A change of heart on vancomycin MICs?

Last year I opined that using exact vancomycin MICs as a guide to antimicrobial selection for serious MRSA infections is not a useful exercise. This position wasn’t particularly controversial at the time, and is consistent with IDSA guidance.

However, I was just directed to this study in Clinical Infectious Diseases, in which the authors conclude that in patients infected with MRSA that have vancomycin MICs of 1.5 or 2 mcg/mL (by Etest, of course, which is the only way you’ll get an MIC of “1.5”), you should consider treatment with daptomycin rather than vancomycin. In response to this paper, apparently, a large tertiary care center lab was poised to begin testing all MRSA isolates with vancomycin MIC of 1 mcg/mL by Etest (to better detect these higher MIC strains).

Really? I will let Eli comment on the finer points if he wishes, but I’m confident stating that I wouldn’t rely on a single-center, retrospective, observational, Cubist-funded study to make a major change in laboratory or clinical practice. The potential confounders, measured and unmeasured, are legion. As a single example, ID consultation occurred twice as often in the daptomycin recipients than in the vancomycin recipients (64% vs. 32%). Now I believe that ID consultation does improve outcome—but even if it doesn’t, it’s probably associated with something that does.

Cubist is funding an RCT to address this question. I’ll be interested in seeing those results. In the meantime, I’m sticking with what I wrote last year, at least as regards the laboratory testing of MRSA.