Eli's group, with Marin Schweizer as first author, has just published a retrospective cohort study in BMC Infectious Diseases (full text
here) that addresses an important and relatively common clinical question: should we treat methicillin-susceptible Staph aureus bloodstream infections with vancomycin? Most infectious diseases experts agree that cefazolin or nafcillin are better for MSSA because these drugs provide better bactericidal activity than vancomycin. Nonetheless, vancomycin's pharmacokinetics usually allows for more convenient dosing. As more patients are being treated at home with IV antibiotics, drugs that require every four hour dosing (e.g., nafcillin) are much more difficult to use unless the patient is willing to use a small programmable pump that must be carried at all times. Vanco may be even more attractive in patients with renal failure since dosing becomes very infrequent. On the other hand, I am finding it harder to maintain therapeutic trough levels with vancomycin. In young patients with high creatinine clearances, I sometimes find that even every 8 hour dosing results in trough levels that are too low. Supratherapeutic troughs occur when renal dysfunction develops, which is not uncommon in acutely ill hospitalized patients. And it seems that as we push the levels higher we are seeing more renal dysfunction. So vancomycin drives me a little crazy.
But what did Eli find? In his cohort of 267 patients with MSSA bacteremia, those that were treated with cefazolin or nafcillin (including those who also received vancomycin) were nearly 80% less likely to die than those who received only vancomycin for the duration of their treatment. What about the common clinical scenario where vancomycin is started empirically then changed to cefazolin or nafcillin once MSSA has been identified? Those that were switched from vancomycin were 69% less likely to die than those who continued on vanco.
Bottom line: think twice before using vancomycin solely on the basis of convenience.
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