A composition for
controlled delivery of at least one active substance into an
aqueous medium by
erosion at a preprogrammed rate of at least one surface of the composition, comprising a matrix comprising the active substance, the matrix being erodible in the
aqueous medium in which the composition is to be used, and a
coating having at least one opening exposing at least one surface of said matrix, the
coating comprising a first
cellulose derivative which has
thermoplastic properties and which is substantially insoluble in the
aqueous medium in which the composition is to be used, and at least one of a second
cellulose derivative which is soluble or dispersible in water, a
plasticizer, and a filler. The
coating is a coating which crumbles and / or erodes upon
exposure to the aqueous medium such as a
body fluid. The first
cellulose derivative may be, e.g., ethylcellulose,
cellulose acetate, cellulose
propionate or cellulose
nitrate, and the second cellulose derivative may be, e.g. methylcellulose, carboxymethylcellulose or salts thereof,
cellulose acetate phthalate,
microcrystalline cellulose, ethylhydroxyethylcellulose, ethylmethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxymethylcellulose or hydroxymethylpropylcellulose.