Monday, January 23, 2012

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.

1 comment:

  1. I agree with everything you said Dan. I would add that there were only 118 patients with few (composite) outcomes to base their analyses on. They even called it a case-control study incorrectly when it is actually a matched cohort study and I could go on. Calling Don Goldmann, Don??

    Since this is a subscription-based publication (not open-access), you can't easily see the conflicts of interest for the authors of the related editorial. I have pasted them in quotes to help you out.

    "H. W. B. serves or has served as an adviser/consultant to Basilea, Cerexa, Durata, J&J, Merck (adjudication committee), Rib-X, Wyeth/Pfizer (DSMB), and Targanta/TMC in the past 2 years. She previously served as a consultant for Cubist."