Tablet
From Pharmpedia
Tablet may be defined as the solid unit dosage form of medicament with or without suitable diluents and prepared either by molding or by compression.
In "pharmaceutical chemist" terminology
A tablet is a combination of ingredients that is compressed into a solid mass. The basic components of an immediate release pharmaceutical tablet are:
active drug substance
diluent or filler
Tablets are the most widely used solid dosage form of medicament because they offer a number of advantages to the patient, prescriber, manufacturer and the manufacturing pharmacist.
Introduction
Tablets are solid unit dosage form of medicaments with or without suitable diluents and prepared either by molding or compression. They are solid, flat or biconvex disc in shape. They vary greatly in shape, size and weight which depend upon amount of medicament used and mode of administration. They also vary in hardness, thickness, disintegration and dissolution characteristics and in other aspects depending upon their intended use and method of manufacture. Tablets are the most widely used solid dosage form of medicament. Because of their advantages their popularity is continuously increasing day by day.
Types and classes of Tablets
(A) Oral tablet for ingestion
2. Multiple compressed tablets
4. Sugar coated
(B) Tablet used in oral cavity
4. Dental cones
(C) Tablet administered by other routes
(D) Tablets used to prepare solution
Properties of an ideal tablet
The objective of formulation and fabrication of tablet is to deliver the correct amount of drug in proper form at or over proper time.
1. Tablet should be elegant having its own identity and free from defects such as cracks, chips, contamination, discoloration etc.
2. It should have chemical and physical stability to maintain its physical integrity over time.
3. It should be capable to prevent any alteration in the chemical and physical properties of medicinal agent(s).
4. It should be capable of withstanding the rigors of mechanical shocks encountered in its production, packaging, shipping and dispensing.
5. An ideal tablet should be able to release the medicament(s) in body in predictable and reproducible manner.
Advantages
1. Tablets are unit dosage forms that provide an accurate, stable dose with greatest precision and least content variability.
2. Tablets are easy to use, handle and carry by the patient.
3. Tablets are attractive and elegant in appearance.
4. Tablets are the most stable dosage form with respect to their physical, chemical and microbiological attributes.
5. The manufacturing cost of tablets is low as compared to other dosage form and their manufacturing speed is also quite high.
6. The packaging and shipping of tablets is comparatively easy and cheap.
7. The unpleasant taste and odor of medicament(s) can be easily masked by sugar coating.
8. The incompatibilities of medicament(s) and their deterioration due to environmental factors are less in case of tablet.
9. Whenever a fractional dose is required, tablets are divided into halves and quarters by drawing lines during manufacturing to facilitate breakage.
10. They are more suitable for large scale production than other oral dosage forms.
11. Tablets provide administration of even minute dose of drug in an accurate amount.
12. Their identification is probably the easiest because of variety of shapes and colors.
13. Tablets are formulated with certain special release profile products such as enteric or delayed release products.
14. They are economical as their cost is lowest as compared to other oral dosage forms.
Disadvantage
1. Drugs that are amorphous in nature or have low density character are difficult to compress into tablet.
2. Hygroscopic drugs are not suitable candidate for compressed tablets.
3. Drugs having poor wetting properties, slow dissolution profile and high optimal gastro intestinal absorption are difficult or impossible to formulate as a tablet.
4. Drugs having bitter taste and objectionable odor requires special treatment like coating or encapsulation which may increase their production cost.
5. Drugs that are sensitive to oxygen or may also require certain treatment like special coating as well as packaging which may increase the overall manufacturing cost.
6. High dose drugs are difficult to formulate as tablet dosage form.
7. Some drugs which preferably get absorbed from the upper part of GIT may cause bioavailability problem in tablet dosage form.
8. Drugs that are liquid in nature are difficult to formulate as a tablet.
9. Swallowing of tablets especially by children and critically ill patients is very difficult.
Commonly used excipients in tablet manufacturing
Substances other than active ingredients are commonly referred as excipients. The commonly used exipients are diluents, binders and adhesives, disintegrants, lubricants, anti adherents, glidants, fillers, colors and sweeteners etc. Tablet excipients must meet certain criteria in the formulation such as;
• They must be non toxic and acceptable to the regulatory agencies in all countries where the product is to be marketed
• They must be commercially available in an acceptable grade in all countries where the product is to be manufactured.
• Their cost must be acceptably low
• They must be physiologically inert.
• They must be physically and chemically stable by themselves and in combination with the drug (s) and other tablet components.
• They must be free of any unacceptable microbiologic load.
• They must be color compatible ( not producing any off-color appearance)
• If the drug product is also classified as a food (e.g. certain vitamins products), the diluents and other exipient must be approved direct to food additives.
• They must have no any deleterious effect on the bioavailability of the drug(s) in the product.
Diluents
These are the inert substances which are added to increase the bulk to make the tablet of a practical size for compression. Diluents like mannitol, lactose, sorbitol, sucrose, and inositol when present in sufficient quantity can impart properties to some compressed tablet that permit disintegration in the mouth by chewing ( Chewable tablet ). In the formulation, the incompatibility of diluents must be considered (Calcium salts used as diluents for the broad spectrum antibiotics like Tetracycline have been shown to interfere with the drug absorption from GIT. Microcrystalline cellulose (Avicel®) usually is used as an excipient in direct compression formula. Hydroxyl propyl methyl cellulose is used to prolong the release from tablet and as a film former in tablet coating.
Binders
Binders are the agents generally used to impart cohesive qualities to the powdered material. In tablet formulation the diluents ensures that the tablet remains intact after compression. It improves free flow qualities by formulation of granules of desired hardness and size. Starch, gelatin, sucrose, glucose, dextrose and lactose are frequently used as binders. Natural and synthetic gums that have been used include acacia, sodium alginate, panwar gum, ghatti gum, CMC, veegum etc. Starch paste in varying concentration from 10-20% are used as a binder. HPMC which is more soluble in cold water as compared to hot water is also used in special cases. Excessive use of binder in the tablet may lead to prolong disintegration time which is not desired. Therefore they are used in prescribed concentration to overcome the same.
Lubricants
Lubricants are the substance which prevent adhesion of the tablet material to the surface of the dies and punches, reduce interparticle friction, facilitate an easy ejection of tablets from the die cavity and improves rate of flow of tablet granulation. Commonly used lubricants are talc, magnesium stearate, calcium stearate, stearic acid, hydrogenated vegetable oil and PEG. The method of adding lubricant is an important factor for satisfactory results. The quantity of lubricant significantly varies from 0.1 to 5%. The additions of lubricant to granules in the form of emulsion or suspension are used to reduce the processing time. The primary problem in the preparation of water soluble tablet is the selection of satisfactory lubricant. Soluble lubricants include Sodium benzoate, sodium acetate, sodium chloride and carbowax 4000.
Glidants
A glidant is a substance that improves the flow characteristics of a powder mixture. These materials are always added in the dry state just prior to compression. The most commonly used glidants are colloidal silicon dioxide (Cabosil®, Cabot®) and asbestos free talc. They are used in concentration less than 1%. Talc is also used and may serve the dual purpose of lubricant/glidant.
Disintegrants
Disintegrants are the substance or a mixture of substances added to a tablet to facilitate its break up or disintegration after administration. Starches, clays, cellulose and cross linked polymers are most commonly used disintegrants. The oldest and still the most popular disintegrants are corn and potato starch. Other ingredients like veegum, methyl cellulose, agar, bentonite, cellulose, citrus pulp and CMC are also used. They are mostly added into two portions, one part is added prior to granulation and the remainder is mixed with the lubricant and finally both are mixed just before the compression.
Colouring agents
Colors in compressed tablet are used to impart aesthetic appearance to the dosage form. Colour helps the manufacturer to control the product during its preparation as well as serves as a means of identification to the user. One of the basic requirements concerning the use of colorant in pharmaceuticals is it must be approved and certified by the FDA. Colourants can be used in solution form or in suspension form. Pproper distribution of suspended colourants in the coating solution requires the use of the powdered colourants (<10 microns). Most commonly used colourants in use are certified FD & C or D & C colourants. These are synthetic dyes or lakes. Lakes are choice for sugar or film coating as they give reproducible results. Concentration of colourants in the coating solutions depends on the colour shade desired, the type of dye, and the concentration of opaquant-extenders. If very light shade is desired, concentration of less than 0.01 % may be adequate on the other hand, if a dark colour is desired a concentration of more than 2.0 % may be required. The inorganic materials (e.g. iron oxide) and the natural colouring materials (e.g. anthrocyanins, carotenoids, etc) are also used to prepare coating solution. Magenta red dye is non absorbable in biologic system and resistant to degradation in the gastro intestinal tract. Flavouring agents Flavours are usually limited to chewable tablets or other tablets intended to dissolve in the mouth. In general flavours that are water soluble have been found little acceptance in manufacturing of tablets because of there poor stability. Flavouring agents do not affect any physical characteristics of the tablet granulation.
Method of tablet preparation
There are three general methods of tablet preparation.
Uses of Tablets
They are easy to carry.
They are easy to swallow.
They are attractive in appearance.
They do not require any measurement of dose. The Strip or blister packing has further facilitated the process of taking the dose by the patient. Moreover it provides a sealed covering which protects the tablets from atmospheric conditions like air, moisture and light etc.
Tablets provide prolonged stability to medicament.
The incompatibilities of medicaments and their deterioration due to environmental factors are less in tablet forms.
Some of the tablets are divided into halves and quarters by drawing lines during manufacturing to facilitate breakage whenever a fractional dose is required.
An accurate amount of medicament even if very small can be incorporated.
Since they are generally produced on large scale therefore their cost of production is relatively low, hence economical.
They are used as birth control in human beings.
Author
The Full article has been contributed by Sanjula Baboota, Javed Ali, Alka Ahuja, Mohd. Faiyazzuddin, Intakhab Alam, Sohail Hasan
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