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Difficulty: MediumInfectious Diseases

An otherwise healthy 45-year-old man presents to the primary care clinic for evaluation of an expanding red rash on his right lower extremity. He first noticed the redness 48 hours ago, and it has since become increasingly tender and warm. His medical history is notable only for recurrent tinea pedis, for which he sporadically uses an over-the-counter antifungal cream. His temperature is 37.2°C (99.0°F), pulse is 78/min, respirations are 14/min, and blood pressure is 126/82 mm Hg. Physical examination of the right lower leg demonstrates a poorly demarcated, erythematous, edematous, and warm plaque extending from the lateral ankle to the mid-calf. There are no fluctuant nodules, purulent exudates, or overlying ulcers. Bilateral pedal pulses are palpable and symmetric. Which of the following is the most appropriate empiric pharmacotherapy for this patient?

  1. Oral cephalexinAnswer
  2. B
    Oral sulfamethoxazole-trimethoprim
  3. C
    Oral ciprofloxacin
  4. D
    Intravenous vancomycin
  5. E
    Topical mupirocin

Answer

Oral cephalexin is the most appropriate empiric pharmacotherapy for this patient's uncomplicated, non-purulent cellulitis.
This patient presents with classic signs of uncomplicated, non-purulent cellulitis: an expanding, poorly demarcated, erythematous, warm, and tender skin plaque. The presence of tinea pedis provides a portal of entry for bacteria, a common risk factor for lower extremity cellulitis. Non-purulent cellulitis is most commonly caused by beta-hemolytic streptococci (particularly Streptococcus pyogenes or Group A Strep) and methicillin-susceptible Staphylococcus aureus (MSSA). Empiric outpatient therapy for mild, non-purulent cellulitis should consist of a narrow-spectrum oral antibiotic with robust activity against these organisms. Oral cephalexin, a first-generation cephalosporin, perfectly matches this profile and is standard first-line therapy.

Step-by-Step Solution

1
Analyze the clinical presentation to establish a diagnosis.
The patient has a spreading, warm, erythematous, and tender plaque without fluctuance or purulence, which is the classic presentation of non-purulent cellulitis.
Correctly identifying the infection type (purulent vs. non-purulent) dictates the most likely causative pathogens and guides empiric antibiotic selection.
2
Identify the most likely causative organisms for this specific infection.
Non-purulent cellulitis is predominantly caused by beta-hemolytic streptococci (especially Group A Streptococcus) and, less commonly, methicillin-susceptible Staphylococcus aureus (MSSA).
Antibiotic stewardship requires targeting the most probable organisms without unnecessarily broadening the spectrum.
3
Select the appropriate pharmacotherapy based on the suspected pathogens and infection severity.
An oral first-generation cephalosporin (such as cephalexin) provides the necessary narrow-spectrum coverage for a hemodynamically stable outpatient.
It effectively treats streptococci and MSSA while avoiding the adverse effects and resistance risks associated with broader spectrum or intravenous agents.

Key Concept

The first-line empiric treatment for mild, non-purulent cellulitis in the outpatient setting targets beta-hemolytic streptococci and methicillin-susceptible Staphylococcus aureus (MSSA) using narrow-spectrum oral agents such as cephalexin, cefadroxil, or dicloxacillin.
Estimated Time:1m 0s
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Topics

Infectious Diseases

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