A 68-year-old woman is evaluated on hospital day 3. She was initially admitted to the inte… — USMLE Step 2 CK

A $68$ -year-old woman is evaluated on hospital day $3$ . She was initially admitted to the intensive care unit with fever, right upper quadrant pain, jaundice, and hypotension. On admission, her temperature was $39.2^\circ\text{C}$ ( $102.6^\circ\text{F}$ ), blood pressure was $88/54\text{ mmHg}$ , and heart rate was $118\text{/min}$ . Laboratory studies showed a leukocyte count of $18,500/\mu\text{L}$ , total bilirubin of $6.2\text{ mg/dL}$ , and alkaline phosphatase of $450\text{ U/L}$ . She was resuscitated with intravenous fluids, started on empiric intravenous piperacillin-tazobactam, and underwent emergent endoscopic retrograde cholangiopancreatography (ERCP), which revealed purulent bile and a common bile duct stone. A biliary sphincterotomy with stone extraction was performed successfully.

Today, she is transferred to the general medical floor. She is afebrile and hemodynamically stable, and her abdominal pain has resolved. Blood cultures drawn on admission now grow *Escherichia coli*. Susceptibility testing demonstrates that the organism is resistant to ampicillin but susceptible to ceftriaxone, cefepime, ciprofloxacin, meropenem, and piperacillin-tazobactam.

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

A
Continue intravenous piperacillin-tazobactam
B
Switch to intravenous cefepime
Switch to intravenous ceftriaxoneAnswer
D
Switch to intravenous ceftriaxone and metronidazole
E
Switch to intravenous meropenem

Answer

The correct action is to switch to intravenous ceftriaxone.

The patient presented with severe acute ascending cholangitis, characterized by Reynolds pentad (fever, jaundice, right upper quadrant pain, hypotension, and likely altered mental status). She was appropriately managed with immediate fluid resuscitation, empiric broad-spectrum antibiotics (piperacillin-tazobactam), and emergent biliary decompression (ERCP). Following definitive source control, her condition stabilized. With blood cultures now isolating Escherichia coli susceptible to ceftriaxone, the core principle of antimicrobial stewardship requires de-escalation from broad-spectrum empiric therapy to the narrowest-spectrum effective agent. Intravenous ceftriaxone is a targeted, third-generation cephalosporin with excellent biliary penetration that is highly effective against this isolate. De-escalation minimizes the risk of adverse drug events and prevents the emergence of resistant organisms.

Step-by-Step Solution

Analyze the patient's clinical presentation and initial management.

The patient had severe acute cholangitis (Reynolds pentad), was appropriately treated with empiric broad-spectrum antibiotics, and achieved complete source control via ERCP.

Establishing the patient's current clinical stability and the success of the primary intervention is required to determine the next phase of treatment.

Evaluate the culture and susceptibility data in the context of the patient's clinical improvement.

Blood cultures identified a single pathogen, Escherichia coli, which is susceptible to several narrower-spectrum antibiotics including ceftriaxone.

Definitive antimicrobial therapy is dictated by culture results and known sensitivities.

Apply the principles of antimicrobial stewardship.

De-escalate therapy from the broad-spectrum piperacillin-tazobactam to the targeted, narrow-spectrum ceftriaxone.

Narrowing therapy once sensitivities are known reduces adverse effects, limits collateral microbiome damage, and prevents antimicrobial resistance.

Key Concept

Antimicrobial stewardship dictates the de-escalation of broad-spectrum empiric antibiotics to targeted, narrow-spectrum therapy once culture and susceptibility results are available and source control is achieved.

Estimated Time:1m 15s

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