the prior art literature discloses the use of dicalcium phosphate as one of the preferred excipients for amlodipine formulations . the inventors have discovered that the presence of dicalcium phosphate in the amlodipine formulation triggers the degradation of amlodipine , which is more pronounced at a ph below 6 . hence , removal of dicalcium phosphate form the composition provides a more stable pharmaceutical compositions of amlodipine . in our attempts to stabilize amlodipine in solid dosage forms we discovered that stability may be improved by replacing dicalcium phosphate with microcrystalline cellulose and mannitol . the term “ stable ” as used herein refers to the chemical stability of amlodipine in solid dosage forms and indicates the presence of less than 2 % w / w of related substances when stored at 40 ° c . and 75 % percent relative humidity for three month . the stability is measured using hplc to measure the presence of related substances . amlodipine as used herein is the free base or besylate salt and can be of any form including , anhydrous , hydrous , crystalline form i , crystalline form ii , amorphous form , and mixtures thereof . pharmaceutically acceptable salts of benazepril include inorganic or organic acids , such as strong mineral acids , for example hydrohalic , e . g . hydrochloric or hydrobromic acid ; sulfuric , phosphoric , nitric or perchloric acid ; aliphatic or aromatic carboxylic or sulfonic acids , e . g . formic , acetic , propionic , succinic , glycolic , lactic , malic , tartaric , gluconic , citric , ascorbic , maleic , fumaric , hydroxymaleic , pyruvic , phenylacetic , benzoic , 4 - aminobenzoic , anthranilic , 4 - hydroxybenzoic , salicylic , 4 - aminosalicyclic , pamoic , nicotinic ; methanesulfonic , ethanesulfonic , hydroxyethanesulfonic , benzenesulfonic , p - toluenesulfonic , naphthalenesulfonic , sulfanilic or cyclohexylsulfamic acid . the term “ dicalcium phosphate ” as used herein includes anhydrous calcium phosphate , anhydrous dicalcium phosphate , dibasic calcium phosphate as well as hydrates and solvates thereof . dicalcium phosphate is normally used as a diluent . the term “ substantially free ” as used herein refers to the use of dicalcium phosphate in a concentration less than that used as a diluent . microcrystalline cellulose is a white , odorless , tasteless , free flowing powder , and is widely accepted in the pharmaceutical industry as a universal diluent . it is purified ; partially depolymerized alpha cellulose derived from purified specialty grades of wood pulp . there are various grades which differ in bulk density , particle size , and moisture content . some of the commercially available grades of microcrystalline cellulose are avicel ®, vivapur ® and tabulos ®. when used without mannitol , the amount of microcrystalline cellulose is increased relative to the prior art , e . g ., greater than 80 % ( w / w ) and , more particularly , greater than 90 % ( w / w ). when used with mannitol , the amount of microcrystalline cellulose is greater than about 60 % ( w / w ). mannitol is a naturally occurring sugar alcohol having a cool taste and 50 % sweetness compared to sucrose . it is non - hygroscopic , chemically inert and does not undergo the maillard reaction , and therefore does not discolor in the presence of free amines . mannitol is available as powder and free flowing granules , and is used widely in pharmaceutical preparations . the granular form is particularly useful in direct compression technique of preparing tablets . some of the commercial grades are mannogem ®, pearlitol ® and partech m ®. the concentration of mannitol may vary from about 5 % to about 80 %, in particular it may vary from 20 % to 60 % by weight of the total uncoated tablet weight . the term “ solid dosage form ” as used herein includes conventionally used dosage forms such as tablet , capsule and the like . the term “ pharmaceutically inert excipient ” as used herein includes substances known in the art as diluents , binders , desiccants , disintegrants , coloring agents , flavoring agents , stabilizers , surfactants , lubricants / glidants , plasticizers and preservatives for pharmaceutical compositions . the excipients are selected based on the desired physical aspects of the final tablets ; e . g ., obtaining a tablet with desired hardness and friability , being rapidly dispersible and easily swallowed , etc . further , the inert excipients may be so selected as to provide slow and / or controlled release of the amlodipine from the tablets . examples of disintegrants include sodium starch glycolate , croscarmellose sodium , crospovidone , low substituted hydroxypropyl cellulose , and mixtures thereof . examples of binders include methyl cellulose , hydroxypropyl cellulose , hydroxypropyl methylcellulose , polyvinylpyrrolidone , gelatin , gum arabic , ethyl cellulose , polyvinyl alcohol , pullulan , pregelatinized starch , agar , tragacanth , sodium alginate , and mixtures thereof . examples of diluents include cellulose powdered , dextrates , dextrins , dextrose excipients , fructose , kaolin , lactitol , lactose , mannitol , sorbitol , starch , starch pregelatinized , sucrose , sugar compressible , sugar confectioners , and mixtures thereof . examples of lubricants and glidants include magnesium stearate , colloidal anhydrous silica , stearic acid , magnesium stearate , calcium stearate , talc , hydrogenated castor oil , sucrose esters of fatty acid , microcrystalline wax , yellow beeswax , white beeswax , and mixtures thereof . examples of desiccants include colloidal silicon dioxide , silicon dioxide and the like . examples of surfactants include both non - ionic and ionic ( cationic , anionic and zwitterionic ) surfactants suitable for use in pharmaceutical compositions . these include polyethoxylated fatty acids and its derivatives , for example polyethylene glycol 400 distearate , polyethylene glycol - 20 dioleate , polyethylene glycol 4 - 150 mono dilaurate , polyethylene glycol - 20 glyceryl stearate ; alcohol - oil transesterification products , for example polyethylene glycol - 6 corn oil ; polyglycerized fatty acids , for example polyglyceryl - 6 pentaoleate ; propylene glycol fatty acid esters , for example propylene glycol monocaprylate ; mono and diglycerides , for example glyceryl ricinoleate ; sterol and sterol derivatives , for example sitosterol ; sorbitan fatty acid esters and its derivatives , for example polyethylene glycol - 20 sorbitan monooleate , sorbitan monolaurate ; polyethylene glycol 8 alkyl ether or phenols , for example polyethylene glycol - 20 cetyl ether , polyethylene glycol 10 - 100 nonyl phenol ; sugar esters , for example sucrose monopalmitate ; polyoxyethylene polyoxypropylene block copolymers known as “ poloxamer ”; ionic surfactants , for example sodium caproate , sodium glycocholate , soy lecithin , sodium stearyl filmarate , propylene glycol alginate , octyl sulfosuccinate disodium , palmitoyl carnitine ; and mixtures thereof . examples of plasticizers include polyethylene glycol , triethyl citrate , triacetin , diethyl plithalate , dibutyl sebacate and mixtures thereof . examples of stabilizers include antioxidants , buffers , alkalizers , chelating agents and mixtures thereof . examples of coloring agents include any fda approved colors for oral use . according to one embodiment , there is provided a process for the preparation of stable solid dosage form comprising : i ) blending an effective amount of amlodipine , and one or more pharmaceutically inert excipients , ( b ) a second component comprising benazepril or pharmaceutically acceptable salts thereof and a carrier , i ) blending an effective amount of benazepril , and one or more pharmaceutically inert excipients , ii ) granulating and compressing the blend into suitable size tablet , iii ) optionally film coating the tablet , in another embodiment , there is provided a process for the preparation of stable solid dosage form comprising : i ) blending an effective amount of amlodipine , and one or more pharmaceutically inert excipients , ii ) granulating and compressing the blend into suitable size tablet , iii ) optionally film coating the tablet , ( b ) a second component comprising benazepril or pharmaceutically acceptable salts thereof and a carrier , i ) blending an effective amount of benazepril , and one or more pharmaceutically inert excipients , in another embodiment , there is provided of a process for the preparation of a stable solid dosage form comprising amlodipine and benazepril or pharmaceutically acceptable salts thereof comprising the steps of : a ) coating inert core with a drug layer comprising amlodipine and b ) coating separate inert cores with a drug layer comprising benazepril , c ) filling the beads of step a ) and b ) into capsules . in another embodiment , there is provided a process for the preparation of a stable solid dosage form comprising amlodipine and benazepril or pharmaceutically acceptable salts thereof comprising the steps of : f ) dispersing or dissolving the benazepril and other inert excipients in a solvent , in another embodiment , there is provided a process for the preparation of a pharmaceutical composition comprising amlodipine and benazepril or pharmaceutically acceptable salts thereof comprising the steps of : f ) dispersing or dissolving the amlodipine and other inert excipients in a solvent , in another embodiment , there is provided a process for the preparation of a pharmaceutical composition comprising amlodipine and benazepril or pharmaceutically acceptable salts thereof comprising the steps of granulation may be carried out by wet granulation or dry granulation techniques . coating may be performed by applying one or more film forming polymers , with or without other pharmaceutically inert excipients , as a solution / suspension using any conventional coating technique known in the art , such as spray coating in a conventional coating pan or fluidized bed processor , or dip coating . the following examples illustrate the invention but should not be construed as limiting the scope of the invention . wt / capsule ( mg ) example 1 example 2 amlodipine powder blend amlodipine besylate eq . 10 — to amlodipine amlodipine besylate — 10 eq . to amlodipine ( micronised ) microcrystalline 117 . 11 117 . 11 cellulose mannitol 63 . 00 63 . 00 sodium starch glycolate 4 . 00 4 . 00 magnesium stearate 2 . 00 2 . 00 benazepril hydrochloride tablet benazepril 20 . 0 20 . 0 hydrochloride lactose monohydrate 54 . 5 53 . 0 pregelatinized starch 4 . 5 4 . 5 purified water qs qs microcrystalline 13 . 0 13 . 0 cellulose crospovidone 2 . 5 3 . 5 colloidal silicone dioxide 1 . 0 1 . 0 magnesium stearate — 0 . 5 hydrogenated castor oil 4 . 5 4 . 5 opadry white 2 . 5 2 . 5 core tablet weight 100 . 0 100 . 0 amlodipine besylate powder blend according to the composition given above was prepared by the following steps : 1 . amlodipine besylate and microcrystalline cellulose were passed through # 44 mesh . 2 . mannitol and sodium starch glycol were passed through # 44 mesh . 3 . blends of step 1 & amp ; step 2 were loaded into blender and blended for 20 minutes . 4 . magnesium stearate was passed through # 60 mesh and lubricated with blend of step 3 for 5 minutes . 1 . benazepril hydrochloride , lactose monohydrate and pregelatinized starch were passed through sieve and mixed in rapid mixer granulator . 2 . the above blend was granulated with purified water and dried . 3 . dried granules were passed through sieve . 4 . microcrystalline cellulose , crospovidone and colloidal silicon dioxide were passed through sieve and blended with blend of step 3 . 5 . hydrogenated castor oil and magnesium stearate ( for example 10 ) were passed through # 60 meshes and the blend of step 4 was lubricated . 6 . the blend of step 5 was compressed into suitable size tablet . 7 . core tablets were coated with opadry . the amlodipine powder blend and benazepril tablet were filled into capsules . the capsules obtained above were subjected to stability evaluation at 40 ° c . and 75 % relative humidity . initially , after one month , the tablets were evaluated for the presence of impurities using hplc . the results of this measurement are listed as percentage ( w / w ) related substances in table 1 . in vitro release of amlodipine and benazepril as per composition of example 1 and 2 was carried out in 500 ml 0 . 01 n hcl in usp type i apparatus at 100 rpm . the results are shown in table 2 . wt / capsule ( mg ) example 11 benazepril hydrochloride tablet benazepril 20 . 0 hydrochloride lactose monohydrate 51 . 5 pregelatinized starch 4 . 5 purified water qs macrocrystalline 13 . 0 cellulose crospovidone 2 . 5 colloidal silicone dioxide 1 . 0 magnesium stearate 0 . 5 hydrogenated castor oil 4 . 5 core tablet weight 100 . 0 opadry white 2 . 5 amlodipine blend amlodipine besylate 13 . 888 microcrystalline 238 . 112 cellulose mannitol 126 . 0 sodium starch glycolate 12 . 0 colloidal silicon dioxide 4 . 0 magnesium stearate 6 . 0 weight 400 . 0 1 . benazepril hydrochloride , lactose monohydrate and pregelatinized starch were passed through sieve and mixed in rapid mixer granulator . 2 . the above blend was granulated with purified water and dried . 3 . dried granules were passed through sieve . 4 . microcrystalline cellulose , crospovidone and colloidal silicon dioxide were passed through sieve and blended with blend of step 3 . 5 . hydrogenated castor oil , colloidal silicon dioxide and magnesium stearate were passed through sieve and the blend of step 4 was lubricated . 6 . the blend of step 5 was compressed into suitable size tablet . 7 . core tablets were coated with opadry . amlodipine besylate powder blend was prepared by using the following steps : 1 . amlodipine besylate and a part of microcrystalline cellulose were passed through sieve . 2 . mannitol , a part of microcrystalline cellulose , colloidal silicon dioxide and sodium starch glycol were passed through sieve . 3 . blends of step 1 & amp ; step 2 were loaded into blender and blended for 20 minutes . 4 . magnesium stearate was passed through sieve and lubricated with blend of step 3 for 5 minutes . amlodipine powder blend was compressed over benazepril hydrochloride tablet to produce a compression coated tablet with benazepril hydrochloride as inner tablet and amlodipine as outer layer . while the present invention has been described in terms of its specific embodiments , certain modifications and equivalents will be apparent to those skilled in the art and are included within the scope of the present invention .
the technical field of the invention relates to stable solid dosage forms of amlodipine besylate and benazepril hydrochloride ; and processes for their preparation . in particular , the solid dosage forms having reduced levels of 3 - ethyl methyl methyl ] methylpyridine - 3 , 5 dicarboxylate and total impurities when free of dicalcium phosphate .