Vancomycin iontophoresis of allograft bone

Abstract

Objectives: The most concerning infection of allografts and operative procedures is methicillin resistant Staphylococcus aureus (MRSA) and no current iontophoresed antibiotics effectively combat this microbe. It was initially hypothesised that iontophoresis of vancomycin through bone would not be effective due to its large molecular size and lack of charge. The aim of this study was to determine whether this was a viable procedure and to find the optimum conditions for its use.

Methods: An iontophoresis cell was set up with varying concentrations of Vancomycin within the medulla of a section of sheep tibia, sealed from an external saline solution. The cell was run for varying times, Vancomycin concentrations and voltages, to gain information on optimisation of conditions for impregnating the graft. Each graft was then sectioned and dust ground from the exposed surface. The dust was serially washed to extract the Vancomycin and concentrations measured and plotted for all variables tested.

Results: Vancomycin was successfully delivered and impregnated to the graft using the iontophoresis technique. The first order fit to the whole data set gave a significant result (p = 0.0233), with a significant concentration (p = 0.02774) component. The time component was the next most significant (p = 0.0597), but did not exceed the 95% confidence level.

Conclusions: Iontophoresis is an effective method for delivering Vancomycin to allograft bone. The concentrations of the vancomycin solution affected the bone concentration, but results were highly variable. Further study should be done on the effectiveness of delivering different antibiotics using this method. Cite this article: Bone Joint Res 2014;3:101-7.

Keywords: Allograft; Bone; Infection; Iontophoresis; Vancomycin.

Fig. 1

Structural diagrammatic comparison between vancomycin and gentamycin molecules.

Fig. 2

Diagram showing the iontophoresis cell.

Fig. 3

Agar showing antibiotic activity (against MRSA) of iontophoresed allograft.

Fig. 4

Graph showing vancomycin in bone, with increasing concentration of vancomycin solution

Fig. 5

Graph showing vancomycin found within allograft when iontophoresed for increasing lengths of time

Fig. 6

Graph showing vancomycin found within allograft when iontophoresed with increasing voltage