Materials useful for an external coating include poly(vinylpyrrolidone) (PVP), poly(ethylene glycol) (PEG), hydroxypropyl ethylcellulose, hydroxypropyl methylcellulose, ethylcellulose, hydroxyethylcellulose, dimethylaminoethyl methacrylate-methacrylate acid ester copolymer, combinations thereof and other such materials known by those of ordinary skill in the art.