Case Study
Here is an example of treating a patient with an infection by the above pathway:
TR is a 63-year-old man with a past medical history of diabetes, hypertension, and coronary artery disease who comes to the hospital complaining of pain, redness and swelling around a wound on his foot. Close inspection reveals that he has an infected diabetic foot ulcer. He is admitted to the hospital (Day 1). The clinician performs surgical debridement that evening and sends cultures from the wound during surgery as well as blood cultures. The clinician initiates empiric therapy with vancomycin and piperacillin/ tazobactam.
On Day 2, Gram stain results from the wound are available. There are many white blood cells with many Gram-positive cocci but no Gram-negative rods, so the clinician discontinues piperacillin/ tazobactam. Blood cultures do not grow any organisms.
The following day (Day 3), culture results from the wound reveal many Staphylococcus aureus. Because vancomycin is usually effective against this organism, its use is continued.
On Day 4, susceptibility results from the wound culture return. The S. aureus is found to be susceptible to methicillin, oxacillin, cefazolin, piperacillin/tazobactam, clindamycin, trimethoprim/ sulfamethoxazole, and vancomycin. It is resistant to penicillin, ampicillin, tetracycline, and levoflox-acin. As the isolate from TR’s wound is methicillin-susceptible Staphylococcus aureus (MSSA), the clinician discontinues vancomycin and initiates definitive therapy with oxacillin.
Note how in TR’s case we began empiric therapy with a broad-spectrum regimen of vancomycin and piperacillin/tazobactam to cover the Gram-positive and Gram-negative aerobes and anaerobes that tend to cause diabetic foot infections but narrowed that therapy gradually as Gram stain and culture data returned. Eventually we were able to choose a highly effective, narrow-spectrum, inexpensive, and safe choice of definitive therapy that was driven by microbiology results. Both vancomycin and piperacillin/ tazobactam were active against TR’s Staphylococcus aureus as well, but both are broader in spectrum than oxacillin and represent less-ideal choices of therapy.