Effect of body mass index and ertapenem versus cefotetan prophylaxis on surgical site infection in elective colorectal surgery.

Background: The effectiveness of prophylactic antibiotics in the prevention of surgical site infection (SSI) after elective colorectal surgery is dependent on many factors, including the body mass index (BMI) of the patient. In this study, the association of BMI and type of antibiotic prophylaxis with SSI was evaluated in patients undergoing elective colorectal surgery.

Method: A post-hoc analysis was performed using data obtained from a multicenter randomized, double-blind study of 1,002 patients undergoing elective colorectal surgery who received prophylactic administration of ertapenem (1 g) or cefotetan (2 g). Among 650 evaluable patients, the effect of BMI and type of antibiotic prophylaxis on SSI rates was assessed four weeks after surgery. Mechanical bowel preparation was standardized, and no patient received oral antibiotics; intravenous antibiotics were not repeated during or after surgery.

Results: The majority of patients had a BMI between 18.5 and 39.9 kg/m2. Regardless of the type of prophylaxis, SSI rates were significantly higher in patients with a BMI > or = 30 kg/m2 than in those with a BMI < 30 kg/m2. However, failure, defined as SSI, was significantly less common after ertapenem than after cefotetan prophylaxis at both BMI < 30 kg/m2 (12.7% vs. 26.4%, respectively; difference -13.7; 95% confidence interval [CI] -21.0, -6.5) and BMI > or = 30 kg/m2 (26.7% vs. 41.9%, respectively; difference -15.3; 95% CI -28.2, -2.0). The most prevalent type of SSI was superficial incisional infection, which was more common with both treatments in patients with a BMI > or = 30 kg/m2; however, the incidence of superficial SSI was lower after ertapenem than cefotetan prophylaxis.

Conclusion: In patients undergoing elective colorectal surgery, the incidence of SSI, specifically superficial incisional SSI, was higher in patients with a BMI > or = 30 kg/m2, regardless of the prophylactic antibiotic given. Ertapenem prophylaxis was more effective than cefotetan in the prevention of SSI at any BMI.