The influence of ultrasound on the release of gentamicin from antibiotic-loaded acrylic beads and bone cements.

Gentamicin-loaded acrylic beads are loosely placed in infected bone cavities, whereas gentamicin-loaded acrylic bone cement is used as a mechanical filler in bone to anchor prosthetic components. Both drug delivery systems are used to decrease infection rates by gentamicin release. The objective of this study is to investigate the effects of pulsed ultrasound on gentamicin release from both materials. Gentamicin release from gentamicin-loaded beads (Septopal) and from three commercially-available brands of gentamicin-loaded bone cement (CMW 1, Palacos R-G, and Palamed G) was measured after 18 h of exposure in PBS to an ultrasonic field of 46.5 kHz in a 1:3 duty cycle with an average acoustic intensity of 167 mW/cm(2). Samples not exposed to ultrasound were used as controls. Pulsed ultrasound significantly enhanced gentamicin release from gentamicin-loaded beads, whereas gentamicin release from the gentamicin-loaded bone cements was not significantly enhanced. Mercury intrusion porosimetry revealed an increased distribution of pores between 0.1 and 0.01 microm in beads after gentamicin release, while in bone cements no increase in the number of pores was found. Increased gentamicin release in beads due to ultrasound may be explained by micro-streaming in a porous structure, whereas the absence of changes in pore structure after gentamicin release in bone cement is concurrent with the lack of an enhanced release of the antibiotic by ultrasound. As an effective treatment of infections requires high local concentrations of antibiotic, increased gentamicin release due to ultrasound may be of clinical significance, especially since ultrasound has been demonstrated to increase bacterial killing by antibiotics.