Elution characteristics of tobramycin from polycaprolactone in a rabbit model

This study investigated the elution characteristics of tobramycin from polycaprolactone, a bioabsorbable polymer, in a rabbit model. Sixty rabbits were divided into two groups. Group 1 had polycaprolactone rods impregnated with 6% tobramycin surgically implanted into the proximal femoral intramedullary canal. Group 2 received polymethylmethacrylate rods of like size, shape, and antibiotic concentration. Serum and urine samples were obtained, and tobramycin levels were determined via fluorescent immunosorbent assay. Rabbits were sacrificed as long as 56 days after surgery. Local bone tobramycin concentration was determined using the agar diffusion method. Polycaprolactone delivered a significantly higher peak bone concentration of tobramycin (22.4 microg/mL) than did polymethylmethacrylate (13.59 microg/mL). Polycaprolactone also had a more gradual decrease in local tobramycin concentration than did polymethylmethacrylate. Neither polycaprolactone nor polymethylmethacrylate yielded consistently detectable (> 0.1 microg/mL) serum tobramycin levels. Urine concentrations mirrored those seen in bone, with polycaprolactone achieving significantly higher tobramycin concentrations than did polymethylmethacrylate. Polycaprolactone had superior elution characteristics compared with polymethylmethacrylate in this lapine model, suggesting that polycaprolactone might be a promising local antibiotic delivery vehicle for the treatment of osteomyelitis.