A 56-year-old woman is evaluated on the medical ward on hospital day 2. She was admitted t… — USMLE Step 2 CK

A 56-year-old woman is evaluated on the medical ward on hospital day 2. She was admitted the previous day for a rapidly spreading, painful, erythematous rash on her right lower leg. Her medical history is notable for type 2 diabetes mellitus and chronic venous insufficiency. On admission, her temperature was $39.1^\circ\text{C}$ ( $102.4^\circ\text{F}$ ), heart rate was $110/\text{min}$ , and blood pressure was $118/74\text{ mmHg}$ . Physical examination revealed a well-demarcated, intensely red, warm, and tender plaque on the right anterior shin without any underlying fluctuance, purulent drainage, or overlying eschar. Due to the high fever and tachycardia, she was empirically started on intravenous vancomycin and piperacillin-tazobactam in the emergency department.

Today, the patient reports feeling much better. Her temperature is $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), heart rate is $82/\text{min}$ , and blood pressure is $124/80\text{ mmHg}$ . The margins of the erythema have not advanced. Blood cultures drawn on admission show no growth to date.

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

Discontinue both antibiotics and initiate intravenous cefazolinCevap
B
Continue the current regimen of vancomycin and piperacillin-tazobactam
C
Discontinue piperacillin-tazobactam and continue intravenous vancomycin
D
Discontinue vancomycin and continue intravenous piperacillin-tazobactam
E
Add intravenous clindamycin to the current regimen

Cevap

Discontinue both antibiotics and initiate intravenous cefazolin.

The correct action is to discontinue the broad-spectrum agents and transition to a targeted beta-lactam such as intravenous cefazolin. This patient presented with non-purulent cellulitis, which is predominantly caused by beta-hemolytic streptococci (particularly Group A Streptococcus) and methicillin-susceptible Staphylococcus aureus (MSSA). While her initial systemic toxicity (fever, tachycardia) justified empiric broad-spectrum coverage with vancomycin (for MRSA) and piperacillin-tazobactam (for gram-negatives and anaerobes), her rapid clinical improvement and lack of purulence clearly indicate a standard gram-positive skin infection. Maintaining broad-spectrum therapy when a narrow-spectrum alternative is effective violates core antimicrobial stewardship principles. Cefazolin is a first-generation cephalosporin that provides excellent, safe, and highly effective coverage against MSSA and streptococci.

Adım Adım Çözüm

Identify the clinical syndrome and its likely microbial etiology.

The patient has a classic presentation of non-purulent cellulitis (erythema, warmth, tenderness without fluctuance or purulence), which is overwhelmingly caused by beta-hemolytic streptococci (e.g., Group A Strep) and methicillin-susceptible Staphylococcus aureus (MSSA).

Correct identification of the infection type and likely pathogens allows for targeted, narrow-spectrum therapy.

Evaluate the patient's clinical trajectory.

The patient initially presented with signs of systemic toxicity (fever, tachycardia) prompting broad-spectrum empiric therapy. She has now defervesced and stabilized.

Clinical improvement indicates the current therapy is effective, but it also provides a safe window to de-escalate to a narrower spectrum.

Apply antimicrobial stewardship principles to select the definitive therapy.

Vancomycin and piperacillin-tazobactam are excessively broad. Intravenous cefazolin is selected as the optimal agent.

Cefazolin provides potent, narrow-spectrum coverage against MSSA and beta-hemolytic streptococci without the unnecessary MRSA, gram-negative, or anaerobic coverage of the empiric regimen.

Anahtar Kavram

Empiric broad-spectrum antibiotics should be de-escalated to targeted, narrow-spectrum therapy (e.g., cefazolin) in patients with non-purulent cellulitis who demonstrate clinical improvement.

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Cevap

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