A primary care physician evaluates a 45-year-old woman who noticed an expanding area of re… — USMLE Step 2 CK

A primary care physician evaluates a 45-year-old woman who noticed an expanding area of redness on her right shin that began 48 hours ago. The affected region is tender to the touch, and she reports feeling mildly fatigued but denies chills, nausea, or recent trauma. Medical history is notable only for mild allergic rhinitis, for which she takes over-the-counter cetirizine. Her temperature is $37.9^\circ\text{C}$ ( $100.2^\circ\text{F}$ ), blood pressure is $122/78 \text{ mmHg}$ , pulse is $84/\text{min}$ , and respiratory rate is $14/\text{min}$ . Physical examination reveals a $10 \times 6 \text{ cm}$ erythematous, warm, and swollen plaque on the anterior right lower leg. The margins are indistinct. There is no palpable fluctuance, purulent exudate, or ulceration. Tender right inguinal lymphadenopathy is present. Which of the following is the most appropriate initial pharmacotherapy for this patient?

Oral cephalexinAnswer
B
Oral trimethoprim-sulfamethoxazole
C
Intravenous vancomycin and piperacillin-tazobactam
D
Oral ciprofloxacin
E
Topical mupirocin

Answer

Oral cephalexin

The correct answer is oral cephalexin. The patient presents with classic signs of uncomplicated, non-purulent cellulitis (erythema, warmth, edema, and tenderness without a purulent exudate or fluctuance). The primary pathogens responsible for this condition are beta-hemolytic streptococci (especially Group A strep) and methicillin-susceptible Staphylococcus aureus (MSSA). Oral cephalexin, a first-generation cephalosporin, provides excellent targeted coverage for these organisms and is a standard first-line outpatient therapy. In accordance with antibiotic stewardship, MRSA coverage is not routinely indicated for non-purulent cellulitis unless the patient has systemic toxicity, prior episodes of MRSA infection, or other significant risk factors.

Step-by-Step Solution

Analyze the clinical presentation.

The patient has a well-demarcated, warm, erythematous, and tender plaque without fluctuance or purulence, consistent with uncomplicated non-purulent cellulitis.

Differentiating purulent from non-purulent skin infections dictates the likely pathogens and guides empiric antibiotic selection.

Identify the most likely causative organisms.

Non-purulent cellulitis is predominantly caused by beta-hemolytic streptococci (e.g., Streptococcus pyogenes) and methicillin-susceptible Staphylococcus aureus (MSSA).

Targeting the correct organism spectrum prevents treatment failure and avoids overly broad antibiotic use.

Select the appropriate pharmacotherapy.

An oral beta-lactam such as cephalexin or dicloxacillin is the treatment of choice, providing excellent coverage against the primary pathogens.

In the absence of systemic toxicity, purulence, or high risk for MRSA, narrow-spectrum oral therapy is indicated in accordance with antibiotic stewardship guidelines.

Key Concept

Uncomplicated, non-purulent cellulitis should be treated empirically with antibiotics that target beta-hemolytic streptococci and MSSA, such as oral cephalexin or dicloxacillin, avoiding unnecessary MRSA or broad-spectrum coverage.

Estimated Time:1m 0s

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