A new concept of gentamicin loaded HAP/TCP bone substitute for prophylactic action: in vivo pharmacokinetic study.

Despite systemic prophylaxis, infection rates after orthopedic surgery can reach more than 1%. A new HAP/TCP bone substitute loaded with 125 mg of gentamicin was designed for prophylactic use. Its aim was to enhance the efficacy of systemic prophylactic treatments by increasing the local antibiotic concentration. The release rate of gentamicin from the bone substitute was investigated after implantation in the femoral condyle of five sheep. In order to investigate the local and systemic gentamicin concentrations, synovial fluids and blood samples were assessed over a 5-day period. The mean gentamicin concentration peak in blood was 4.2 μg/ml and the mean local concentration in synovial fluids during the first 8 h was 305 μg/ml. After 48 h, the concentrations in blood and synovial fluids were less than 0.5 μg/ml. No remaining gentamicin was detected in bone substitutes explanted after 8 days of implantation. The gentamicin release rate from the bone substitutes assessed corresponds to the recommendations for the prophylactic use of antibiotics: high local concentration but limited in time (less than 48 h) not to select antibiotic-resistant bacterial strains. Our results indicated that this implant should be an effective prophylactic tool in orthopedic surgery in combination with systemic prophylaxis.