Polyanhydride implant for antibiotic delivery--from the bench to the clinic

A polyanhydride implant (Septacin) containing gentamicin sulfate was developed for sustained local delivery of the drug to the site of infection in the treatment of osteomyelitis. Laboratory-scale injection molding equipment was utilized to fabricate the implant for in vitro characterization. Molding conditions were optimized to produce implants with a skin-core structure which was found to be critical in preventing the initial cracking of the implant during in vitro drug release test in water. A manufacturing process consisting of twin-screw extrusion, pelletizing, and injection molding was developed. Polymer-drug pellets were characterized with respect to copolymer molecular weight and drug content uniformity. The implants were terminally sterilized by gamma-radiation which was found to cause increase in copolymer molecular weight as a result of polymer chain extension. The stability of Septacin was evaluated as a function of storage temperature and time. A marked decline in copolymer molecular weight occurred in samples stored above freezing temperatures and significantly slower drug-release profiles were also exhibited by these samples. In vivo drug release from Septacin in rats showed that the gentamicin plasma levels were extremely low, indicating the low systemic exposure to gentamicin. Furthermore, Septacin samples have demonstrated efficacy in the rat skin-abscess and horse-joint infection models. Results from a human in vivo study also showed high local drug concentrations at implantation sites while systemic exposure to the drug was minimal.