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Medicines to be taken orally are very often supplied in tablet form; indeed the word tablet without qualification would be taken to refer to a medicinal tablet. Medicinal tablets are usually called pills. Other products are manufactured in the form of tablets which dissolve; e.g., for cleaning and deodorizing.
Medicinal tablets are usually intended to be swallowed, and are of a suitable size and shape. A coating may be applied to hide the taste of the tablet’s components or to make it resistant to environmental conditions. Tablets for other purposes, e.g., effervescent medicinal tablets and non-medicinal tablets, may be larger.
Medicinal tablets were originally made in the shape of a disk of whatever color their components determined, but are now made in many shapes and colors to help users to distinguish between different medicines that they take. Tablets are often stamped with symbols, letters, and numbers which enable them to be identified. Sizes of tablets to be swallowed range from a few millimeters to about a centimeter. Some tablets are in the shape of capsules, and are called “caplets”.
When Tylenol (paracetamol/acetaminophen) capsules were laced with cyanide (an incident referred to as the Tylenol scare), many people stopped buying capsules because they are easy to contaminate, in favor of tablets, which are not. Some makers of OTC (over-the-counter) drugs responded by starting to make what they termed “caplets”, which were actually just tablets made in the shape of a capsule.
Tablets are often scored to allow them easily to be broken into equal halves for smaller doses.
In the tablet-pressing process, it is important that all ingredients be dry, powdered, and of uniform grain size as much as possible. Mixed grain sizes tend to separate out due to operational vibrations which can result in inconsistent tableting.
Some substances may be tableted as pure substances, but this is usually not the case; most formulations include excipients. Normally, an inactive ingredient termed a binder is added to help hold the tablet together and give it strength. A wide variety of binders may be used, some common ones including lactose powder, sucrose powder, tapioca starch (cassava flour) and microcrystalline and other forms of modified cellulose.
Often, an ingredient is also needed to act as an disintegrant that dissolves readily in water to help the tablet disperse once swallowed. Some binders, such as starch, are also excellent disintegrants.
Small amounts of lubricants are usually added, as well. The most common of these are stearic acid (stearin) and magnesium stearate. These help the tablets, once pressed, to be more easily ejected from the die.
Many tablets today are coated after being pressed. Although sugar-coating was popular in the past, the process has many drawbacks. Modern tablet coatings are polymer and polysaccharide based, with plasticizers and pigments included. Tablet coatings must be stable and strong enough to survive the handling of the tablet, must not make tablets stick together during the coating process, and must follow the fine contours of embossed characters or logos on tablets. Coatings can also facilitate printing on tablets, if required. Coatings are necessary for tablets that have an unpleasant taste, and a smoother finish makes large tablets easier to swallow. Tablet coatings are also useful to extend the shelf-life of components that are sensitive to moisture or oxidation. Opaque materials like titanium dioxide can protect light-sensitive actives from photodegradation. Special coatings (for example with pearlescent effects) can enhance brand recognition.
If the active ingredient of a tablet is sensitive to acid, or is irritant to the stomach lining, an enteric coating can be used, which is resistant to stomach acid and dissolves in the high pH of the intestines. Enteric coatings are also used for medicines that can be negatively affected by taking a long time to reach the small intestine where they are absorbed. Coatings are often chosen to control the rate of dissolution of the drug in the gastro-intestinal tract. Some drugs will be absorbed better at different points in the digestive system. If the highest percentage of absorption of a drug takes place in the stomach, a coating that dissolves quickly and easily in acid will be selected. If the rate of absorption is best in the large intestine or colon, then a coating that is acid resistant and dissolves slowly would be used to ensure it reached that point before dispersing. The area of the gastro-intestinal tract with the best absorption for any particular drug is usually determined by clinical trials. Coating can be performed broadly by two ways a) enteric coating, b) sugar coating
Tablet presses, also called tabletting machines, range from small, inexpensive bench-top models that make one tablet at a time (single-station presses), no more than a few thousand an hour, and with only around a half-ton pressure, to large, computerized, industrial models (multi-station rotary or eccentric presses) that can make hundreds of thousands of tablets an hour with much greater pressure. Some tablet presses can make extremely large tablets, such as some of the toilet cleaning and deodorizing products or dishwasher soap. Others can make smaller tablets, from regular aspirin to some the size of a bb gun pellet. Tablet presses may also be used to form tablets out of a wide variety of materials, from powdered metals to cookie crumbs. The tablet press is an essential piece of machinery for any pharmaceutical manufacturer.
It is sometimes necessary to split pills into halves or quarters. Tablets are easier to break accurately if scored, but there are devices called.
Sumber : http://en.wikipedia.org/wiki/Tablet