The Pharmaceutics and Compounding Laboratory
Tablets

Introduction

Without question, the compressed tablet is one of the most popular dosage forms today. About one-half of all prescriptions dispensed are for tablets. Usually one considers a compressed tablet as an oral medication; however, tablets have many other uses. The sublingual tablet, the pellet, the wafer, the troche, and the vaginal insert are manufactured by the same procedure as an oral tablet.

There are three methods of commercially making compressed tablets:

  • The direct compression method

    A compressible vehicle is blended with the medicinal agent, and if necessary, with a lubricant and a disintegrant, and then the blend is compressed. Substances that are commonly used as directly compressible vehicles are: anhydrous lactose, dicalcium phosphate (Emcompress), granulated mannitol, microcrystalline cellulose (Avicel), compressible sugar (Di-Pac), starch (Sta-Rx 1500), hydrolyzed starch (Celutab), and a blend of sugar, invert sugar, starch and magnesium stearate (Nutab).

  • The dry granulation method (slugging method)

    The ingredients in the formulation are intimately mixed and precompressed on heavy duty tablet machines. The slug which is formed is ground to a uniform size and compressed into the finished tablet.

  • The wet granulation method

    This method has more operational manipulations, and is more time-consuming than the other methods. The wet granulation method is not suitable for drugs which are thermolabile or hydrolyzable by the presence of water in the liquid binder. The general steps involved in a wet granulation process are:

    1. The powdered ingredients are weighed and mixed intimately by geometric dilution.
    2. The granulating solution or binder is prepared.
    3. The powders and the granulation solution are kneaded to proper consistency.
    4. The wet mass is forced through a screen or wet granulator.
    5. The granules are dried in an oven or a fluidized bed dryer.
    6. The dried granules are screened to a suitable size for compression.
    7. A lubricant and a disintegrating agent are mixed with the granulation.
    8. The granulation is compressed into the finished tablet.