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Difficulty: MediumInfectious Diseases

An otherwise healthy 54-year-old man is evaluated in the hospital on the third day of his admission for a severe skin infection. He initially presented to the emergency department with diffuse, non-purulent erythema and warmth extending from his left ankle to his knee, along with a temperature of 38.8°C (101.8°F). He was empirically started on intravenous vancomycin and piperacillin-tazobactam.

Today, his temperature is 37.0°C (98.6°F), heart rate is 76/min, blood pressure is 126/78 mmHg, and respiratory rate is 14/min. The area of erythema has receded significantly, and his pain is markedly improved. The patient is conversing comfortably and tolerating a regular diet. Two sets of blood cultures drawn upon admission have both grown *Streptococcus pyogenes* (Group A Streptococcus).

Which of the following is the most appropriate next step in this patient's pharmacotherapy?

  1. Transition to oral amoxicillinAnswer
  2. B
    Transition to oral amoxicillin-clavulanate
  3. C
    Transition to oral linezolid
  4. D
    Transition to oral doxycycline
  5. E
    Continue intravenous vancomycin and piperacillin-tazobactam

Answer

Transition to oral amoxicillin.
The correct approach is transitioning to oral amoxicillin. This patient was appropriately started on broad-spectrum intravenous antibiotics (vancomycin for MRSA and piperacillin-tazobactam for Gram-negatives/anaerobes) for severe cellulitis with systemic toxicity. However, by hospital day 3, he is clinically stable, afebrile, and tolerating oral intake. His blood cultures identified Streptococcus pyogenes (Group A Strep), which is universally susceptible to penicillins. Principles of antimicrobial stewardship mandate de-escalating therapy to the narrowest effective agent as soon as the pathogen is identified. Amoxicillin (or Penicillin V) is the ideal narrow-spectrum oral choice for completing therapy.

Step-by-Step Solution

1
Evaluate the patient's clinical trajectory and readiness for oral therapy.
The patient is afebrile, hemodynamically stable, demonstrating clinical improvement of the cellulitis, and tolerating a regular oral diet.
These findings fulfill the standard criteria for transitioning a patient from intravenous to oral antimicrobial therapy, allowing for early discharge and minimizing line-associated risks.
2
Analyze the microbiological data to identify the targeted pathogen.
Blood cultures definitively isolated Streptococcus pyogenes (Group A Streptococcus).
Identifying the specific organism allows the clinician to discontinue empiric broad-spectrum coverage designed to treat unknown pathogens (such as MRSA or Pseudomonas).
3
Select the most appropriate narrow-spectrum oral agent based on the pathogen.
Amoxicillin (or penicillin V) is selected.
Group A Streptococcus is universally susceptible to penicillins and does not produce beta-lactamases, making narrow-spectrum beta-lactams the drugs of choice. Amoxicillin is preferred due to excellent oral bioavailability.

Key Concept

In a clinically stable patient with resolving infection and documented Streptococcus pyogenes bacteremia, empiric broad-spectrum intravenous antibiotics should be promptly de-escalated to a narrow-spectrum oral beta-lactam (e.g., amoxicillin or penicillin).
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Topics

Infectious Diseases

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