Design and preparation of pulsatile release tablet as a new oral drug delivery system. 
To achieve time-controlled or site specific delivery of a drug in the gastrointestinal tract, an orally applicable pulsatile drug release system with the dry-coated tablet form was developed.  The system consisted of a less water permeable outer shell and a swellable core tablet; from such a system, the drug was expected to be rapidly released after a certain period of time on the basis of time-controlled disintegration mechanism.  Various model disks of outer shell, consisting of hydrogenated castor oil and polyethyleneglycol 6000, were tested for their water penetration rate.  The experimental results showed that water penetration proceeded obeying the boundary retreating mechanism, so that the lag time of the system could be controlled by changing either the thickness or the composition of the outer shell.  The swelling force of various commercially available disintegrants was quantitatively compared, and it was found that carboxymethylcellulose calcium was the preferable disintegrant to be used for the core tablet.  On the basis of the results of a series of fundamental studies, various pulsatile release tablets of isoniazide with different lag times were designed.  In the in vitro dissolution test, typical pulsatile release was achieved for all the tablets prepared, and a good correlation was found between the observed lag time and the estimated lag time calculated from an empirical equation deduced from the thickness and polyethyleneglycol 6000 content of the outer shell.