NAPLEX Question of the Week: Culture and Susceptibilities

Interpreting cultures is a common part of practice for many pharmacists.
NAPLEX Question of the Week: Culture and Susceptibilities

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KP is a 72-year-old male who was admitted to the hospital with worsening erythema to his right lower leg. The patient states 3 days prior he had scraped his leg while gardening. Upon physical examination it was noted that the leg was edematous, painful to the touch, and had purulent drainage. Patient reports a rash with bactrim therapy.  The patient's vital signs were as follows: HR 93 beats/minute, BP 112/67 mm Hg, Temperature 38C. The patient was admitted to the internal medicine ward and initiated on intravenous vancomycin therapy.  After incision and drainage upon admission, a wound culture was sent to the microbiology lab and the results showed S. aureus with the following susceptibilities: 
Cefazolin                                          S       
Cephalexin                                       S
Clindamycin                                     R
Doxycycline                                      S
Erythomycin                                     R
Oxacillin                                            S
Tetracycline.                                     S
Trimethoprim/Sulfamethoxazole       S
Vancomycin                                      S
On hospital day 3, the patient's has clinically improved significantly and is ready to be discharged on oral therapy. Which of the following therapies would be best for our patient?
A. Vancomycin 
B. Trimethoprim/sulfamethoxazole 
C. Clindamycin 
D. Cephalexin
E. Cefazolin 
Answer with rationale:
The correct answer is D. S. aureus is one of the most common pathogens associated with acute bacterial skin/skin structure infections, especially abscesses. The patient has had incision and drainage (important therapy) along with vancomycin IV therapy. Because susceptibilities show methicillin-susceptible S. aureus, the patient should receive a drug of choice for this pathogen, which would be an antistaphylcoccal penicillin, amoxicillin/clavulanate, or a first generation cephalosporin such as cephalexin. Therefore answer D is correct. Answer E is incorrect as while cefazolin is a 1st generation cephalosporin, it is only available IV. Answer A is incorrect as oral vancomycin is only used in management of C. difficile infection. Answer B is incorrect as this would be preferred if the patient had MRSA. In addition, the patient reports an allergy to bactrim making this inappropriate. Answer C is incorrect as this patient's susceptibility report demonstrated resistance to clindamycin. 

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