Background: Currently, the standard for prophylaxis against surgical
infection consists of perioperative systemic antibiotics. In this study, we
investigated the relative efficacy of various methods of antibiotic delivery
for the prevention of surgical wound infections. We hypothesized that
sustained release of local antibiotics inside the wound cavity by a drug
delivery system would be more effective than systemically administered
antibiotics.
Methods: Using a rat model, we inoculated a surgical wound in the
quadriceps muscle with 8.0 × 105 colony-forming units of
Staphylococcus aureus and then administered one of seven types of
treatment: no treatment (control), bacitracin irrigation, calcium sulfate
flakes, systemic gentamicin, local aqueous gentamicin, local gentamicin-loaded
calcium sulfate flakes, and a combination of local gentamicin-loaded calcium
sulfate and systemic gentamicin. The seven treatment groups consisted of ten
rats each. To further evaluate a trend, the group treated with systemic
gentamicin and the one treated with local gentamicin solution were extended to
include twenty-five and twenty-seven rats, respectively. At forty-eight hours
postoperatively, specimens from the wounds were obtained for quantitative
culture.
Results: The control group, the group treated with bacitracin
irrigation, and the one treated with plain calcium sulfate had very high
bacterial counts and high mortality rates while the groups treated with
gentamicin had low bacterial counts and a 100% survival rate. Local gentamicin
was significantly more effective than systemic gentamicin in reducing
bacterial counts.
Conclusions: The gentamicin-loaded calcium sulfate flakes did not
result in bacterial counts that were significantly lower than those following
systemic administration of gentamicin, which refuted our hypothesis. However,
gentamicin solution injected directly into the closed wound did result in
levels of bacteria that were significantly lower than those following
treatment with the systemic gentamicin.
Clinical Relevance: We believe that a high initial concentration of
locally applied antibiotic inside the wound effectively kills bacteria present
in the wound cavity, where systemic antibiotics have poor penetration,
suggesting that this method of antibiotic administration may be a desirable
adjunct for prophylaxis against infection in surgical wounds.