Release of netilmicin and vancomycin from cancellous bone

First, we studied the effect of the following variables used for netilmicin- and vancomycin-impregnation of cancellous bone: a) antibiotic concentration of the impregnation fluid, b) time used for impregnation, c) pH of the impregnation fluid, d) the degree of bone morselizing and e) antibiotic combination. An increase in the antibiotic concentration of the impregnation fluid increased the amount of antibiotics released from bone. In addition, the amount of vancomycin eluted was also dependent on the time used for impregnation. The fraction of the total amount of netilmicin and vancomycin released after 24 h was 80% and 30%, respectively. More netilmicin and vancomycin were eluted from bone impregnated with antibiotics at pH 7 than the amount eluted from bone impregnated at pH 3. More netilmicin was eluted from fine morselized bone than from coarse morselized bone. By combining netilmicin and vancomycin in the impregnation fluid, the release of vancomycin was reduced. Secondly, we analyzed if the release of antibiotics from bone was complete: 99.9% of the total amount of netilmicin adsorbed to the bone was released by elution during 6 weeks. Finally, after implantation of netilmicin-impregnated bone in rabbit femur condyle, we measured netilmicin and vancomycin in serum: peak serum values of netilmicin were 4.2 (3.7-4.7) mg/L 2-3 h postoperatively.