A 68-year-old woman is evaluated in the hospital on the third day of admission for acute p… — USMLE Step 2 CK

A 68-year-old woman is evaluated in the hospital on the third day of admission for acute pyelonephritis. She initially presented with fever, right-sided flank pain, nausea, and vomiting. She was empirically started on intravenous piperacillin-tazobactam. Today, the patient reports feeling much better. Her temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure is $126/82\text{ mm Hg}$ , heart rate is $78\text{/min}$ , and respiratory rate is $14\text{/min}$ . Physical examination shows resolution of costovertebral angle tenderness. She is tolerating a regular diet without nausea.

The urine culture obtained on admission has finalized, showing $>10^5\text{ CFU/mL}$ of *Escherichia coli*. Susceptibility testing results are as follows:

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

Blood cultures obtained on admission show no growth to date.

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

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

Answer

The most appropriate next step is to transition to oral trimethoprim-sulfamethoxazole.

The correct management for this patient is to transition to oral trimethoprim-sulfamethoxazole. She was appropriately admitted and started on empiric intravenous antibiotics for acute pyelonephritis. Now that she is clinically stable, afebrile, and able to tolerate an oral diet, standard antimicrobial stewardship principles dictate stepping down to an oral agent. This reduces the risk of line-associated complications and facilitates hospital discharge. The culture results demonstrate an *Escherichia coli* isolate susceptible to trimethoprim-sulfamethoxazole, which is an excellent oral option because it achieves high concentrations in the renal parenchyma and urinary tract.

Step-by-Step Solution

Assess the patient's clinical trajectory and stability.

The patient is afebrile, hemodynamically stable, and tolerating oral intake.

This establishes that the patient is ready to transition from intravenous (IV) to oral (PO) antimicrobial therapy.

Analyze the culture and susceptibility data.

The infection is caused by E. coli that is susceptible to ceftriaxone, nitrofurantoin, piperacillin-tazobactam, and trimethoprim-sulfamethoxazole, but resistant to amoxicillin and ciprofloxacin.

Guides the selection of a targeted, narrow-spectrum agent for step-down therapy.

Select the appropriate oral agent based on pharmacokinetics.

Trimethoprim-sulfamethoxazole is selected over nitrofurantoin.

Trimethoprim-sulfamethoxazole achieves excellent concentration in the renal parenchyma, whereas nitrofurantoin concentrates only in the bladder and is ineffective for pyelonephritis.

Key Concept

Patients hospitalized for acute pyelonephritis who achieve clinical stability should be transitioned to a targeted oral antibiotic (e.g., TMP-SMX or a susceptible fluoroquinolone) to facilitate hospital discharge. Nitrofurantoin must be avoided because it does not achieve adequate tissue levels in the renal parenchyma.

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