in the inventor &# 39 ; s investigations , it was found that there are three major reasons for instability problems in case of a pharmaceutical formulation containing an active substance and in case of a bulk active substance . first , the active substance as such is very hygroscopic and it is impossible to remove all water from it . this is illustrated by the following experiment : 111 . 07 mg of pravastatin in crystal form ( prava izh ) and 109 . 8 mg of lyophilized pravastatin ( prava lio ) were exposed to air moisture . their weights were measured in different time intervals . the growth of weight of both samples and the difference in the starting weight and the weight in time are illustrated in fig1 a and 1b . another observation was that carbon dioxide from the air may irreversibly and reversibly bind to the active substance and can cause a drop of ph . this is illustrated by the following experiment : 5 g of pravastatin sodium were dissolved in 30 ml of methanol , the ph was adjusted to 10 with 3 % aqueous solution of naoh . 400 ml of ethylacetate were added and the crystals of pravastatin sodium were formed . crystals werelfiltered and dried and then put into three different atmospheres : normal air , nitrogen atmosphere and carbon dioxide atmosphere . in normal air and in the nitrogen atmosphere the ph remained the same during a period of 24 hours ( normal air : 9 . 2 , nitrogen : 9 . 5 ), but in the carbon dioxide atmosphere the ph dropped in the first two minutes from 9 . 2 to 6 . 9 . after 12 minutes the ph was 6 . 6 and after 1 hour the ph was 6 . 5 . after that , the ph remained constant . the third observation is that a sufficient stabilization of the active substance is already obtained at a ph of at least 7 . 0 , but a beneficially high stability is effected at a ph of at least 8 . 0 . we have noticed that at a ph below 8 the formation of lactone has occurred and also the amount of other impurities has increased . the presence of humidity in the air and a carbon dioxide - rich atmosphere makes the negative effect of a low ph even stronger . this is illustrated by the following experiment : pravastatin was dissolved in different buffers with the ph in a range between 7 and 11 ( f = phosphate , c = citrate , b = borate ). the occurrence of pravastatin in lactone form and the formation of different degradation products ( impurities ) was measured after 1 , 5 , 13 and 28 days . the results are shown in fig2 and 3 . in the present invention , we have surprisingly found that a sufficient stability of the active substance , which is a hmg - coa reductase inhibitor preferably in the form of salt , can be also obtained by using a pharmaceutical formulation which does not create a marked alkaline environment in an aqueous dispersion . in order to achieve this efficiently , it is significant that the hmg - coa reductase inhibitor is present in a homogeneous mixture by co - crystallization and / or co - precipitation with the buffering substance or the basifying substance in the composition according to the present invention , before the mixed composition is incorporated into the pharmaceutical formulation as the active substance . the composition of the present invention , which is the pharmaceutically active substance , may essentially consist only of said homogeneous , co - crystallized or co - precipitated hmg - coa reductase inhibitor and buffering substance or basifying substance , but may contain further components and additives as desired . another surprising finding was that a sufficient stability of a hmg - coa reductase inhibitor in the form of a salt in bulk can be obtained even when amount of the buffering substance or the basifying substance crystallized or precipitated with the hmg - coa reductase inhibitor is low . in the conventional stabilization concept described in ep - a - 0 336 298 , the basifying substance is added to the pharmaceutical formulation in an amount from 1 to 75 wt .-%, and in the examples the weight ratio of the basifying substance relative to pravastatin is from 33 to 500 %. according to the present invention , a protective effect can be achieved at lower ratios of the buffering substance or the basifying substance , such as below 30 wt .-%, while this ratio is preferably 10 wt .-% or less , more preferably 5 wt .-% or less and in particular 1 wt .-% or less , relative to the ; amount of co - crystallized or co - precipitated hmg - coa reductase inhibitor . the lower limit mainly depends on the environmental conditions and the kind and amounts of other components to be used for the pharmaceutical formulation , but an amount of at least 0 . 05 or 0 . 1 wt .-% of the buffering substance or the basifying substance , relative to the amount of hmg - coa reductase inhibitor , is generally sufficient to provide a desired protective effect . such an addition of small amounts of buffering substances or basifying substances avoids the negative effect of water already present in the bulk substance and of moisture from the air , avoids the negative effect of low ph caused by other ingredients which will be co - admixed to the pharmaceutical formulation , and avoids the possible lowering of the ph caused by carbon - dioxide . accordingly , the active substance and the pharmaceutical formulation according to the present invention were designed to avoid the negative effect of the water present in the bulk substance and in the pharmaceutical formulation , to avoid the negative effect of low ph which can be caused by other ingredients of the pharmaceutical formulation and to avoid possible lowering of the ph caused by carbon dioxide . furthermore , we have recognized that the protecting effect , especially the resistance against the negative effect of carbon dioxide , is better when the buffering substance or the basifying substance is co - crystallized and / or co - precipitated rather than merely admixed by mixing , milling or granulating , which is assumed to be attributable to a more homogeneous , fine distribution in the composition according to the present invention . accordingly , a corresponding stabilizing effect can be achieved with lower amounts of buffering substance or basifying substance . thus , it is possible to mix hmg - coa reductase inhibitor with other ingredients of the pharmaceutical formulation without fear that a degradation can be caused by the contact of hmg - coa reductase inhibitor with acidic ingredients , because a microenvironment of hmg - coa reductase inhibitor is effectively made slightly basic or markedly basic due to the addition of small amounts of a buffering substance or basifying substance . this addition of a buffering substance or basifying substance is also important for an easier handling of the hmg - coa reductase inhibitor bulk composition without special requirements for a carbon dioxide free atmosphere . further , we have found that for the stability and digestibility of a pharmaceutical formulation both the ph generated by the formulation in an aqueous medium ( usually being a dispersion ) and the ph of the active substance ( i . e . the hmg - coa reductase inhibitor - containing composition alone ) preferably should be adjusted . the most acceptable stability of the active substance in the formulations is obtained with the above composition , as the active substance , which is capable of providing a ph in the range from 7 to 12 and preferably from 8 to 11 . the ph value is the one which is obtained when the ph of an aqueous medium containing said composition would be measured . in the stable pharmaceutical formulation according to the present invention , the basic ph of the active substance has a minimal influence on the ph of the formulation . by creating locally an environment around the active substance which affords the best stability for the active substance , the potential of negative impact of other ingredients of the composition of the pharmaceutical formulation is reduced , and possible reactions among the active substance and the rest of the ingredients of the composition of the pharmaceutical formulation are also less favored . accordingly , the specific composition or active substance is maintained in a stable form when an active substance which is capable of providing a ph in an aqueous medium in the range from 7 to 12 and preferably in the range from 8 to 11 is added to the pharmaceutical formulation . the hmg - coa reductase inhibitor used for obtaining the specific composition or active substance of the present invention generally is in the form of a salt and may be selected from the group consisting of pravastatin , atorvastatin , fluvastatin , cerivastatin . since the stabilizing effect becomes particularly pronounced in these cases , the hmg - coa reductase inhibitor is preferably a calcium salt of atorvastatin ( atorvastatin ca ) and most preferred a sodium salt of pravastatin ( pravastatin na ). nonetheless , stability can be improved in accordance with the present invention also in the case of other hmg - coa reductase inhibitors . a process suitable for preparing the aforementioned specific composition including the stabilized hmg - coa reductase inhibitor will now be further described . the characteristic step is the crystallization and / or precipitation of both the hmg - coa reductase inhibitor and the buffering substance or basifying substance from the same medium . this step may be performed as the final step in the course of conventionally isolating and purifying the hmg - coa reductase inhibitor , but it may also be performed by using an already isolated hmg - coa reductase inhibitor which suitably has a ( hplc ) purity of at least 98 %, preferably of at least 99 . 5 %. first , a solution or dispersion of the hmg - coa reductase inhibitor and the buffering substance or basifying substance is provided . a common solvent or medium may be used for providing this solution or dispersion , for example low alkyl alcohols such as methanol , ethanol , propanol and isopropyl alcohol , low alkyl ketones such as acetone and methyl ethyl ketone , low alkyl glycol ethers such as methyl glycol , ethyl glycol , propyl glycol and ethyl diglycol , and dipolar aprotic solvents such as n , n - dimethyl - formamide ( dmf ), n , n - dimethylacetamide ( dma ) and dimethyl sulfoxide ( dmso ), including mixtures of these solvents . acetone and low alkyl alcohols such as methanol are preferred . then , an orlganic solvent , in which the compounds are less or hardly soluble or insoluble , is added in order to allow the hmg - coa reductase inhibitor and the buffering substance or basifying substance to crystallize and / or precipitate together . examples for the organic solvent include : higher alkyl alcohols such as butanol , isobutanol amyl alcohol , hexanol , 2 - ethylhexanol , benzyl alcohol and cyclohexanol , higher alkyl ketones such as methylbutyl ketone , methyl isobutyl ketone and cyclohexanone , esters such as methyl acetate , ethyl acetate , n - propyl ( and isopropyl ) acetate , n - butyl ( and iso - butyl or sec - butyl ) acetate and amyl acetate , ethers such as diethyl ether and diisopropyl ether , chlorinated hydrocarbons such as methylene chloride and chloroform , acetonitrile and the like , including mixtures of these solvents . ethyl acetate is particularly preferred as the organic solvent . the ph of the composition ( active substance ) is adjusted , preferably within the above specified range , by means of the co - crystallized or co - precipitated buffering substance or basifying substance in the aforementioned amounts . the buffering substance or agent is suitable selected from the group consisting of salts of inorganic acids , salts of organic bases or salts of organic acids . examples of salts of inorganic acids include sodium or potassium citrate , sodium or potassium phosphate or hydrogen phosphate , dibasic sodium phosphate , sodium , potassium , magnesium or calcium carbonate or hydrogen carbonate , sulphate , or mixtures of such buffering agents , or the like ; carbonate buffer or phosphate buffer , such as sodium carbonate of sodium phosphate , being preferred . examples for salts of organic bases include aminoguanidine carbonate or hydrogen carbonate , guanidine carbonate or hydrogen carbonate , succinimide carbonate or hydrogen carbonate , 1 - adamantil amine carbonate or hydrogen carbonate , n , n ′- bis ( 2 - hydroxyethyl ) ethylendiamine carbonate or hydrogen carbonate , tris ( hydroxymethyl ) aminometan carbonate or hydrogen carbonate , d (-)- n - methylglucamine carbonate or hydrogen carbonate , or the like . examples for salts of organic acids include potassium or sodium salts of acetic acid , citric acid , lactic acid , ascorbic acid , maleic acid , phenylacetic acid , benzoic acid , lauryl sulphuric acid , or the like . the basifying substance or agent is suitable selected from the group consisting of metal oxides , inorganic bases , organic bases and organic acids with basic character . examples of metal oxides include magnesium oxide and aluminum oxide . examples of inorganic bases include alkali metal hydroxide such as sodium hydroxide , potassium hydroxide , alkali earth metal hydroxide such as calcium hydroxide or magnesium hydroxide . examples of organic bases include succinimide , 1 - adamantyl amine , n , n ′- bis ( 2 - hydroxyethyl ) ethylendiamine , tris ( hydroxymethyl ) aminomethane , d (-)- n - methylglucamine , or the like . examples of organic acids with basic character include 3 -( n - morpholino ) propanesulfonic acid , 4 -[[ cyclohexyl amino ]]- 1 - butansulfonic acid , 4 -[[ cyclohexyl amino ]]- 1 - etansulfonic acid and the alkaline metal or alkaline earth metal salts of these acids , arginine , ornithine , lysine , or the like . the buffering or basifying substance may also be generated in situ , for example by adding an alkali metal or alkali earth metal hydroxide to the solution and then blowing carbon dioxide into the solution until a desired ph is adjusted . the composition or active substance of the present invention as described above is then added to the final pharmaceutical formulation by means of an appropriate formulation process . besides the composition ( pharmaceutically active substance ) of the present invention , the pharmaceutical formulation according to the present invention maylfurther comprise at least one constituent selected from the group consisting of a filler , a binder , a disintegrating agent , a glidant , a buffering agent ; optionally further comprising at least one constituent selected among coloring agents , lakes , aromas , adsorbents , film formers and plasticizers . by means of adding further buffering or basifying substances to the formulation , it is possible to effectively improve and maintain the resistance of the final formulation against carbon dioxide by neutralizing the acidifying effect thereof . any one of the above described buffering or basifying substances may be additionally used for the pharmaceutical formulation . in order to avoid a negative impact on the patient &# 39 ; s gastric mucosa during the administration of the pharmaceutical formulation , it is preferable to use additional buffering substance , and to adjust the ph of the formulation , i . e . the provided ph when the pharmaceutical formulation is brought in solution or dispersion , to a range below 9 , preferably below 8 . 5 , whereas the lower limit of the ph generated by the pharmaceutical formulation suitably is 6 , preferably 7 . the amount of additional buffering or basifying substance may be 20 wt .-% or less , more preferably 10 wt .-% per weight or less based on the total weight of the tablet . the pharmaceutical formulation of this invention may include , in addition to the hmg - coa reductase inhibitor which is sensitive to a low ph environment , one or more fillers , such as microcrystalline cellulose , lactose , sugars , starches , modified starch , mannitol , sorbitol and other polyols , dextrin , dextran and maltodextrin , calcium carbonate , calcium phosphate and / or hydrogen phosphate , sulphate , one or more - binders such as lactose , starches , modified starch , dextrin , dextran and maltodextrin , microcrystalline cellulose , sugars , polyethylene glycols , hydroxypropyl cellulose , hydroxypropyl methylcellulose , ethylcellulose , hydroxyethyl cellulose , methylcellulose , carboxymethyl cellulose , gelatin , acacia gum , tragacanth , polyvinylpyrrolidone , magnesium aluminium silicate , one or more disintegrating agents such as croscarmellose sodium , cross - linked polyvinylpyrrolidone , cross - linked carboxymethyl starch , starches and microcrystalline cellulose , magnesium aluminium silicate , polyacrylin potassium , one or more different glidants such as magnesium stearate , calcium stearate , zinc stearate , calcium behenate , sodium stearyl fumarate , talc , magnesium trisilicate , stearic acid , palmitic acid , carnauba wax , silicon dioxide , one or more buffering agents such as sodium or potassium citrate , sodium phosphate , dibasic sodium phosphate , calcium carbonate , hydrogen phosphate , phosphate , sulphate , sodium or magnesium carbonate , sodium ascorbinate , benzoate , sodium or potassium hydrogen carbonate , lauryl sulphate , or mixtures of such buffering agents . if required any , the formulation may also include surfactants and other conventional components for solid , pharmaceutical formulations such as coloring agents , lakes , aromas and adsorbents . as surfactants the following may be used : ionic surfactants , such as sodium lauryl sulphate or non - ionic surfactants such as different poloxamers ( polyoxyethylene and polyoxypropylene copolymers ), natural or synthesized lecithins , esters of sorbitan and fatty acids ( such as span ®, manufactured by atlas chemie ), esters of polyoxyethylenesorbitan and fatty acids ( such as tween ®, manufactured by atlas - chemie ), polyoxyethylated hydrogenated castor oil ( such as cremophor ®, manufactured by basf ), polyoxyethylene stearates ( such as brij ®, manufactured by atlas chemie ), dimethylpolysiloxane or any combination of the above mentioned surfactants . if the solid pharmaceutical formulation is in the form of coated tablets , the coating may be prepared from at least one film - former such as hydroxypropyl methylcellulose , hydroxypropyl cellulose , at least from one plasticizer such as polyethylene glycols , dibutyl sebacate , triethyl citrate , and other pharmaceutical auxiliary substances conventional for film coatings , such as pigments , fillers and others . the solid pharmaceutical formulations according to the present invention may be prepared as described below : the mixture of the active substance , filler , binder , buffering agent , disintegrating agent and if required a surfactant and other conventional ingredients for solid pharmaceutical formulations is homogenized employing suitable mixers . glidants and / or lubricants are added and the mixture is re - homogenized . the resulting mixture is compressed into tablets or filled into capsules . if needed , tablets can be film - coated . the mixture of the active substance , filler , binder , buffering agent , disintegrating agent and if required a surfactant and other conventional ingredients for solid pharmaceutical formulations is homogenized employing suitable mixers , granulated with a suitable solvent such as water , ethanol , methanol , isopropyl alcohol , n - butyl alcohol , acetone , diethyl ether , ethyl acetate , isopropyl acetate , methyl acetate , dichloromethane and methanol , and mixtures of these solvents such as ethanol and acetone , methanol and acetone , dichloromethane and methanol , and the mixtures thereof . the resulting granulation is dried in suitable dryers such as standard plate dryers , fluid bed dryers , vacuum and microwave dryers . to the dried granulation , glidants and / or lubricants and if required other conventional ingredients for solid pharmaceutical formulations are added . the resulting mixture is rehomogenized and compressed into tablets or filled into capsules . optionally , tablets are film - coated . the present invention is illustrated but by no means limited by the following examples . the following instrumentation was used in the examples : ldc hplc system : column ( 30 × 4 . 6 ) mm lichrospher , detector 236 nm , sample ≈ 500 mg / l injector 5 μl , mobile phase a : 15 % acn , mobile phase b : 90 % acn , gradient 0 ′: 100 % a , 3 . 5 ′ 100 % b , flow 2 . 8 ml / min ; ph meter : iskra ma 5741 ( i ) stabilizing of hmg - coa reductase inhibitor by addition of salts of inorganic acids pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), sodium carbonate ( 10 mg , dissolved in 0 . 15 ml of water ) was added and finally , ethylacetate ( 400 ml containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 9 . 5 ( 1 %)/ 9 . 8 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), sodium hydrogen carbonate ( 10 mg , dissolved in 0 . 15 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 4 g ) was 99 . 6 % and ph was 9 . 2 ( 1 %)/ 9 . 6 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), di - sodium hydrogen phosphate ( 10 mg , dissolved in 0 . 15 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 8 . 0 ( 1 %)/ 8 . 4 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), sodium hydroxide was added to reach ph = 9 . 5 , carbon dioxide was blown into the solution to reach ph of 8 . 3 ( equilibrium ) and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 7 . 7 ( 1 %)/ 8 . 3 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), aminoguanidine hydrogen carbonate ( 10 mg , dissolved in 1 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 2 g ) was 99 . 6 % and ph was 8 . 1 ( 1 %)/ 8 . 8 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), sodium acetate ( 10 mg , dissolved in 0 . 15 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 7 . 9 ( 1 %)/ 8 . 3 ( 5 %). pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), magnesium oxide ( 10 mg ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 8 . 7 ( 1 %)/ 9 . 3 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), l - arginine ( 10 mg , dissolved in 0 . 15 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh . ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuo . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 8 . 9 ( 1 %)/ 9 . 3 ( 5 %). the results of the stability measurements are shown in table 1 . pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), 3 -( n - morpholino ) propanesulfonic acid sodium salt ( 50 mg , dissolved in 0 . 3 ml of water ) was added and finally , ethylacetate ( 400 ml containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuum . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 5 % and ph was 8 . 1 ( 1 %)/ 8 . 5 ( 5 %). pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), tris ( hydroxymethyl ) aminomethane ( 50 mg , dissolved in 0 . 4 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuum . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 8 . 0 ( 1 %)/ 8 . 3 ( 5 %). pravastatin sodium ( i - 17226103b , 5 g ) with chromatographic purity 99 . 5 % and ph 7 . 4 ( 1 %)/ 7 . 7 ( 5 %) was dissolved in methanol ( 30 ml ), n , n ′- bis ( 2 - hydroxyethyl ) ethylenediamine ( 50 mg , dissolved in 0 . 4 ml of water ) was added and finally , ethylacetate ( 400 ml , containing 2 % of water ) was added . after 1 hour the resulted crystals were filtered off , washed with fresh ethylacetate ( 50 ml ) and dried at 40 ° c . for 6 hours in vacuum . the chromatographic purity of resulted crystals ( 4 . 3 g ) was 99 . 6 % and ph was 8 . 3 ( 1 %)/ 8 . 9 ( 5 %). the main cause for the unstability of hmg - coa reductase inhibitor in bulk , such as pravastatin sodium , is carbon dioxide from the air and the consecutive lowering of the ph of the active substance . the result of lowering of the ph is conversion pravastatin sodium to the lacton form . using various buffers or basifying agents in co - precipitation and or co - crystallization with the hmg - coa reductase inhibitor , it is possible to make a very homogeneous composition as the pharmaceutically active substance where the hmg - coa reductase inhibitor is effectively protected from being destabilized , see the results shown in tables 1 and 2 . at the same time , the ph of bulk active substance may be set to an appropriate value as desired . for example , pravastatin sodium is stable especially at a ph of between 8 and 10 . in the above examples 0 . 2 wt .-% of buffering or basifying agent relative to pravastatin sodium was used , but lower or higher amount also work effectively . the compositions according to the present invention obtained as described above can be incorporated in typical amounts into the pharmaceutical formulation , for example as described in the earlier pct application no . pct / ib99 / 01749 incorporated herein by reference , where the active substance is replaced by the compositions according to the present invention .
lovastatin , pravastatin , simvastatin , mevastatin , atorvastatin , and derivatives and analogs thereof are known as hmg - coa reductase inhibitors and are used as antihypercholesterolemic agents . the majority of them are produced by fermentation using microorganisms of different species identified as species belonging to aspergillus , monascus , nocardia , amycolatopsis , mucor or penicillium genus , and some are obtained by treating the fermentation products using the methods of chemical synthesis or they are the products of total chemical synthesis . the aforementioned active substances may be destabilized by the environmental factors , their degradation may also be accelerated by interactions with other pharmaceutical ingredients , such as fillers , binders , lubricants , glidants and disintegrating agents , therefore the pharmaceutical ingredients and the process for preparation of the pharmaceutical formulation should be meticulously chosen to avoid the aforementioned undesired interactions and reactions . the present invention relates to a hmg - coa reductase inhibitor which is stabilized by forming a homogeneous composition with a buffering substance or a basifying substance . this homogeneous composition is suitably used as the active substance in a pharmaceutical formulation for the treatment of hypercholesterolemia and hyperlipidemia .