tablets are solid dosage forms of medicinal substances..............
Zhion@zhion.com updated on May 27, 2006.
WHY ORAL SOLID DOSAGE FORM NEEDED?
The vast majority of drug substances are administrated in milligram quantities. It
is almost impossible for a layman to measure such tiny quantities out accurately
without a sensitive laboratory balance.
In addition to the accuracy of dosage, dosage form is needed to protect the drug
from oxidation, moisture, gastric acid, to conceal the better or offensive taste of the
medicine, and or to achieve certain desired objectives such as a better efficacy and
If the medication is designed for systemic use and oral administration is desired,
tablets or capsules are usually prepared.
Tablets are solid dosage forms of medicinal substances (i.e. the active
ingredients) usually prepared with the aid of various inactive ingredients. Tablets
may have different shape, size, weight, hardness, thickness and disintegration
PHARMACEUTICAL INACTIVE INGREDIENTS
DILUENT Diluents are fillers to add the necessary bulk to a formulation to prepare
tablets of the desired size. Examples of diluents include pregelatinized starch,
microcrystalline cellulose and lactose.
BINDER Binders promote the adhesion of the formulation particles and maintain
the final tablet integrity. The most common binding agent is microcrystalline
cellulose. However, if the blend has a flow problem, wet granulation is usually
used to improve the bulk flow in the manufacturing process. During the granulation
process, a binder solution is added to the drug and other excipients to form larger
particles, i.e. granules. Granules have a better flow, because they are heavy and
bigger. Hydroxypropyl methylcellulose and povidone are widely used in the binding
Vinylpyrrolidone-vinyl acetate copolymer [Copolyvidone, copovidone] Kollidon VA 64
(BASF) and Plasdone S-630 (ISP)] Â– 60:40 copolymer of vinylpyrrolidone and vinyl
acetate [K-value 25-24]; good in direct, dry and wet granulation; good
Polyvinylpyrolidone, Povidone [Plasdone K (ISP) and Kollidon (BASF)] - linear
homopolymers of vinylpyrrolidone [K-17, K-25, K-29/32 & L-90], good for wet
DISINTEGRANT Disintegrating agents assist the breakup of the tablet into small
particles for absorption after administration. Disintegrating agents include corn and
potato starches, starch derivatives (e.g. sodium starch glycolate), cellulose
derivatives (e.g. sodium carboxymethylcellulose), alginic acid, crosslinked polyvinyl
polypyrrolidone (or crospovidone USP/NF). Commercially available crospovidones
are Polyplasdone XL (ISP) and Kollidon CL (BASF). They are insoluble in water,
highly compressible and swellable.
LUBRICANT Lubricants assist the particle flow and prevent powder sticking during
blending and compression. Examples are talc and magnesium stearate. Usually,
the required amount of lubricants is about 0.1% to 5%.
MISCELLANEOUS ADJUNCTS Miscellaneous adjuncts include colorants and
MANUFACTURING PROCESS - DIRECT COMPRESSION
Typically, the drug substance is blended with diluents, binders, disintegrating
agents in a V-shell (or slant-cone) blender for a few minutes or long. Then, the
lubricants are added into the blend and mixed for another few minutes. After
blending, the powder mixture is compressed into tablets.
After tablet compression, some compressed tablets may be further coated for
sustained release, taste-masking, appearance or/and some other purposes.
Sugarcoating of tablets involves five basic steps: waterproofing, subcoating,
smoothing, coloring and polishing. The process is usually conducted in a coating
pan. With the pan rotating, the coating mixture is sprayed onto the tablets. The
waterproofing layer is to protect the tablet core from moisture. The subcoating
consisting of heavy syrup, gelatin or acacia is applied to Â“roundÂ” the tablets to the
desired shape. Then, a thick sucrose-syrup is applied to smooth and final-round
the tablets. To achieve the final smoothness and the appropriate color to the
tablets, a thin syrup containing the desired colorant are applied. Finally, tablet
polishing is achieved by applying carnauba wax to the tablets in the coating pan.
Because sugarcoating process is tedious and time-consuming, most
manufacturers prefers film-coating. Film-coating solutions usually contain a film
former, a pore-former, a plasticizer, colorants and a volatile solvent. Usually, film-
former is the material for the film formation and plasticizer assists the film-
formation process to produce a film with a good mechanical strength.