ABSTRACT
The oldest of the phthalate-containing polymers used in enteric coating, it is prepared by reacting a partial acetate ester of cellulose with phthalic anhydride. Ellis and others stated that CAP comes very close to fulfilling the requirements of an ideal enteric coating material. While this is an advantage over shellac, which does not dissolve below pH 7, if a lower pH-releasing value is sought, as for example to reduce the onset of action, other enteric polymers may be required. A property of PVAP that makes it a superior enteric polymer in some situations is that it is much less permeable to water vapor and simulated gastric fluid, compared with CAP and other polymers typically used. It is clear from the figure that PVAP has the lowest viscosity among the polymers studied, at the same concentration. The types of methacrylic acid polymers used in enteric coatings are methacrylic acidmethylmethacrylate copolymers, and methacrylic acid ethyl acrylate copolymer.
