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Difficulty: MediumPediatric Infectious Diseases

A 7-year-old girl is evaluated in the pediatric ward on hospital day 3. She was admitted with high fever, severe right thigh pain, and refusal to bear weight. Magnetic resonance imaging (MRI) of the right lower extremity at admission demonstrated bone marrow edema and a subperiosteal fluid collection in the distal femur consistent with acute hematogenous osteomyelitis. In the emergency department, she was started on empiric intravenous vancomycin and ceftriaxone. Over the past 48 hours, her temperature has trended down, and she reports decreased pain. Blood cultures drawn on admission are now growing Staphylococcus aureus. Susceptibility testing reveals the isolate is sensitive to oxacillin, cefazolin, and clindamycin, but resistant to penicillin and ampicillin. Vital signs today show a temperature of 37.1°C (98.8°F), blood pressure of 105/65 mm Hg, pulse of 92/min, and respiratory rate of 18/min. Which of the following is the most appropriate modification to her pharmacotherapy?

  1. Switch to intravenous cefazolinAnswer
  2. B
    Continue intravenous vancomycin and ceftriaxone
  3. C
    Switch to intravenous vancomycin
  4. D
    Switch to intravenous meropenem
  5. E
    Switch to intravenous ceftriaxone

Answer

Switch to intravenous cefazolin
The patient has acute hematogenous osteomyelitis caused by methicillin-susceptible Staphylococcus aureus (MSSA). While empiric therapy with vancomycin (to cover MRSA) and ceftriaxone (to cover gram-negative organisms) is appropriate initially for severe pediatric osteomyelitis, principles of antimicrobial stewardship dictate narrowing the spectrum of therapy once culture and susceptibility results are available. For MSSA, beta-lactamase-resistant penicillins (e.g., oxacillin, nafcillin) or first-generation cephalosporins (e.g., cefazolin) are the drugs of choice. Cefazolin provides excellent bone penetration and a narrower spectrum compared to empiric broad-spectrum regimens. Importantly, targeted beta-lactams have superior bactericidal activity against MSSA compared to vancomycin, leading to faster bacterial clearance and better clinical outcomes.

Step-by-Step Solution

1
Analyze the patient's current diagnosis and clinical status.
The patient has acute hematogenous osteomyelitis and is clinically improving on empiric therapy.
Establishing the clinical trajectory ensures the patient is stable enough to transition therapies based on new microbiological data.
2
Evaluate the microbiology and susceptibility results.
Blood cultures grew methicillin-susceptible Staphylococcus aureus (MSSA).
Identification of the specific pathogen and its sensitivity profile guides the transition from empiric broad-spectrum to definitive narrow-spectrum therapy.
3
Select the optimal targeted antimicrobial agent based on stewardship principles.
Intravenous cefazolin is selected.
Cefazolin (or oxacillin/nafcillin) provides excellent, targeted bactericidal activity against MSSA with good bone penetration, whereas continuing vancomycin or broad gram-negative coverage is unnecessary and promotes resistance.

Key Concept

In patients with methicillin-susceptible Staphylococcus aureus (MSSA) infections, antimicrobial stewardship dictates stepping down from empiric broad-spectrum therapy (e.g., vancomycin) to a targeted narrow-spectrum beta-lactam agent (e.g., cefazolin, oxacillin) to improve clinical outcomes and prevent resistance.
Estimated Time:1m 30s
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Topics

Pediatric Infectious Diseases

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