Solid Dosage Forms - tablets

December 4, 2018, 9:57 1077

Dosage forms (also called unit doses) are pharmaceutical drug products in the form in which they are marketed for use, with a specific mixture of active ingredients and inactive components (excipients), in a particular configuration, and apportioned into a particular dose. The term dosage form can also sometimes refer only to the pharmaceutical formulation of a drug product's constituent drug substance(s) and any blends involved, without considering matters beyond that (like how it is ultimately configured as a consumable product such as a capsule, patch, etc.).

Solid dosage formulations are the most important dosage forms for pharmaceuticals, e.g. tablets, capsules, granules, powders, sachets, reconstitutable powders, dry powder inhalers and chewables.

The oral route of drug administration is the most convenient for patients, with tablets emerging as the most popular solid oral dosage form used today.  A wide range and diversity of ingredients are often included in tablet formulations.

Two key traits of solid dosage forms of drugs are solubility and stability. Insoluble or unstable drugs slow down the approval of drugs.

Classification of solid dosage forms:


A tablet is a pharmaceutical dosage form. Tablets may be defined as the solid unit dosage form of medicament or medicaments with or without suitable excipients and prepared either by molding or by compression. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose. Most of the tablet is administered orally. However, the tablet for application as implant, solution, vaginal use, and external use are also available.



Pills are thought to date back to around 1500 BC. Earlier medical recipes, such as those from 4000 BC, were for liquid preparations rather than solids. The first references to pills were found on papyruses in ancient Egypt, and contained bread dough, honey or grease. Medicinal ingredients, such as plant powders or spices, were mixed in and formed by hand to make little balls, or pills. In ancient Greece, such medicines were known as katapotia ("something to be swallowed"), and the Roman scholar Pliny, who lived from 23-79 AD, first gave a name to what we now call pills, calling them pilula

Different Types of tablets:

In broad sense tablets are classified as

  • Compressed tablets

  • Molded tablets

The molded tablet is softer than the compressed tablet. The molded tablet dissolves rapidly when administered by placing under the tongue. The compressed tablet offers many advantages to the patient, the prescriber and the manufacturer. There may be single or multiple compressed drug following oral administration.

Tablet may be uncoated or coated. Uncoated tablets are chewable tablet, effervescent tablet, lozenge tablet, soluble tablet, and sublingual tablet. Coated tablets are enteric coated tablet, film coated tablet, implant, sugar coated tablet, and modified-release tablet. A broken section of a coated tablet shows a core which is surrounded by a continuous layer of a different texture. The reasons for coating a tablet are:

a) to protection of the active ingredients from air, moisture, light,

b) to mask the unpleasant tastes and odor; and

c) to improve appearance


Compressed tablets:

1. Oral tablets

2. Chewable tablets

The tablet which is intended to be broken and chewed in between the teeth before ingestion. Antacid and vitamin tablets are usually prepared as chewable tablets. It is given to the children who have difficulty in swallowing and to the adults who dislike swallowing.

3. Buccal or sublingual tablets

The drug which is destroyed or inactivated within the gastrointestinal tract but can be absorbed through the mucosal tissue of the oral cavity is usually given in this formulation. The tablet is required to be placed below the tongue for the slow release of drug. But for immediate effect some medicaments are formulated in such a way to dissolve within 1 to 2 minutes. Nitroglycerin is prepared in this formulation.

4. Lozenges

The tablet that is intended to produce continuous effect on the mucous membrane of the throat. There is no disintegrating agent. The quality of the binding agent is increased so as to produce slow dissolution. Suitable sweetening (sugar), coloring and flavoring agents must be including in this formulation.

5. Effervescent tablets

The tablet that contains acid substances and carbonate or hydrogen carbonate that react rapidly in the presence of water to release carbon dioxide. Sodium bicarbonate, citric acid and tartaric acid are added to the active ingredients to make the tablet effervescent. This preparation makes the tablet palatable.

6. Enteric coated tablets

Some drugs are destroyed by gastric juice or causes irritation to the stomach. These two factors can be overcome by coating the tablet with cellulose acetate phthalate. This polymer is insoluble in gastric contents but readily dissolves in intestinal contents. So there is delay in the disintegration of dosage form until it reaches the small intestine. Like coated tablet, enteric coated tablet should be administered in whole form broken or crushed form of the enteric coated tablet causes destruction of the drug by gastric juice or irritation to the stomach.

7. Sustained release tablets

Modified-released tablet is either uncoated or coated. This contains special additives or prepared by special procedure which, separately or together, is intended to modify the rate of release of the drug into the gastrointestinal tract. It prolongs the effect of drug and also reduces the frequency of administration of drug. Several drugs are available in modified release tablet such as indomethacin. Sustained-release dosage forms are dosage forms designed to release (liberate) a drug at a predetermined rate in order to maintain a constant drug concentration for a specific period of time with minimum side effects. This can be achieved through a variety of formulations, including liposomes and drug-polymer conjugates (an example being hydrogels). Sustained release's definition is more akin to a "controlled release" rather than "sustained".

8. Vaginal tablets

9. Sugar coated tablets

The tablet that contains active ingredient(s) of unpleasant taste may be covered with sugar to make it more palatable. This type of tablet should be administered in whole form, otherwise the patient will experience the unpleasant taste of the active ingredient.

10. Film coated tablets

The tablet that is covered with a thin layer or film of polymeric substance which protects the drug from atmospheric conditions and mask the objectionable taste and the odor of drug.

11. Layered tablets

Multi-layer tablet is a new era for winning development of controlled release formulation along with various features to provide successful drug delivery. Bi-layer tablets can be crucial option to avoid chemical incompatibilities between active pharmaceutical ingredients (APIs) by physical separation and to facilitate the development of different drug release profiles. Multi-layer tablet is appropriate for chronological release of two drugs in combination and also for sustained release of tablet in which one layer is for immediate release as loading dose and second layer is maintenance dose. So use of bi-layer tablets is a very different aspect for anti-hypertensive, diabetic, anti-inflammatory and analgesic drugs where combination therapy is often used. Several pharmaceutical companies are currently developing bi-layer tablets, for a variety of reasons: patent extension, therapeutic, marketing to name a few.

12. Implants

A small tablet that is prepared for insertion under the skin by giving a small surgical cut into the skin which is stitched after the insertion of the tablet. This tablet must be sterile one. The drug used in this preparation is usually water insoluble and the tablet provides a slow and continuous release of drug over prolonged period of time ranging from 3 to 6 months or even more Contraceptive tablet is formulated as implant.

13. Soluble tablets

The tablet that dissolves completely in liquid to produce solution of definite concentration. Mouth wash, gargle, skin lotion, douche; antibiotic, certain vitamins, and aspirin are given in this formulation.

14. Pressed coated tablets

A new dry-coated device for the release of drug after a programmable period of time is proposed. It is intended to be used mainly in the therapy of those diseases which depend on circadian rhythms. Some core formulations, characterized by different release rates and mechanisms (containing diltiazem hydrochloride or sodium diclofenac as model drugs), were coated by compression with different polymeric barrier layers (press-coated systems). The shell formulations tested contained either gellable or erodible polymers.


Molded tablets:

These are of two types as

1.Hypodermic tablets

        A tablet that dissolves completely in water to form an injectable solution.

2.Dispensing tablets

        A tablet that contains a clinically effective large amount of an active drug.



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