Tablet multi-layered tablets

Multi-layered tablets A multilayered tablet consists of several different granulations compressed on top of each other to form a single tablet. They may also be bi-layer when incompatible drug substances are used, e.g., phenylephedrine HCl in one layer and ascorbic acid and paracetamol in another. 

Streubel A, Siepmann J, Peppas NA, Bodmeier R. Bimodal drug release achieved with multi-layer tablets transport mechanisms and device design. J Control Release 2000 69 455 68. 

Abdul S, Poddar SS. A flexible technology for modified release of drugs multi-layered tablets. J Control Release 2004, 7 Jul 97(3) 393-405. 

While the drug release from wax matrix tablets followed the square root of time relationship, approximately zero-order release of ephedrine hydrochloride and procaine hydrochloride could be obtained with multi-layered matrices of hydrogenated castor oil containing different concentrations of the active compound in each layer. 

Conte, U., Maggi, L., 1996. Modulation of the dissolution profiles from Geomatrix multi-layer matrix tablets containing drags of different solubility. Biomaterials 17, 889—896. 

SPE, chromatography (i.e., thin-layer chromatography, gel-permeation chromatography and HPLC) and on-line multi-dimensional chromatography. These techniques are rarely used in routine tablet assays due to their technical difficnlties, labor intensity and problems with recovery. 

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