Investigation of the mechanisms governing the release of levamisole from poly-lactide-co-glycolide delivery systems

The release of levamisole from poly-lactide-co-glycolide microspheres and co-evaporate discs was investigated. In addition to drug release, polymer release, estimated from polymer weight loss and molecular weight change, was monitored from the disc systems. Drug release profiles were sigmoidal and were fitted to a model indicative of polymer degradation controlled release. Model parameters representing the induction and acceleration of decomposition were estimated from drug release profiles and used successfully to fit polymer mass loss profiles, thus strongly supporting the degradation controlled release model. The drug dramatically accelerated polymer degradation on increasing the drug loading. The presence of levamisole base increased the rate of co-polymer decomposition by factors of 7, 8 and 10.7 when present in concentrations of 5%, 10% and 20% in the co-evaporate discs.