Polymer release system

A pharmaceutical composition for controlled release of at least one therapeutically, prophylactically and/or diagnostically active substance into an aqueous medium by erosion of at least one surface of the composition, the composition comprising an erodible matrix composition comprising:

• (a) polyethylene oxide having a molecular weight (MW) of 200,000 daltons,
• (b) an active substance, and
• optionally, (c) one or more pharmaceutically acceptable excipients,
• with the proviso that the matrix composition does not contain a water dispersible or water soluble surface active agent that has at least one domain, which is compatible with the polymer in the matrix composition and at least one other domain which is lipophilic, and which has a melting point that is lower than the polymer in the matrix, and
• wherein the matrix is provided with a single coating having two openings exposing at least one surface of said matrix, the coating being insoluble in and impermeable to fluids and comprising either:
• (a) a polymer selected from the group consisting of cellulose acetate, polyamide, polyethylene, polyethylene terephthalate, polypropylene, polyurethane, polyvinyl acetate, polyvinyl chloride, silicone rubber, latex, polyhydroxybutyrate, polyhydroxyvalerate, teflon, polylactic acid or polyglycolic acid and copolymers thereof, copolymers such as ethylene vinyl acetate (EVA), styrene-butadienestyrene (SBS) and styrene-isoprene-styrene (SIS), or
• (b) a first cellulose derivative which is insoluble in the aqueous medium in which the composition is to be used and is selected from the group consisting of ethylcellulose, cellulose acetate, cellulose propionate and cellulose nitrate, and at least one of
• (i) a second cellulose derivative which is soluble or dispersible in water and is selected from the group consisting of methylcellulose, carboxymethylcellulose and salts thereof, cellulose acetate phthalate, microcrystalline cellulose, ethylhydroxyethylcellulose, ethylmethylcellulosc, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylcellulose, hydroxymethylcellulose and hydroxymethylpropylcellulose,
• (ii) a plasticizer selected from the group consisting of phosphate esters, phthalate esters, amides, mineral oils, fatty acids and esters thereof with polyethylene glycol;
• fatty alcohols and ethers thereof with polyethylene glycol, glycerin or sugars;
• vegetable oils and hydrogenated vegetable oils;
• nitrobenzene, carbon disulfide, β-naphtyl salicylate, phthalyl glycolate, and diocyl phthalate, or
• (iii) a filler,
• wherein any matrix surface exposed to the aqueous medium erodes at a substantially constant rate, so that a zero order release is obtained of at least about 60% w/w of the active substance from the pharmaceutical composition when subject to an in vitro dissolution test according to USP 24, NF 19, 711 Dissolution, employing Apparatus 2 equipped with a paddle,
• the composition having a cylindrical shape optionally with one or more tapered ends.