A 54-year-old man is reviewed by the medical team during his inpatient hospitalization. He… — USMLE Step 2 CK

A 54-year-old man is reviewed by the medical team during his inpatient hospitalization. He was admitted 72 hours ago after presenting to the emergency department with an acutely painful, erythematous, and swollen right knee accompanied by shaking chills. Initial arthrocentesis yielded turbid synovial fluid containing $85,000 \text{ leukocytes}/\mu L$ with $92\%$ neutrophils. Following the procedure, he was empirically started on intravenous vancomycin and piperacillin-tazobactam. Today, his temperature has improved to $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), blood pressure is $128/82 \text{ mmHg}$ , and pulse is $84/\text{min}$ . The right knee shows decreased swelling and erythema. Blood cultures and synovial fluid cultures obtained on admission are both positive for *Staphylococcus aureus*. Antimicrobial susceptibility testing reveals the following:

Antibiotic	Susceptibility
Penicillin	Resistant
Oxacillin	Susceptible
Cefazolin	Susceptible
Vancomycin	Susceptible
Trimethoprim-sulfamethoxazole	Susceptible

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

Discontinue current antibiotics and initiate intravenous cefazolinCevap
B
Continue intravenous vancomycin and discontinue intravenous piperacillin-tazobactam
C
Discontinue intravenous vancomycin and continue intravenous piperacillin-tazobactam
D
Discontinue current antibiotics and initiate oral trimethoprim-sulfamethoxazole
E
Add oral rifampin to the current antibiotic regimen

Cevap

Discontinue current antibiotics and initiate intravenous cefazolin

The patient has septic arthritis and bacteremia caused by Methicillin-Susceptible *Staphylococcus aureus* (MSSA). The current standard of care and core principle of antibiotic stewardship is to de-escalate broad-spectrum empiric therapy (vancomycin and piperacillin-tazobactam) to a targeted, narrow-spectrum agent once culture sensitivities are available. For invasive MSSA infections, anti-staphylococcal penicillins (e.g., nafcillin, oxacillin) or first-generation cephalosporins (e.g., cefazolin) are the drugs of choice. These beta-lactam agents are rapidly bactericidal and have been conclusively shown to lower mortality, decrease hospital length of stay, and reduce the risk of relapse compared to vancomycin. Therefore, the correct approach is to discontinue both empiric medications and begin intravenous cefazolin.

Adım Adım Çözüm

Analyze the culture and susceptibility data provided in the vignette.

The pathogen is identified as Staphylococcus aureus that is resistant to penicillin but susceptible to oxacillin, confirming a diagnosis of Methicillin-Susceptible Staphylococcus aureus (MSSA).

Accurate interpretation of sensitivities is required to tailor the empiric antibiotic regimen to definitive therapy.

Evaluate the current empiric antibiotic regimen (vancomycin and piperacillin-tazobactam) against standard of care for MSSA.

Both agents are suboptimal for definitive MSSA treatment. Vancomycin has inferior bactericidal activity against MSSA compared to beta-lactams, and piperacillin-tazobactam is unnecessarily broad.

Antibiotic stewardship principles mandate de-escalating to the narrowest-spectrum, most effective agent once a pathogen and its susceptibilities are known.

Select the optimal targeted therapy for invasive MSSA infection (septic arthritis and bacteremia).

An intravenous anti-staphylococcal penicillin (e.g., nafcillin, oxacillin) or a first-generation cephalosporin (e.g., cefazolin) is the treatment of choice.

These agents have proven superiority over vancomycin in clearing MSSA bacteremia and improving patient survival, requiring immediate transition to intravenous cefazolin.

Anahtar Kavram

Definitive management of Methicillin-Susceptible Staphylococcus aureus (MSSA) bacteremia requires de-escalation to an intravenous narrow-spectrum beta-lactam (such as cefazolin, nafcillin, or oxacillin), which provides superior clinical outcomes compared to vancomycin.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru