis revealed cloudy fluid with a leukocyte count of $1,200/\text{mm}^3$ and a neutrophil count of $950/\text{mm}^3$ . Due to his recent hospitalization, he was empirically started on intravenous piperacillin-tazobactam. Intravenous albumin was also administered.

Today, the patient is alert and oriented. His abdominal pain has resolved. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $112/68\text{ mm Hg}$ , and pulse is $78/\text{min}$ . Ascitic fluid cultures from admission grow *Klebsiella pneumoniae*. The isolate's antimicrobial susceptibility profile is as follows:

Antibiotic	Result
Ampicillin	Resistant
Ciprofloxacin	Resistant
Trimethoprim-sulfamethoxazole	Resistant
Ceftriaxone	Susceptible
Cefepime	Susceptible
Piperacillin-tazobactam	Susceptible
Meropenem	Susceptible

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

Switch to intravenous ceftriaxoneAnswer
B
Continue intravenous piperacillin-tazobactam
C
Switch to intravenous cefepime
D
Switch to intravenous meropenem
E
Add intravenous metronidazole

Answer

Switch to intravenous ceftriaxone

The correct answer is to switch to intravenous ceftriaxone. This patient has spontaneous bacterial peritonitis (SBP) complicating his cirrhosis. Initial empiric therapy with a broad-spectrum agent like piperacillin-tazobactam was appropriate due to his recent hospitalization, which is a risk factor for healthcare-associated SBP. However, once ascitic fluid cultures isolate a specific pathogen (*Klebsiella pneumoniae*) and susceptibility data are available, antimicrobial stewardship principles mandate de-escalating to the narrowest-spectrum effective agent. The isolate is pan-susceptible to the tested parenteral beta-lactams. Ceftriaxone is a third-generation cephalosporin with excellent peritoneal fluid penetration and efficacy for SBP. It provides targeted coverage without the unnecessary anti-pseudomonal and anti-anaerobic activity of piperacillin-tazobactam. Timely de-escalation minimizes the risk of adverse effects, reduces selection pressure for multidrug-resistant organisms, and lowers the risk of *Clostridioides difficile* infection.

Step-by-Step Solution

Analyze the patient's diagnosis and initial management.

The patient has spontaneous bacterial peritonitis (SBP) and was correctly started on broad-spectrum empiric therapy (piperacillin-tazobactam) due to his recent healthcare exposure.

Establishing the baseline clinical scenario and rationale for initial therapy is necessary to determine the next step.

Interpret the microbiology and susceptibility results.

The culture grew Klebsiella pneumoniae, which is susceptible to ceftriaxone and several broader agents, but resistant to ampicillin and common oral step-down options like ciprofloxacin.

Susceptibility data dictates the definitive antimicrobial regimen.

Apply principles of antimicrobial stewardship.

De-escalate from piperacillin-tazobactam to ceftriaxone.

To minimize toxicity, resistance, and C. difficile risk, patients should be transitioned to the narrowest-spectrum effective agent once susceptibility is known.

Key Concept

Antimicrobial stewardship in the treatment of spontaneous bacterial peritonitis requires de-escalation from empiric broad-spectrum coverage to the narrowest-spectrum effective agent once culture and susceptibility data are available.

Estimated Time:1m 30s

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