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Difficulty: EasyPediatric Infectious Diseases

A 5-year-old girl is admitted to the pediatric ward with severe right thigh pain, fever, and an inability to bear weight. Magnetic resonance imaging confirms acute hematogenous osteomyelitis of the right femur. She is empirically started on a regimen of intravenous vancomycin and ceftriaxone. On hospital day 3, her clinical condition has significantly improved, and she has been afebrile for 24 hours. Blood cultures and a deep tissue aspirate obtained on admission both grow *Staphylococcus aureus*. Antimicrobial susceptibility testing reveals the isolate is resistant to penicillin, but susceptible to oxacillin, cefazolin, and clindamycin. The patient has no known drug allergies. Which of the following is the most appropriate antimicrobial regimen for this patient at this time?

  1. Intravenous cefazolinAnswer
  2. B
    Intravenous vancomycin and ceftriaxone
  3. C
    Intravenous linezolid
  4. D
    Intravenous meropenem
  5. E
    Intravenous daptomycin

Answer

The most appropriate regimen is intravenous cefazolin, which is a targeted, narrow-spectrum agent highly effective against methicillin-susceptible Staphylococcus aureus (MSSA).
The correct answer is intravenous cefazolin. The patient has acute hematogenous osteomyelitis caused by methicillin-susceptible *Staphylococcus aureus* (MSSA). Once culture and susceptibility results are available, empiric broad-spectrum therapy (vancomycin and ceftriaxone) must be de-escalated to a definitive, narrow-spectrum agent. Beta-lactam antibiotics such as cefazolin, oxacillin, or nafcillin are the gold standard for MSSA infections. They are superior to vancomycin because they are more rapidly bactericidal, have excellent tissue penetration into the bone, and are associated with lower rates of treatment failure and mortality in MSSA bacteremia and osteomyelitis.

Step-by-Step Solution

1
Interpret the culture and sensitivity data.
The pathogen is confirmed as methicillin-susceptible Staphylococcus aureus (MSSA).
Identifying the specific organism and its susceptibility profile is required to transition from empiric to definitive therapy.
2
Apply principles of antimicrobial stewardship.
The empiric broad-spectrum regimen (vancomycin and ceftriaxone) must be discontinued in favor of a targeted agent.
Continuing broad-spectrum antibiotics when a susceptible organism is identified promotes antibiotic resistance and exposes the patient to unnecessary drug toxicity.
3
Select the optimal targeted therapeutic agent.
Intravenous cefazolin is selected.
First-generation cephalosporins (like cefazolin) or anti-staphylococcal penicillins (like oxacillin/nafcillin) are the superior drugs of choice for severe MSSA infections.

Key Concept

Antibiotic de-escalation for methicillin-susceptible Staphylococcus aureus (MSSA)
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Topics

Pediatric Infectious Diseases

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