Gel matrix tablets

Rabiskova M, Vostalova L, Medvecka G, Horackova D. [Hydrophilic gel matrix tablets for oral administration of drugs]. Ceska Slov Farm 2003 Sep 52(5) 211-217. Czech. 

The ionic concentration in the test medium can affect both the drug solubility and the release mechanism for modified-release formulations. One example of the latter case is hydrophilic gel matrix tablets, a type of ER tablet that forms a gel layer in contact with the GI fluids. Solutes will affect the hydration of the gel matrix and, thereby, affect the drug release rate. 

Abrahamsson, B., M. Alpsten, B. Bake, A. Larsson, and J. Sjogren, J. 1998a. In vitro and in vivo erosion of two different hydrophilic gel matrix tablets. Eur. J. Pharm. Biopharm. 46 69-75. 

The effect of electrolytes and drugs on the cloud point of hydroxypropylmethylcellulose gels and the dissolution of drugs from hydroxypropylmethylcellulose matrix tablets... 

Monolithic non-gas-generating systems are matrix tablets consisting of hydrocolloids that form an external gel layer when hydrated. The internal tablet core remains dry with an overall density lower than that of the gastric fluid. Hydroxypropylmethycellulose (HPMC) is the most commonly used hydrocolloid. This approach has been developed into marketed drug products as the Hydrodynamically Balanced System (HBS) invented by Sheth and Tossounian.93 Gastric retention and flotation times up to 6 hours were achieved. Valrelease (diazepam) and Madopar (levodopa and benserazide) were two marketed products developed using this approach. 

Drug release from swellable matrix tablets is based on the glassy-rubbery transition of the polymer which occurs as a result of water penetration into the matrix. Therefore, the gel layer is physically delimited by the erosion (swollen matrix-solvent boundary) and swelling (glassy-rubbery polymer boundary) fronts. 

The release process for hydrophilic matrix tablets can be schematically described as in Figure 5. The left side of the figure shows a hydrophilic tablet undergoing dissolution, swelling, and release. An interface between the solution and gel layer, here... 

This oral CrDDS is prepared by granulating Valium, an antidepression drug, with hydrocolloids (20-75 wt%) and pharmaceutical excipients. The granules are then compressed to form an oral tablet. After oral intake, the hydrocolloids absorb the gastric fluid and are activated to form a colloid gel matrix surroimding the tablet surface (Fig. 22). The release of Valium molecules... 

Ford, J.L. Thermal analysis of hydroxypropylmethycellu-lose and methylcellulose powders, gels and matrix tablets. Int. J. Pharm. 1999, 179, 209-220. 

The mechanism of drug release from hydrophilic matrix tablets after ingestion is complex but it is based on diffusion of the drug through, and erosion of, the outer hydrated polymer on the surface of the matrix. Typically, when the matrix tablet is exposed to an aqueous solution or gastrointestinal fluids, the surface of the tablet is wetted and the polymer hydrates to form a gelly-like structure around the matrix, which is referred to as the gel layer . This process is also termed as the... 

Mitchell, K., Ford, J.L., Armstrong, D.J., EUiott, P.N., Rostron, C. and Hogan, J.E. (1990) The influence of additives on the cloud point, disintegration and dissolution of hydroxypropyl methylceUulose gels and matrix tablets. Int J Pharm, 66, 233-242. 

Ford, J.L. Mitchell, K. (1995) Thermal analysis of gels and matrix tablets containing cellulose ethers, Thermochim. Acta, 248, 329-345. 

Hydrophilic sustained release matrix tablets are often prepared from cellulose ethers, e.g., hydroxypropyl methyl cellulose. When these materials are exposed to water, the surface of the polymer becomes hydrated. In this way, a gel layer is formed on the glassy core. This changes the barrier properties that are controlling the drug release by a diffusion mechanism. 

R46 U. Mikac, L. Kristi and S. Baumgartner, Using Quantitative Magnetic Resonance Methods to Understand Better the Gel-Layer Formation on Pol5uner-Matrix Tablets , Expert Opin. Drug Delivery, 2011, 8, 677. 

M.S. Attia, and M.M. Aboaly, Highly sensitive and selective spectrofluorimetric determination of metoclopramide hydrochloride in pharmaceutical tablets and serum samples using Eu + ion doped in sol-gel matrix, Talanta, 82,76-82,2010. 

It was outlined in the previous section that the thermal analysis of polymers is not without problems caused by moisture. Pharmaceutically, the presence of moisture may be desirable, unavoidable or part of the functional aspects of the polymer. Thus the presence of low levels of moisture improves the compaction of HPMC by plasticisation [123], increases tablet strength by hydrogen bonding, is part of the function by which hydrophilic polymers perform in matrix tablets [123], or are used as water absorbents in wound dressings [125]. Finally, gels containing water, formed at the surface of a matrix tablet, or as gels for topical delivery contain defined quantities of water. Whichever system is examined, their use is controlled by their properties, some of which can be assessed by thermal analysis. 

The physical model for studying formation of the refractive index distribution of selfocs may be described in the following manner. In the initial stage, in order to obtain a gel-matrix, polymerization is performed not in a tube, but between two glass plates with a thin (100 - 200 pm) polyethylene layering between them. A round hole is cut off in the layer, in which the component A is installed. When the initial stage is finished, the polyethylene layer is removed, and the plate together with clamped gel-polymeric tablet is placed in a cuvette with the component B. The whole system is thermostatically controlled and placed into one of the shoulders of the Mach - Zender laser interferometer [27]. 

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. 

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