According to IP "tablets are solid dosage forms each containing a unit dose of one or more ingredients".(1) 90%of the drugs thar are administered to produce systemic effect are through oral dosage forms. The advantage of the tablets and the capsules over liquid dosage forms includes elixirs, syrups,solutions is that the exact dose of the drug can be given to the patient.(2) William Brockedon got the first patent for tablet press and showed a route for the future development.(3)The main aim in using a tablet is to provide required amount and to dispense a unit dose of drug to patient. By the time it reaches the target action organ, the drug should not change chemically.(2) And the amount of active ingredient varies a lot. E.g. L-thyroxine has 25ug of active ingredient whereas amoxicillin has about 1g of active ingredient. The weight of the active ingredient ranges from 0.1 to 90% of the total weight of the drug.(3) Tablets should be both physically and chemically stable. They should have capability to withstand the stress during packaging and transport. Physical stability is more important as its effects the bioavailability of the tablet. In the tablet the drug should not undergo any chemical change and the effect of dug on the body must be an expected one.(2) And the drugs have different physical and chemical properties like water solubility, crystalline nature etc
.(3) INGREDIENTS: Diluents: whenever the dose of the drug is less then in order to increase the bulk of the tablet, diluents are used. The diluents also increase the flow properties, the cohesive forces. E.g. lactose USP, Dibasic calcium phosphate, mannitol (used in chewable tablets) Using Calcium phosphate to increase the bulk of the drug tetracycline decreases the bioavailabilty.(2) Binders: These are used in the wet granulation process to give compactness to the powder. It can be added in two ways whch will be described later.(2) e.g. acacia, tragacanth, gelatin Gelatin is better than the former two as making of gelatin solution is easy.(2) Disintegrants: These are the substances that absorb the water in the body, swell and cause the breakup of the particles into individual particles.(2) e.g. Veegum HV and bentonite Matrix forming agents: These are agents that are intended to raise the compactness. If the materials are elastic, when ever the forces are removed reduces the compactness and these agents are intended to prevent this. (3) e.g. Methyl cellulose, mannitol, gelatine Agents used to reduce friction include -Lubricant which will decrese the friction between walls of tablet and die cavity. -Glidant are added to increase the flow properties e.g. talc -Antiadherants which will increase the friction between the punch face and tablet i.e. they reduce the friction during the compression. .(2) Coloring agents, flavoring agents and sweetening agents are used to improve organoleptic properties of a tablet. Coprocessed excipient products: diluents+binders (They may also contain disintegrating agent)(3) CLASSIFICATION Basic classification includes 1) Tablets ingested orally 2) Tablets used in the oral cavity 3) Tablets administered by other routes A) Tablets ingested orally a) Standard compressedtablets: These tablets are prepared by either direct compression or wet granulation or double compaction. The disintegration should be fast in case of these tablets. Antacids and adsorbent which produce local effects comes into this category. Tablets intended for the systemic circulation are soluble in water to some extent and are absorbed into the body. And dissolution is directly proportional to surface area.(2) b) Multiple compressed tablets: these are of two types 1) Layered tablets: they may be two or three laters 2) Compression coated tablets: they may tablets within a tablet(two component) or tablet within a tablet within a tablet (three component) In two layered tablets, the two layers are separated and so the contents that can interact whereas in case of three layered system, a physical barrier is present between the two layers. In case of compression coated tablets the layer present in the outer side disintegrated in the stomach and the inner layer is made to disintegrate in the intestine region. (2) c) Repeat action tablets: compression coated tablets will also come into this category. Other method is use of sugar coated tablet. Here the tablet part containing the drug is covered with shellac and then the drug is added to the sugar solution and coated on the outer layer. Drug if present as solution or suspension in the sugar solution results in the formation of uniform outer dose. (2) d) Delayed action tablets: As the name specifies there will be some late in the action of the drug present in the tablet. (2) e.g. Enteric coated tablet. In this case, the tablets remain in contact with the stomach, but the drug release occurs in the intestine. Materials of enteric coating polyvinyl acetate and phthalate & hydroxyl propyl methyl cellulose and phthalate. The materials generally consists ester group. This prevents the drug to get solubilized in stomach. They will pass to small intestine where these agents disintegrate at alkaline conditions. Advantages: -To prevent irritation -To safe guard the drug harmful acidic stomach environment -To release the drug more at the intestine region(2) e) Sugar coated tablets: The patience will feel comfortable while taking the tablet and also acts as a barrier between the core and other ingredients. it is used excessively in the preparation of multivitamin and multimineral tablets. (2) f) Film-coated tablets: The drug is not essential in this coating and this process completes within less time. The film consists of plasticizer(acts as polymer) and surfactant(which enhances the spreading) Adv: there will be a slight raise in weight of the tablet. Sugar is avoided which is not suitable for some patients. Film coated Tablets are stronger than sugar coated tablet (2) g) Chewable tablets: These tablets should be chewed in the mouth. This has an advantage that children and old people as they feel tough to swallow the whole tablet. They will give unit dosage. This is mainly used in antacid preparations, which are very bulky and so its tough to swallow. (2) B) Tablets used in the oral cavity: a) Buccal and sublingual tablets: Buccal tablets will be placed in between cheeks and teeth whereas sublingual tablets will be placed below the tongue. In these the drug will be absorbed directly from oral mucosa and then into blood circulation and gives systemic effect. This helps the drug to escape the first pass metabolism. (2) b) Troches and lozens: Lozens are prepared by compression or fusion or candy molding process whereas Lozens are prepared by compression. Both will produce local effect in mouth and throat. These tablets should not break in the mouth but they should get dissolved slowly. (2) c) Dental cones: These are placed wherever there is empty socket in the mouth. They usually contain a coagulant (prevents bleeding) or antibacterial agent. Sodium chloride and sodium bicarbonate re the common vehicles used. (2) C) Tablets administered by other route a) Implantation tablets: These tablets will be placed below the skin. Limitation includes the need of surgery to remove the tablet and these type of tablets causes tissue irritation. (2) b) Vaginal tablets: These will be inserted in the vagina. Dissolution in slow and hence the drug release. They are mainly intended to release steroids or may contain antibacterial agent. (2) D) Tablets administered by other route: a) Effervescent tablets: they release carbon dioxide gas when they are dissolved in water. They contain: drug + acid (citric acid/tartaric acid) + sodium bicarbonate When they are dissolved in water, carbon dioxide will be released due to reaction between acid and sodium bicarbonate. (2) b) Hypodermic tablets: these tablets are readily dissolved in sterile water and can be used for IV purpose. (2) MANUFACTURE: There are three well known methods for the preparation of granules. I) Direct compression method: It is useful for the moderate dosage drugs. The diluents used should be inert. It should be compressed easily and it should loose this quality when drug and other excepients are added. Some of the materials for which this method is used are KCl, NaCl, NaBr But this is not used for most of the drugs because, the drug do not attain attraction forces on compression or the molecules will be covered by a layer of air Advantages: Very less number of steps are involved Disadvantages: -The variations in particle size and density when compared to diluents leads to the formation of layers. This is problematic especially in case of low potet drugs. Most of the large dosage form drugs are need large quantities of binder which increase both bulk and cost of the tablet. -Drug may react with diluents in some cases. e.g. Amine drugs with spray dried lactose(2) II) Compression granulation: In compression granulation the powder is compressed in dies having large capacity. This will form 'slug' and the process s known as slugging. Then these masses are passed through the screen and again compressed to form tablets. This greatly increases the strength of bonds between the particle within a tablet. Advantages: -There is no wetting and drying -Less space and equipment is enough E.g. Aspirin tablets. (2) III) Wet granulation: here binders in the formof solution or suspension are added. It is of two methods. (2) Method 1: When only small amount of solvent is allowed in formulation, then powder +binder+solvent Method 2: If large amount of solvent is allowed, then powder +binder solution and then mixing is performed. After mixing, wet screening should be done. In this process, the powder mass is passed into the hammer mill and then through the large perforated screens. This increases the surface area of the powdered mass and so the rate of drying increases. In the drying process, the damp mass is dried in order to remove excess solvent. Now screening is performed and then finally compressed(2) Advantages of tablets: (2) -Through tablets, the exact dose of the drug can be administered to the patient. -Transportation is cheap and easy -Microbial contamination chances will be less -Large scale production can be easily achieved.
1) Indian Pharmacopoeia, volume2, Published by controller of Publications, page no.735
2) The theory and practice of Industrial Pharmacy by Leon Lachman, Herbert A. Liberman, Joseph L. Kaing, and Joseph L. Kaing, Third edition, Varghese Publishing House, page no. 293 to 336 3) Modern Pharmaceutics basic principles and systems, edited by Florence and Siepmann, volume 1, informa healthcare publishers, page no 481 to 487 "This blog does not contain any plagiarized material"