SUBSTAINED RELEASE TABLETS AND METHOD FOR PREPARATION THEREOF

Abstract: The invention relates to sustained-release pharmaceutical preparations comprising a drug-containing tablet and a coating surrounding the same, wherein the coating is insoluble in water and gastrointestinal fluids and consists essentially of a ter­ polymer of polyvinylchloride, polyvinylacetate, and polyvinyl­ alcohol and a water-soluble pore-creating substance, the said pore-creating substance being randomly distributed in the ter­ polymer coating, the pore-creating substance being present in amount of one part to 20 parts for each one to ten parts of terpolymer and being essentially pharmacologically inactive in the amount used. The invention also includes a method for the manufacture of the preparation.

Description: The sustained release of a medicine or drug is important for several reasons. For example it serves to provide the body with medica­ tion over a long time and thereby eliminates the need for swallowing an ordinary tablet at frequent intervals. Another advantage could be that a sudden release of a large amount of medicine which often occurs when conventional tablets are used can be avoided. Thereby the onset of toxic symptoms can be eliminated. One type of commercially used slow release tablets comprises a firmly coherent skeleton structure composed of non-toxic synthetic resin substantially insoluble in the fluid of the human or animal body with which the tablet comes into contact. The structure includes pore-­ like inter-connected canals or ducts open to the exterior of the struct­ ure and a material which comprises or contains a medical substance, which is soluble in the fluid contained in such canals or ducts. Slow release tablets of this type are disclosed in the GB patent 808,014. Another type of commercially used slow release preparation known as "osmotic device" has been developed by Alza Co. This device comprises a wall surrounding a reservoir containing an active agent and having a passageway for releasing the agent from the device. The wall is comprised of a material permeable to external fluid. A third type of slow release tablet is disclosed in e.g. the GB patent 1,186,990 and US patent 3,538,214. These patents disclose pharma­ ceutical preparations consisting of a tablet core comprising a medica­ ment, which is soluble in the gastro-intestinal fluids, and a coating on said core. The coating consists of a polymer substance which remains substantially intact and insoluble in the gastro-intestinal fluids. Fine particles of a readily water-soluble substance are randomly distri­ buted in the coating. Furthermore, it is disclosed in the patent that the preparation can be provided with an additional coating which i.a. may contain another pharmacologically active substance. According to the GB patent 1,186,990 the polymer substance is a polyamide and according to the US patent 3,538,314 the polymer substance is cellulose acetate, ethyl cellulose or low water soluble polyvinyl alcohol. However, to the best of our knowledge, none of the technical solutions disclosed in these two patents has led to a practically useful product. As regards the US patent 3,538,214 the reason seems to be clear, as the tables of the dissolution rate disclose that the dissolution rate is neither pH-independent nor essentially constant over any longer period of time, two requirements that must be fulfilled in modern slow release preparations. The polymer substance used in the GB patent 1,186,990 has rather poor film-forming properties, and it is difficult to get a proper adhesion to the tablet core surface. Another slow release composition is disclosed in the US patent 4,244,941. This composition comprises a drug including a core of a soluble substance and a rigid porous coating completely surrounding the core. The coating is substantially free of substances soluble or swellable in the gastrointestinal liquids. Furthermore, the coating is selected from substances insoluble in the medium, in which they are intended to be used. The substances are compressed in powder form to form an inert non-disintegrating, noneroding porous coating on the core. The coating could e.g. consist of a copolymer of vinyl chloride and vinyl acetate. However, this compression coating principle produces tablets, which consist of up to about 50% of coating material. This in contrary to what is sought after in the medical and pharmaceutical fields today. Objects of the invention An object of the present invention is to provide a slow-release preparation, in which the dissolution rate of the active substance is substantially constant over a long period of time. This means that the rate determining characteristics of the coating is substantially independ­ ent of any mechanical influence, enzymes, surface tension, pH and salt concentration. Another object of the invention is to provide an inexpensive slow release preparation. A third object is to provide a slow release preparation generally useful for different kinds of orally active drugs. A fourth object is to provide a slow release preparation, which is small in size due to a favourable ratio between the amount of active substance and inactive ingredients. A further object of the invention is to provide a slow release preparation, which can be manufactured in a simple process without problems with roughness of the tablet surface ("orange peel") or other problems related to poor adhesion of the coating to the tablet core surface. Summary of the invention A slow-release tablet according to the present invention comprises a drug containing tablet and a coating surrounding the same. The coating is insoluble in water and in the gastrointestinal fluids and consists essentially of a terpolymer of polyvinyl chloride, polyvinyl acetate and polyvinyl alcohol and a pore-creating substance being randomly distributed in the terpolymer. The pore-creating substance is present in an amount of 1-20 parts for each 1-10 parts of terpolymer. The method of producing the coated tablet according to the inven­ tion comprises the steps of dissolving the terpolymer in a solvent, preparing a suspension or solution of the pore-creating substance, providing a pharmaceutical tablet, combining the suspension or solution of pore-creating substance and solvent solution of the terpolymer to form a coating fluid, applying the coating fluid in the form of a solu­ tion or suspension to the tablet, and drying the coating fluid on the tablet to provide a terpolymer-coated tablet having the water-soluble pore-creating substance randomly distributed within the coating. Detailed description of the invention Preferably the terpolymer contains 80-95% weight per weight of polyvinyl chloride, 1 to 19% weight per weight of polyvinyl acetate and 1 to 10% weight per weight of polyvinyl alcohol. In this context it can be mentioned that a coating comprising a copolymer consisting of only polyvinyl chloride and polyvinyl acetate can be used but the adhesion properties to different kinds of drug containing tablet cores are not sufficiently good to avoid roughness of the tablet surface ("orange peel") and/or other problems related to poor adhesion. Furthermore, such a copolymer has not sufficient mechanical strength. The pore-creating substance used according to the present invention should be highly water-soluble, pharmacologically acceptable and essential­ ly free from own pharmacological effects in the amounts used. Especially preferred as pore-creating substance is saccarose (sucrose). Other substances which may be used include polyvinyl pyrrolidone, polyethylene glycol 1500, 4000 or 6000 and sodium chloride. The ratio pore-creating agent to terpolymer depends on the desired dissolution rate and time and can be decided in each separate case from simple experiments in the laboratory. Generally it can be said that in order to get practically useful dissolution from tablets for oral use the ratio should vary between 1 to 5, preferably between 1.5 and 3. The pore-creating substance is preferably but not necessary in­ soluble in the solvent used for coating the tablets. The particle size of the pore-creating substance may vary between 0.5 and 50 millimicrons. Preferably a plasticizer is also present in the terpolymer. The amount of this plasticizer may vary between 0.1 and 4% weight by weight of the coating fluid. Examples of suitable plasticizers are acetyltributyl­ citrate, polyethylene glycol, blown castor oil and glyceryl triacetate. Furthermore, the coating may include sodium bicarbonate as stabilizing agent. Depending on the size and area of the tablet the coating weight may vary between 10 and 170 mg per tablet and the coating thickness may vary between 25 and 300 µm, preferably 50 and 200 µm. According to the present invention the drug included in the core could be almost any drug that can be orally administered. In order to improve the solubility properties of the drugs the core may include conventionally used additives such as buffering agent, e.g. sodium bi­ carbonate or citric acid. Examples of drugs that suitably are administered in the form of sustained and constant release preparations according to the present invention include, but are not limited to, e.g. phenylpropanolamine, cefalosporin (Cefaclorum), bensodiazepine derivatives, potassium chlo­ ride, sodium salicylate, choline theophyllinate, acetaminophen, acetyl­ cystein, terbutaline, dextromethorphan, ascorbic acid, diltiazem, noscapine, oxybutynin, ibuprophen, urapidil, melperone, salbutamol, cimetidine, chlorpheniramine maleate, propanolol, L-dopa, piracetam, isosorbide dinitrate, indomethacin, zinc sulfate, diclofenac, litium sulfate, ferrous sulfate, pseudoephedrine, sodium cromoglycate, sodium PAS and meclomen. The starting preparations are produced in the following manner: 1) A terpolymer containing (w/w%) 80-95% PVC (polyvinylchloride), 1-19% PVAC (polyvinylacetate), and 1-10% PVOH (polyvinylalcohol) is dissolved in a solvent, e.g. acetone, methylenechloride, methylethyl­ ketone, or mixtures of acetone and ethanol, acetone and methylene­ chloride, or the like. 2) A suspension or solution of the pore-creating substance is produced as follows: The pore-creating particles are ground either by dry milling in a ball mill or by wet-milling in a glass bead milling device to a defined particle size, preferably between 0.5 um and 50 um. The particles are dispersed in solvents or mixtures or solvents, such as those previously mentioned, and mixed with the terpolymer solution. The ratio between pore-creating substance and terpolymer in the coating fluid is as previously described for the ratio in the coating. The coating fluid may, as previously stated, include a plasticizer and sodium bicarbonate. The coating fluid, in the form of a solution or suspension, is then applied on drug-containing cores by conventional coating procedure. Examples of such coating procedures are pan coating, manual or spray-­ coating, Würster coating, and other fluid-bed coating procedures. Coloring matter can also be incorporated in the coating fluid, and insoluble coloring materials are preferred. A second coating can be applied, and may contain one or more same or different drugs, for which a rapid release is desirable. This coat­ ing fluid is preferably a water-based sugar coating and, therefore, a seal coating between the latter and the terpolymer membrane coating is frequently necessary or desirable. The invention is further illustrated by the following examples. Example 1 Coating on tablets containing potassium chloride 1 gram. Composition of the coating fluid: The coating process is performed in a coating pan and the coating fluid is sprayed onto the tablets with an airless spray-coating device. Five thousand tablets are coated and the average membrane weight is 60 mg per tablet. The following table discloses that the dissolution rate of the drug is essentially constant during 8 hours and essentially independent of pH. Example 2 Coating applied on tablets containing 500 mg of sodium salicylate Composition of the coating fluid: The coating weight is 50 mg per tablet and the coating procedure is the same as in Example 1. As diclosed in the following Table II this formulation is an example of how the inherent pH dependency of the drug active substance can be used in order to obtain a desired dissolution rate at a certain pH. The dissolution rate of the drug will be about four times slower in the stomach than in the intestine and the solid drug substance does not get into direct contact with the mucous membranes. Thus the local irritating effect of sodium salicylate on the gastric mucosa is minimized. Example 3 Noscapine HCl is a weak base and has low solubility in natural and basic media, while the solubility in acidic media is high. Below, two tablet compositions are listed, one buffered B, and one without buffer A. Both tablet batches are coated with the same coating and the dis­ solution rate is determined according to USP XX. Example 4 Meclomen, Mefenanic acid, is a weak acid with a pKa of 10 which means that the drug is practically insoluble in physiological fluids having pH between 1 and 8. The tablet was buffered with sodium bi­ carbonate and the internal pH rises to about 10.5 where Mefenamic acid is freely soluble. As in the earlier experiments two formulations were manufactured, one containing buffer and one without. Example 5 Melperone, a weak base, has a pK₆ of 8.8 and shows pH-dependent release rate. Two formulations, one containing citric acid as buffering agent, and one without, were manufactured. The following Table III discloses the differences in dissolution rate for the preparations with and without buffer according to the examples 3-5. Example 6 Coated Choline Theophyllinate Tablets Coating applied on tablets containing 270 mg of choline theo­ phyllinate. The weight of the membrane is 40 mg per tablet and the coating procedure is the same as in Example 1. Example 7 Coated bensodiazepine tablets Coating applied on tablets containing 6 mg nitrazepame (bensodi­ azepinderivative) The ingredients except for Mg-stearate were mixed and moistened with ethanol. After drying Mg-stearate was added and the powder was compressed to tablets. Example 8 Coated Paracetamole Tablets Coating applied on tablets containing 500 mg of paracetaminophenol Example 9 Terpolymer Variation Coating applied on tablets containing 1 g of potassium chloride. The weight of the dried membrane was 60 mg per tablet and the coating procedure was the same as in Example 1.

Claims: 1. A sustained-release coated pharmaceutical tablet exhibiting a substantially constant dissolution rate during a major portion of its dissolution time when exposed to gastrointestinal fluids, and comprising a drug-containing tablet and a coating surrounding the same, wherein the coating is insoluble in water and gastrointesti­ nal fluids and consists essentially of a terpolymer of polyvinyl­ chloride, polyvinylacetate, and polyvinylalcohol and a water-­ soluble pore-creating substance, the said pore-creating substance being randomly distributed in said terpolymer coating, said pore-­ creating substance being present in amount of one part to 20 parts for each one to ten parts of terpolymer and being essentially phar­ macologically inactive in the amount used. 2. A coated tablet according to claim 1, wherein the terpolymer con­ tains 80 to 95% weight per weight of polyvinylchloride, 1 to 19% weight per weight of polyvinylacetate, and 1 to 10% weight per weight of polyvinylalcohol. 3. A coated tablet according to claim 2, wherein the pore-creating substance is a water-soluble substance selected from the group consisting of saccharose, sodium chloride, polyvinylpyrrolidone and a polyethylene glycol. 4. A coated tablet according to any of the claims 1-3, wherein the ratio pore-creating substance to terpolymer varies between 1 and 5 and preferably between 1.5 and 3. 5. A coated tablet according to any of the preceding claims, wherein the tablet also includes a buffering agent. 6. A coated tablet according to any of the preceding claims, wherein the coating also includes a plasticizer selected from acetyltri­ butylcitrate, polyethylene glycol, blown castor oil and glyceryl triacetate. 7. A coated tablet according to claim 6, wherein the plasticizer is present in a concentration of 0.1 to 4% weight by weight of coating fluid. 8. Method of producing a coated tablet exhibiting a substantially constant dissolution rate during a major portion of its dissolution time when exposed to gastrointestinal fluids, and comprising a drug-containing tablet and a coating surrounding the same, wherein the coating is insoluble in water and gastrointestinal fluids and consists essentially of a terpolymer of polyvinylchloride, poly­ vinylacetate, and polyvinylalcohol and a water-soluble pore-creating substance, the said pore-creating substance being randomly distribut­ ed in said terpolymer coating, said pore-creating substance being present in amount of one part to 20 parts for each one to ten parts of terpolymer and being essentially inactive in the amount used, comprising the steps of dissolving the said terpolymer in a solvent, preparing a suspension or solution of the pore-creating substance, providing a pharmaceutical tablet, combining the sus­ pension or solution of pore-creating substance and solvent solution of the terpolymer to form a coating fluid, applying the coating fluid in the form of a solution or suspension to the tablet, and drying the coating fluid on the tablet to provide a terpolymer-­ coated tablet having water-soluble pore-creating substance randomly distributed within the coating or membrane. 9. A method according to claim 8, wherein the terpolymer contains 80 to 95% weight per weight of polyvinylchloride, 1 to 19% weight per weight of polyvinylacetate, and 1 to 10% weight per weight of polyvinylalcohol. 10. A method according to claim 8 or 9, wherein the pore-creating substance is a water-soluble substance selected from the group consisting of saccharose, sodium chloride, polyvinylpyrrolidone and a polyethylene glycol. 11. A method according to any of the claims 8-10, wherein the ratio pore-creating substance to terpolymer varies between 1 and 5 and preferably between 1.5 and 3. 12. A method according to any of the claims 8-11, wherein the tablet also includes a buffering agent. 13. A method according to any of the claims 8-12, wherein a plasticizer is also present in the terpolymer. 14. A method according to claim 13, wherein the plasticizer is present in a concentration of 0.1 to 4% weight by weight of coating fluid, preferably selected from acetyltributylcitrate, polyethylene glycol, blown castor oil, and glyceryl triacetate.

Inventors: ERLANDSSON, STIG ALBIN BERTIL, LINDAHL, AKE RIKARD
Applicants: AB LEO
Application year: 1985
Main classification: A61K9
IPC codes: A61K31, A61K47, A61K9