bioadhesive macrosphere delivery systems having prolonged gastric retention time due to bioadhesion rather than physical density or size are described . in general , the macrospheres have diameters that are greater than 200 microns , more preferably greater than 500 microns . the bioadhesive macrospheres are released in the stomach where they reside in close proximity to the gastric mucosa for a prolonged period of time . increased residence of bdds in the upper gi can lead to increased systemic absorption of drug in the preferred site of systemic absorption , namely the upper gi tract . the bdds may be engineered either as a capsule with drug delivery controlled by a diffusion - limited membrane or degradable shell , or as a solid matrix system with drug delivery controlled by a combination of diffusion and polymer degradation kinetics .