For other meanings please see Tablet (disambiguation)
Common disk-shaped tablets
A tablet is a mixture of active substances and excipients, usually in
powder form, pressed or compacted into a solid. The excipients include binders,
glidants (flow aids) and lubricants to ensure efficient tabletting; disintegrants to ensure that the tablet breaks up in the
digestive tract; sweetners or flavours to mask the taste of bad-tasting active ingredients; and pigments to make uncoated tablets
visually attractive. A coating may be applied to hide the taste of the tablet's components, to make the tablet smoother and
easier to swallow, and to make it more resistant to the environment, extending its shelf life.
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 and capsules are often called pills. Other products are manufactured in the form of tablets
which are designed to dissolve or disintegrate; e.g. cleaning and deodorizing products.
Medicinal tablets are usually intended to be swallowed, and are of a suitable size and
shape. 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Medicinal tablets were originally made in the shape of a disk of whatever color their components determined, but are now made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 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 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 to be easily broken into equal halves for smaller doses.
Some people have difficulty swallowing tablets, this is called dysphagia. This is often
caused by a gag reflex.
Tabletting formulations
Capping (top) and lamination (right) tablet failure modes
In the tablet-pressing process, it is important that all ingredients be fairly dry, powdered or granular, somewhat uniform in
particle size, and freely flowing. Mixed particle sized powders can segregate due to operational vibrations, which can result in
tablets with poor drug or active pharmaceutical ingredient (API) content uniformity. Content uniformity ensures that the same API
dose is delivered with each tablet.
Some APIs may be tableted as pure substances, but this is rarely the case; most formulations include excipients. Normally, an inactive ingredient (excipient) 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, dibasic calcium phosphate, sucrose, corn (maize) starch,
microcrystalline cellulose and modified cellulose (for example hydroxymethyl cellulose).
Often, an ingredient is also needed to act as a disintegrant that hydrates readily in water to aid tablet dispersion
once swallowed, releasing the API for absorption. Some binders, such as starch and cellulose, are also excellent
disintegrants.
Small amounts of lubricants are usually added, as well. The most common of these is magnesium stearate; however, other
commonly used tablet lubricants include stearic acid (stearin), hydrogenated oil, and
sodium stearyl fumarate. These help the tablets, once pressed, to be more easily ejected from the die.
Tablet coating
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.
Tablet presses
An old Cadmach rotary tablet press
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 to millions 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 and nutraceutical manufacturer.
Pill-splitters
It is sometimes necessary to split tablets into halves or quarters. Tablets are easier to break accurately if scored, but
there are devices called pill-splitters which cut unscored and scored tablets. Tablets
with special coatings (for example enteric coatings or controlled-release coatings) should not be broken before use, as this will
expose the tablet core to the digestive juices, short-circuiting the intended delayed-release effect.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
