In vitro efficacy of antibiotic beads in treating abdominal vascular graft infections

ObjectiveAbdominal aortic vascular graft infection often involves several different organisms. Antibiotic polymethyl methacrylate (PMMA) beads may be effective in controlling infection after débridement, but bacterial species identification and antibiotic susceptibility are often not available at the time of operation, generating a need for a broad-spectrum drug combination for empirical use. We sought to determine an effective antibiotic in PMMA beads for use in abdominal vascular graft infection.MethodsPMMA beads were impregnated with combinations of antibiotics, consisting of daptomycin, tobramycin, and meropenem. Antibiotics were selected on the basis of activity spectrum and heat stability. Beads were placed on separate agar plates with vancomycin-resistant Enterococcus faecalis, Klebsiella pneumoniae, Staphylococcus epidermidis, and methicillin-resistant Staphylococcus aureus. Antibiotic inhibition was recorded by use of a modified agar-based disk-diffusion method.ResultsDaptomycin alone was not active against K. pneumoniae (average = 0 mm). Tobramycin alone was not active against vancomycin-resistant E. faecalis, K. pneumoniae, or methicillin-resistant S. aureus. Tobramycin and daptomycin in combination had moderate broad-spectrum activity with 8- to 14-mm mean inhibition halos. Meropenem showed strong activity against all tested organisms with >15-mm mean inhibition halos. The addition of daptomycin to meropenem provided improved coverage of gram-positive organisms. The presence of tobramycin reduced the efficacy of meropenem.ConclusionsAntibiotic PMMA beads containing 10% meropenem with 2.5% daptomycin had excellent in vitro activity against typical bacterial species associated with abdominal vascular graft infections. The addition of antibiotic beads may be a useful adjunct in managing such cases. Further studies are required to determine efficacy in clinical practice.

Clinical RelevanceRegardless of revascularization technique or conduit, repair of infected abdominal aortic aneurysms and infected prosthetic grafts has nearly 50% 5-year mortality despite improved in-hospital mortality rates. We believe that this is mostly due to local reinfection. Antibiotic beads have the potential to help sterilize the contaminated field and have been successfully used in infections involving extremity vascular grafts, orthopedic hardware, and ventricular assist devices. This technique may also be useful in trauma and military settings, where vascular anastomoses may be required in contaminated fields. This report describes the formulation of cement beads for use against organisms commonly found in abdominal vascular graft infections.