A 58-year-old male is evaluated in the hospital on hospital day 3. He was initially admitt… — USMLE Step 2 CK

A $58$ -year-old male is evaluated in the hospital on hospital day $3$ . He was initially admitted for worsening abdominal distension, lethargy, and confusion. He has a past medical history of alcoholic cirrhosis and esophageal varices. On admission, his temperature was $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), blood pressure was $105/65\text{ mmHg}$ , and pulse was $92/\text{min}$ . Physical examination revealed scleral icterus, spider angiomas, a prominent fluid wave, and mild, diffuse abdominal tenderness. Laboratory studies on admission showed:

Laboratory Study	Result
Serum total bilirubin	$2.5\text{ mg/dL}$
Serum creatinine	$1.1\text{ mg/dL}$
Blood urea nitrogen	$22\text{ mg/dL}$

A diagnostic paracentesis yielded hazy fluid with a leukocyte count of $750/\text{mm}^3$ and $80\%$ polymorphonuclear cells. Due to a prolonged hospitalization for a variceal bleed one month prior, he was empirically started on intravenous piperacillin-tazobactam.

Today, his mental status has returned to baseline, and his abdominal discomfort has resolved. Ascitic fluid cultures from admission have grown *Escherichia coli*. Susceptibility testing shows the isolate is resistant to ciprofloxacin but sensitive to ceftriaxone, cefotaxime, piperacillin-tazobactam, and meropenem. Which of the following is the most appropriate next step in the pharmacologic management of this patient's infection?

A
Continue therapy with intravenous piperacillin-tazobactam
B
Add intravenous vancomycin to the current regimen
Switch therapy to intravenous ceftriaxoneCevap
D
Escalate therapy to intravenous meropenem
E
Transition therapy to oral ciprofloxacin

Cevap

Switch therapy to intravenous ceftriaxone

The most appropriate next step is narrowing the antimicrobial regimen to intravenous ceftriaxone. This patient has spontaneous bacterial peritonitis (SBP), diagnosed by an ascitic fluid absolute neutrophil count greater than

250/\text{mm}^3

(calculated as

750 \times 0.80 = 600/\text{mm}^3

). While empiric therapy with piperacillin-tazobactam was appropriately initiated due to his recent healthcare exposure, the culture results now definitively show a monomicrobial *E. coli* infection. The isolate is highly susceptible to ceftriaxone. A core principle of antimicrobial stewardship is de-escalation: once a pathogen and its susceptibilities are identified, therapy should be narrowed to the most targeted, effective agent available. Continuing broad-spectrum agents with anti-pseudomonal and anaerobic coverage (like piperacillin-tazobactam) when unnecessary promotes the development of multidrug-resistant organisms. Intravenous third-generation cephalosporins, such as ceftriaxone or cefotaxime, are the gold standard targeted therapy for acute SBP.

Adım Adım Çözüm

Calculate the ascitic absolute neutrophil count (ANC) to confirm the diagnosis.

ANC is

750 \times 0.80 = 600/\text{mm}^3

. Because this is

> 250/\text{mm}^3

, the diagnosis is spontaneous bacterial peritonitis (SBP).

Accurate diagnosis dictates the need for and duration of antibiotic therapy.

Evaluate the clinical response to initial empiric antibiotic therapy.

The patient's confusion and abdominal pain have resolved, indicating treatment success with empiric piperacillin-tazobactam.

Clinical stability allows the physician to safely tailor antibiotics rather than escalate.

Interpret the culture and susceptibility results.

The infection is caused by a monomicrobial *E. coli* isolate that is sensitive to ceftriaxone, cefotaxime, piperacillin-tazobactam, and meropenem.

Culture data allows transition from broad empiric therapy to targeted definitive therapy.

Apply principles of antimicrobial stewardship to select the definitive regimen.

De-escalate from the broad-spectrum piperacillin-tazobactam to the narrower-spectrum, highly effective ceftriaxone.

Narrowing the spectrum minimizes the risk of multidrug-resistant organisms and adverse effects like *C. difficile* infection while effectively treating the primary infection.

Anahtar Kavram

Antimicrobial stewardship in spontaneous bacterial peritonitis (SBP) requires de-escalation of empiric broad-spectrum antibiotics to targeted, narrow-spectrum agents (such as third-generation cephalosporins) once culture and susceptibility data become available.

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