A NEW MULTIPARTICULATE DELAYED RELEASE SYSTEM .1. DISSOLUTION PROPERTIES AND RELEASE MECHANISM

A multiparticulate delayed release system based on coated pellets cont aining an osmotic active ingredient is presented. The coating consists of a semipermeable membrane of cellulose acetate. After application w ater penetrates into the core and forms a saturated solution of the so luble components. The osmotic pressure gradient induces a water influx resulting in a rapid expansion of the membrane leading to the formati on of pores. The osmotic ingredient and the drug are released through these pores according to a zero order kinetic. In comparison with the sodium chloride free formulation the inclusion of the osmotically acti ve ingredient results in a completely different dissolution behavior. Lag time and dissolution rate are dependent on the coating level and t he osmotic properties of the dissolution medium. However, the dissolut ion rate is sufficient even with high coating levels to obtain delayed release properties. The model proposed is supported by data from dete rmination of pellet swelling behaviour, sodium chloride release, singl e pellet dissolution and release in media of different pH and osmolali ty.