A 68-year-old woman is evaluated in the intensive care unit on hospital day 3. She was adm… — USMLE Step 2 CK

A 68-year-old woman is evaluated in the intensive care unit on hospital day 3. She was admitted with fever, left-sided flank pain, and hypotension. She was diagnosed with septic shock secondary to acute complicated pyelonephritis. Empiric therapy with intravenous piperacillin-tazobactam and aggressive fluid resuscitation were initiated. Her clinical status has improved, and vasopressor support was successfully discontinued yesterday. Today, her temperature is $37.9^{\circ} \text{C}$ ( $100.2^{\circ} \text{F}$ ), blood pressure is $118/72 \text{ mmHg}$ , and heart rate is $88/\text{min}$ . Blood and urine cultures collected on admission both grow *Escherichia coli*. The susceptibility profile of the isolate is reported as follows:

Antimicrobial	Susceptibility
Ampicillin	Resistant
Ceftriaxone	Resistant
Ciprofloxacin	Resistant
Piperacillin-tazobactam	Susceptible
Cefepime	Susceptible
Meropenem	Susceptible
Gentamicin	Susceptible

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

A
Continue intravenous piperacillin-tazobactam
Discontinue piperacillin-tazobactam and initiate intravenous meropenemAnswer
C
Discontinue piperacillin-tazobactam and initiate intravenous cefepime
D
Discontinue piperacillin-tazobactam and initiate intravenous tigecycline
E
Continue piperacillin-tazobactam and add intravenous gentamicin

Answer

Discontinue the current beta-lactam/beta-lactamase inhibitor combination and switch to a carbapenem.

The correct action is to escalate the patient's therapy to a carbapenem. This patient has an Escherichia coli bloodstream infection. The isolate's resistance to ceftriaxone (a third-generation cephalosporin) strongly suggests it is an extended-spectrum beta-lactamase (ESBL) producer. For invasive ESBL infections, particularly bacteremia, carbapenems (such as meropenem, imipenem, or ertapenem) are the definitive standard of care. Large randomized controlled trials (such as the MERINO trial) have demonstrated that utilizing piperacillin-tazobactam for the definitive treatment of ESBL bacteremia results in higher 30-day mortality and increased clinical failure rates compared to carbapenems, even when the isolate tests as susceptible in vitro. Therefore, despite her clinical improvement, standard antimicrobial stewardship and infectious disease guidelines require changing the regimen to a carbapenem to ensure complete clearance and prevent relapse.

Step-by-Step Solution

Analyze the microbiology culture and susceptibility results.

The blood culture confirms a bloodstream infection (bacteremia) with Escherichia coli.

Identifying the source and extent of infection is critical for antibiotic selection.

Interpret the specific resistance pattern.

The isolate is resistant to ceftriaxone (a third-generation cephalosporin), which strongly indicates the presence of an extended-spectrum beta-lactamase (ESBL) enzyme.

Ceftriaxone resistance in E. coli or Klebsiella is the primary surrogate marker for ESBL production.

Determine the definitive treatment standard for ESBL bacteremia.

Select a carbapenem (such as meropenem or ertapenem) over piperacillin-tazobactam, despite the latter showing in vitro susceptibility.

Clinical trial data demonstrates that carbapenems provide a significant mortality and clinical cure benefit over piperacillin-tazobactam for invasive ESBL infections.

Key Concept

For bloodstream infections caused by extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae, carbapenems are the gold standard of therapy; piperacillin-tazobactam should be avoided due to higher rates of mortality and clinical failure.

Estimated Time:2m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic