Antibiotic prophylaxis for cardiac surgery — are we getting it right?

To the Editor: In her editorial, Christiansen states that the 2010 edition of Therapeutic guidelines: antibiotic (version 14) is very likely to recommend 24 hours of antibiotic prophylaxis for cardiac surgery,1 rather than the present regimen, which recommends that patients having routine cardiac surgery be given a large dose of cephazolin at induction, with a second dose if the operation is prolonged for more than 3 hours, and no doses after surgery.2 The only evidence presented in support of this proposed change is a single randomised controlled trial that purported to show a higher rate of surgical site infections after a single dose of cephazolin, than after a prolonged, multidose regimen.3 The study was flawed, for two reasons. First, cephazolin was not given until 20–30 minutes after induction of anaesthesia, which is likely to have been too late, because, as Christiansen points out, β-lactams should be given 30–60 minutes before incision.1 Second, the trial was analysed on a per-protocol, rather than an intention-to-treat basis, and 189 of the 1027 participants (18%) were excluded, so the findings may be seriously biased.4