A number of multiple dose divisible tablet designs have been reported, most of them for the conventional fast release tablets with the laterally extending grooves. Derwent abstract 35867W/21; 13237: 70026V/40; 18289; 19988; 37707; and 20761U-B give examples of such divisible fast release tablets. None of these designs specify the relationship between laterally opening side grooves and laterally extending top and bottom grooves as described in the present invention, nor do they refer to the sustained release dosage forms.
Tablets having laterally extending grooves on the top and bottom surfaces and a small laterally opening groove on the sides are described in Derwent abstracts 71600C/41 and 5873C/33. However, these grooves are provided to facilitate ease in breaking the tablet, and not for the purpose of prescribing sustained release dosage forms. Since division of these tablets exposes a substantial amount of new surface, these tablets will not be suitable for sustained release preparations.
A controlled release theophylline tablet with laterally extending grooves on the flat tablet surfaces is described in Derwent abstract 85413D/47. Here again, substantial new surface is produced upon division of the tablet. No mention has been made of the laterally opening grooves to minimize the exposed surface as in the present invention.
Derwent abstract 28075 mentions a sustained release divisible tablet using a V-shaped center core and layering of the active ingredient. This design also would result in the exposure of appreciable new surface upon tablet division and thus, change in the drug release rate.
The controlled release divisible tablet designs described in the U.S. Pat. No. 4,353,887 come closest to achieving comparable drug release rates for the whole tablet and its fragments. However, as with the other above described designs, here also, tablet division produces relatively large new surface. To control the rate of release, the drug must be arranged in longitudinal layers within the tablet, which precludes its application to simple matrix tablets as in the present invention.
Although the above mentioned patents describe a variety of divisible tablet forms for sustained (controlled) release preparations, none attempt to effectively minimize the amount of new surface area exposed after division. None of them refer to having laterally opening side grooves along with the laterally extending grooves on the faces of the tablet in order to minimize the exposed new surface upon division of the tablet. Laterally opening and laterally extending grooves described in the present invention significantly reduce the exposure of new surface upon tablet division and, therefore, the fragments will retain the release rate of the whole tablet.
The major objective of the invention is to provide divisible tablets that will retain their sustained release property when divided into two or more discrete segments. The unique designs described in the present invention provide partial dose fragments with a minimum of exposed new surface created after the division of the whole tablet. As a result, the sustained release characteristics of the whole tablet are retained by each segment of the tablet.