ABSTRACT
Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is a new enteric coating material developed by Shin-Etsu Chemical Co., and is marketed under the trade name Shin-Etsu (AQOAT® [49]. It is available in three grades: AS-L(F or G), AS-M(F or G), and AS-H(F or G), corresponding to an average succinyl to acetyl substitution ratio of 22.86%, 13.3%, and 0.5%, respectively. The LF, MF, and HF grades are fine powders and used to prepare aqueous dispersions, whereas LG, MG, and HG are granular and recommended for organic-based coating applications. The higher the SA ratio the lower the dissolution pH of the polymer. Table 7 lists the percentage compositions of various functional groups and the pH at which the polymer dissolves. Compared to CAP and HPMC, HPMCAS is more stable toward hydrolysis (Fig. 11) [50].
