Anenteric coating is apolymer barrier applied to oralmedication that prevents its dissolution or disintegration in the gastric environment.[1] This helps by either protecting drugs from the acidity of the stomach, the stomach from the detrimental effects of the drug, or to release the drug after the stomach (usually in the upper tract of the intestine).[2] Some drugs are unstable at thepH of gastric acid and need to be protected from degradation. Enteric coating is also an effective method to obtaindrug targeting (such as gastro-resistant drugs). Other drugs such as someanthelmintics may need to reach a high concentration in a specific part of the intestine.[1] Enteric coating may also be used during studies as a research tool to determine drug absorption.[3] Enteric-coated medications pertain to the "delayed action" dosage form category.Tablets, mini-tablets, pellets and granules (usually filled intocapsule shells) are the most common enteric-coateddosage forms.[3]
Most enteric coatings work by presenting a surface that is stable at the intensely acidicpH found in the stomach, but breaks down rapidly at a higher pH (alkaline pH). For example, they will not dissolve in the gastric acids of thestomach (pH ~3), but they will in the alkaline (pH 7–9) environment present in thesmall intestine.[4][5] The time required for an enteric-coated dosage form to reach the intestine mostly depends on the presence and type of food in the stomach. It varies from 30 minutes up to 7 hours, with an average time of 6 hours.[6] Although some studies indicated that larger sized dosage forms may require additional time for gastric emptying, others suggested that the size, shape, or volume of the tablet possess no significant effects instead.[7][8][9] Enteric coated granules emptying rate is, however, less affected by the presence of food and present the more uniform release and reproducible transit time typical of the multiparticulatesdispersion.[clarification needed][3][8]
By preventing the drug from dissolving into the stomach, enteric coating may protectgastric mucosa from the irritating effects of the medication itself. When the drug reaches the neutral or alkaline environment of the intestine, its active ingredients can then dissolve and become available for absorption into the bloodstream. Drugs that have an irritant effect on the stomach, such asaspirin orpotassium chloride, can be coated with a substance that will dissolve only in the small intestine. However, it has been shown that enteric coated aspirin may lead to incomplete inhibition ofplatelets,[10] potentially negating the intended effect for those being treated for vascular disease. Likewise, certain groups ofproton pump inhibitors (esomeprazole,omeprazole,pantoprazole and all grouped azoles) are acid-activated. For such drugs, enteric coating added to the formulation tends to avoidactivation in themouth andesophagus.
Materials used for enteric coatings includefatty acids,waxes,shellac,plastics, and plant fibers. Conventional materials used are solutions of film resins. However, as the solvents for such solutions are organic solvents, there is a concern about the toxicity potential of the traces of the residual solvents in the tablet coating.[11]
The first form of gastro-resistant coating was introduced by Unna in 1884 in the form ofkeratin-coated pills, although it was later discovered that they were not able to withstand gastricdigestion.[12]Salol was also used by Ceppi as one of the first forms of enteric coating.[13] However, the first material that was extensively used as enteric coating agent wasshellac, since its introduction in 1930. Properly treated or hydrolyzed shellac showed different enteric release properties.[3]
Recently, some companies have begun to apply enteric coatings tofish oil (omega-3 fatty acids) supplements. The coating prevents the fish oil capsules from being digested in the stomach, which has been known to causegastroesophageal reflux.
Sometimes the abbreviation "EC" is added beside the name of the drug to indicate that it has an enteric coating.