Starch-based coatings for colon-specific delivery. Part II: Physicochemical properties and in vitro drug release from high amylose maize starch films

Abstract

This work reports an investigation into free-film properties of a high amylose maize starch-based film coating that has been used in the preparation of formulations for drug delivery to the colon (WO 2008/012573 A1) and relates these properties to in vitro drug release from pellets. Maize starch/ethylcellulose free films were prepared and characterised by scanning electron microscopy (SEM), light microscopy, modulated differential scanning calorimetry (mDSC), Fourier-transform infrared (FT-IR), X-ray and % swelling in aqueous fluids with pH conditions similar to the stomach and small intestine. 5-ASA release from film-coated pellets was tested in enzyme free simulated gastric fluid and phosphate buffer pH 7.2. Selected formulations were further assessed in simulated gastric and intestinal fluids containing pepsin and pancreatin, respectively. The free films prepared were smooth and homogeneous in their appearance. The two polymers are immiscible, and neither mDSC nor FT-IR could detect interactions between them. Films made from high amylose starches were found to have a considerably lower swelling ability than high amylopectin-based films, and they suppressed drug release in the enzyme free media successfully. 5-ASA release from pellets coated with mixtures of high amylose starches (Hylon ® VII, Hylon ® V or LAPS) and Surelease ® in a ratio of 1 to 2 w/w was found to be minimal in simulated gastric and intestinal fluids. This suggests that these mixed films provide starch domains that are resistant to the enzymes present in the upper GI tract and thus can potentially be used in the preparation of colon-specific delivery devices. Starches with a minimum amylose content of 56% such as the starches used in this study (Hylon ® VII and Hylon ® V) are preferred, and although pure amylose can also be used this is not essential.