Enteric-coated capsules are those with a polymer coating that protects the drug from dissolution in the gastric environment. This prevents adverse reactions of the drug to the stomach and the acidity of the stomach. It also protects the drug from dissolution after the stomach is empty.Cellulose acetate phthalate is an excipient used in enteric-coated capsules. It plays an important role in the gastric fluid-resistant coating and matrix binder. It also functions as a flavor masker and may be used in combination with other excipients.

The polymer used to form the enteric coating is cellulose acetate phthalate (CAP). It has an inherent viscosity of 0.68 dL/g and is a solid at 20 degrees C. This polymer can be degraded to various extents.This polymer is the oldest synthetic enteric coating polymer. It was first patented by Eastman Kodak Company in 1940. It is synthesized by adding a phthalic anhydride to cellulose. CAP has a very enteric character and is soluble in aqueous solutions.Cellulose acetate phthalate is available commercially as a white powder. It is identical to CAP, except for its slightly acidic taste and odour.

In the development of Eudragit L100-55 enteric capsules, scientists incorporated a carboxylic group into a gelatin capsule to prevent the drug from being degraded by a gastric enzyme. The resulting pH-dependent delivery system also improved the bioavailability of the drug. This formulation was characterized using Fourier-transformed infrared spectroscopy (FTIR) and a scanning electron microscope (SEM).The capsule-based delivery system preserves 45-54% of the released protein activity. The capsule contains a gelatin shell and is coated with the Eudragit family of pH-responsive enteric polymers.

These polymers dissolve at pH 6 or lower and are intended for targeted release in the colon and small intestine.Eudragit L100-55 enteric capsules have been formulated to be easily administered to patients with difficulty swallowing. The enteric-coated formulation is the result of complex coacervation, a process that involves two oppositely-charged polymers (Eudragit is anionic and chitosan is cationic). The resulting mucoadhesive nanoparticles are biocompatible and nontoxic.