An
enteric coating is a barrier applied to oral
medicationA pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
that controls the location in the digestive system, where it is absorbed.
Enteric refers to the small intestine, therefore enteric coatings prevent release of medication before it reaches the
small intestineThe small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
.
Most enteric coatings work by presenting a surface that is stable at the highly acidic
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
found in the stomach, but breaks down rapidly at a less acidic (relatively more basic) pH. For example, they will not dissolve in the acidic juices of the
stomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
(pH ~3), but they will in the alkaline (pH 7-9) environment present in the small intestine. Materials used for enteric coatings include
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s,
waxthumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...
es,
shellacShellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes , which are dissolved in ethyl alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish...
,
plasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s, and plant fibers.
Drugs that have an irritant effect on the stomach, such as
aspirinAspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...
, can be coated with a substance that will dissolve only in the small intestine. Likewise, certain groups of
azoleAn azole is a class of five-membered nitrogen heterocyclic ring compounds containing at least one other non-carbon atom of either nitrogen, sulfur, or oxygen. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs with fewer...
s (
esomeprazoleEsomeprazole is a proton pump inhibitor developed and marketed by AstraZeneca which is used in the treatment of dyspepsia, peptic ulcer disease , gastroesophageal reflux disease and Zollinger-Ellison syndrome...
,
omeprazoleOmeprazole is a proton pump inhibitor used in the treatment of dyspepsia, peptic ulcer disease , gastroesophageal reflux disease , laryngopharyngeal reflux and Zollinger–Ellison syndrome...
, pan and all grouped azoles) are acid-unstable. For such types of drugs, enteric coating added to the formulation tends to avoid the stomach's acidic exposure, delivering them instead to a basic pH environment (intestine's pH 5.5 and above) where they do not degrade, and give their desired action.
Recently, some companies have begun to utilize enteric coatings on
fish oilFish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid , and docosahexaenoic acid , precursors of certain eicosanoids that are known to reduce inflammation throughout the body, and are thought to have many health benefits.Fish do not...
(
omega-3 fatty acidN−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
s) supplements. The coating prevents the fish oil capsules from being digested in the stomach, which has been known to cause a fishy reflux (fish burps).
Sometimes the abbreviation "EC" is added beside the name of the drug to indicate that it has an enteric coating.
Composition of coatings
- methyl acrylate-methacrylic acid copolymers
- cellulose acetate succinate
- hydroxy propyl methyl cellulose phthalate
- hydroxy propyl methyl cellulose acetate succinate (hypromellose
Hypromellose , short for hydroxypropyl methylcellulose , is a semisynthetic, inert, viscoelastic polymer used as an ophthalmic lubricant, as well as an excipient and controlled-delivery component in oral medicaments, found in a variety of commercial products.As a food additive, hypromellose is an...
acetate succinate)
- polyvinyl acetate phthalate
Polyvinyl acetate phthalate is a commonly used polymer phthalate in the formulation of pharmaceuticals, such as the enteric coating of tablets or capsules. It is a vinyl acetate polymer that is partially hydrolyzed and then esterified with phthalic acid. Its main use in pharmaceutics is with...
(PVAP)
- methyl methacrylate-methacrylic acid copolymers
- Sodium alginate and stearic acid
Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...
External links
Definition of "enteric coating" in the free dictionary website