Reducing surgical site infections after hysterectomy: metronidazole plus cefazolin compared with cephalosporin alone

Organisms that are isolated from vaginal cuff infections and pelvic abscesses after hysterectomy frequently include anaerobic vaginal flora. Metronidazole has outstanding coverage against nearly all anaerobic species, which is superior to both cefazolin and second-generation cephalosporins. Cefazolin plus metronidazole has been demonstrated to reduce infectious morbidity compared with either cefazolin or second-generation cephalosporins in other clean-contaminated procedures, which include both as colorectal surgery and cesarean delivery.

The purpose of this study was to evaluate whether the combination of cefazolin plus metronidazole before hysterectomy was more effective in the prevention of surgical site infection than existing recommendations of cefazolin or second-generation cephalosporin.

This was a retrospective cohort study of patients in the Michigan Surgical Quality Collaborative from July 2012 through February 2015. The primary outcome was surgical site infection. Patients who were >18 years old and who underwent abdominal, vaginal, laparoscopic, or robotic hysterectomy for benign or malignant indications were included if they received 1 of the following prophylactic antibiotic regimens: cefazolin, second-generation cephalosporin, or cefazolin plus metronidazole. Multivariate logistic regression modeling was performed to evaluate the independent effect of an antibiotic regimen, and propensity score matching was used to validate the findings.

The study included 18,255 hysterectomies. The overall rate of surgical site infection was 1.8% (n=329). The unadjusted rate of surgical site infection was 1.8% (n=267) for cefazolin, 2.1% (n=49) for second-generation cephalosporin, and 1.4% (n=13) for cefazolin plus metronidazole. After adjustment for differences in patient and operative factors among the antibiotic cohorts, compared with cefazolin plus metronidazole, we found the risk of surgical site infection was significantly higher for patients who received cefazolin (odds ratio, 2.30; 95% confidence interval, 1.06-4.99) or second-generation cephalosporin (odds ratio, 2.31; 95% confidence interval, 1.21-4.41).

In this large cohort, the use of prophylactic cefazolin plus metronidazole resulted in lower surgical site infection rates after hysterectomy compared with cefazolin or second-generation cephalosporin.