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Difficulty: MediumInfectious Diseases

A 54-year-old man presents to the urgent care clinic with a 2-day history of a red, warm, and tender rash on his right lower leg. The area has been progressively enlarging. He has a history of type 2 diabetes mellitus and hypertension. His temperature is 37.9∘C37.9^\circ\text{C} (100.2∘F100.2^\circ\text{F}), blood pressure is 128/82 mm Hg128/82\text{ mm Hg}, pulse is 88/min88/\text{min}, and respirations are 16/min16/\text{min}. Physical examination of the right lower extremity reveals a poorly demarcated, erythematous, warm, and tender area of skin extending from the ankle to the mid-calf. There is no fluctuance, purulent drainage, or palpable crepitus. Sensation to light touch is intact. His leukocyte count is 10,500/mm310,500/\text{mm}^3. Which of the following is the most appropriate next step in pharmacotherapy?

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

Answer

Oral cephalexin
The patient's presentation of a spreading, erythematous, warm, and tender area of skin without fluctuance or purulence is classic for non-purulent cellulitis. The most common pathogens responsible for non-purulent cellulitis are beta-hemolytic streptococci (especially Group A Streptococcus) and methicillin-susceptible Staphylococcus aureus (MSSA). For mild infections (defined as those lacking systemic signs of severe illness or hemodynamic instability), empiric oral antibiotic therapy targeting these organisms is indicated. Oral cephalexin, a first-generation cephalosporin, provides excellent coverage for both streptococci and MSSA and is a standard first-line agent. Other appropriate oral options include dicloxacillin or penicillin (if solely targeting streptococci).

Step-by-Step Solution

1
Identify the clinical syndrome based on the physical examination.
The patient has a spreading, warm, erythematous, and tender plaque without fluctuance or purulent drainage, consistent with non-purulent cellulitis.
Differentiating between purulent and non-purulent skin and soft tissue infections (SSTIs) dictates the microbiological etiology and subsequent empiric antibiotic choice.
2
Determine the most likely causative pathogens for this specific syndrome.
Non-purulent cellulitis is primarily caused by beta-hemolytic streptococci (e.g., Group A Streptococcus) and, less commonly, methicillin-susceptible Staphylococcus aureus (MSSA).
Empiric antibiotic therapy must be active against the most probable organisms.
3
Select the appropriate pharmacotherapy based on severity and pathogen.
The patient has a mild infection without systemic toxicity, meaning outpatient oral therapy targeting streptococci and MSSA is indicated. Oral cephalexin is the optimal choice.
Using narrow-spectrum oral agents for mild infections aligns with antibiotic stewardship guidelines, avoiding unnecessary broad-spectrum coverage or intravenous administration.

Key Concept

Mild, non-purulent cellulitis should be empirically treated with an oral antibiotic active against beta-hemolytic streptococci and MSSA, such as cephalexin, dicloxacillin, or amoxicillin.
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Topics

Infectious Diseases

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