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Difficulty: MediumInfectious Diseases

A 32-year-old woman comes to the urgent care clinic 8 hours after sustaining a bite to her right hand from a neighbor's cat. The incident occurred while she was attempting to feed the animal. Immediately after the bite, she washed the hand with soap and warm water. Her past medical history is unremarkable, and she takes no daily medications. She received a tetanus, diphtheria, and pertussis (Tdap) booster vaccination 2 years ago. Her temperature is 37.1°C (98.8°F), blood pressure is 118/76 mm Hg, and pulse is 74/min. Physical examination of the right hand reveals three deep puncture wounds on the dorsal surface. There is surrounding erythema extending approximately 1 cm from the wounds, accompanied by mild localized edema and tenderness to palpation. There is no active bleeding or purulent discharge. Sensation and active range of motion are intact, although movement exacerbates the pain. The wounds are copiously irrigated. Which of the following is the most appropriate pharmacotherapy for this patient?

  1. Oral amoxicillin-clavulanateAnswer
  2. B
    Oral cephalexin
  3. C
    Oral clindamycin
  4. D
    Oral ciprofloxacin
  5. E
    Intravenous ampicillin-sulbactam

Answer

Oral amoxicillin-clavulanate
The most appropriate pharmacotherapy for this patient is oral amoxicillin-clavulanate. Cat bites carry a high risk of infection due to the sharp, narrow feline teeth that create deep puncture wounds. This mechanism inoculates oral flora deep into the tissue, making the wounds difficult to irrigate effectively. Furthermore, bites to the hand are at particularly high risk for severe complications such as tenosynovitis or osteomyelitis due to the proximity of joints and tendon sheaths to the skin surface. Therefore, preemptive antibiotic prophylaxis is strongly indicated. The oral flora of cats predominantly includes Pasteurella multocida (a Gram-negative coccobacillus), along with various oral anaerobes, Streptococcus species, and Staphylococcus aureus. Amoxicillin-clavulanate is the first-line agent because it provides comprehensive coverage against all these potential pathogens. The amoxicillin component is highly active against Pasteurella, while the addition of clavulanate (a beta-lactamase inhibitor) ensures activity against beta-lactamase-producing S. aureus and certain anaerobes.

Step-by-Step Solution

1
Analyze the mechanism of injury and patient presentation.
The patient has deep puncture wounds on the hand resulting from a cat bite, presenting with early localized inflammatory signs.
Cat bites have a high rate of infection (often >50%) due to deep tissue inoculation, and hand bites risk rapid deep space spread, indicating a strong need for preemptive antibiotic prophylaxis.
2
Identify the likely pathogens transmitted by the bite.
The prominent pathogen in feline oral flora is Pasteurella multocida, alongside Staphylococcus aureus, Streptococcus species, and oral anaerobes.
Empiric antibiotics must provide comprehensive coverage for this specific polymicrobial flora.
3
Select the appropriate targeted antimicrobial therapy.
Oral amoxicillin-clavulanate is selected as the optimal prophylactic agent.
It adequately covers Pasteurella (via the amoxicillin component) as well as beta-lactamase producing organisms and anaerobes (via the clavulanate component) in a convenient oral formulation.

Key Concept

Cat bite wound management and appropriate empiric antimicrobial prophylaxis targeting Pasteurella multocida and polymicrobial flora.
Estimated Time:1m 0s
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Infectious Diseases

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