In vitro drug release from acetylated high amylose starch-zein films for oral colon-specific drug delivery

This study describes the preparation of free films of zein with and without acetylated high amylose maize starch (HAS) and their corresponding coated tablets as a novel approach to colonic drug delivery. We hypothesise that the embedding of a digestible starch component within the inert zein would allow the film to remain intact until the large intestine is reached. Free films of zein alone and starch/zein were prepared and characterized. SEM and AFM images of film surface showed that films were morphologically inhomogeneous, particularly at lower HAS/Zein ratios; however, nanothermal analysis data suggested that these differences in appearance within the same film are not compositional differences. Moreover, FT-IR could detect no molecular interaction between the two polymers. Paracetamol tablets were coated with HAS/Zein aqueous based coatings of different compositions to a TWG of 20%. Drug release from zein alone and 1:5 HAS/Zein coated tablets under upper gastrointestinal conditions (pH 1.2, pH 6.8 with pepsin and pancreatin included) was very similar (for example approximately 12% and 14% of the drug was released, respectively, after 6 h in a sequential in vitro test), suggesting that release in this region is limited and is not influenced by the presence of HAS in the ratio to zein under study. Studies using an in vitro colon model showed that under simulated colonic conditions, the drug release was significantly (p < 0.05) more rapid from 1:5 HAS/Zein, compared to the zein alone coating formulation. These data therefore support the potential use of zein-starch mixed films for colonic targeting purposes.