In vivo-in vitro study of biodegradable and osteointegrable gentamicin bone implants

Three implants composed of phosphate (25% hydroxyapatite, 75% tricalcium phosphate), 20% poly(DL-lactide) (DL-PLA; weight-average molecular weight (Mw), 30 kD) and 3% gentamicin sulphate (GS) were assayed in vitro and in vivo to study their release profiles as potential drug delivery systems to prevent or treat osteomyelitis. To prolong GS release, some implants were coated with poly(lactide-co-glycolide) (PLGA; Mw, 100 kD; I-PLGA) or DL-PLA (Mw, 200 kD; I-PLA). GS levels were measured in bone, kidney and blood after implantation into the femur of rats. The release profiles show a burst in the first few days, followed by a slower release rate. After I-PLA implantation, bone antibiotic concentrations higher than the minimum bactericidal concentration were maintained for 4 weeks. A linear correlation between in vitro and in vivo GS release was found to continue until complete drug release. Histological and radiological analysis showed that the implants were well tolerated and gradual new bone formation was observed.