In vitro release characteristics of hard shell capsule products coated with aqueous- and organic-based enteric polymers

In this article, an overview of the rationale for the use of enteric coated (EC) dosage forms is presented. The benefits and disadvantages inherent in the use of aqueous dispersions and organic solutions of the various polymers to generate these products are discussed. The comparative dissolution stability of a hard shell capsule product coated with enteric polymers applied as either aqueous dispersions, or as organic solutions, were assessed under accelerated conditions of storage. Polymethacrylic acid methacrylate copolymer, cellulose acetate phthalate (CAP) and polyvinyl acetate phthalate (PVAP), along with the corresponding commercially available aqueous dispersions, Eudragit L30D, Aquateric, and Coateric, were employed in these studies as enteric polymers. Diethyl phthalate (DEP) was used as the plasticizer and procainamide HCl 250 mg capsules served as the substrate. Storage of the coated capsules at 37 degrees C/80% RH and at 45 degrees C for 2 months revealed that, while the stability of Eudragit L30D coatings are comparable or superior to the corresponding organic-based coatings, Coateric films are markedly unstable when compared with PVAP coatings applied through the use of organic vehicles. After storage at 37 degrees C/80% RH, Aquateric-based capsules demonstrated stability comparable to CAP organic-based coatings only when a protective seal coat was present. The performance failures of the capsules that occur upon storage primarily result in a loss of gastric resistance. Scanning Electron Microscopy (SEM) and thermomechanical analysis (TMA) of the different coatings revealed differences in the film-forming properties of the polymer films and provide an explanation for the changes that occur during storage of the coated capsules.