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Tablets are pharmaceutical dosage forms composed of a mixture of an active therapeutic ingredient and excipients prepared by either granulation or compression which are intended to deliver the desired pharmacologic action to the body. It is taken orally, the most convenient route of administration. Excipients are added to solid dosage forms in purpose of long-term stabilization and with regards to manufacturing process; it aids the tablet to keep intact in the handling of the active substance (Nagashree, 2015).
Excipients include: diluents which are normally used as fillers that are added to increase the bulk of the tablet, binders which are used to hold the tablet components together until it reaches its target site, lubricants which prevent sticking of tablets to dies and punches while glidants reduce the friction and thus aid in free flow of granules or powder. Coloring agents are also excipients which are used to enhance tablet appearance while sweetening and flavoring agents improve their taste. Lastly, one of the main excipients added to promote the break-up of the tablet in the site of action are known as disintegrants (Nagashree, 2015).
Coating is an additional step in the manufacture of tablets. It is the process of compressing a layer of granules around a tablet. Coating has been extensively used as a protective barrier and for the management of drug release from the dosage form to its target site, it is intended to either to delay or prolong its release. The nature of coating may be simple or complex. A simple coating consists of a thin varnish film applied to a tablet to make it dust free and provide a smooth finish. A complex coating may consist of an inner and outer shell that encloses different types of drugs which may be incompatible to the environment of the gastric mucosa or required to be released in a specific target site and at a specific time (MD. Saiful Islam et al, 2016).
Tablet coating takes place after making a good tablet. It has distinct functions and purposes in the tablet formulation, however, the reason for coating may vary. For this reason, tablet coatings are used to protect active therapeutic ingredients and excipients from the environment and prevents from light and moisture, it masks the unpleasant taste of uncoated tablets and it improves the identity of the product (MD. Saiful Islam et al, 2016).
There are a number of drugs which, if directly exposed to gastric mucosa, will result in gastric irritation, and in some cases, actual corrosion of the gastric wall. Such drugs are enteric coated to protect the individuals taking them from their harmful side effects. Enteric coatings also protect drugs from degradation. Some drugs are unstable when released in the stomach and may cause undesired reactions. Thus, other reasons for introducing enteric coating have emerged with the function to better deliver drugs that are absorbed from a region of the intestine, to provide a delayed component for repeat action dosage forms and to prevent interaction of certain drugs with pepsin and peptones that would lead to a hindrance of gastric digestion (Tarcha, 1990).
Enteric coated tablets are also known as Delayed Release tablets. An enteric coated tablet will remain intact in the stomach but dissolves and releases its contents once it reaches its target site, the small intestine. Enteric coating is employed to delay the release of the drug that is normally inactivated by the stomach. In addition, such coatings provide a simple repeat-action effect. A repeat-action effect is when an additional drug is applied over the enteric coating which is intended to be released within the stomach while the remaining drug content enclosed and protected by the coating is released in the small intestine (Allen et al., 2014).
Enteric coating materials may be applied either to whole compressed tablets or to drug particles or granules used in the fabrication of tablets or capsules. The coatings may be applied in multiple portions to build a thick coating or as a thin film coat. The coating system may be aqueous or organic solvent based and effective as long as the coating material resists breakdown in the gastric fluid (Allen et al., 2014).An enteric coating is a polymer barrier that is applied on oral solid dosage forms. It is employed to protect the drugs from the acidic pH of the stomach. On the other hand, a coating solution may also include ingredients that may aid in the application of the coating material to the tablet for a better coating character. Several materials have been used as enteric coating which includes cellulose acetate phthalate (CAP), cellulose acetate trimellitate (CAT), polyvinyl acetate phthalate (PVAP) and hydroxypropyl methylcellulose phthalate (HPMCP).
Other materials such as shellac, waxes, fatty acids and plant fibers may also be used as enteric coating material (Hussan et al, 2012).Shrimp and crab wastes are the main sources of the industrial production of chitosan. Chitosan is obtain from chitin, which is a component of the exoskeleton of these crustaceans. The exoskeletons are wastes from the seafood industries. It is estimated that the total global annual generation of seafood wastes is approximately 5.1×106 metric tons. The chitin content in the dried exoskeletons varies from 5% to 42% depending in the crustacean species. In brief, chitosan obtained from shrimp and crab wastes is very attractive, since these sources are available, renewable, and have zero cost. Furthermore, it is an alternative form of appropriate management of solid waste in the seafood industries (Dotto & Pinto, 2017).
Arthropods are invertebrates that have exoskeleton and classified to three large groups that includes Insects, Crustaceans and Arachnids. The word “crustacean” comes from the Latin word crusta, meaning “shell”. Crustaceans are mainly found in sea water among of which are crabs, lobsters, shrimps, barnacles, crayfish, krill and woodlice. Their anatomy includes a hard but flexible exoskeleton, two compound eyes, two pairs of antenna and three pairs of mouthparts. Among the large group of arthropods, shrimps have been the most common and widely used (Shea, 2017). Bodies of crustaceans are covered with secreted cuticle composed of chitin, protein and calcareous material. Shrimp exoskeleton is relatively thin and soft compared to crabs and lobsters and their shell wastes are the main commercial sources of chitin (Hickman, 2017).
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