A 19-year-old male college student presents to the emergency department accompanied by his… — USMLE Step 2 CK

A $19$ -year-old male college student presents to the emergency department accompanied by his roommate after developing a severe headache, confusion, and high fever over the previous $12$ hours. His temperature is $39.6^\circ\text{C}$ ( $103.3^\circ\text{F}$ ), blood pressure is $108/68\text{ mmHg}$ , and heart rate is $118\text{ beats/min}$ . Physical examination reveals marked nuchal rigidity and a non-blanching petechial rash on his lower extremities. A lumbar puncture is performed, and empiric therapy with intravenous ceftriaxone, vancomycin, and dexamethasone is promptly initiated. Cerebrospinal fluid (CSF) analysis shows a leukocyte count of $3,200\text{ cells/mm}^3$ ( $92\%$ neutrophils), a glucose level of $22\text{ mg/dL}$ , and a protein level of $165\text{ mg/dL}$ . The following day, the patient's mental status improves. CSF culture grows *Neisseria meningitidis*. Antimicrobial susceptibility testing is pending. Which of the following is the most appropriate next step in this patient's antimicrobial management?

A
Administer the full treatment course with both ceftriaxone and vancomycin.
B
Replace the current antibiotics with intravenous meropenem.
C
Switch the antimicrobial therapy to oral ciprofloxacin.
Stop the vancomycin infusion and maintain the ceftriaxone.Cevap
E
Include intravenous ampicillin in the current therapeutic regimen.

Cevap

Stop the vancomycin infusion and maintain the ceftriaxone.

The correct answer is to discontinue the vancomycin infusion and maintain the ceftriaxone. Empiric therapy for acute bacterial meningitis in immunocompetent adults between the ages of

2

and

50

consists of a third-generation cephalosporin (e.g., ceftriaxone or cefotaxime) plus vancomycin. The sole purpose of adding vancomycin to this empiric regimen is to provide adequate coverage against highly penicillin-resistant strains of *Streptococcus pneumoniae*. Once cerebrospinal fluid cultures definitively identify *Neisseria meningitidis*, the risk of resistant *S. pneumoniae* is eliminated. Antimicrobial stewardship principles strongly dictate that broad-spectrum or additional agents should be discontinued (de-escalated) as soon as culture results allow. *N. meningitidis* is highly susceptible to ceftriaxone, which also boasts excellent central nervous system penetration. Therefore, maintaining ceftriaxone and stopping vancomycin is the most appropriate, targeted management.

Adım Adım Çözüm

Analyze the patient's presentation and initial management.

The patient presented with classic signs of acute bacterial meningitis and was appropriately started on empiric ceftriaxone, vancomycin, and dexamethasone.

Empiric therapy must cover the most likely pathogens, including highly penicillin-resistant Streptococcus pneumoniae (covered by vancomycin) and Neisseria meningitidis (covered by ceftriaxone).

Evaluate the new culture data.

CSF culture has isolated Neisseria meningitidis.

Identifying the specific pathogen allows for targeted therapy, optimizing efficacy while minimizing toxicity and resistance.

Determine the appropriate modification to the antibiotic regimen based on stewardship principles.

Vancomycin is no longer needed because the pathogen is not S. pneumoniae. Ceftriaxone alone provides reliable coverage for N. meningitidis.

Discontinuing unnecessary broad-spectrum coverage (de-escalation) is a core component of antimicrobial stewardship.

Anahtar Kavram

In patients with acute bacterial meningitis, empiric vancomycin is used specifically to cover penicillin-resistant Streptococcus pneumoniae and should be discontinued once a different pathogen, such as Neisseria meningitidis, is identified.

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