Matrix-type tablets

Binders improve the strength of compacts through increased plastic deformation or chemical bonding. They may be classified as matrix type, film type, and chemical. Komarek [Chem. Eng., 74(25), 154 (1967)] provides a classification of binders and lubricants used in the tableting of various materials. 

Extensions of BCS beyond the oral IR area has also been suggested, for example to apply BCS in the extended-release area. However, this will provide a major challenge since the release from different formulations will interact in different ways with in vitro test conditions and the physiological milieu in the gastrointestinal tract. For example, the plasma concentration-time profile differed for two felodipine ER tablets for which very similar in vitro profiles had been obtained, despite the fact that both tablets were of the hydrophilic matrix type based on cellulose derivates [70], This misleading result in vitro was due to interactions between the gel strength of the matrix and components in the dissolution test medium of no in vivo relevance. The situation for ER formulations would be further complicated by the need to predict potential food effects on the drug release in vivo. 

J.L.Ford, M.H.Rubinstein and F.McCaul, Importance of drug type, tablet shape and formulation on release from hydroxypropylmethylcellulose matrix tables, Proc. 6th Pharmaceutical Technology Conf. Canterbury, 7—9 April, 1987, Vol. 1, pp. 82-87. 

The use of cellulose ethers in producing matrix-type sustained release tablets is well documented [7]. Hydrophilic matrices of ketoprofen with hydroxypropylmethylcellulose (KET-R)... 

J. L. Ford, M. H. Rubinstein, F. McCaul, et al. Importance of drug type, tablet shape and added diluents on drug release kinetics from hydroxypropymethylcellulose matrix tablets. Int. J. Pharm. 40 223-234, 1987. 

Application of the percolation theory allows explanation of the changes in the release and hydration kinetics of swellable matrix-type controlled delivery systems. According to this theory, the critical points observed in dissolution and water uptake studies can be attributed to the excipient percolation threshold. Knowledge of these thresholds is important in order to optimize the design of swellable matrix tablets. Above the excipient percolation threshold an infinite cluster of this component is formed which is able to control the hydration and release rate. Below this threshold the excipient does not percolate the system and drug release is not controlled. 

Gl lesions Potassium chloride tablets have caused stenotic or ulcerative lesions of the small bowel and death. These lesions are caused by a concentration of potassium ion in the region of a rapidly dissolving tablet, which injures the bowel wall and produces obstruction, hemorrhage, or perforation. The reported frequency of small bowel lesions is much less with wax matrix tablets and microencapsulated tablets than with enteric coated tablets. Immediately discontinue either type of tablet and consider the possibility of bowel obstruction or perforation if severe vomiting. 

At pH 9 there is a further slight increase in the amount which is released, over that from the two lower pH values, at all three compression forces. However, the same release patterns hold, with more being released after lower compression force and a higher amount from the matrix as against the microcap tablet. Only with the latter type, at a ration of 1 1, is this trend not followed and, as at other pH values, with this system there appears to be only an insignificant effect of compression. 

Soluble matrix systems. The third matrix system is based on hydrophilic polymers that are soluble in water. For these types of matrix systems, water-soluble hydrophilic polymers are mixed with drugs and other excipients and compressed into tablets. On contact with aqueous solutions, water will penetrate toward the inside of the matrix, converting the hydrated polymer from a glassy state (or crystalline phase) to a rubbery state. The hydrated layer will swell and form a gel, and the drug in the gel layer will dissolve and diffuse out of the matrix. At the same time, the polymer matrix also will dissolve by slow disentanglement of the polymer chains. This occurs only for un-cross-linked hydrophilic polymer matrices. In these systems, as shown in Fig. 5.3, three fronts are formed during dissolution9-11 ... 

Figure 2.7 The figure shows the layout of a tablet matrix comprised of tablet types A, B and C, in addition to pure components acetaminophen, aspirin and caffeine. Each tablet is 10 mm in diameter, and the overall sample and pure component matrix covers an area 9x7 cm2.

One of the best understood mineralization systems in terms of the microenvironment of nucleation is the mollusk shell, and in particular one of the seven structural types of mollusk shell, the nacre [99], The nacre has a simple geometry and is therefore a most convenient system to study in terms of nucleation. Observations of growing aragonitic tablet-shaped crystals show that the matrix surface at the location where the first crystals form is different from the remaining surfaces. This location can be differentially stained using dyes that have affinities for calcium and sulfate, for example [100], The surface topography is... 

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