1 -[ 2 -( dimethylamino )- 1 -( 4 - methoxyphenyl ) ethyl ] cyclohexanol hydrochloride is polymorphic . of the forms isolated and characterized to date , form i is considered to be the kinetic product of crystallization which can be converted to form ii upon heating in the crystallization solvent . forms i and ii cannot be distinguished by their melting points but do exhibit some differences in their infrared spectra and x - ray diffraction patterns . any of the polymorphic forms such as form i or form ii may be used in the formulations of the present invention . the extended release formulations of this invention are comprised of 1 -[ 2 -( dimethylamino )- 1 -( 4 - methoxyphenyl ) ethyl ] cyclohexanol hydrochloride in admixture with microcrystalline cellulose and hydroxypropylmethylcellulose . formed as beads or spheroids , the drug containing formulation is coated with a mixture of ethyl cellulose and hydroxypropylmethyl cellulose to provide the desired level of coating , generally from about two to about twelve percent on a weight / weight basis of final product or more preferably from about five to about ten percent ( w / w ), with best results obtained at from about 6 to about 8 percent ( w / w ). more specifically , the extended release spheroid formulations of this invention comprise from about 30 to 40 percent venlafaxine hydrochloride , from about 50 to about 70 percent microcrystalline cellulose , nf , from about 0 . 25 to about 1 percent hydroxypropylmethylcellulose , usp , and from about 5 to about 10 percent film coating , all on a weight / weight basis . and preferably , the spheroid formulations contain about 35 percent venlafaxine hydrochloride , about 55 to 60 percent microcrystalline cellulose nf ( avicel ®) ph101 ), about one half percent hydroxypropylmethylcellulose 2208 usp ( k3 , dow , which has a viscosity of 3 cps for 2 % aqueous solutions , a methoxy content of 19 - 24 % and a hydroxypropoxy content of 4 - 13 %), and from about 6 to 8 percent film coating . the film coating is comprised of 80 to 90 percent of ethyl cellulose , nf and 10 to 20 percent hydroxypropylmethylcellulose ( 2910 ), usp on a weight / weight basis . preferably the ethyl cellulose has a ethoxy content of 44 . 0 - 51 % and a viscosity of 50 cps for a 5 % aqueous solution and the hydroxypropylmethylcellulose is usp 2910 having a viscosity of 6 cps at 2 % aqueous solution with a methoxy content of 28 - 30 % and a hydroxypropoxy content of 7 - 12 %. the ethyl cellulose used herein is aqualon hg 2834 . other equivalents of the hydroxypropylmethylcelluloses 2208 and 2910 usp and ethyl cellulose , nf , having the same chemical and physical characteristics as the proprietary products named above may be substituted in the formulation without changing the inventive concept . important characteristics of suitable hydroxypropylmethylcelluloses include a low viscosity , preferably less than 10 cps and more preferably 2 - 5 cps , and a gel temperature above that of the temperature of the extrudate during extrusion . as explained below , these and other characteristics which enable the extrudate to remain moist and soft ( pliable ) are preferred for the hydroxypropylmethylcellulose . in the examples below , the extrudate temperature was generally 50 - 55 ° c . it was completely unexpected that an extended release formulation containing venlafaxine hydrochloride could be obtained because the hydrochloride of venlafaxine proved to be extremely water soluble . numerous attempts to produce extended release tablets by hydrogel technology proved to be fruitless because the compressed tablets were either physically unstable ( poor compressibility or capping problems ) or dissolved too rapidly in dissolution studies . typically , the tablets prepared as hydrogel sustained release formulations gave 40 - 50 % dissolution at 2 hrs , 60 - 70 % dissolution at 4 hrs and 85 - 100 % dissolution at 8 hrs . numerous spheroid formulations were prepared using different grades of microcrystalline cellulose and hydroxypropylmethylcellulose , different ratios of venlafaxine hydrochloride and filler , different binders such as polyvinylpyrrolidone , methylcellulose , water , and polyethylene glycol of different molecular weight ranges in order to find a formulation which would provide a suitable granulation mix which could be extruded properly . in the extrusion process , heat buildup occurred which dried out the extrudate so much that it was difficult to convert the extruded cylinders into spheroids . addition of hydroxypropylmethylcellulose 2208 to the venlafaxine hydrochloride - microcrystalline cellulose mix made production of spheroids practical . the encapsulated formulations of this invention may be produced in a uniform dosage for a specified dissolution profile upon oral administration by techniques understood in the art . for instance , the spheroid components may be blended for uniformity with a desired concentration of active ingredient , then spheronized and dried . the resulting spheroids can then be sifted through a mesh of appropriate pore size to obtain a spheroid batch of uniform and prescribed size . the resulting spheroids can be coated and resifted to remove any agglomerates produced in the coating steps . during the coating process samples of the coated spheroids may be tested for their distribution profile . if the dissolution occurs too rapidly , additional coating may be applied until the spheroids present a desired dissolution rate . the following examples are presented to illustrate applicant &# 39 ; s solution to the problem of preparation of the extended release drug containing formulations of this invention . a mixture of 44 . 8 parts ( 88 . 4 % free base ) of venlafaxine hydrochloride , 74 . 6 parts of the microcrystalline cellulose , nf , and 0 . 60 parts of hydroxypropylmethyl cellulose 2208 , usp , are blended with the addition of 41 . 0 parts water . the plastic mass of material is extruded , spheronized and dried to provide uncoated drug containing spheroids . stir 38 . 25 parts of ethyl cellulose , nf , hg2834 and 6 . 75 parts of hydroxypropylmethylcellulose 2910 , usp in a 1 : 1 v / v mixture of methylene chloride and anhydrous methanol until solution of the film coating material is complete . to a fluidized bed of the uncoated spheroids is applied 0 . 667 parts of coating solution per part of uncoated spheroids to obtain extended release , film coated spheroids having a coating level of 3 %. the spheroids are sieved to retain the coated spheroids of a particle size between 0 . 85 mm to 1 . 76 mm diameter . these selected film coated spheroids are filled into pharmaceutically acceptable capsules conventionally , such as starch or gelatin capsules . same as for example 1 except that 1 . 11 parts of the film coating solution per part of uncoated spheroids is applied to obtain a coating level of 5 %. same as for example 1 except that 1 . 33 parts of the film coating solution is applied to 1 part of uncoated spheroids to obtain a coating level of 6 %. same as for example 1 except that 1 . 55 parts of the film coating solution is applied to 1 part of uncoated spheroids to obtain a coating level of 7 %. in the foregoing failed experiments and in examples 1 - 4 , the extrusion was carried out on an alexanderwerk extruder . subsequent experiments carried out on hutt and nica extruders surprisingly demonstrated that acceptable , and even improved , spheroids could be made without the use of an hydroxypropylmethylcellulose . in such further experiments the applicability of the invention was extended to formulations wherein the weight percentage of venlafaxine hydrochloride is 6 % to 40 %, preferably 8 % to 35 %. thus , the extended release spheroid formulations of this invention comprise from about 6 to about 40 percent venlafaxine hydrochloride , from about 50 to about 94 percent microcrystalline cellulose , nf , optionally , from about 0 . 25 to about 1 percent hydroxypropylmethylcellulose , and from about 2 to about 12 percent , preferably about 3 to 9 percent , film coating . spheroids of the invention were produced having 8 . 25 % ( w / w ) venlafaxine hydrochloride and the remainder ( 91 . 75 %, w / w ) being microcrystalline cellulose , with a coating of from 3 to 5 % ( w / w ), preferably 4 %, of the total weight . the spheroids with 8 . 25 % venlafaxine hydrochloride and 4 % coating were filled into no . 2 white opaque shells with a target fill weight of 236 mg . further spheroids of the invention were produced having 16 . 5 % ( w / w ) venlafaxine hydrochloride and the remainder ( 83 . 5 %, w / w ) being microcrystalline cellulose , with a coating of from 4 to 6 % ( w / w ), preferably 5 %, of the total weight . the spheroids 16 . 5 % venlafaxine hydrochloride and 5 % coating were filled into no . 2 white opaque shells with a target fill weight of 122 mg . the test for acceptability of the coating level is determined by analysis of the dissolution rate of the finished coated spheroids prior the encapsulation . the dissolution procedure followed uses usp apparatus 1 ( basket ) at 100 rpm in purified water at 37 ° c . conformance with the dissolution rate given in table 1 provides the twenty - four hour therapeutic blood levels for the drug component of the extended release capsules of this invention in capsule form . where a given batch of coated spheroids releases drug too slowly to comply with the desired dissolution rate study , a portion of uncoated spheroids or spheroids with a lower coating level may be added to the batch to provide , after thorough mixing , a loading dose for rapid increase of blood drug levels . a batch of coated spheroids that releases the drug too rapidly can receive additional film - coating to give the desired dissolution profile . batches of the coated venlafaxine hydrochloride containing spheroids which have a dissolution rate corresponding to that of table 1 are filled into pharmaceutically acceptable capsules in an amount needed to provide the unit dosage level desired . the standard unit dosage immediate release ( ir ) tablet used presently provides amounts of venlafaxine hydrochloride equivalent to 25 mg , 37 . 5 mg , 50 mg , 75 mg and 100 mg venlafaxine . the capsules of this invention are filled to provide an amount of venlafaxine hydrochloride equivalent to that presently used in tablet form and also up to about 150 mg venlafaxine hydrochloride . dissolution of the venlafaxine hydrochloride er capsules is determined as directed in the u . s . pharmacopoeia ( usp ) using apparatus 1 at 100 rpm on 0 . 9 l of water . a filtered sample of the dissolution medium is taken at the times specified . the absorbance of the clear solution is determined from 240 to 450 nanometers ( nm ) against the dissolution medium . a baseline is drawn from 450 nm through 400 nm and extended to 240 nm . the absorbance at the wavelength of maximum absorbance ( about 274 nm ) is determined with respect to this baseline . six hard gelatin capsules are filled with the theoretical amount of venlafaxine hydrochloride spheroids and measured for dissolution . standard samples consist of venlafaxine hydrochloride standard solutions plus a gelatin capsule correction solution . % ⁢ ⁢ venlafaxine ⁢ ⁢ hydrochloride ⁢ ⁢ released = ( as ) ⁢ ( wr ) ⁢ ( s ) ⁢ ( v1 ) ⁢ ( 0 . 888 ) ⁢ ( 100 ) ( ar ) ⁢ ( v2 ) ⁢ ( c ) where as is absorbance of sample preparation , wr is weight of reference standard , mg ; s is strength of the reference standard , decimal ; v1 is the volume of dissolution medium used to dissolve the dosage form , ml ; 0 . 884 is the percent free base , ar is the absorbance of the standard preparation , v2 is the volume of reference standard solution , ml ; and c is the capsule claim in mg . table 2 shows the plasma level of venlafaxine versus time for one 75 mg conventional immediate release ( ir ) tablet administered every 12 hours , two 75 mg extended release ( er ) capsules administered simultaneously every 24 hours , and one 150 mg extended release ( er ) capsule administered once every 24 hours in human male subjects . the subjects were already receiving venlafaxine hydrochloride according to the dosage protocol , thus the plasma blood level at zero time when dosages were administered is not zero . table 2 shows that the plasma levels of two 75 mg / capsule venlafaxine hydrochloride er capsules and one 150 mg / capsule venlafaxine hydrochloride er capsule provide very similar blood levels . the data also show that the plasma level after 24 hours for either extended release regimen is very similar to that provided by two immediate release 75 mg tablets of venlafaxine hydrochloride administered at 12 hour intervals . further , the plasma levels of venlafaxine obtained with the extended release formulation do not increase to the peak levels obtained with the conventional immediate release tablets given 12 hours apart . the peak level of venlafaxine from ( er ), somewhat below 150 ng / ml , is reached in about six hours , plus or minus two hours , based upon this specific dose when administered to patients presently under treatment with venlafaxine hydrochloride ( ir ). the peak plasma level of venlafaxine , somewhat over 200 ng / ml , following administration of ( ir ) is reached in two hours and falls rapidly thereafter . table 3 shows venlafaxine blood plasma levels in male human subjects having a zero initial blood plasma level . again , a peak blood plasma concentration of venlafaxine is seen at about 6 hours after dosing with venlafaxine hydrochloride extended release capsules in the quantities indicated . the subjects receiving the single 50 mg immediate release tablet showed a peak plasma level occurring at about 4 hours . for comparative purposes , the plasma levels of venlafaxine for subjects receiving the conventional formulated tablet can be multiplied by a factor of three to approximate the plasma levels expected for a single dose of 150 mg . conventional formulation . the blood plasma levels of venlafaxine were measured according to the following procedure . blood samples from the subjects were collected in heparinized evacuated blood tubes and the tubes were inverted gently several times . as quickly as possible , the tubes were centrifuged at 2500 rpm for 15 minutes . the plasma was pipetted into plastic tubes and stored at − 20 ° c . until analysis could be completed . to 1 ml of each plasma sample in a plastic tube was added 150 μl of a stock internal standard solution ( 150 μg / ml ). saturated sodium borate ( 0 . 2 ml ) solution was added to each tube and vortexed . five ml of ethyl ether was added to each tube which were then capped and shaken for 10 minutes at high speed . the tubes were centrifuged at 3000 rpm for 5 minutes . the aqueous layer was frozen in dry ice and the organic layer transferred to a clean screw cap tube . a 0 . 3 ml portion of 0 . 01 n hcl solution was added to each tube and shaken for 10 minutes at high speed . the aqueous layer was frozen and the organic layer removed and discarded . a 50 μl portion of the mobile phase ( 23 : 77 acetonitrile : 0 . 1m monobasic ammonium phosphate buffer , ph 4 . 4 ) was added to each tube , vortexed , and 50 μl samples were injected on a supelco supelcoil lc - 8 - db , 5 cm × 4 . 6 mm , 5 p column in a high pressure liquid chromatography apparatus equipped with a waters lambda max 481 detector or equivalent at 229 nm . solutions of venlafaxine hydrochloride at various concentrations were used as standards . manufactured by the techniques described herein , another preferred formulation of this invention comprises spheroids of from about 30 % to about 35 % venlafaxine hydrochloride and from about 0 . 3 % to about 0 . 6 % hydroxypropylmethylcellulose . these spheroids are then coated with a film coating , as described above , to a coating level of from about 5 % to about 9 %, preferably from about 6 % to about 8 %. a specific formulation of this type comprises spheroids of about 33 % venlafaxine hydrochloride and about 0 . 5 % hydroxypropylmethylcellulose , with a film coating of about 7 %. lower dosage compositions or formulations of this invention may also be produced by the techniques described herein . these lower dosage forms may be administered alone for initial titration or initiation of treatment , prior to a dosage increase . they may also be used for an overall low - dose administration regimen or in combination with higher dosage compositions , such as capsule formulations , to optimize individual dosage regimens . these lower dose compositions may be used to create encapsulated formulations , such as those containing doses of venlafaxine hydrochloride from about 5 mg to about 50 mg per capsule . particular final encapsulated dosage forms may include , but are not limited to , individual doses of 7 . 5 mg , 12 . 5 mg , 18 . 75 mg , or 28 . 125 mg of venlafaxine hcl per capsule . the spheroids useful in these lower dose formulations may comprise from about 5 % to about 29 . 99 % venlafaxine hcl , preferably from about 5 % to about 25 %, from about 75 % to about 95 % microcrystalline cellulose , and , optionally from about 0 . 25 % to about 1 . 0 % hydroxypropylmethylcellulose . the spheroids may be coated as described above , preferably with a film coating of from about 5 % to about 10 % by weight . in some preferred formulations , the spheroids comprise the cited venlafaxine hcl and microcrystalline cellulose , with no hydroxypropylmethyl cellulose . spheroids comprising 16 . 5 % venlafaxine hcl and 83 . 5 % microcrystalline cellulose were mixed with approximately 50 % water ( w / w ) to granulate in a littleford blender model fm - 50e / 1z ( littleford day inc ., p . o . box 128 , florence , ky . 41022 - 0218 , u . s . a .) at a fixed speed of 180 rpm . the blended material was extruded through a 1 . 25 mm screen using a nica extruder / speronization machine ( aeromatic - fielder division , niro inc ., 9165 rumsey rd ., columbia , md . 21045 , u . s . a .) for a 12 / 20 mesh cut after drying . two portions of the resulting spheroids were coated with a 5 % and 7 % coating level , respectively , by techniques described above using the coating formulation : ingredient % ( w / w ) methylene chloride 60 . 000 methanol anhydrous 35 . 500 ethylcellulose , nf , hg 2834 , 50 cps 3 . 825 hydroxypropyl methylcellulose , 2910 usp , 6 cps 0 . 675 these 5 % and 7 % coated lots were tested for dissolution on a hewlett packard automated dissolution system over a 24 hour period , resulting in the following dissolution patterns : % dissoluded % dissolved time / hr 16 . 5 %/ 15 % 16 . 5 %/ 7 % 2 12 . 4 5 . 6 4 42 . 8 25 . 4 8 70 . 7 60 . 4 12 82 . 2 75 . 4 24 94 . 3 92 . 7 a formulation of spheroids containing 8 . 25 % venlafaxine hcl and 91 . 75 % microcrystalline cellulose was prepared according to the techniques of example no . 6 and coated with a 5 % film coating . in the hewlett packard automated dissolution system these spheroids provided the following dissolution profile : % dissolved time / hr 8 . 25 %/ 5 % 2 4 . 4 4 24 . 2 8 62 . 9 12 77 . 8 24 93 . 5 thus , the desired dissolution rates of sustained release dosage forms of venlafaxine hydrochloride , impossible to achieve with hydrogel tablet technology , has been achieved with the film - coated spheroid compositions of this invention .
this invention relates to a 24 hour extended release dosage formulation and unit dosage form thereof of venlafaxine hydrochloride , an antidepressant , which provides better control of blood plasma levels than conventional tablet formulations which must be administered two or more times a day and further provides a lower incidence of nausea and vomiting than the conventional tablets . more particularly , the invention comprises an extended release formulation of venlafaxine hydrochloride comprising a therapeutically effective amount of venlafaxine hydrochloride in spheroids comprised of venlafaxine hydrochloride , microcrystalline cellulose and , optionally , hydroxypropylmethylcellulose coated with a mixture of ethyl cellulose and hydroxypropylmethylcellulose .