Pharmaceutical Manufacturing Handbook: Production and

Calcium phosphate, dibasic offers high hardness and faster dissolution profi le
than lactose for α - methyldopa tablets in wet granulation.
6.3.5
TABLET DESIGN FOR MATRIX SYSTEM
TABLET DESIGN FOR MATRIX SYSTEM 995
The advantages of controlled - release systems include maintenance of drug levels
within a desired range, the need for fewer administrations, optimal use of the drug
in question, and increased patient compliance. Evaluation of matrix tablets is the
same as for conventional formulations but the dissolution profi le and stability have
to be carefully studied. Numerous methods for development of matrix tablets can
be used, such as direct compression, wet granulation, pelletization, and spheronization
exclusion. Nevertheless, the potential disadvantages cannot be ignored: the
possible toxicity or no biocompatibility of the materials used, undesirable by -
products of degradation, any surgery required to implant or remove the system,
the chance of patient discomfort from the delivery device, and the higher cost of
controlled - release systems compared to traditional pharmaceutical formulations.
The importance of matrix systems that they release bioactive component over an
extended period of time has long been recognized in the pharmaceutical fi eld.
Matrix systems can be divided into three groups depending on the type of polymer
formed:
1. Inert Matrices Polymers that after compression form an indigestible and
insoluble porous skeleton [14] constitute the inert matrices. The main challenge in
the preparation of these systems is to achieve, by means of a suitable design, total
drug release from the device as well as adequate and precise drug release, guaranteeing
the integrity of the matrix.
2. Hydrophilic Matrices Cellulose derivatives have been widely used in the
formulation of hydrogel matrices for controlled drug delivery. Among them hydroxypropyl
methylcellulose (HPMC) is the most extensively employed because of its
ease of use, availability, and very low toxicity [15] . Drug release from these systems
is controlled by the hydration of HPMC, which forms a gelatinous layer at the
surface of the matrix through which the included drug diffuses.
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.
Water - soluble drugs are released primarily by diffusion of dissolved drug molecules
across the gel layer, while poorly water soluble drugs are released predominantly
by erosion mechanisms.
The factors infl uencing the release of drugs from hydrophilic matrices include
viscosity of the polymer, ratio of the polymer to drug, mixtures of polymers, compression
pressure, thickness of the tablet, particle size, pH of the matrix, entrapped
air in the tablet, solubility of the drug, the presence of excipients or additives, and
the mode of incorporation of these substances.
3. Lipid Matrices These matrix tablets are formed with lipid polymers with low
melting point. The drug is dissolved or solubilized in the melted lipid, such as cetyl