Delivery of antibiotics from temporary hip prostheses (spacers) for local treatment of orthopaedic infections

The delivery of antibiotics to surgical area is a method to reduce the frequency or to treat the infections in total hip replacement (THR). Two-stage reimplantation with the use of an antibiotic loaded cement spacer performs both mechanical and biological (antimicrobial) objectives. Aim of the study was to evaluate the delivery of gentamicin (G) and vancomycin (V) from polymethylmethacrylate (PMMA) spacers before and after implantation for THR infections treatment. Methods. 20 spacers industrial products impregnated with G (1.9% concentration) were utilised. V (2.5% final concentration) was mixed with PMMA cement and then was used to fill holes made on the surface of 14/20 spacers immediately before implantation. Spacers were removed from 20 patients (mean age 69.3+7.1 years) when clinical signs and parameters of infection and inflammation returned to normality (3- 6 months following implantation), then immersed in defined volumes of phosphate buffer (PB) at 37°C for ten days. G and V concentrations were determined by microbiological method (agar-well diffusion) and polarised fluorimetry (TDx) in PB samples after 1, 3 and 10 days of elution. Results. G and V were still present and effective in all removed spacers. After an initial release peak the drugs showed a reduced but time-constant elution in the next days. The release of G alone and in combination ranged from 0.05% to 0.4% of the initial concentration before implantation, while the release of superficial V ranged from 0.8% to 3.3%. Our previous data showed a reduced release of V when combined with gentamicin in PMMA cement. Most of the drug was released within the first three months of implantation and only small amounts were released subsequently. The antimicrobial activity of the combination showed a synergistic effect against B. subtilis as well as E. faecalis and E. coli. Conclusions. The delivery of G and V from PMMA cement was prompt and effective. The difference between drug concentrations in controls and removed spacers should be the amount released at the implantation site. The external application of V seems to favourite high concentrations of antibiotic at the site of infection. V and G in combination showed a potential clinical efficacy to treat local THR infections according to defined patient conditions and bacteria susceptibility.