it is the object of the present invention to provide a preparation of a drug with very low solubility that shows prolonged and nearly constant rate of drug absorption for a long period of time and concurrently maintains a high extent of bioavailability . the object is reached by using a solubilizer which is mixed with the drug with very low solubility . the solubilizers suitable according to the invention are defined below . the active compound is preferably dissolved or dispersed in the solubilizer . the mixture of active compound ( drug ) and solubilizer can be diluted with water or intestinal juice without significant precipitation of the dissolved drug . in the solution the drug is included in a micell - structure formed by the solubilizer . with other commonly used solubilizers or co - solvents dilution may cause precipitation of the drug . the mixture of the drug and the solubilizer is incorporated into a pharmaceutical formulation , which gives prolonged release . drugs suitable for the extended release preparation according to the invention are compounds characterized by their very low solubility , that is less than 0 . 1 per cent by weight in water . in addition they are solubilizable in a solubilizer or in a combination of a solubilizer and water . examples of drugs suitable according to the invention are some substituted dihydropyridines , such as nifedipine and felodipine . felodipine is 4 -( 2 , 3 - dichlorophenyl )- 1 , 4 - dihydro - 2 , 6 - dimethyl - 3 , 5 - pyridinedicarboxylic acid ethyl methyl ester . nifedipine is 1 , 4 - dihydro - 2 , 6 - dimethyl - 4 -( 2 - nitrophenyl )- 3 , 5 - pyridinedicarboxylic acid dimethylester . felodipine and nifedipine both are practically insoluble compounds and therefore they are very suitable to solubilize . other examples of drugs with very low solubility are griseofulvin , digoxin , oxazepam , phenytoin and cyclosporine . the solubilizers suitable for the preparations according to the invention are semi - solid or liquid non - ionic surface active agents , especially such containing polyethyleneglycols as esters or ethers . the are preferably chosen from polyethoxylated fatty acids , hydroxylated fatty acids and fatty alcohols . it is especially preferred to choose the solubilizer from the group polyethoxylated castor oil , polyethoxylated hydrogenated castor oil , polyethoxylated fatty acid from castor oil or polyethoxylated fatty acid from hydrogenated castor oil . commercially available solubilizers , which can be used are known under the trade names cremophor , myrj , polyoxyl 40 stearate , emerest 2675 , lipal 395 and hco 50 . a specially preferred solubilizer is cremophor ® rh 40 ( basf ). the active compound mixed with the solubilizer is incorporated into different kinds of known controlled release systems , e . g . a hydrophilic gel system , beads coated with a rate controlling membrane , which can be a diffusion retarding coating or a disintegrating coating or tablets with an inert porous matrix . according to the invention the solubilized drug is preferably combined with a hydrophilic gel system , namely a hydrophilic swelling matrix e . g . hpmc . this form of controlled release mechanism is a suitable way to control the release of the micelles of drug and solubilizer . the technical properties are good and also the performance in vivo is good . among different hydrophilic materials tested , hpmc , hydroxypropyl methylcellulose , is the best gel - forming material . other examples of suitable compounds effecting the release of the active compound from the hydrophilic gel system are guar gum , xanthan gum , carboxypolymethylene , different cellulosic materials e . g . sodium carboxymethylcellulose and hydroxypropyl cellulose , lactose and aluminium silicate . the preparation according to the invention contains 20 - 80 % by weight , preferably 30 - 50 % by weight of the hydrophilic gel system . the major part of the hydrophilic gel system has a viscosity below 100 cps . it is especially preferable to use hpmc having a hydroxypropoxyl content of 4 - 12 % by weight , especially about 8 . 5 % by weight and a viscosity lower than 100 cps , e . g . 6 , 15 and / or 50 cps . the viscosity is measured by a standardized method described e . g . in united states pharmacopeia xxi , 1985 , p . 672 . the final preparation is e . g . in the form of a gel tablet . by a careful choice of fillers and binders as well as gel forming material the preparation can be manufactured into a commercially acceptable form , e . g . a tablet or a hard gelatin capsule comprising the gel forming granulate , that shows unexpectedly good absorption of the active compound as well as a prolonged duration of action . in the preparation according to the invention the proportions between the active compound and the solubilizer varies in the range from 1 : 1 to 1 : 10 , preferably in the range from 1 : 2 to 1 : 6 . also other types of controlled release preparations may be used according to the invention e . g . tablets with an inert porous matrix ; capsules comprising granules with a diffusion retarding coating or a disintegrating coating . the tablets with an inert porous matrix are obtained by mixing the drug and the solubilizer with water insoluble polymers or waxes and with fillers and binders . polyviny . lacetate , polyvinylchloride , ethylcellulose , paraffin and cellulose acetate phthalate could be used as suitable diffusion - retarding polymers . the fillers and binders are solid , powdered carriers such as lactose , saccharose , sorbitol , mannitol , starch , amylopectin , cellulose derivative , gelatine or other suitable carrier . the mixture is moistened with a solvent , e . g . water or ethanol or a solution consisting of e . g . water and a polymer e . g . polyvinylpyrrolidone . also a lubricating agent e . g magnesium stearate , calcium stearate , sodium stearyl fumarate and polyethyleneglycol wax may be added . the mixture is then formed to tablets . the capsules comprising of granules with extended release characteristics are obtained by making a core material consisting of the drug and the solubilizer together with fillers . the surface of the core is then coated with diffusion - retarding water insoluble polymers or waxes . the granules are then filled into hard gelatine capsules . the core material could e . g . be prepared by mixing the drug and the solubilizer with carefully selected fillers such as lactose , sorbitol , starch , cellulose derivatives or other suitable fillers . the mixture is moistened with a solvent , e . g . water or ethanol or a solution consisting of e . g . water and a polymer e . g . polyvinylpyrrolidone . the mass is formed to granules e . g . by extrusion and spheronization . the surfaces of the cores formed are coated with a solution consisting of a solvent e . g . methylene chloride and / or isopropyl alcohol and water insoluble polymers e . g . ethylcellulose . the granules are filled in hard gelatine capsules . ______________________________________ g______________________________________felodipine 10cremophor rh 40 90calcium phosphate 250hydroxypropyl methylcellulose 2910 6 cps 250xanthan gum 25guar gum 25sodium stearyl fumarate 13______________________________________ the composition according to example 1 was formed to hydrophilic matrix tablets containing 10 mg of felodipine / tablet . the tablets were prepared in the following way : felodipine was dissolved in cremophor rh 40 and the solution obtained was carefully mixed with the carrier materials , hpmc , xanthan gum , guar gum and calcium phosphate . the mixture was granulated with ethanol and dried . sodium stearyl fumarate was added as a lubricant and tablets were prepared by compression in a tabletting machine . ______________________________________ g______________________________________felodipine 10cremophor rh 60 90aluminium silicate 100paraffin 80hydroxypropyl cellulose 7 . 4sodium stearyl fumarate 5 . 0______________________________________ the composition according to example 2 was formed to controlled release tablets , inert porous matrix type , containing 10 mg of felodipine / tablet . the tablets were prepared in the following way : felodipine was dissolved in cremophor rh 60 and the solution obtained was mixed carefully with the carrier materials aluminium silicate and paraffin . the mixture was granulated with a solution of hydroxypropyl cellulose in ethanol and dried . sodium stearyl fumarate was added as a lubricant and tablets were prepared by compression in a tabletting machine . a controlled release of felodipine was achieved according to the in vitro results , 50 % released after 2 hours and 100 % released after 6 hours . ______________________________________ g______________________________________felodipine 20cremophor rh 40 100polyvinylpyrrolidone 66 . 5cellulose , microcrystalline 62maize starch 29 . 5lactose 157ethylcellulose 36hydroxypropyl methylcellulose 2910 6 cps 12gelatin capsules______________________________________ the composition according to example 3 was formed to controlled release capsules containing 20 mg of felodipine / capsule . the capsules were prepared in the following way : felodipine was dissolved in cremophor and the solution obtained was mixed carefully with the carrier , polyvinylpyrrolidone , cellulose , maize starch and lactose . the mixture was moistened with water and spheronized . the granules obtained were dried and sieved , the fraction 0 . 71 - 1 . 12 mm was used . the cores were coated with ethylcellulose dissolved in a mixture of methylene chloride and ethanol . the coated granules were filled into hard gelatine capsules . ______________________________________ g______________________________________felodipine 20myrj 51 120hydroxypropyl methylcellulose 2910 50 cps 200cellulose , microcrystalline 20lactose 167sodium stearyl fumarate 10 . 5______________________________________ the composition according to example 4 was formed to controlled release tablets containing 20 mg of felodipine / tablet . the tablets were prepared in the same way as described in example 1 . ______________________________________ g______________________________________nifedipine 20cremophor rh 40 50hydroxypropyl methylcellulose 2910 50 cps 70hydroxypropyl methylcellulose 2910 6 cps 160cellulose microcrystalline 6lactose 56aluminium silicate 94sodium stearyl fumarate 10______________________________________ the composition according to example 5 was formed to hydrophilic matrix tablets containing 20 mg of nifedipine / tablet . the tablets were prepared in the same way as described in example 1 . the best mode of carrying out the invention is at present considered to be example 5 . the following example illustrates the reference tablet used in in vivo studies the composition according to reference example a was formed to fast - dissolving , conventional tablets containing 25 mg of felodipine / tablet . the tablets were prepared in the following way : felodipine was micronized and mixed with lactose and methylcellulose . the mixture was granulated with water and dried . polyvinylpyrrolidone and magnesium stearate were added and the mass was compressed to tablets . ______________________________________ g______________________________________felodipine 66methylcellulose 13mannitol 870polyvinylpyrrolidone 30cellulose , microcrystalline 40ethylcellulose n 10 34polyethyleneglycol 6000 41 . 8______________________________________ the composition according to reference example b was formed to controlled release capsules containing 10 mg felodipine / capsule . the capsules were prepared in the following way : felodipine was micronized and carefully mixed with the carrier , mannitol , methylcellulose , polyvinylpyrrolidone and cellulose . the mixture was moistened with water and spheronized . the granules obtained were dried and sieved , the fraction 0 . 71 - 1 . 12 mm was used . the cores were coated with ethylcellulose and polyethyleneglycol dissolved in a mixture of methylene chloride and isopropyl alcohol . the coated granules were filled into hard gelatine capsules . in the attached fig1 the average plasma values ( nmol / 1 ) for the compositions according to example 1 , 4 and reference example a have been illustrated . a single dose of 20 mg felodipine in a controlled release preparation according to the present invention was administered to 6 healthy male subjects . the plasma concentrations of felodipine were compared with the plasma concentrations after a single dose of a fast dissolving tablet containing 25 mg of felodipine . as can be seen the preparations according to the invention gave lower peaks in the plasma concentration whereas the fast - dissolving tablet gave an unwanted high peak . the area under the plasma concentration curve ( auc ) from time 0 to infinity was ______________________________________preparation dose mg auc / dose nmol · h . sup .- 1 · l · mg . sup .- 1______________________________________reference a 25 7 . 2example 1 20 8 . 8example 4 20 7 . 4______________________________________ as can be seen from this table the bioavailability of felodipine was not decreased with the controlled release preparations . in the attached fig2 the average plasma values ( nmol / 1 ) for the compositions according to example 3 and reference example b have been illustrated . a single dose of 20 mg felodipine in a controlled release preparation according to the present invention was administered to 5 healthy male subjects . the plasma concentrations of felodipine were compared with the plasma concentrations after a single dose of a conventional controlled release preparation , that is without the solubilizer , containing 10 mg of felodipine . as can be seen the preparation according to the invention gave a low peak in the plasma concentration and a considerable extent of bioavailability . the reference gave no detectable plasma concentration which clearly indicates the need of a solubilizer if a controlled release effect is wanted . in the attached fig3 the average plasma values ( nmol / 1 ) for the composition according to example 5 and a reference formulation containing nifedipine , adalat ® 10 mg ( bayer ) ( reference c ) have been illustrated . adalat ® is a fast release preparation on the market . a single dose of 20 mg nifedipine in the controlled release preparation according the present invention was administered to 6 healthy male subjects . the plasma concentrations of nifedipine were compared with the plasma concentration after a single dose of the reference formulation containing 10 mg nifedipine . as can be seen the preparation according to the invention gave a lower peak in the plasma concentration , whereas the reference preparation gave an unwanted high peak in spite of the fact that the dose is the half . no substantial reduction in bioavailability can be seen when the reference c was compared with example 5 . the area under the plasma concentration curve from time 0 to infinity was : ______________________________________preparation dose mg auc / dose nmol · h . sup .- 1 · l · mg . sup .- 1______________________________________adalat ®, 10 46 . 5bayerexample 5 20 36 . 0______________________________________ the examples above and the attached fig1 and 3 illustrate the advantages of the controlled release preparation according to the invention in comparison with a conventional preparation or a controlled release preparation without solubilizer , all containing the same active compound . by the solubilization of the active compound with very low solubility it is possible to obtain a tablet having a more constant plasma concentration profile and without any unwanted high peaks . also an effect during an extended period of time was obtained . often there is a reduction in the extent of the bioavailability , when drugs with very low solubility are formulated . this invention provides however a technique of making controlled release preparations of drugs with very low solubility with the above - mentioned advantages and without any substantial reduction in the extent of the bioavailability .
an extended release perparation of an active compound with very low solubility containing the active compound dissolved or dispersed in a semi - solid or liquid non - ionic solubilizer and whereby the amount by weight of the solubilizer is at least equal to the amount by weight of the active compound as well as a process for the preparation thereof .