Enteric Coating

PREPARED BY: YUSUF NAWAZ KHAN

Y1507A06

An enteric coating is a barrier that controls the location of oral medication in the digestive system where it is absorbed.

The word “enteric” indicates the small intestine.These are polymer coatings which are insoluble

at low pH, but soluble at high pH.Enteric coatings are prepared from gastric

resistant polymers.Drug release rate is controlled by its exposed pH.

Introduction….

To protect acid labile drugs.For optimal absorption.To prevent gastric stress due to drug

irritation.To show local action on intestine.To provide delayed release.

REASONS FOR ENTERIC COATING

Resistance to gastric fluid.Susceptible/permeable to intestinal fluid.Formation of continuous film.Compatibility.Stability.Non toxic or no pharmacologic activity.Ease of printing.

IDEAL PROPERTIES

Polymers used for enteric coating

1. Cellulose acetate phthalate (CAP)

CAP is widely used but it has major disadvantage that it dissolves above pH 6, thus delaying the drug release as the ideal material may dissolve around pH 5. It is having hygroscopic nature and relatively permeable to gastric fluids. It form brittle film so it required hydrophobic plasticizers.

2. Acrylate polymers Two types of commercial available acrylic resins are i) Eudragit L ii)Eudragit S Soluble at pH 6 and 7 respectively. Eudragit L is available as an organic solution (Isopropanol), solid or aqueous dispersion. Eudragit S is available only as organic solution and solid.

3. Hydroxypropyl Methylcellulose Phthalate (HPMCP)

Three grades are available i)HPMCP 55 (HP 50) ii) HPMCP 50 (HP 55) iii)HPMCP 55S (HP 55S)These polymers dissolved at a lower pH (around 5 to 5.5) than CAP and acrylic copolymers.They show higher bioavailability of some drugs. HP 55 used for general enteric preparations.These are quit stable then CAP because of absence of acetyl group.

4. Polyvinyl Acetate Phthalate (PVAP)

Prepare by esterification of partially hydrolyzed polyvinyl acetate with phthalic anhydride.It is similar to HP-55 in terms of stability and pH-dependent solubility.Supplied as ready-to-use.

Examples of enteric coated formulation

Brand Generic Manufacturer

Omez Omeprazole Dr. Reddy’sCardizem CD 360mg Diltiazem Aventis

ADVANCEMENT IN TABLET COATING MATERIAL

Aqueous based coating materials like colloidal dispersion (30%) of polymer Ethyl Cellulose (aqua coat and aquateric) are now replacing organic solvent based coating materials.

Water based controlled tablet coatings by Latex and Pseudo latex of acrylate polymers and ethyl cellulose have been reported.

Cross-linked product of hydroxyl-end blocked polydimethyl- siloxane has been developed as water based controlled release tablet coating system.

References ….. Aulton, Michael E., Taylor, Kevin M. G., Aultons pharmaceutics :

the design and manufacturing of medicines, 4th edition (International), churchill livingstone, Elsevier publication, page no. 562.

Khar, Roop K, Vyas, S. P., Ahmad, Farhan J, Jain, Gaurav K, The Theory and Practice of Industrial Pharmacy, 4th edition, CBS publishers and distributers, page no. 502

Sharma, Kapil, Sharma, Priyanka, A review on formulation and evaluation aspects of enteric coated pellets on http://www.pharmatutor.org/articles/review-on-formulation-evaluation-aspects-of-entric-coated-pellets .

Dhilman, Vandna, Modgil, Swati, Nagpal Meenu, Jain, Uprendra K, Coating technology and its recent advances – a review on http://www.pharmatutor.org/articles/coating-technology-its-recent-advances-review%20?page=0,1 .