Formulation of Tablets
In addition to active ingredients, tablets contain a number of inert materials known as “Additives” or “Excipients“.
Different Categories of Excipients are as follows:
- Binders and Adhesives
- Lubricants and Glidants
- Coloring Agents
- Flavoring Agents
Excipients for Compressed Tablets
Compressed tablets usually contain a number of pharmaceutical adjuncts known as Excipients. In addition to the medicinal substance, the use of appropriate excipients is important in the development of optimum tablets.
Properties of Excipients:
- Excipients determines the bulk of the final product i.e., dosage form such as tablets, capsules etc.
- The speed of disintegration, rate of dissolution and release of the drug is also governed by the use of excipients
- Excipients aids or helps in protection against moisture
- Excipients increase the stability of dosage forms during storage
- Excipients should be neutral with no bio-activity and no reaction with the main drug substance
Functions of Excipients:
- To improve solubility of dosage forms
- To increase the stability of dosage forms
- To impart weight, accuracy and volume to the dosage forms
- To modify the drug release
- To assist in product identification
- To increase patient acceptability
- To enhance bio-availability of drug substance
Diluents, also known as Fillers, increase the volume of a formulation to prepare tablets of the desired size. Widely used fillers are Lactose, Dextrin, Micro-crystalline Cellulose Starch, Pregelatinized Starch, Powdered Sucrose and Calcium Phosphate.
Properties of Diluents:
- They must be non-toxic
- They must be commercially available in acceptable grade
- Their cost must be low and affordable
- They must be physiologically inert and inactive
- They should not alter the bio-availability of the active drug
- They must be color compatible
Ex.: Lactose, Micro-crystalline Cellulose Starch
Binders promote the adhesion of the particles of the formulation, such adhesion enables preparation of granules and maintains the integrity of the final tablet.
Most commonly used binding agents include: Starch, Gelatin and Sugars
- Carboxymethyl Cellulose Sodium – Karaya Gum
- Cellulose Micro Crystalline – Starch, Pregelatinized
- Ethyl Cellulose – Tragacanth Gum
- Methyl Cellulose – Polyvinyl Pyrrolidine
- Acacia Gum – Gelatin
- Agar – Dextrin
Disintegrants are those substances which are added to formulations to facilitate its breaking or disintegration when it comes in contact with water in the Gastro-Intestinal Tract (GIT).
- Starch – 5 to 20% of Tablet Weight
- Starch Derivative – Primogel and Explotab (1 to 8%)
- Cellulose Derivatives – Ac Di Sol (Sodium Carboxymethyl Cellulose)
Lubricant is a substance capable of reducing or preventing friction, heat and wear when introduced as a film between solid surfaces. It works by coating on the surface of particles and thus preventing adhesion of the tablet material to the dies and punches of formulation punching machines.
Properties of lubricants:
- Lubricants improve the flow of granules in the hopper to the die cavity of the punching machines
- Lubricants give a sheer to the finished tablets
- They must be inert and inactive
Commonly used lubricants include
- Magnesium Stearate
- Calcium Stearate
- Stearic Acid
- Hydrogenated Vegetable Oils
- PEG – Polyethylene Glycol
Water molecules attract each other equally in all directions. Water molecules on the surface, however can only be pulled into the bulk water by water molecules underneath, since there are no water molecules to pull in opposite direction these agents are used.
Wetting agents are chemical substances which are used to increase the spreading and penetrating properties of liquid by lowering or reducing its surface tension i.e., the tendency of its molecules to adhere to each other. They are also known as “Surfactants”.
In simple sense, wetting agent reduce the surface tension of solid particles of formulation thereby allowing the external liquid to easily penetrate followed by disintegration and dissolution.
- Anionic, Cationic and Amphoteric Wetting Agents
Flavor refers to a mixed sensation of taste, touch, smell, sight and sound, all of which involve a combination of physio-chemical and physiological actions that influence the perception of substances. Flavoring agents are those substances which are added to food and medicines to improve the quality of the taste and smell.
The types of flavoring agent used in the preparations or formulations are:
- Sweetening agents: Sweetening agents are used to mask the taste of food, beverages and medications and to make them palatable to the consumer. These include sucrose, invert syrup, treacle (used in chlorodyne i.e. chloroform and morphine tincture BPC), sorbitol , saccharine sodium etc.
- Flavored syrup: These include fruit flavored syrup, syrups with weak therapeutic activity for example the pleasantly aromatic odor and pungent taste of Ginger syrup make it a satisfactory flavor for laxative mixtures containing rhubarb while its carminative action (ability in relieve flatulence) is helpful in this type of preparation, and cocoa syrup.
- Aromatic Oils: Like caraway, clove, dill, lemon, orange, pepper-mint etc.
- Synthetic flavors: These include synthetic sweeteners, chloroform, vanillin, benzaldehyde etc. and variety of organic compounds like alcohols, aldehydes, esters, ketones, fatty acids and lectones are used alone or combined with essential oils.