Sustained release dosage form

1. An osmotic dosage form comprising:

(a) a core comprising

(i) a drug layer comprising, based on the total weight of the drug layer, from 4 to 50 weight percent of the biologically active ingredient, and

(ii) a push layer comprising, based on the total weight of the push layer, from 15 to 60 weight percent of one or more ethylene oxide polymers, from 1 to 10 weight percent of one or more binding agents selected from the group consisting of methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, and polyvinyl pyrrolidone, and from 15 to 50 weight percent of one or more osmotic agents;

(b) a semi-permeable membrane covering said core, comprising

(i) from 30 to 70 weight percent of ethyl cellulose,

(ii) from 5 to 40 weight percent of a homopolymer or copolymer of an acrylic or methacrylic acid ester and

(iii) from 10 to 40 weight percent of a water-soluble plasticizer selected from the group consisting of triethyl citrate, triacetin, and glycerol, with the provisos that (1) the semi-permeable membrane comprises no or not more than 5 weight percent of a water-soluble material excluding any water-soluble plasticizer and (2) the semi-permeable membrane does not comprise cellulose acetate as the film-forming material and (3) components (i), (ii) and (iii) make up from 85 to 100 percent of the film-forming membrane, based on the total dry weight of the semi-permeable membrane, wherein the semi-permeable membrane maintains its physical and chemical integrity during the time the biologically active ingredient is released; and

(c) at least one drilled osmotic passageway through the semi-permeable membrane to the core, wherein the dosage form provides controlled release of the biologically active agent.

2. The osmotic dosage form of claim 1 , wherein the weight ratio between the ethyl cellulose and the homopolymer or copolymer of an acrylic or methacrylic acid ester in the semi-permeable membrane is from 0.1 to 15:1.

3. The osmotic dosage form of claim 1 , wherein the total weight of ethyl cellulose, the homopolymer or copolymer of an acrylic or methacrylic acid ester, and the water-soluble plasticizer is from 95 to 100 percent, based on the total dry weight of the semi-permeable membrane.

4. The osmotic dosage form of claim 1 , wherein the drug layer in the core further comprises from 15 to 90 weight percent of one or more ethylene oxide polymers.

5. The osmotic dosage form of claim 1 , wherein the accumulated drug release in percent between 2 and 12 hours meets the formula for zero order release when t is between 2 and 12 hours:

Y=100k(t−Tlag) after fitting test, wherein Tlag is a lagging time of 2 hours, Y is the accumulated drug release in percent and k is a constant, and

after linear fitting the correlation coefficient R 2 is >0.9.

6. The osmotic dosage form of claim 1 , characterized by not having a lag-time between the intake of the osmotic dosage form and the onset of the release biologically active ingredient.