In vitro evaluation of antibiotic release from and bacteria growth inhibition by antibiotic-loaded acrylic bone cement spacers

The antibiotic release from and the bacteria growth inhibition by antibiotic-loaded acrylic bone cement hip spacers were studied. The cement used was Palacos R, and it was loaded with either one antibiotic powder (gentamicin, vancomycin, teicoplanin, or synercid) monoantibiotic case] or two antibiotic powders (gentamicin + vancomycin or gentamicin + teicoplanin) biantibiotic case] and then tested against Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecalis, and methicillin-resistant Staphylococcus aureus (MRSA). Antibiotic elution and bacteria growth were measured every 24 h simultaneously by fluorescence polarization immunoassay and photometrically, respectively. The gentamicin + vancomycin combination achieved the longest growth inhibition on S. epidermidis and MRSA (mean of 20 and 14 days, respectively). Gentamicin + teicoplanin-loaded spacers were capable of inhibiting growth on E. faecalis and S. aureus for the longest period (11 and 16 days, respectively). The highest concentrations of gentamicin and vancomycin could be assayed during the first 4 days. Teicoplanin concentrations could be detected only during the first 72 h, synercid was not detected at all, possibly because of the limitation of the detection technique used. A greater percentage of the gentamicin was released than of the vancomycin. The aminoglycosid-glycopeptid combination showed a synergistic effect on the release of gentamicin, but not on vancomycin or teicoplanin. Biantibiotic-impregnated hip spacers proved to be superior to monoantibiotic ones. Because of important differences between the conditions used for the present tests and the in vivo environment, any recommendation with regard to the use of monoantibiotic- and biantibiotic-loaded acrylic bone cement spacers must await the results of further investigations.