Letters
Cardiovascular diseases Infectious diseases Pharmacology
Volume 193 - Issue 1

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

Author:  Frank Shann

Med J Aust 2010; 193 (1): 62-63. || doi: 10.5694/j.1326-5377.2010.tb03752.x
Published online: 5 July 2010
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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

Three other trials have compared one or two doses of a cephalosporin with multiple doses of the same antibiotic in patients having cardiac surgery; none found that multiple doses were superior, although all three were small studies with faults in their design.5-7

In 1998, McDonald and colleagues published a detailed review of single versus multiple doses of antimicrobial prophylaxis for major surgery. The analysis was in response to a suggestion by Christiansen and others that single-dose antibiotic prophylaxis may be inadequate for patients undergoing vascular surgery.8 McDonald and colleagues pointed out that the recommendation for single-dose surgical prophylaxis in Therapeutic guidelines: antibiotic (version 13),2 is based on microbiological first principles, published studies reporting efficacy, convenience of administration, reduced antibiotic resistance and toxicity, and relatively low cost. Their careful analysis of 28 randomised trials, in which the same antimicrobial was used in each arm, showed no advantage from the administration of multiple doses; the odds ratio for infection was 1.06 (95% CI, 0.89–1.25). There is no microbiological reason to suppose that the crucial interaction between contaminating bacteria and the prophylactic antibiotic in the heart is any different from that in the lung, biliary tree, uterus, bowel, prostate or bone.8 In the absence of such evidence, there is no sound reason to change the current, long-standing Therapeutic guidelines: antibiotic2 recommendation.

Author

  • Frank Shann1
  • 1. Royal Children’s Hospital, Melbourne, VIC.

Correspondence: frank.shann@rch.org.au

References

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