A novel pulsed-release system based on swelling and osmotic pumping mechanism

A novel pulsed-release system based on bilayer coated tablets containing an osmotically active agent is presented. Hydroxypropylmethylcellulose (HPMC) and the mixture of Eudragit RS and RL were applied as the swelling layer and semipermeable outer coat, respectively. To examine the mechanism of drug release from this pulsed-release system, drug release behaviors were investigated under conditions of various osmotic pressures. Both lag time and release rate were dependent on the coating level and the osmotic pressure of the dissolution medium. The swelling of tablets and the dynamics of water uptake during the dissolution were investigated to further elucidate the mechanism of drug release. The osmotic active agent induces a continuous water influx resulting in a rapid expansion of the membrane. The subsequent formation of fractures leads to a fast drug release after an initial lag time. All the results obtained in the present study indicated that both diffusion and osmotic pumping effect were involved in drug release from the device, but the latter was more dominant.