Controlled drug release from Poloxamer formulations: Diffusion vs erosion mechanism

We report the in vitro release kinetics of low molecular weight hydrophilic drugs from Poloxamer block copolymer gels (consisting of close-packed spherical micelles) and from tablets formed from bulk Poloxamer. Sustained drug release has been achieved. The drug release kinetics depended on two contributions: (i) diffusion of the drug molecules through the water channels present in gel structure (approximately t^0.5), and (ii) release concurrent with the erosion of the Poloxamer gel matrix (approximately t). The experimentally determined release profiles were fitted to an equation that included a diffusion and an erosion term, and the two contributions were quantified. The release from the tablet followed closely the erosion (zero order) mechanism, while that from the gel had a diffusion contribution. The interplay between the drug molecules and the self-assembled microstructures formed by Poloxamer gels can be utilized into controlled delivery applications.