SAN DIEGO, CA—Dual therapy with vancomycin plus a beta-lactam antibiotic may reduce surgical site infections (SSI) by up to 63%, a study presented at IDWeek 2015 has found, with the strongest association seen in cardiac procedures.

This benefit was observed whether a beta-lactam was added to vancomycin, or vancomycin to a beta-lactam, reported Westyn Branch-Elliman, MD, MMSC, from the University of Colorado, Aurora, CO.

Current standard of care is to give a single agent. A beta-lactam is preferred for most surgeries, with vancomycin viewed as an alternative in patients who are allergic to beta-lactams. In addition, vancomycin is “generally considered inferior to a beta-lactam due to inferior coverage of MSSA and lack of gram-negative coverage,” she said.

However, while “mounting evidence suggests that a single agent is not always optimal,” other studies have suggested a potential harm of dual therapy, such as increased incidence of kidney failure.

To compare the effectiveness of dual antimicrobial prophylaxis vs. monotherapy for prevention of SSI, Dr. Branch-Elliman and colleagues examined a large cohort of patients who had surgery within the national VA healthcare system from October 1, 2008, through September 30, 2013 and had received antimicrobial prophylaxis.

The study’s primary outcome was SSI incidence among patients receiving vancomycin vs. vancomycin + a beta-lactam. A subanalysis examined incidence of SSI stratified by type of surgical procedure and MRSA colonization status.

At baseline, of the 81,161 patients included in the study, 2,841 had SSI, with 2,325 receiving a beta-lactam only, 141, vancomycin only, and 197, a combination.

Of the 58,945 procedures included in the study, 15,889 were cardiac cases and 28,210, total joint replacement cases. Among these, 3,064 patients—4.26% of the total cohort—screened positive for MRSA, with 417 receiving vancomycin only, 1,808, a beta-lactam only, and 733, a combination.

Results showed that patients treated with dual therapy had a 62.3% relative risk reduction vs. monotherapy (P<0.0001). For those undergoing cardiac surgery, this reduction was 30.9% (P=0.075) and, for total joint replacement, 7.1% (P=0.580). When stratified by MRSA colonization, the relative risk reduction was 52.3% for dual therapy vs. vancomycin alone (P=0.0179).

“Future investigations will focus on the incidence of C. difficile, antimicrobial resistance, and post-operative acute kidney injury as well as potential operating room delays associated with dual antibiotic therapy vs. monotherapy,” Dr. Branch-Elliman. She also recommended that future studies “weigh potential risks and benefits of screening vs. universal use of dual therapy for selected surgeries, with a particular focus on cardiac procedures.”