Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Tablets – lozenges – or pills
Patent
1998-01-07
2000-07-04
Spear, James M.
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Tablets, lozenges, or pills
424468, 424469, 424470, A61K 924, A61K 926
Patent
active
060835338
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a layered tablet for the controlled release of active substances in a liquid medium, which comprises at least one active substance-containing layered matrix having contact surfaces to the liquid medium, its contact surfaces being provided, at least partially, with a cover layer delaying or preventing the active substance release. Said layered tablet is characterized by the fact that the cover layer is a layer lying with thickness gradients on contact surfaces of the layered matrix, and which is applied on the layered matrix by means of pressing on powdery or granular material which is erodable in the liquid medium. The present invention in particular relates to a layered tablet for the controlled release of pharmaceutical active substances in the fluids of the gastrointestinal tract or in liquids suitable to test drugs.
BACKGROUND OF THE INVENTION
In the art of pharmaceutical technology layered tablets are tablets consisting of several, firmly adhering, parallel or concentrically curved layers of compressed powder or granulate particles (cf. Hunnius Pharmazeutisches Worterbuch, 6th edition, Berlin 1986). In contrast to press-coated tablets, which are defined as tablets with a preformed core having a material completely surrounding the core and formed by compressing a powder or granular material, conventional layered tablets are manufactured in one operation and in a tablet press by repeatedly compressing different kinds of particles, the layers obtaining a characteristic form owing to the fact that the same press is used in each compression. For this reason, the forms of the individual layers cannot be chosen freely, i.e., independently of each other. The use of biplanar punches results in layered tablets having consistently parallel layers, except for the border areas in the region of the optional facet. If curved punches are used, the lower layer, which is pressed first, assumes a biconvex shape, whereas the upper or second layer has a uniform thickness and is parallel with the curved upper boundary surface of the layer pressed first.
In 1917, layered tablets and a process for their production were described for the first time (U.S. Pat. No. 1,248,571). They are used in pharmacy for several considerations. On the one hand, they offer the possibility of combining incompatible active substances in one tablet in a spatially separated form. On the other hand, they permit combination of several formulations having different release properties. For instance, the one layer may be used to release an initial dose of the active substance in the form of a fast-disintegrating, quick-releasing formulation, whereas the second layer comprises a maintenance dose in retarded form.
Quite recently, special layered tablets for the controlled release of active substances, in particular for zero-order release, have been described (U. Conte et al., J. Controlled Rel. 26, pp. 39-47, 1993). These layered tablets comprise an active substance-containing swelling matrix and at least one excipient ingredient layer pressed thereon and covering the matrix surface on one side. The layer of inactive ingredients is substantially inert and impermeable to active substances. The active substance-containing matrix releases the active substance in liquid media by means of diffusion.
Swelling of the matrix in aqueous medium is intended to ensure that the release rate does not decrease in the course of substance release--owing to progressive active substance depletion of the matrix and simultaneous extension of the diffusion path, but is maintained in terms of a zero-order process. This swelling causes a substantial enlargement of the matrix surface as compared to its dry state. However, the published data relating to the actual release behavior of these layered tablets show that the swelling effect in most practical cases is not sufficient to maintain the initial release rate. If, on the other hand, the swelling matrix is formulated such that it swells in an aqueous medium to an extreme extent, insufficient
REFERENCES:
patent: 4786507 (1988-11-01), Schmidt
patent: 4966772 (1990-10-01), Ohm et al.
patent: 5279832 (1994-01-01), Greissinger et al.
patent: 5549913 (1996-08-01), Colombo et al.
LTS Lohmann Therapie-Systeme GmbH
Spear James M.
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