Bactericidal activity of antimicrobial coated polyurethane sleeves for external fixation pins

Abstract

This study was conducted to assess the potential of gentamicin coated polyurethane sleeves to inhibit bacterial colonization on external fixation pins and wires. These antimicrobial sleeves have been designed to be fitted over the pins and wires, at the time of surgery, as a prophylactic approach to combat the major complication of external fixation treatment, pin tract infection. Elution testing was conducted to estimate the amount of gentamicin released into the pin tract. These gentamicin concentrations were compared to the gentamicin minimal inhibitory concentration (MIC) level for common pin tract pathogens. Elution testing revealed that the gentamicin coated polyurethane sleeves released significant quantities of the antibiotic for up to 26 weeks. The initial bolus release was characterized by predicted pin tract gentamicin concentrations of >80 μg/ml at the 2 h and 1 day elution time points. These amounts of gentamicin, delivered directly to the pin tract, are far beyond those that could be achieved via oral or intravenous administration. Furthermore, the expected concentration of gentamicin in the pin tract remained above the National Committee for Clinical Laboratory Standards (NCCLS) MIC breakpoint of 4 μg/ml, [Performance standards for antimicrobial susceptibility testing: twelfth informational supplement M100-S12, NCCLS, Wayne, PA, 2002], for at least 20 weeks. Data from the SENTRY antimicrobial surveillance program (1997–2002) established a high level of bactericidal activity for gentamicin, with 83.1% of the common pin tract pathogen isolates found to be susceptible to the antibiotic. The initial burst and subsequent long-term sustained local delivery of effective amounts of gentamicin from the antimicrobial sleeves would be expected to inhibit bacterial colonization on external fixation pins and wires. This inhibition of bacterial colonization should substantially reduce the incidence of pin tract infection, and improve the overall outcome and cost effectiveness of external fixation fracture management.