the present invention discloses a gastroretentive , extended release composition which comprises ; ( a ) a graft copolymer which exhibits ph dependent behavior , represented by formula 1 i . a backbone having the formula p [ a ( x ) b ( y ) c ( z ) ] comprising : a dial ( a ), a dicarboxylic acid or acid anhydride ( b ) and a monomer containing pendent unsaturation ( c ) wherein ( x )= 41 - 45 %, ( y )= 49 - 53 % ( z )= 4 - 7 % by mole ; and ii . a graft which is a polymer of the basic monomer ( d ) and ‘ w ’ is a weight percent of the total weight of said graft copolymer such that ‘ w ’ is 22 - 52 %. the backbone of ph dependent graft copolymer is polyester . the components for the preparation of said polyester selected are as follows . the diol ( a ) is selected from the group comprising aliphatic diols and cycloaliphatic dials . the aliphatic diols are selected from 1 , 2 - ethane diol , 1 , 3 - propane diol , 1 , 2 - propane diol , 2 - methyl - 1 , 3 - propane diol , 1 , 4 - butane diol , 1 , 3 - butane diol , 1 , 2 - butane diol , 1 , 5 - pentane diol , 1 , 6 - hexane diol , 1 , 7 - heptane diol , 1 , 8 - octane diol , 1 , 9 - nonane diol , 1 , 12 - dodecane dial . the cycloaliphatic dial is 1 , 4 - cyclohexanedimethanol . the dicarboxylic acids or acid anhydrides ( b ) are selected from aliphatic dicarboxylic acid such as succinic acid , glutaric acid , adipic acid , pimelic acid , suberic acid , azelaic acid , sebacic acid dodecanedioic acid and succinic anhydride . the aromatic anhydride is phthalic anhydride . in one aspect of the invention , b is an aromatic dicarboxylic acid . the monomer containing pendent unsaturation ( c ) is selected from an epoxy compound such as glycidyl methacrylate , glycidyl acrylate and such like . in another aspect of the invention , c is a diol compound selected from trimethylolpropane monomethacrylate , trimethylolpropane mono acrylate and such like . the basic monomer ( d ) for the preparation of ph dependent graft copolymer is selected from 2 - vinylpyridine , 3 - vinylpyridine and 4 - vinylpyridine . the therapeutically active agent incorporated in the gastroretentive , extended release composition is selected from but not limited to the group comprising antibiotic drugs , cardiovascular drugs and vitamins . the gellable polymer incorporated in the gastroretentive , extended release composition is selected from the group comprising cellulosic polymers , alginate polymers and polyalkene oxide . the gas generating system incorporated in the gastroretentive , extended release composition comprises a gas generating agent and a carboxyl compound . the gas generating agent is alkali carbonates and bicarbonates such as sodium carbonate , calcium carbonate , sodium bicarbonate , potassium bicarbonate and such like . the carboxyl compound is selected from succinic acid , malic acid , maleic acid , fumaric acid , tartaric acid , citric acid and ascorbic acid . the gastroretentive , extended release composition further comprises various pharmaceutically acceptable ingredients such as lubricants , fillers , binders , flavours , colours , anti adherents , glidants , other aides and such like . the gastroretentive , extended release composition is prepared in pharmaceutical solid dosage form such as tablets , pills and capsules . in one of the embodiment the compositions are in the form of tablets . such a tablet comprises a therapeutically active agent in the range of 10 - 50 %, at least one ph dependent graft copolymer in the range of 20 - 40 %, at lease one gellable polymer in the range of 20 - 40 %, a gas generating system in the range of 12 - 18 % of the total weight of the formulation . the gastroretentive , extended release tablet was prepared by dry granulation method . a therapeutically active agent , a ph dependent graft copolymer , a gellable polymer and a gas generating system were dry granulated . to this a pharmaceutically acceptable lubricant was added and mixed thoroughly . the granular mixture was compressed into the tablet in the size of 13 mm in diameter . in - vitro evaluation of gastroretentive , extended release composition was carried out by usp dissolution apparatus using paddle method . the solid dosage forms as exemplified herein displayed floating behavior in acidic ph and swelled and expanded on floating . the following examples are presented in order to further illustrate the invention . these examples should not be construed in any manner to limit the invention . in the examples the diol , dibasic acid , unsaturated monomer and acidic monomer are described by the following abbreviations . 1 , 4 bd - 1 , 4 butane diol , 1 , 12 dd - 1 , 12 dodecane diol , 1 , 4 cd - 1 , 4 cyclohexane dimethanol , sa - succinic acid , seb - sebacic acid , aa - adipic acid , dda - dodecanedioic acid , gma - glycidyl methacrylate , tmpma - trimethylolpropane monomethacrylate , 4vp - 4 vinylpyridine . the synthesis of ph sensitive graft copolymers based on the above monomers is described in our copending indian patent application 0530del2010 , the content of which is incorporated and included as if set forth fully herein . this example describes the preparation and the dissolution profile of diltiazem hydrochloride tablet comprising the ph dependent copolymer of methylmethacrylate , dimethylaminoethyl methacrylate and butylmethacrylate . the drug diltiazem hydrochloride , the ph dependent copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the tablet is given in table 1 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . the tablet did not swell but dissolved and released the drug within 3 hours . since this composition did not swell and released the drug within 3 hours it does not serve as a gastroretentive device . this example describes the preparation and the dissolution profile of diltiazem hydrochloride comprising the ph dependent copolymer of methylmethacrylate , dimethylaminoethyl methacrylate and butylmethacrylate . the drug diltiazem hydrochloride , the ph dependent copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the tablet is given in table 2 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . although the drug was released over a period of 6 hours , the tablet did not swell . the composition therefore is not suitable as a gastroretentive delivery device . this example describes the preparation and the dissolution profile of diltiazem hydrochloride tablet comprising the ph dependent copolymer of methylmethacrylate , dimethylaminoethyl methacrylate and butylmethacrylate . the drug diltiazem hydrochloride , the ph dependent copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the tablet is given in table 3 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . although the drug was released over a period of 7 hours , the tablet did not swell . the composition therefore is not suitable as a gastroretentive delivery device . this example describes the preparation and the dissolution profile of ciprofloxacin hydrochloride gastroretentive tablet comprising the ph dependent graft copolymer the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 4 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 5 . the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 6 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 7 . the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k4m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 8 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 9 . the drug cephalexin monohydrate , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k100m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 10 . the dissolution of cephalexin monohydrate was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 11 . the drug cephalexin monohydrate , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k100m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 12 . the dissolution of cephalexin monohydrate was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c ., a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 13 . the drug cephalexin monohydrate , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k100m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 14 . the dissolution of cephalexin monohydrate was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 15 . the drug riboflavin 5 ′- phosphate sodium , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the as generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 16 . the dissolution of riboflavin 5 ′- phosphate sodium was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 17 . the drug riboflavin 5 ′- phosphate sodium , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 18 . the dissolution of riboflavin 5 ′- phosphate sodium was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained , its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 19 . the drug diltiazem hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k15m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 20 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 21 . the drug diltiazem hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k15m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 22 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 23 . the drug diltiazem hydrochloride , the ph dependent graft copolymer , the gellable polymer hydroxypropylmethyl cellulose ( k15m ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 24 . the dissolution of diltiazem hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 25 . the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the as generating system comprising sodium bicarbonate and citric add were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 26 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 27 . the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 28 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 29 . the drug ciprofloxacin hydrochloride , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 30 . the dissolution of ciprofloxacin hydrochloride was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 31 . the drug ofloxacin , the ph dependent graft copolymer , the gellable polymer polyethylene oxide ( wsx 303 ), the gas generating system comprising sodium bicarbonate and citric acid were dry granulated . to this the lubricant magnesium stearate was added and mixed thoroughly and then compressed into tablet 13 mm in diameter . the composition of the gastroretentive tablet is given in table 32 . the dissolution of ofloxacin was monitored using a usp dissolution apparatus and paddle method at 50 rpm . the dissolution medium was 0 . 1 n hcl and the temperature was maintained at 37 ± 0 . 5 ° c . a known volume of releasing solution was collected at predetermined intervals and analyzed for drug concentration . the tablet swelled in the release medium upon floating and retained its integrity for the entire duration over which the drug is released from the dosage form . the cumulative percent dissolution of the drug is summarized in the table 33 .
a gastroretentive , extended release composition which floats and swells at acidic ph prevalent in the stomach . the composition includes a ph dependent graft copolymer , a gellable polymer , a therapeutic agent , a gas generating system and pharmaceutically acceptable ingredients . the disclosed composition is useful to deliver the therapeutic agent within the stomach for an extended period of time .