Local Versus Systemic Antibiotics for Surgical Infection Prophylaxis in a Rat Model

The purpose of this study was to compare the local application of a variety of antimicrobial agents with intravenous (IV) antibiotics for infection prophylaxis in a rat model.

A total of 120 adult male Sprague-Dawley rats were implanted with an expanded polytetrafluoroethylene (ePTFE) vascular graft in a submuscular position and challenged with 2 × 10 colony-forming units of methicillin-sensitive Staphylococcus aureus (MSSA). Twenty rats received pretreatment with IV cefazolin and 20 rats were pretreated with IV vancomycin. The remaining 80 rats had application of local antimicrobials in the wound at the conclusion of the procedure: 20 rats received vancomycin powder; 20 rats, cefazolin powder; and 20 rats, tobramycin powder; 20 rats underwent dilute 0.35% Betadine (povidone-iodine) lavage for 3 minutes. One week after surgery, the grafts were retrieved and cultured.

Twenty (100%) of 20 rats in each of the IV cefazolin, IV vancomycin, and dilute Betadine lavage groups had grossly positive cultures for MSSA (95% confidence interval [CI], 84% to 100%). Eighteen (90%) of 20 rats in the cefazolin local powder group demonstrated positive cultures for MSSA (95% CI, 77% to 100%). Four (20%) of 20 rats in the tobramycin local powder and vancomycin local powder groups demonstrated positive cultures for MSSA (95% CI, 3% to 38%). The infection rates for the local application of vancomycin and tobramycin powder were significantly lower compared with Betadine lavage, IV vancomycin, IV cefazolin, and local cefazolin powder (p < 0.000001).

Local antimicrobial prophylaxis with vancomycin and tobramycin powder for infections in the rat model was statistically superior to systemic prophylaxis with IV antibiotics, local cefazolin powder, and Betadine lavage.

This study supports the findings of prior clinical reports that intrawound vancomycin powder reduces the risk of surgical site infection. Local application of tobramycin powder was equivalent to vancomycin powder in this model. Additionally, the superiority of local antibiotic surgical prophylaxis suggests that clinical studies should be considered to determine the relative efficacy of local versus systemic antibiotics for surgical infection prophylaxis in humans.