PHARMACEUTICAL PRODUCTS IN SUSTAINED-RELEASE FORM, AND THEIR PREPARATION PROCESS

Abstract: A new sustained-release form is described for the oral administration of drugs which produce a pH value of less than or equal to 5 when in aqueous solution. The new sustained-release form can also be used for drugs which do not produce an acid pH when in solution but which can be formulated with excipients of acid pH. The formulation comprises essentially: a) a nucleus constituted by a continuous rigid polymer matrix which incorporates the drug, this polymer matrix being insoluble at acid pH values but biodegradable at pH values exceeding 5. b) a first film which is applied over the nucleus and is arranged to regulate the diffusion of the drug by means of a membrane effect; c) a second film which does not obstruct the diffusion the drug, which protects the preceding film and which possibly carries a quantity of drug to compensate for the release time lag.

Description: PHAESACEUTICAL PRODUCTS IN SUSTAINED-RELEIBSE FORIJI, AND THEIR PREPARATION PROCESS This invention relates to pharmaceutical sustained release products and the process for their preparation. The problem of preparing sustained-release forms for oral administration is widely felt in the pharmaceutical industry. A sustained-release form is a pharmaceutical form which makes the active principle available to the organism at a rate which is as constant as possible over a sufficiently long time period. In practice, this implies finding the means for covering the organism with the drug over the 24 hours without using too frequent administration, which could be poorly tolerated by the patient, including psychologically. It also implies preventing large fluctuations in the hematic levels, with corresponding very high values which can induce undesirable side-effects. This type of problem is particularly felt in the case of drugs with a short half-life. Various sustained-release forms are either proposed in the literature or have been prepared in practice, but always for specific drugs, with very limited objectives, and results which are only partly satisfactory. A completely new form for oral administration has now been found, and forms the subject matter of the present invention, which enables a wide class of drugs to be administered in sustained-release form, independently of their chemical structure or type of activity. Nore specifically, the administration form according to the present invention enables a single dose of drug to be introduced into the organism and to be released at a constant determined rate over a programmed time. The new sustained-release form is characterised by the following essential parts: a) a nucleus which contains the drug and is constituted by a polymer arranged to incorporate the drug and any excipients or diluents, and which is in the form of a rigid continuous matrix insoluble at acid pH but soluble practically totally at pH values exceeding 5; b) a first film covering the nucleus and constituted by a filmogenic polymer which is soluble but not swellable in water, is chemically unalterable in an aqueous environment at physiological pH, and is absolutely free of toxicity. The purpose of this first film is to regulate the release of the drug by means of a membrane effect. It must there fore be permeable to the drug and its thickness must vary as a function of the rate of diffusion of the drug. ore specifically, this first film has a thickness, expressed in 2 gZcm , which is directly proportional to the rate of diffusion of the drug expressed in g/h; c) a second film, applied over the first film, and constituted by a filmogenic polymer which is insoluble in water at any pH, but is preferably swellable, is free from toxicity and is totally permeable to the drug. The purpose of this second film, which must in no way obstruct or regulate the release of the drug, is purely to protect the first film so as to prevent any slight surface damage altering the completeness and consequently modifying the regularity of the membrane effect. In this respect, it should be noted that the new sustainedrelease form according to the present invention utilises the membrane diffusion principle governed by the first Fick law: dQ - dt = AS (Cl-C2) dQ where - dt is the diffusion rate, A is the diffusion dt constant, S is the membrane surface ares, C1 is the drug concentration on the inside of the membrane, and C2 is the drug concentration on the outside of the membrane. To enable the objectsof the invention to be attained, the rate of diffusion of the drug must be as constant as possible, the drug quantity made available to the organism in unit time being consequently constant. Considering the aforesaid equation, it is apparent that as C2 is negligible, because of the fact that the drug is continuously removed from the outside of the membrane, the proposed system will attain its object if S and C1 are constant with time. With regard to C1, it has been found that by using a suitable filmogenic polymer for the first film applied on to a matrix, C1 remains constant and equal to the concentration of the saturated aqueous solution of the drug, while this latter is present in the solid state within the matrix. With regard to S, it has been found that when the drug is inserted into the rigid polymer matrix of point (a), this matrix creates a dimensionally stable support for the diffus ive film of point (b), and thus maintains the surface area of the membrane constant for the entire required period. In order to determine this period and make it coincide with the useful time period during which the drug can be absorbed by the organism, it has been found necessary to use polymers for preparing the matrix nucleus which are insoluble at acid pH, and in particular insoluble at pH values less than 5, but are totally soluble at pH values exceeding 5. In this manner, the nucleus containing the drug remains unaltered while in the presence of gastric juices of pH between 1.2 and 3, whereas it dissolves completely at the intestinal pH of between 5.5 and 7.5. The new system is constructed in such a manner that the dissolving of the rigid polymer matrix coincides with the exhaustion of the drug dose. The presence of a drug of acid hydrolysis pH ensures that the pH of the internal environment of the matrix is kept below the solubility limit of the polymer. This facility for the nuclei to be totally biodegradable at intestinal pR is highly advantageous, because it prevents any residue accumulation at the intestinal level. An important aspect of the present invention is that the essential characteristic of the polymers used in the nuclei in the new sustained-release form, i.e. their insolubility within the pH range of 1 to 5 or rather their biodegradability at pH values exceeding 5, also creates precise limits on the drugs which can be administered by the new system. In this respect, as already stated, the drugs administered with the new formulation must give a pH of between 1 and 5 in saturated aqueous solution in order to prevent the nuclei dissolving. Drugs which have a higher pH can also be administered, provided they can be used in mixture with pharmaceutically acceptable acid substances such as tartaric acid, citric acid and the like, which maintain the pH of the system at the required value. The preparation process for the new pharmaceutical forms comprises the following essential stages: 1. Preparation of the nuclei using polymers soluble in non toxic organic solvents, such as alcohol, ketones, ethers and the like. Examples of particularly suitable polymers are cellulose acetophthalate, polyvinyl aceto phthalate, methylcellulose phthalate, hydroxypropyl methylcellulose phthalate and the like. The solvent used must preferably not dissolve the drug. The active principle in powder form, possibly mixed with diluents and excipients, is wetted with a polymer solution to such an extent that the weight of polymer is 10-20% of the weight of active principle or of powder material generally. The uniformly mixed wetted mass obtained in this manner is granulated and dried. The granulate, possibly mixed with other excipients, is compressed into tablet form. It is critical for the purpose of the invention that the ratio of the polymer to the other components and the method of preparation used are such as to enable a "continuous" matrix to be formed. 2. Application of the first film to the nuclei for control ling the drug diffusion in an aqueous environment. For this stage, filmogenic polymers are used which are soluble in non-toxic- organic solvents which do not dissolve the active principle. Examples of particularly suitable polymers are acrylic polymers, acrylic copolymers, vinyl polymers, vinyl copolymers, polymers deriving from cellulose or cellulose derivatives. This film is preferably applied in a pan by spraying the polymer solution on to the preformed nuclei. The film is applied in successive cold-dried layers until the 2 required thickness expressed in vem is obtained. 3. Application of the second protective film for protecting the first film. Filmogenic polymers soluble in non toxic organic solvents are used for this stage. From the chemical aspect, the classes of polymers which can be used for this second film are the same as used for forming the first film, i.e. acrylic, vinyl or cellulose polymers, but chosen so as to in no way obstruct the drug diffusion. This film is also applied by spraying the polymer solution on to the properly dried nuclei coated with the first film. In this case, the film thickness is not critical, and is in fact limited to the minimum necessary for obtaining the protective effect. Thy thus finished pharmaceutical forms are cold-dried and possibly covered with a film of talc or other substance of lubricant action. It has been found that the new system has an action time lag of one to two hours, i.eO a certain time passes before the films become permeated by the water and the uniform release of the drug commences. If it is not convenient to leave the organism "uncovered" for such a long period, it is possible to incorporate into the outer second film a quantity of drug which is immediately released1 so acting within the time period necessary for the sustained-release form to attain its release equilibrium. If a time lag of one hour is determined, then a drug quantity is incorporated into the second film equivalent to the hourly dose released by the sustained-release form. According to this alternative, the purpose of the second film is then not only to protect the first film, but to act as a carrier for the immediate release of the drug. The drug is incorporated into the polymer of the second film before its application by various methods. It is possible to use a solvent for the polymer which is also a solvent for the active principle, and to apply the film as a solution. It is also possible to prepare the drug in the form of an aqueous solution and use a solvent for the polymer which is able to totally mix with the drug solution. In this case the second film is also applied in the form of a solution. Excellent results have also been obtained by uniformly suspending the drug in powder form in the polymer solution, and applying the suspension in the described manner. As already stated, the drugs which can be administered in the new sustained-release form are all those drugs which in aqueous solution give a pH of between 1 and 5, such as the hydrochlorides of weak bases or drugs which themselves contain acid groups. If basic drugs are to be administered, they can be put into the sustained-release form in mixture with a pharmaceutically acceptable acid substance. A non-limiting example of the invention is given herein after using Tiapride, i.e. N-diethy1aminoethy12-methoxy 5-methylsulphonyl-benzamide hydrochloride, which is normally administered in a daily dosage of 4 x 100 mg. ExAE The optimum hourly dose of Tiapride was calculated for a subject weighing 70 kg on the basis of pharmacokinetic parameters obtained in man as follows: - half life 4 hours - elimination constant (Eel) : 40.693 = 0.173 h-l - hematic peak after administering 100 mg (Cp): 0.8 m 1 - therapeutic range: 0.6 - 0.9 m g/l of plasma - distribution volume (Vd) : 100 1. Constant-rate release for a subject weighing 70 kg Cp x Vd . Kel = 0.8 x 100 x Q173 = 0.1977 mg/h/kg W 70 giving a total of 0.1977 x 70 = 13.84 mesh. The quantity of Tiapride necessary to keep the hematic level constant over 12 hours is 13.84 x 12 = 166 mg. a) The following quantities of substances were used for preparing 1000 nuclei: - Tiapride hydrochloride 166 g - Cellulose acetophthalate biodegradable at pH 5 31 g - talc 100 g - magnesium stearate 3 g The Tiapride hydrochloride and talc were placed in a powder mixer and mixed for a sufficient time to give a completely homogeneous mixture. A solution of the polymer was prepared in 60 ml of a 6 : 2 acetone : alcohol mixture, and this was used to wet the powder mixture. The wetted mass was granulated through a mesh with apertures, dried and repassed through a mesh with 500/um apertures. The granulate obtained was mixed with the magnesium stearate and compressed by using concave punches of 9 mm 2 diameter at a pressure of 2000 kgfcm b) The following substances were used for the application of the first film for controlling the drug diffusion: - low permeability acrylic polymer 5.Q4 g - high permeability acrylic polymer 1.26 g - dimethylpolysiloxane 1 g - acetone 25 ml - isopropanol 25 ml The film was applied to the nuclei in a copper pan, by spraying the filmogenic polymer solution in short bursts followed by pauses for drying with cold air. It was founi that the weight increase had to be 7.3 g in order to obtain the necessary film thickness. The weight increase was checked after drying the coated nuclei in an oven until their weight was constant. c) The following substances were used for the application of the second protective film: - high permeability acrylic polymer 6.25 g - dimethylpolysiloxane 1 g - acetone 25 ml - isopropanol 25 ml The polymer solution was again applied in a pan to the dry coated nuclei originating from the preceding stage, using the method heretofore described A film thickness equivalent to a weight increase of about 5 g was applied. After the second film had been applied, the nuclei were rolled in a drum lined with a minimum quantity of talc. The Tiapride release was monitored for the uncoated nuclei, the nuclei with the first film applied, and the finished nuclei also comprising the second film. A USP XX paddle apparatus was used, the dissolving medium being distilled water at 37 C. The obtained results given hereinafter are the average of 6 determinations. A - Tiapride release from the nuclei, expressed as a percent age of the total initial quantity: Time (min.) X drug released 15 37.8 30 51.6 60 71.1 90 80.3 120 86.O B - Tiapride release from the nuclei covered with the first film: Time (hours) Dh drug released 1 2 2 4 3 14 3.5 19.3 4.5 34 5 47 6 57 7 69 8 83 C - Tiapride release from the nuclei covered with the first and second films: : Time (hours) % drug released 1 0 2 1 3 16 4.5 34 5.5 44 6.5 57 7.5 71 8.5 83 As can be clearly seen from the reported data, when simply pasted into the polymer support matrix the drug is totally released within two hours, whereas if covered with the diffusion regulating film it is released in practice within a time period of 9 to 10 hours, during which the release kinetics remain of zero order, with a release rate within the acceptable limits of 10-15 m vh for a calculated optimum dose of 13.84 mg/h. It is also apparent that the second film has practically no influence on the drug diffusion rate but in fact provides improved release regularity practically until the drug is exhausted. By using the new sustained-release form, the Tiapride dosage can be changed from 4 x 100 mg to 2 x 166 mg over the 24 hours. EXAMPLE 2 The optimum hourly dose of MLTIAZEM was calculated for a subject weighing 70 kg and based on pharmacokinetic parameters obtained from humans as follows: - half life 4 hours 0.693 - elimination constant (Kel): 4 = 0.123 h-1 - hematic peak after administration of 60 mm (Cp): 0.072 mg/ml - therapeutic range: 0.4 - 0.9 mg/l.of plasma - distribution volume (Vd): 1065 Constant-rate release for 70 kg subject: Cp x Vd . Kel = w 0.1347 mg/h/kg for a total of 0.1977 x 70 = 9.43 mvh. The quantity of Diltiazem for maintaining a constant hematic level over a 12-hour period is 9.43 x 12 = 115 mg (rounded off to the hiz,h side). a) The preparation of 1000 nuclei requires the following product amounts: - Diltiazem hydrochloride 115 g - Biodegradable cellulose acetophthalate at pH 5 31 g - Talc 150 g - Magnesium stearate 3g The Dialtiazem hydrochloride and talc are put inside a powder mixer and mixed long enough to produce a completely homogeneous mixture. A solution of polymer was prepared in 60 ml of 6:2 acetone alcohol mixture and was used to wet the powder mixture. The wetted mass was granulated through a screen having an 800 mesh and then dried and repassed through a screen having a 500 mesh. The obtained granulate was dried and mixed with the magnesium steara te followed by compression under 9 mm dia. concave punches under 2 a pressure of 2000 kgtom b) The following products were used to apply the first film layer for controlling drug diffusion: - low-permeability acrylic polymer 5.04 g - high-permeability acrylic polymer 1.26 g - dimethylpolysiloxane 1.00 g - acetone 25 ml - isopropanol 25 ml The film was applied to the nuclei, held in a copper pan, by alter namely spraying with filmogenic polymer solution in short bursts and drying with cold air. It was found that in order to obtain the requi red film thickness, the increase in weight of the entire lot had to be 7.3 g1 which amounted to an increase of 7.3 mg for each nucleus. The increase in weight was checked after drying the coated nuclei in an oven until the weight became constant. c) The following products were used for applying the second protective film coating: - high-permeability acrylic polymer 6.25 g - dimethylpolysiloxane 1 g - acetone 25 ml - isopropanol 25 ml The film was applied to the nuclei, held in a copper pan1 in the same manner as described above, using the polymer solution and the nuclei processed in the preceding phase. A film coating was applied which amounted to an increase of weight of about 5 g. After having applied the second coating, the nuclei were rolled in a drum having a minimum quantity of talc liner. The Diltiazem release rate was measured on noncoated nuclei, nuclei coated with the first film and the finalized form with the second film coating. A USP XX paddle apparatus was used and the dissolving medium was distilled water at 370C. The results shown below are the average values of 6 determinations: A - Diltiazem release from the nuclei, expressed as per cent of the total initial quantity: Time (min.) % release 15 37.8 30 51.6 60 71.1 90 80.3 120 86.0 B - Diltiazem release from the nuclei with one layer of drug-release control film: Time (hrs) % release 1 3 2 10.3 3 16 3.5 19 Time (hrs) % release 4.5 35 5 48 6 59 7 70 8 86 C - Diltiazem release from the nuclei coated with the first and second films: Time (hrs) % release 1 2 2 8 3 16 4.5 35 5.5 46 6.5 58 7.5 72 8.5 84 As can clearly be seen from the above data, when the drug is simply mixed in with the polymer support matrix, it is totally released within two hours; whereas when it is covered with the diffusion regulating film, it is practically completely released within 9 to 10 hours, during which the release kinetics remain on the order of zero with the release rate remaining between the acceptable limits of between 10-15 mgSh for a calculated optimum dose of 9.43 mg/h. It is also apparent that the second film coating has practically no effect on the diffusion rate, while it does provide for more release regularity almost until the drug is completely exhausted. By using the new retarding formula, the Diltiazem dosage can be changed from 3 x 60 mg to 2 x 115 mg per 24 hour period.

Claims: PATENT CLAIMS 1. A pharmaceutical product in sustsined-release form for oral administration, characterised by comprising: a) a nucleus constituted by a continuous rigid polymer matrix which incorporates the drug and is biodegradable at pR values exceeding 5, b) a first film applied over the nucleus and constituted by a filmogenic polymer arranged to regulate the drug diffusion by a membrane effect, c) a second film applied over the preceding and which does not obstruct the drug diffusion but mechanically protects the underlying film. 2. A pharmaceutical product in sustained-release form ss claimed in claim 1, wherein the nucleus comprises 10-20% of biodegradable polymer with respect to the incorporated powder materials. 3. A. pharmaceutical product in sustained-release form as claimed in claim 1, wherein the nucleus comprises 40-60 of active principle. 4. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the biodegradable polymer is chosen from the group comprising cellulose acetophthalate, polyvinyl acetophthalate, methylcellulose phthalate and hydroxypropylmethylcellulose phthalate. 5. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the thickness of the first film is proportional to the drug diffusion rate. 6. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the first film is constituted by a polymer chosen from the group comprising acrylic polymers, acrylic copolymers, vinyl polymers, vinyl copolymers, cellulose and cellulose derivatives which are filmogenic, partly permeable to the drug in an aqueous environment, and insoluble in water at any pH value. 7. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the second film is constituted by a polymer chosen from the group comprising acrylic polymers, acrylic copolymers, vinyl polymers, vinyl copolymers, cellulose and cellulose derivatives which are filmogenic, totally permeable to the drug in an aqueous environment, insoluble in water, and swellableO 8. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein a small quantity of drug is incorporated into the second protective film in order to compensate for the release time lag. 9. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the drug is a compound which produces an acid pH not exceeding 5 when in aqueous solution. 10. A pharmaceutical product in sustained-release form as claimed in claim 1, wherein the drug is miscible with acid excipients such that the mixture produces an acid pH not exceeding 5 when in aqueous solution. 11. A process for' preparing a pharmaceutical product in sustained-release form, characterised in that (1) the active principle in powder form, possibly mixed with excipients and diluents, is wetted with a solution of polymer which is biodegradable at pH values exceeding 5, then granulated and dried under cold conditions, (2) a solution of filmogenic polymer insoluble in water is applied over the nuclei thus formed and the solvent is evaporated under cold conditions to form the first film, (3) a solution of filmogenic polymer is applied over the first formed film and the solvent is evaporated under cold conditions to form a second protective film. 12. A process as claimed in claim 11, characterised in that the solution of biodegradable polymer is prepared using a non-toxic organic solvent which is not a solvent for the active principle. 13. A process as claimed in claim 11, characterised in that the first and. second films are applied in the form of successive concentric layers applied on to the preformed nuclei until the required thickness is attained1 by spraying a solution of polymer in a non-toxic organic solvent. 14. A process as claimed in claim 11, characterised in that before the second film polymer solution is applied, either a solution of active principle is dissolved therein or the active principle as such is suspended therein. PATENT CLAIMS 1. A process for preparing a pharmaceutical product in sustained-release form, characterised in that (1) the active principle in powder form, possibly mixed with excipients and diluents, is wetted with a solution of polymer which is biodegradable at pH values exceeding 5, then granulated and dried under cold conditions, (2) a solution of filmogenic polymer insoluble in water is applied over the nuclei thus formed and the solvent is evaporated under cold conditions to form the first film, (3) a solution of filmogenic polymer is applied over the first formed film and the solvent is evaporated under cold conditions to form a second protective film. 2. A process as claimed in claim 1, characterised in that the solution of biodegradable polymer is prepared using a non-toxic organic solvent which is not a solvent for the active principle. 3. A process as claimed in claim 1, characterised in that the first and second films are applied in the form of successive concentric layers applied on to the preformed nuclei until the required thickness is attained, by spraying a solution of polymer in a non-toxic organic solvent. 4. A process as claimed in claim 1, characterised in that before the second film polymer solution is applied, either a solution of active principle is dissolved therein or the active principle as such is suspended therein.

Inventors: COLOMBO, PAOLO, CONTE, UBALDO
Applicants: LABORATORI PROPHIN INDUSTRIA CHIMICA FARMACEUTICA S.P.A.
Application year: 1983
Main classification: A61K9
IPC codes: A61K9