Evaluation of a new matrix obtained by direct compression and thermal treatment in tablet press-coating

Coatings are very important in pharmaceutical formulation for taste masking, drug protection, and drug release modification. Most film coatings are applied using polymer solutions but the use of organic solvents implies some disadvantages, like solvent exposure, solvent disposal and product contamination by residual. Furthermore, such solvents are flammable and toxic for operators and their use cannot be considered pollution-free. Although the use of water as a coating-solvent eliminates many of these disadvantages, it could lead to other problems like processing time increase and long-term stability issues for some products. Among the various solventless processes, compression coating retains some importance, for example to delay or to control drug release, to associate incompatible drugs in the fixed dose combination, to target two drugs in different areas of the gastrointestinal tract, to obtain a pulsatile time-dependent release and to incorporate poorly compactable materials in the core. This coating procedure has been shaded by the difficulty to develop a manufacturing process able to localize the core in the center of the coated tablet. In the last years different manufacturing methods have been proposed to overcome this inconvenient. In particular a one-step dry-coating tablet manufacturing method implemented by Ozeky et al. is noteworthy for producing thinner coatings. Recently we have developed a thermal procedure to obtain, from a direct compression (DC) tablet containing a cross-linked polycarboxylic acid and a cellulose derivative, a bioadhesive matrix able to control the drug release. The mechanism controlling drug release is based on the formation of a non-erodible water-swellable matrix, whose behaviour can be modulated on the basis of thermal procedure and excipient composition. The unique features of this procedure make it also applicable to the manufacturing of coated tablets. Here we illustrate the preliminary experimental evidence gathered using this matrix in compression-coated tablets.