A novel three-layered tablet for extended release with various layer formulations and in vitro release profiles.

A novel three-layered tablet consisting of a water-soluble mid-layer and two barrier layers with swellable polymers was investigated to develop a preferable once-a-day formulation containing terazosin HCl as a hydrophilic model drug. When the tablet was exposed to a release medium, the medium quickly permeated to the mid-layer and the two barrier layers swelled surrounding the mid-layer rapidly. It facilitated the tablet to absorb a lot of water compared with monolithic matrix. Moreover, formation of a lot of pores in the tablet during dissolution could be observed, suggesting significant water absorption in the inner matrix and swollen polymers of the tablet. Barrier layers influenced drug release profiles significantly, potentially due to differences in viscosity after swelling that produce different diffusion coefficients and mechanical strength. The drug in the mid-layer showed the sigmoid type of release pattern because a period of time might be needed to release the drug from the mid-layer through the barrier layers, but the drug in barrier layers showed the typical release pattern of monolithic matrix. As the amount of water-soluble excipient in the mid-layer increased, the degree of swelling also increased, suggesting that its amount in the layer may affect the overall swelling properties of the tablet. It was also shown that more hydrophilic mid-layer caused faster erosion rate, which was related to the results of swelling property. The three-layered tablets showed more consistent release kinetics than the matrix tablets. These results can give good information for the development of sustained drug delivery systems, especially once-a-day administration.