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 safety.
If the medication is designed for systemic use and oral administration is desired, tablets or capsules are usually prepared.
TABLET INGREDIENTS
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 properties.
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 solution preparation.
Vinylpyrrolidone-vinyl acetate copolymer [Copolyvidone, copovidone] Kollidon VA 64 (BASF) and Plasdone S-630 (ISP)] – 60:40 copolymer of vinylpyrrolidone and vinyl acetate [K-value 25-24]; good in direct, dry and wet granulation; good compressibility.
Polyvinylpyrolidone, Povidone [Plasdone K (ISP) and Kollidon (BASF)] - linear homopolymers of vinylpyrrolidone [K-17, K-25, K-29/32 & L-90], good for wet granulation
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 flavorants.
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 TABLET
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 sub-coating consisting of heavy syrup, gelatin or acacia is applied to “round” 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.
FILM-COATING TABLET
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.
