A caplet 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 caplet breaks up in the digestive tract; sweeteners or flavours to mask the taste of bad-tasting active ingredients; and pigments to make uncoated caplets visually attractive. A coating may be applied to hide the taste of the caplet's components, to make the tablet smoother and easier to swallow, and to make it more resistant to the environment, extending its shelf life. The compressed caplet is the most popular dosage form in use today. About two-thirds of all prescriptions are dispensed as solid dosage forms, and half of these are compressed tablets. A tablet can be formulated to deliver an accurate dosage to a specific site; it is usually taken orally, but can be administered sublingually, rectally or intravaginally. Tablet formation represents the last stage in down-stream processing within the pharmaceutical industry. It is just one of the many forms that an oral drug can take such as syrups, elixirs, suspensions, and emulsions. It consists of an active pharmaceutical ingredient (A.P.I.) with biologically inert excipients in a compressed, solid form.
Medicinal caplets were originally made in the shape of a disk of whatever color their components determined, but are now made in many shapes and colors to help users to distinguish between different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. Caplets 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". Medicines to be taken orally are very often supplied in caplet form; indeed the word tablet without qualification would be taken to refer to a medicinal caplet. Medicinal tablets and capsules are often called pills. Other products are manufactured in the form of caplets which are designed to dissolve or disintegrate; e.g. cleaning and deodorizing products. 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 caplet.
Many caplets today are coated after being pressed. Although sugar-coating was popular in the past, the process has many drawbacks. Modern caplet coatings are polymer and polysaccharide based, with plasticizers and pigments included. Caplet coatings must be stable and strong enough to survive the handling of the caplet, must not make caplets stick together during the coating process, and must follow the fine contours of embossed characters or logos on caplets. Coatings can also facilitate printing on caplets, if required. Coatings are necessary for caplets 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.