The in vitro elution of gentamicin sulfate from a commercially available gentamicin-loaded acrylic bone cement, VersaBond AB.

The present study was designed to yield results that would be used to contribute to the ongoing debate about the mechanism of the in vitro elution of an antibiotic from an antibiotic-loaded acrylic bone cement. To this end, the elution rates (R) of gentamicin sulfate (expressed as a weight percentage of the initial mass of the antibiotic in the specimen, normalized with respect to the duration of the test) from statically loaded (STATIC) and dynamically loaded (+/-10 MPa; 2 Hz; until fracture; DYNAMIC) specimens fabricated from a commercially available acrylic bone cement (VersaBond AB), in phosphate-buffered saline solution at 37 degrees C, were obtained with the use of a spectrophotometric method. There was evidence of microcracking in the fracture surfaces of DYNAMIC specimens, but no such evidence in the case of STATIC specimens. The surface area of the DYNAMIC specimens, during the tensile phase of the cyclical loading, was estimated to be about 3% larger than for the STATIC specimens (1742 mm(2) versus 1696 mm(2)). The bulk porosities P of the specimens in both sets were also determined and found to not be statistically different, with P for the STATIC and DYNAMIC specimens being 8.55 +/- 0.10 and 8.88 +/- 0.18%, respectively. At the end of the test period, R was found to be 0.36 +/- 0.20 and 1.28 +/- 0.14 wt %/day for the STATIC and DYNAMIC specimens, respectively. It is suggested that the present results provide support for the postulate that the elution mechanism of gentamicin in this cement is a surface phenomenon.