The effect of storage temperatures on the in vitro properties of a polyanhydride implant containing gentamicin

Septacin is a biodegradable sustained-release implant containing 20% (w/w) gentamicin sulfate. The matrix of the implant is a polyanhydride copolymer composed of erucic acid dimer (EAD) and sebacic acid (SA) in a one-to-one weight ratio. The effect of storage temperatures (-15 degrees C and 25 degrees C) on the stability of Septacin was evaluated with respect to gentamicin potency, copolymer molecular weight, and in vitro drug release. The drug in polymer matrix was stable for at least 12 months when stored at 25 degrees C, but the molecular weight of the copolymer declined rapidly at this temperature. At -15 degrees C, there was no change in the molecular weight of the copolymer. However, the placebo (copolymer without gentamicin) exhibited a significant drop in copolymer molecular weight at both temperatures. The drug release profiles showed no change for samples stored at -15 degrees C for the duration of this study, while the release of drug slowed down significantly for samples stored at 25 degrees C for longer than one month. A pronounced difference in the morphology of the -15 degrees C samples and the 25 degrees C samples was observed during the in vitro dissolution test; cracking of the -15 degrees C samples was evident, but the 25 degrees C samples remained intact.