Amylopectin as a subcoating material improves the acidic resistance of enteric-coated pellets containing a freely soluble drug

The effect of an aqueous amylopectin subcoating on the acidic resistance and dissolution behaviour of enteric-coated pellets was studied. Freely water-soluble riboflavin sodium phosphate (RSP) was used as a model drug, and microcrystalline cellulose (MCC) and lactose as fillers in the pellet cores. The pellets were subcoated with 5% aqueous amylopectin solution or with 5% hydroxypropyl methylcellulose (HPMC) solution, and subsequently film-coated with aqueous dispersion of cellulose acetate phthalate (CAP). Drug release of enteric-coated pellets was investigated by confocal laser scanning microscopy (CLSM). Dissolution tests showed that amylopectin subcoating improved the acidic resistance of the enteric-coated pellets in 0.1 N hydrochloric acid (HCl) compared with HPMC subcoating. As the amylopectin subcoating load was increased to 4% and the aqueous CAP coating load to 35%, the coated pellets resisted in 0.1 N HCl solution for approximately 1 h (the amount of drug released was below 10%), and they dissolved in the SIF without enzymes in less than 10 min. Confocal microscopy images and profiles of mean fluorescence intensities of RSP (obtained in the range of the interface of the pellet core and the film and the film coating surface) showed consistent results with dissolution tests. It seems that amylopectin subcoating can prevent the influx of the dissolution medium into the pellet core, and thus decrease the premature dissolution and release of the drug from the enteric-coated pellets in 0.1 N HCl solution. The drug release mechanism appeared to be osmotically driven release, and followed by diffusion through the polymer film.