Tablets are solid dosage forms usually containing active pharmaceutical ingredient and excipients in powder, crystalline or granular form with or without diluents which is prepared either by moulding or compression process. They are solid, biconvex or flat in shape and vary in size, shape and weight which is depends on the medicaments which are used for preparation. They are also varying in hardness, disintegration; dissolution characteristics and thickness depend on their intended use and method of manufacture. Tablets are the most widely used solid dosage forms because of their advantages and popularity increasing day by day. Tablet usually contains filler, diluents, binders, lubricants, glidants, disintegrants, antiadherent, colouring agents and flavouring agents as excipients.
Advantages of tablets
Unit dosage forms with accurate, stable dose and great precision and least variability.
Most stable with respect to physical, chemical and microbiological attributes.
Cheapest oral dosage form, easy to handle, use and carry out with attractive and elegant appearance.
Cheap, easy to swallow and production does not require and additional processing steps.
Provide protection of medicaments from atmospheric conditions like air, moisture and light, etc.
Provide prolonged stability to medicaments.
Low manufacturing cost as compare to other solid dosage forms and large scale production is possible.
Administration of minute dose of drug in accurate amount.
Unpleasant taste can be masked by sugar coating.
Easy to divide into halves and quarters whenever fraction dose is required.
Formulate as a special release products such as enteric or delayed release products.
Packing and production is cheap and does not require more space for storage.
Types of tablets
There are many types of tablets according to the intended of use and manufacturing process.
[A] Oral tablet intended for ingestion
Compressed tablets: Tablets can be made by compression of one or more active pharmaceutical ingredient with excipients by basic methods of tablet manufacturing. These types of tablets usually intended to provide raid drug release and disintegration. Tablets are coated after compression.
Multiple compressed tablets: Multiple compressed tablets are prepared by compressing the material more than once. These are known as multiple layered tablets or tablet within tablet. Layered are depends on number of fills. Layered tablets are prepared by compaction of fill material in die followed by additional of fill material and compression.
Delayed action or Enteric coated tablets: These types of tablets contain a coating which resist dissolution of tablets in Gastro Intestinal Track (GIT) and disintegrate in intestinal fluids thus rendering delayed release features. Enteric coating is generally apply when drug substance is unstable in gastric fluid and may destroyed or may cause irritation in gastric mucosa or to extent absorption of drug from intestine. Normally coating materials mixed with acid and acid functionality or modified natural polymers. Most commonly used coating polymers are: Cellulose acetate phthalate (CAP), polyvinyl acetate phthalate (PVAP) and hydroxyl propyl methyl cellulose phthalate.
Sugar coated tablet: Compressed tablets may be coated with coloured or uncoloured sugar coating and the coater is water soluble and dissolve quickly after swallowing. Sugar coat protects drug from environment, remove bitter taste and odour, enhance the appearance of tablet and permit identifying information. Sugar coating has some disadvantages like increase coat of production, require expertise for coating, increase size and weight.
Film coated tablets: Tablets are compressed with a thin layer of polymer which forms a skin like film over tablet. The film is usually coloured, more durable and less bulky. The coating is designed to rupture and expose of tablet at desired location within GIT. Most commonly used polymers are Hydroxy propyl cellulose, Hydroxy ethyl and propyl methyl cellulose.
Chewable tablet: These types of tablets have smooth surface, creamy base and usually flavoured and coloured mannitol, rapid disintegration which allow dissolving quickly in mouth. These types mostly useful for administration of large dose to children and adults.
[B]Tablet used for oral cavity
Buccal tablets and sublingual tablets: Buccal and sublingual tablets are flat in shape and intended to dissolve drug in buccal cavity or beneath the tongue for mucosa absorption. These techniques useful for drugs which are destroyed by gastric fluid or poor absorption in GIT. Buccal tablets erode slowly and sublingual tablets dissolve quickly and produce rapid effect.
Troches and Lozenges: They are intended to slowly dissolution mostly for local effect but sometimes for systemic absorption. Troches and Lozenges are disc shaped which contain active ingredient and flavouring agent in hard candy or sugar base.
Dental cones: dental cones are designed to place in the empty socket for prevention of bacterial growth and sometime bleeding by containing coagulant. Dental cones release slowly for long duration.
[C] Tablets for other routes
Vaginal tablet: Vaginal tablets are prepared by compression and shaped to fit snugly on plastic inserter devices in uncoated bullet shaped or ovoid tablets which are inserted into vagina for local effects with slow dissolution. They contain anti bacterial effect and also called vaginal inserts.
Implantation tablet: Implantation tablets are injected under the skin by giving a small surgical cut into the skin. A special injector a hallow needle and plunger may require for administration. Purpose of these tablets is to prolong drug effect from month to year. These tablets are implanted intramuscularly or subcutaneous so they must be sterile and packed in sterile container. [Pharmaceutics – I, P.V. KASTURE, S.R. PARAKH, S.A. HASAN, S.B. GOKHALE, June 2008, pp-14-7,21]
[D] Tablets for solution
Effervescent tablet: Effervescent tablets prepared by compression of granular salts which release in contact with water.
Dispensing tablets: These types of tablets are no longer use because they had dangerous potential. They might be termed compounding tablets because it contain highly potent drug and pharmacist use it for compound prescription.
Hypodermic tablets: Hypodermic tablets are soft moulded tablets which contain soluble ingredient and used for extemporaneous parenteral preparation by physician. They are no longer in use because it is difficult to achieve sterility and availability of stable liquid.
Tablet triturates: tablet triturates are rarely use now a days because they are obsolete. They are small, cylindrical, molded which contain small amount of potent drug. They must be readily soluble in water and minimum amount pressure require during manufacture. Triturates inserted into capsules or dissolved in liquid to provide accurate potent drug.