Paraffin ointment or mupirocin ointment did not differ from no ointment under moist occlusive dressings on non-contaminated surgical wounds for wound infections

摘要

Case studies suggest that dressings or topical applications are effective for surgical wounds. Few properly conducted clinical trials have been done, in part, because they are expensive and difficult to do. The high quality trial by Dixon et al had a sufficient sample size to detect clinically significant differences in infection rates if they existed. Based on wound infection rates of 4% and a clinically significant reduction to < 1 %, the authors determined that 1500 wounds would be needed; they, in fact, recruited patients with a total of 1801 wounds. They found no differences in wounds treated in the paraffin, mupirocin, and no ointment groups for any of the outcomes, except for an increased risk of skin necrosis with mupirocin ointment compared with the other 2 groups. The authors acknowledge some limitations. It is unclear if allocation was concealed as balls were drawn from a bag to indicate treatment groups. This introduces the possibility of selection bias. Although study groups appeared to be similar for age and sex, it is possible that they differed for other attributes. As well, the power calculation was done on the basis of wounds, whereas patients were the unit of randomisation; some patients had > 1 wound. However, this is unlikely to be a problem because no patient had > 1 infected wound, and the authors conducted a subanalysis of first wounds in each patient, which showed similar results. A further problem is that it was not entirely possible to blind both patients and clinicians applying the treatments. Although patients and the surgeon assessing wounds were not told which treatment was given, patients might have been aware that they had received ointment. However if a placebo effect did exist, one would expect it in the group that believed they had an active treatment, and no such difference was observed. Finally, the infection rate was lower than anticipated, reducing the power of the trial. Despite these minor limitations, it is clear that in this patient population with low infection rates, applying ointment does not seem to improve outcomes, and applying mupirocin ointment may be associated with increased skin necrosis.