the extended release matrix formulations comprise morphine or salts thereof , one or more hydrophilic controlled - release polymers and one or more pharmaceutically acceptable excipients such that when administered orally the formulations release morphine or salts thereof in an extended release manner over a prolonged period of time . according to one embodiment , the formulations prepared show an in vitro dissolution profile of morphine or salts thereof , when measured using usp i method , at 100 rpm , in 900 ml aqueous buffer ( ph 1 . 2 to 6 . 8 ), at 37 ± 0 . 5 ° c ., to be between 20 % and 45 % released after 1 hour , between 30 % and 65 % released after 2 hours , between 60 % and 90 % released after 4 hours , and between 70 % and 100 % released after 6 hours . the formulation releases morphine in an extended manner , thereby avoiding dose dumping upon oral administration . surprisingly , this aspect could be achieved with the use of hydrophilic controlled release polymers alone . thus , the formulations can consist essentially of the materials described above . usp i method is the basket method described , e . g ., in u . s . pharmacopoeia xxv ( 2002 ), page no : 2011 - 2012 . the extended release formulation may contain morphine in the range of between 1 to 500 mg , e . g ., between about 15 to 250 mg . morphine is preferably present in an amount suitable for twice daily dosing . the formulation may contain morphine or salts thereof , e . g ., morphine sulfate . the “ hydrophilic controlled0 - release polymer ” may be selected , for example , from one or more of cellulose derivatives selected from hydroxypropyl methylcellulose , hydroxyethyl cellulose , hydroxypropyl cellulose , carboxymethyl cellulose , sodium carboxymethyl cellulose ; and gums selected from xanthan gum , karaya gum , locust bean gum , alginic acid and sodium alginate . the hydroxypropyl methylcellulose may be , for example , the commercially available products such as methocel ® premium product grades having specific apparent viscosities , e . g ., viscosities ranging from about 100 - 150 , 000 cp ( 2 % in water at 20 ° c .) such as k100 , k4m , k15m , k100m , e4m , e10m ; viscosities ranging from 80000 - 120 , 000 cp ( 2 % in water at 20 ° c .) such as methocel k100m cr . surprisingly , it was observed that the amount of the hydrophilic controlled - release polymer per unit dose of morphine or salt thereof plays a major role in the release characteristic of the formulation . the amount of hydrophilic controlled - release polymer may range from about 20 - 40 mg per unit dose of morphine or salt thereof e . g . the amount may range from about 22 - 30 mg per unit dose of morphine or salt thereof . the formulations may contain other release - retarding polymers along with the hydrophilic polymers . however , hydrophilic polymers alone can be used to obtain the extended - release formulations with desirable characteristics of the invention . thus , the extended - release formulation can consist essentially of morphine or salts thereof , one or more hydrophilic controlled - release polymers and one or more pharmaceutically acceptable excipients . the extended release formulation may also contain “ pharmaceutically acceptable excipients ” selected from , for example , one or more of diluents , binders , lubricants and glidants . the diluent may , for example , be selected from , for example , one or more of microcrystalline cellulose , lactose , dicalcium phosphate and starch . the binder may be selected from , for example , one or more of starch , polyvinylpyrrolidone , natural or synthetic gum and cellulosic polymers . the lubricants and glidants may be selected from , for example , one or more of talc , colloidal silicon dioxide and magnesium stearate . the extended - release formulation of morphine may be obtained in the form of tablet , bead , pellet or capsule . the tablet may be uncoated tablet , coated tablet , or minitablets e . g . the extended - release formulation may be a matrix tablet with or without a non - functional coating . the tablet may be prepared by wet granulation , dry granulation / slugging methods or direct compression processes . according to one embodiment , the extended - release matrix formulation of morphine of the present invention is bioequivalent to the branded formulation . the term “ branded formulation ” as used herein refers to tablet formulation of morphine sulfate , commercially available in u . s . as ms contin ® tablets , from purdue frederick company . the following non - limiting examples further illustrate the extended - release formulations of morphine or salt thereof , and process of making such formulations . 2 . morphine sulfate , hydroxypropyl methylcellulose and lactose monohydrate were sifted through a suitable mesh and mixed in rapid mixer granulator ( rmg ). 5 . the granules obtained in step 4 were dried in fluid bed drier ( fbd ) to remove isopropyl alcohol . 7 . colloidal silicon dioxide was sifted through sieve # 30 and stearic acid was sifted through sieve # 40 . 8 . blend of step 7 was mixed with granules of step 6 in a v - blender . 9 . magnesium stearate was sifted through sieve # 40 and then mixed with the blend of step 8 in a v - blender to obtain a final blend . 10 . the final blend was compressed into tablets using suitable toolings . 11 . the tablets were then coated using the dispersion of opadry in purified water to achieve a desired weight build up . the in vitro release profile of morphine from formulations given in examples 1 - 5 , measured by the method described herein ( usp i , 900 ml , 100 rpm ), is given below . 2 . morphine sulfate , hydroxypropyl methylcellulose and lactose monohydrate were sifted through a suitable mesh and mixed in rapid mixer granulator ( rmg ). 5 . then granules obtained in step 4 were dried in fluid bed drier ( fbd ) to remove isopropyl alcohol . 7 . colloidal silicon dioxide was sifted through sieve # 30 and stearic acid was sifted through sieve # 40 . 8 . blend of step 7 was mixed with granules of step 6 in a v - blender . 9 . magnesium stearate was sifted through sieve # 40 and then mixed with the blend of step 8 in a v - blender to obtain the final blend . 10 . the final blend was compressed into tablets using suitable toolings . 11 . the tablets were then coated using the dispersion of opadry in purified water to achieve a desired weight build up . the in vitro release profile of morphine from formulations given in example 6 - 7 , measured by the method described herein ( usp i , 900 ml , 100 rpm ), is given below . summary statistics of bioequivalence studies * auc 0 - t auc 0 -∞ product / statistics c max ( ng / ml ) ( ng · h / ml ) ( ng · h / ml ) t max ( h ) product a mean 36 . 35 241 . 84 254 . 14 2 . 98 cv (%) 11 . 44 69 . 57 69 . 28 1 . 40 product b mean 39 . 44 250 . 39 261 . 55 3 . 95 cv (%) 14 . 48 76 . 71 76 . 12 0 . 88 product c mean 39 . 45 253 . 29 267 . 64 3 . 59 cv (%) 12 . 58 83 . 95 83 . 69 1 . 42 10 / 23 ratio of least squares mean a / c (%) 92 . 77 97 . 26 96 . 36 — 90 % confidence intervals ( a / c ) lower limit 83 . 34 93 . 36 92 . 57 — upper limit 103 . 27 100 . 69 100 . 3 — ratio of least squares mean b / c (%) 98 . 86 100 . 09 98 . 70 — 90 % confidence intervals ( b / c ) lower limit 88 . 81 96 . 69 94 . 8 — upper limit 110 . 04 103 . 61 102 . 73 — * number of subjects ( human volunteers ) = 18 in each case . as evident from the above pharmacokinetic data , extended - release matrix formulations of morphine as per the present invention are bioequivalent to the branded formulation .
the present invention provides extended - release matrix formulations comprising a therapeutically effective amount of morphine or salt thereof , one or more hydrophilic controlled release polymers and one or more pharmaceutically acceptable excipients . the formulations provide extended release of morphine or salt thereof over a specified period of time after oral administration in humans or animals .