Combination of Metronidazole and Cefazolin Halves Surgical Site Infection Rates in Gynecologic Surgery, Study Shows

USA: In a recent study conducted at a comprehensive cancer center, researchers have uncovered compelling evidence that adding metronidazole to cefazolin significantly reduces the incidence of surgical site infections (SSIs) in gynecologic surgeries. The study, which analyzed data from various procedures, including hysterectomies, highlights a notable improvement in infection prevention when combining these antibiotics.

The researchers suggest that providers be encouraged to use this combination regimen for women undergoing gynecologic surgery, particularly in cases such as hysterectomies. The findings were published online in the American Journal of Obstetrics and Gynecology.

Surgical site infections are among the most frequent complications associated with gynecologic cancer surgeries. Traditionally, cefazolin has been the standard prophylactic antibiotic used to prevent SSIs in various surgical procedures due to its efficacy against a broad spectrum of bacteria. However, gynecologic surgeries often involve a complex microbial environment where anaerobic bacteria play a substantial role. This complexity can limit cefazolin’s effectiveness when used alone.

Against the above background, Jolyn S. Taylor, The University of Texas MD Anderson Cancer Center, Houston, TX, and colleagues aimed to assess the effect of a quality improvement initiative that includes adding metronidazole to cefazolin for antibiotic prophylaxis on the rate of surgical site infections in women undergoing gynecologic surgery at a comprehensive cancer center.

For this purpose, the researchers conducted a retrospective, single-center cohort study encompassing patients who underwent surgery in the gynecologic oncology department from 2017 to 2023. The study excluded patients with penicillin allergies and those undergoing concurrent bowel resections or joint cases. The cohort was divided into two groups: the preintervention group, consisting of patients who had surgery from May 2017 to April 2022, and the postintervention group, which included patients treated from 2022 to 2023.

The primary outcome of interest was the rate of surgical site infections within 30 days. Sensitivity analyses were performed to evaluate infection rates based on the antibiotics administered and assess outcomes specifically for patients who underwent hysterectomy. To identify factors independently associated with surgical site infections, a multivariable logistic regression model was employed, adjusting for potential confounders.

The study led to the following findings:

• Of 3343 patients, 2572 and 771 were in the pre-post intervention groups, respectively.
• Most patients (74.7%) had a hysterectomy performed. Thirty-four percent of cases were for nononcologic (benign) indications.
• Preintervention patients were more likely to receive appropriate preoperative antibiotics (95.6% versus 90.7%).
• The overall surgical site infection rate before the intervention was 4.7% compared with 2.6% after.
• The surgical site infection rate for all patients who underwent hysterectomy was 4.9% (preintervention) versus 2.8% (postintervention); a similar trend was seen for benign cases (4.4% versus 2.4%).
• On multivariable analysis, the odds ratio for surgical site infection was 0.49 for the postintervention compared with the preintervention group.
• In a sensitivity analysis (n=3087), the surgical site infection rate was 4.5% for those who received cefazolin alone compared with 2.3% for those who received cefazolin plus metronidazole, with significantly decreased odds of surgical site infection for the cefazolin plus metronidazole group (adjusted odds ratio, 0.40).
• Among only those who had a hysterectomy performed, there was a significant reduction in the odds of surgical site infection for those in the postintervention group (adjusted odds ratio, 0.63).

The findings showed that the inclusion of metronidazole with cefazolin before gynecologic surgery reduced the surgical site infection rate by 50%, even after adjusting for established predictors of infection and variations in practice patterns over time.

Reference:

Knisely, A., Iniesta, M. D., Marten, C. A., Chisholm, G., Schmeler, K. M., & Taylor, J. S. (2024). Metronidazole and cefazolin vs cefazolin alone for surgical site infection prophylaxis in gynecologic surgery at a comprehensive cancer center. American Journal of Obstetrics and Gynecology, 231(3), 326.e1-326.e13. https://doi.org/10.1016/j.ajog.2024.03.043