A 58-year-old man is evaluated in the hospital on the third day of his admission for acute… — USMLE Step 2 CK

A 58-year-old man is evaluated in the hospital on the third day of his admission for acute pyelonephritis. He originally presented with right flank pain, chills, and dysuria. At the time of admission, his temperature was $39.2^\circ \text{C}$ ( $102.6^\circ \text{F}$ ), heart rate was $110/\text{min}$ , and blood pressure was $105/65 \text{ mmHg}$ . He was empirically started on intravenous piperacillin-tazobactam.

Today, the patient reports significant improvement in his symptoms. His flank pain has resolved, and he has been afebrile for the past 24 hours. Current vital signs are temperature $37.1^\circ \text{C}$ ( $98.8^\circ \text{F}$ ), heart rate $82/\text{min}$ , and blood pressure $122/78 \text{ mmHg}$ . He is tolerating a regular diet.

Blood cultures drawn on admission show no growth. Urine cultures from admission grow $>100,000 \text{ CFU/mL}$ of *Escherichia coli*. Antimicrobial susceptibility testing results are as follows:

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

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

Transition to oral trimethoprim-sulfamethoxazoleAnswer
B
Continue intravenous piperacillin-tazobactam
C
Transition to oral nitrofurantoin
D
Transition to intravenous ceftriaxone
E
Transition to oral fosfomycin

Answer

Transition to oral trimethoprim-sulfamethoxazole

The most appropriate next step is to transition the patient to oral trimethoprim-sulfamethoxazole. This patient was admitted with acute pyelonephritis and has demonstrated significant clinical improvement on empiric intravenous piperacillin-tazobactam. He is now afebrile, hemodynamically stable, and able to tolerate oral intake. According to principles of antibiotic stewardship, he should be transitioned (stepped down) to a targeted, narrow-spectrum oral antibiotic to complete his treatment course. The urine culture results demonstrate that the *E. coli* isolate is susceptible to trimethoprim-sulfamethoxazole, which has excellent oral bioavailability and achieves high concentrations in the renal parenchyma.

Step-by-Step Solution

Evaluate the patient's clinical trajectory.

The patient is afebrile, hemodynamically stable, symptomatically improved, and tolerating a regular oral diet.

Clinical stability dictates whether a patient can be safely transitioned from intravenous to oral therapy.

Analyze the microbiological data.

The causative organism is E. coli, which is resistant to ampicillin and ciprofloxacin, but susceptible to ceftriaxone, nitrofurantoin, piperacillin-tazobactam, and trimethoprim-sulfamethoxazole.

Susceptibility data guides the de-escalation of empiric broad-spectrum antibiotics to targeted, narrow-spectrum agents.

Select the optimal targeted oral antimicrobial agent.

Trimethoprim-sulfamethoxazole is chosen because it is highly bioavailable and achieves excellent concentrations in the renal parenchyma.

Certain susceptible antibiotics (like nitrofurantoin and fosfomycin) concentrate only in the bladder and cannot treat upper urinary tract infections.

Key Concept

Antibiotic stewardship in pyelonephritis involves transitioning stable patients to highly bioavailable, targeted oral antibiotics while avoiding agents with poor renal parenchymal penetration (e.g., nitrofurantoin).

Estimated Time:1m 0s

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