Enteric coating

Description

Most enteric coatings work by presenting a surface that is stable at the intensely acidic pH 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 the stomach (pH ~3), but they will in the alkaline (pH 7–9) environment present in the small intestine. 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.{{Cite journal | doi-access = free

By preventing the drug from dissolving into the stomach, enteric coating may protect gastric 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 as aspirin or potassium 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 of platelets,{{Cite journal | doi-access =

Materials used for enteric coatings include fatty 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.

The first form of gastro-resistant coating was introduced by Unna in 1884 in the form of keratin-coated pills, although it was later discovered that they were not able to withstand gastric digestion. Salol was also used by Ceppi as one of the first forms of enteric coating. However, the first material that was extensively used as enteric coating agent was shellac, since its introduction in 1930. Properly treated or hydrolyzed shellac showed different enteric release properties.

Recently, some companies have begun to apply enteric coatings to fish oil (omega-3 fatty acids) supplements. The coating prevents the fish oil capsules from being digested in the stomach, which has been known to cause gastroesophageal reflux.

Sometimes the abbreviation "EC" is added beside the name of the drug to indicate that it has an enteric coating.

Composition

• Methyl acrylate-methacrylic acid copolymers
• Cellulose acetate phthalate (CAP)
• Cellulose acetate succinate
• Hydroxypropyl methyl cellulose phthalate
• Hydroxypropyl methyl cellulose acetate succinate (hypromellose acetate succinate)
• Polyvinyl acetate phthalate (PVAP)
• Methyl methacrylate-methacrylic acid copolymers
• Shellac
• Cellulose acetate trimellitate
• Sodium alginate
• Zein
• enteric coating aqueous solution (ethylcellulose, medium chain triglycerides [coconut], oleic acid, sodium alginate, stearic acid) (coated softgels)

References

References

1. Tarcha, Peter J.. (1990). "Polymers for Controlled Drug Delivery". CRC Press.
2. (1982). "Optimization of drug delivery: proceedings of the Alfred Benzon Symposium 17 held at the premises of the Royal Danish Academy of Sciences and Letters, Copenhagen 31 May-4 June 1981". Munksgaard.
3. (2011). "Oral Controlled Release Formulation Design and Drug Delivery: Theory to Practice". John Wiley & Sons.
4. Juliano, R. L.. (1980). "Drug delivery systems: characteristics and biomedical applications". Oxford University Press.
5. (1995). "Pharmaceutical Coating Technology". Taylor & Francis.
6. Patell, Mahesh K.. (Oct 4, 1988). "Enteric coated tablet and process for making".
7. Unna, Keratinirte Pillen, ''Pharm. Zentrahlle,'' 25, 577, 1884.
8. (1945). "History, literature, and theory of enteric coatings". Journal of the American Pharmaceutical Association (Scientific Ed.).