A medical team is rounding on a 59-year-old man admitted 3 days ago with fever, abdominal … — USMLE Step 2 CK

A medical team is rounding on a $59$ -year-old man admitted $3$ days ago with fever, abdominal pain, and confusion. He has a known history of decompensated cirrhosis due to chronic hepatitis C. At the time of admission, an emergency diagnostic paracentesis yielded cloudy fluid with an absolute neutrophil count of $850/\text{mm}^3$ , confirming spontaneous bacterial peritonitis. Because he had been hospitalized $4$ weeks prior for a variceal bleed, the inpatient team initiated empiric therapy with intravenous piperacillin-tazobactam to cover potential healthcare-associated pathogens.

Currently, the patient is clinically stable. His confusion has cleared, and he reports no abdominal pain. Vital signs today show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $112/70\,\text{mmHg}$ , and a heart rate of $78/\text{min}$ . The microbiology laboratory reports that the admission ascitic fluid culture is positive for *Escherichia coli*. Antimicrobial susceptibility testing demonstrates that the isolate is sensitive to ceftriaxone, cefotaxime, and ciprofloxacin, but resistant to ampicillin.

Which of the following is the most appropriate next step in pharmacotherapy?

Change to intravenous ceftriaxoneAnswer
B
Continue intravenous piperacillin-tazobactam
C
Change to intravenous meropenem
D
Change to intravenous cefepime
E
Add intravenous vancomycin

Answer

Change the antibiotic regimen to intravenous ceftriaxone.

The correct step is to de-escalate the antibiotic regimen to intravenous ceftriaxone. This patient was appropriately started on broad-spectrum empiric therapy (piperacillin-tazobactam) for spontaneous bacterial peritonitis (SBP) due to his recent hospitalization risk factor. However, once the offending organism (*Escherichia coli*) is identified and susceptibilities are known, standard antibiotic stewardship principles dictate narrowing the spectrum of coverage. Because the isolate is susceptible to ceftriaxone—a third-generation cephalosporin that is highly effective for SBP—transitioning to this narrower agent minimizes collateral damage to the patient's microbiome and reduces the risk of developing resistance.

Step-by-Step Solution

Evaluate the patient's clinical response and microbiology data.

The patient shows clinical improvement, and the ascitic fluid culture has isolated E. coli susceptible to ceftriaxone.

Confirming clinical stability allows for the safe de-escalation of empiric antibiotic therapy based on definitive culture results.

Apply principles of antimicrobial stewardship to select definitive therapy.

Identify that the current broad-spectrum regimen (piperacillin-tazobactam) is wider than necessary for a ceftriaxone-susceptible organism.

Using the narrowest effective agent minimizes adverse effects, reduces collateral damage to normal flora, and prevents the emergence of multidrug-resistant pathogens.

Determine the optimal targeted antibiotic for Spontaneous Bacterial Peritonitis.

Transition to intravenous ceftriaxone to complete the treatment course.

Third-generation cephalosporins are the standard of care for SBP caused by susceptible Gram-negative enteric organisms.

Key Concept

Once antimicrobial susceptibility results are available, empiric broad-spectrum antibiotics should be de-escalated to the narrowest effective targeted agent (e.g., ceftriaxone) to promote antibiotic stewardship and minimize resistance.

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