Patent Publication Number: US-2011052685-A1

Title: Gastric retentive pharmaceutical compositions for immediate and extended release of acetaminophen

Description:
This application claims the benefit of priority to U.S. Provisional Application No. 61/238,374, filed on Aug. 31, 2009, incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present subject matter relates generally to a dosage form for both immediate release and extended release of acetaminophen into the stomach of a patient in the fed mode and to methods of treatment using the dosage forms. 
     BACKGROUND 
     Acetaminophen is widely accepted as an over-the-counter pain reliever and is offered in a number of brand name and generic products. Acetaminophen is used to treat indications including pain and arthritis, and is also effective in reducing fever. Currently available dosage forms include tablets, caplets, and oral suspensions. These dosage forms provide acetaminophen release over periods of 3, 4, 6 or 8 hours. 
     The Tylenol ER (extended release) preparation became available in 1995. The tablet is available in 650 mg caplets intended to release 325 mg immediately and 325 mg more slowly. These tablets or caplets provide both immediate release and sustained release or sustained release alone such that the dosing interval can be extended to at least eight hours. 
     Acetaminophen has reduced bioavailability from the colon. Accordingly, dosage forms that provide an extended exposure of acetaminophen to the intestine upstream of the colon are desired. Release of acetaminophen upstream of the colon offers the possibility of twenty-four hour pain relief through twice-daily dosing. 
     Gastric retained oral dosage forms are one approach for delivery of drugs in the upper portions of the gastrointestinal (GI) tract, and have been previously described, for example, in Gusler et al. (U.S. Pat. No. 6,723,34), Berner et al. (U.S. Pat. No. 6,488,962), Shell et al., (U.S. Pat. No. 6,340,475) and Shell et al. (U.S. Pat. No. 6,635,280). These formulations make use of one or more hydrophilic polymers that swell upon intake of water from gastric fluid. When administered to a subject in the fed mode, when the size of pyloric sphincter is reduced, the dosage form swells to a size effective for its retention in the stomach for a minimum of about four hours. 
     Successful formulation of a gastric retentive dosage form for any given drug requires careful design and selection of the formulation components. For example, the gastric retentive dose form requires an amount of swellable polymer such that upon administration, it will swell to a size sufficient for gastric retention. However, too much swellable polymer will result in a pill too large to swallow. Too little polymer will result in insufficient swelling such that the pill escapes through the pylorus too soon. Additionally, the dosage form must contain enough of the pharmaceutically active agent to maintain desired levels in the blood, thereby providing pain relief over the desired period of time, for example, about 12 hours. Adding to the difficulty of formulating such a tablet for gastric delivery of acetaminophen is the fact that acetaminophen powder does not compress well into tablets. 
     BRIEF SUMMARY 
     The present disclosure provides, among other aspects, gastric retentive dosage forms for oral administration to a subject, such as a human patient, for relief from a pain state. The dosage form in some embodiments is a gastric retentive dosage form that contains a first dose of acetaminophen as an extended release (“ER”) dosage form. The dosage form may alternatively contain a first dose of acetaminophen within an ER layer and a second dose of acetaminophen within an immediate release (“IR”) layer. 
     In one aspect, the ER layer or portion of the dosage form comprises the first dose of acetaminophen dispersed in a polymer matrix comprising at least one hydrophilic polymer. Upon administration, the polymer matrix swells upon imbibition of fluid to a size sufficient such that the ER portion of the dosage form is retained in a stomach of a subject in a fed mode and the first dose of acetaminophen is released over an extended period of time. 
     In one embodiment, the ER layer comprises a hydrophilic polymer having an average molecular weight ranging from about 200,000 Da (Daltons) to about 10,000,000 Da, about 900,000 Da to about 5,000,000 Da, about 2,000,000 Da to about 5,000,000 Da, from about 4,000,000 Da to about 5,000,000 Da, from about 2,000,000 Da to about 4,000,000 Da, from about 900,000 Da to about 5,000,000 Da, or from about 900,000 Da to about 4,000,000 Da. In another embodiment, the ER layer comprises a hydrophilic polymer having an average molecular weight of equal to or greater than about 200,000 Da, 600,000 Da, 900,000 Daltons, 1,000,000 Da, 2,000,000 Da, 4,000,000 Da, 5,000,000 Da, 7,000,000 Da or 10,000,000 Da. 
     In one embodiment, the ER layer comprises a total amount of hydrophilic polymer which ranges from about 25 mg to 320 mg, about 100 mg to 225 mg (milligrams) or about 125 mg to 200 mg. In another embodiment, the total amount of hydrophilic polymer in the ER layer is about 25 mg, 50 mg, 75 mg, 100 mg, 110 mg, 115 mg, 120 mg, 125 mg, 130 mg, 135 mg, 140 mg, 145 mg, 150 mg, 155 mg, 160 mg, 165 mg, 170 mg, 175 mg, 180 mg, 200 mg, 225 mg, 250 mg, 275 mg, 300 mg, or 320 mg. In yet another embodiment, the total amount of hydrophilic polymer in the ER layer is present in an amount which is about 50 wt % to about 40 wt % or about 10 wt % to about 30 wt % (weight percent) of the ER layer. In yet another embodiment, the total amount of hydrophilic polymer in the ER layer is present in an amount which is about 10 wt %, 12 wt %, 14 wt %, 15 wt %, 17 wt %, 18 wt %, 20 wt %, 22 wt %, 24 wt %, 25 wt %, 27 wt % or 30 wt % of the ER layer. 
     In one embodiment, the at least one hydrophilic polymer in the ER layer is a polyalkylene oxide. In another embodiment, the at least one hydrophilic polymer is poly(ethylene oxide). In yet another embodiment, the at least one hydrophilic polymer in the ER layer is a cellulose. In yet another embodiment, the cellulose is hydroxypropyl methylcellulose. In yet another embodiment, the ER layer comprises two hydrophilic polymers in a ratio of 3:1, 3:1.5, 3:2, 2:1, 2:1.5, 1:1, 1:1.5, 1:2, 1:2.5, or 1:3. 
     In one embodiment, the ER layer comprises between about 500 mg to about 1000 mg of acetaminophen. In another embodiment, the ER layer comprises about 500 mg, 525 mg, 550 mg, 575 mg, 600 mg, 625 mg, 650 mg, 675 mg, 700 mg, 725 mg, 750 mg, 775 mg, 800 mg, 825 mg, 850 mg, 875 mg, 900 mg, 925 mg, 950 mg, 975 mg, 1000 mg, 1025 mg, or 1050 mg acetaminophen. 
     In one embodiment, the ER layer comprises acetaminophen that is present in an amount that ranges from about 65 wt % to 90 wt %, or about 75 wt % to 85 wt % of the ER layer. In another embodiment, the ER layer comprises acetaminophen that is present in an amount that is about 65.0 wt %, 70.0 wt %, 70.5 wt %, 71.0 wt %, 71.5 wt %, 72.0 wt %, 72.5 wt %, 73.0 wt %, 73.5 wt %, 74.0 wt % 74.5 wt %, 75.0 wt %, 75.5 wt %, 76.0 wt %, 76.5 wt %, 77.0 wt %, 77.5 wt %, 78.0 wt %, 78.5 wt %, 79.0 wt %, 79.5 wt %, 80.0 wt %, 80.5 wt %, 81.0 wt %, 81.5 wt %, 82.0 wt %, 82.5 wt % 83.0 wt %, 83.5 wt %, 84.0 wt %, 84.5 wt %, 85.0 wt %, 85.5 wt %, 86.0 wt %, 86.5 wt %, 87.0 wt %, 87.5 wt %, 88.0 wt %, 88.5 wt %, 89.0 wt %, 89.5 wt %, or 90.0 wt % of the ER layer. 
     In one embodiment, the ratio of acetaminophen to hydrophilic polymer in the ER layer ranges from about 1.5:1 to about 35:1. In another embodiment, the ratio of acetaminophen to hydrophilic polymer in the ER layer is about 1.5:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, or 35:1. 
     In one embodiment, the acetaminophen is released from the ER layer over a time period of 6 h to 10 h (hours), 6 h to 9 h, 7 h to 9 h, 8 h to 9 h, 8 h to 10 h, or 9 h to 10 h. In another embodiment, acetaminophen is delivered to the small intestine of the subject over a time period of at least 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or 13 h. 
     In one embodiment, the acetaminophen is released from the ER layer via diffusion. In another embodiment, the acetaminophen is released from the ER layer via erosion. In yet another embodiment, the acetaminophen is released from the ER layer via a combination of diffusion and erosion. 
     In one embodiment, the ER layer comprises a binder which is polyvinylpyrrolidone, polyvinylalcohol, ethyl cellulose, polyethylene glycol, hydroxypropyl cellulose, hydroxyethyl cellulose, or hydroxypropylmethyl cellulose. In yet another embodiment, the polyvinylpyrrolidone is povidone, copovidone, or crospovidone. In yet another embodiment, the ER layer comprises a combination of more than one binder. 
     In one embodiment, the ER layer further comprises one or more binders. In another embodiment, the one or more binders is in an amount ranging from about 15 mg to about 80 mg. In another embodiment, the total amount of the one or more binder in the ER layer is about 15 mg, 17 mg, 19 mg, 20 mg, 21 mg, 23 mg, 25 mg, 27 mg, 30 mg, 32 mg, 34 mg, 35 mg, 37 mg, 39 mg, 40 mg, 45 mg, 47 mg, 50 mg, 55 mg, 57 mg, 60 mg, 65 mg, 67 mg, 70 mg, 75 mg, or 80 mg. In yet another embodiment, the amount of the one or more binder in the ER layer is about 2.5 mg, 2.7 mg, 3.0 mg, 3.2 mg, 3.5 mg, 3.7 mg, 4.0 mg, 4.3 mg, 4.5 mg, 4.7 mg, 5.0 mg, 5.3 mg, 5.5 mg, 5.7 mg, 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg, 9.5 mg, or 10.0 wt % of the ER layer. 
     In one embodiment, the ER layer further comprises a lubricant which is magnesium stearate, calcium stearate, sodium stearyl fumarate, stearic acid, stearyl behenate, glyceryl behenate, or polyethylene glycol. 
     In one embodiment, the ER layer comprises one or more lubricants which is present in an amount ranging from about 0.3 mg to 20 mg or from about 1 mg to 10 mg. In yet another embodiment, the amount of the one or more lubricants in the ER layer is about 0.3 mg, 0.4 mg, 0.5 mg, 0.6 mg, 0.7 mg, 0.8 mg, 0.9 mg, 1.0 mg, 1.2 mg, 1.4 mg, 1.6 mg, 1.8 mg, 2.0 mg, 2.5 mg, 3.0 mg, 3.5 mg, 4.0 mg, 4.5 mg, 5.0 mg, 5.5 mg, 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg, 9.5 mg, 10 mg, 12 mg, 14 mg, 16 mg, 18 mg or 20 mg. In yet another embodiment, the amount of the one or more lubricants in the ER layer is about 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1.0 wt %, 1.2 wt %, 1.4 wt %, 1.6 wt %, 1.8 wt %, 2.0 wt %, 2.2 wt %, 2.4 wt %, or 2.5 wt % of the ER layer. 
     In one embodiment, the ER layer comprises a chelating agent. Examples of chelating agents include ethylenediamine tetracetic acid (EDTA) and its salts (including a sodium salt), N-(hydroxy-ethyl)ethylenediaminetriacetic acid, nitrilotriacetic acid (NIA), ethylene-bis(oxyethylene-nitrilo)tetraacetic acid, 1,4,7,10-tetraazacyclodo-decane-N,N′,N″,N′″-tetraacetic acid, 1,4,7,10-tetraaza-cyclododecane-N,N′,N″-triacetic acid, 1,4,7-tris(carboxymethyl)-10-(2′-hydroxypropyl)-1,4,7,10-tetraazocyclodecane, 1,4,7-triazacyclonane-N,N′,N″-triacetic acid, 1,4,8,11-tetraazacyclotetra-decane-N,N′,N″,N′″-tetraacetic acid; diethylenetriamine-pentaacetic acid (DTPA), ethylenedicysteine, bis(aminoethanethiol)carboxylic acid, triethylenetetraamine-hexaacetic acid, and 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid. The chelating agent may be present in the ER layer in an amount that is about 0.01 wt % to about 0.10 wt % or about 0.02 to about 0.08 wt % of the tablet. Alternatively, the tablet may comprise about 0.01 wt %, 0.02 wt %, 0.03 wt %, 0.04 wt %, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt % or 0.10 wt % of the chelating agent. 
     In one embodiment, the ER layer of the dosage form comprises an anti-oxidant which is ascorbic acid, citric acid, ascorbyl palmitate, butylated hydroxyanisole, a mixture of 2 and 3 tertiary-butyl-4-hydroxyanisole, butylated hydroxytoluene, sodium isoascorbate, dihydroguaretic acid, potassium sorbate, sodium bisulfate, sodium metabisulfate, sorbic acid, potassium ascorbate, vitamin E, 4-chloro-2,6-ditertiarybutylphenol, alphatocopherol, or propylgallate. In another embodiment, the antioxidant is present in the ER portion of the dosage form at a wt % ranging from about 0.10 wt % to about 0.20 wt %, or from about 0.05 wt % to about 0.30 wt %. In yet another embodiment, the antioxidant is present in the ER layer of the dosage form at a wt % of about 0.01 wt %, 0.05 wt %, 0.10 wt %, 0.15 wt %, 0.20 wt %, 0.25 wt %, 0.35 wt %, 0.50 wt %, 0.75 wt %, 1.00 wt %, 2.00 wt %, 3.00 wt % or 4.00 wt % of the ER layer. 
     In one embodiment, the ER layer comprises one or more additional excipients which are diluents, coloring agents, flavoring agents, and/or glidants. 
     In one embodiment, the dosage form further comprises an IR layer which comprises a second dose of acetaminophen. In another embodiment, the second dose of acetaminophen is between about 100 mg to about 500 mg or between about 250 mg to about 350 mg acetaminophen. In another embodiment, the IR layer comprises about 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 350 mg, 400 mg, 450 mg, or 500 mg acetaminophen. In yet another embodiment, the IR layer comprises a second dose of acetaminophen which is present in an amount which is about 80 wt % to about 96 wt % of the IR layer. In yet another embodiment, the second dose of acetaminophen is present in an amount which is about 78 wt %, 79 wt %, 80 wt %, 81 wt %, 82 wt %, 83 wt %, 84 wt %, 85 wt %, 87 wt %, 88 wt %, 90 wt %, 92 wt %, 94 wt %, or 96 wt % of the IR layer. 
     In one embodiment, the IR layer further comprises a binder. In another embodiment, the binder is polyvinylpyrrolidone, polyvinylalcohol, ethyl cellulose, polyethylene glycol, hydroxypropyl cellulose, hydroxyethyl cellulose or hydroxypropylmethyl cellulose. In yet another embodiment, the polyvinylpyrrolidone is povidone, copovidone, or crospovidone. In yet another embodiment, the IR layer comprises a combination of more than one binder. 
     In one embodiment, the IR layer comprises a binder in an amount ranging from about 6 mg to about 50 mg or from about 6 mg to about 12 mg. In another embodiment, the total amount of the binder in the IR layer is about 5 mg, 5.5 mg, 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg, 9.5 mg, 10.0 mg, 10.5 mg, 11.0 mg, 11.5 mg, 12.0 mg, 15.0 mg, 17.0 mg, 19.0 mg, 20.0 mg, 23.0 mg, 25.0 mg, 27.0 mg, 30.0 mg, 33.0 mg, 35.0 mg, 37.0 mg, 40.0 mg, 45.0 mg, 47.0 mg, 50.0 mg, 55.0 mg, 57.0 mg, or 60.0 mg. In yet another embodiment, the amount of binder in the IR layer is in an amount which is about 2.5 wt %, 2.7 wt %, 3.0 wt %, 3.2 wt %, 3.5 wt %, 3.7 wt %, 4.0 wt %, 4.3 wt %, 4.5 wt %, 4.7 wt %, 5.0 wt %, 5.3 wt %, 5.5. wt %, 5.7 wt %, 6.0 wt %, 6.5 wt %, 7.0 wt %, 7.5 wt %, 8.0 wt %, 8.5 wt %, 9.0 wt %, 9.5 wt %, or 10.0 wt % of the IR layer. 
     In one embodiment, the IR layer comprises a lubricant which is magnesium stearate, calcium stearate, sodium stearyl fumarate, stearic acid, stearyl behenate, glyceryl behenate, or polyethylene glycol. 
     In one embodiment, the IR layer comprises a lubricant which is present in an amount ranging from about 0.2 mg to about 10.0 mg or from about 1.0 mg to about 10.0 mg. In yet another embodiment, the amount of lubricant in the IR layer is about 0.2 mg, 0.3 mg, 0.4 mg, 0.5 mg, 0.6 mg, 0.7 mg, 0.8 mg, 0.9 mg, 1.0 mg, 1.2 mg, 1.4 mg, 1.6 mg, 1.8 mg, 2.0 mg, 2.5 mg, 3.0 mg, 3.5 mg, 4.0 mg, 4.5 mg, 5.0 mg, 5.5 mg, 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg, 9.5 or 10 mg. In yet another embodiment, the amount of lubricant in the IR layer is about 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1.0 wt %, 1.2 wt %, 1.4 wt %, 1.6 wt %, 1.8 wt %, 2.0 wt %, 2.1 wt %, 2.2 wt %, 2.4 wt %, or 2.5 wt % of the IR layer. 
     In one embodiment, the IR layer comprises a chelating agent. Examples of chelating agents include ethylenediamine tetracetic acid (EDTA) and its salts (including a sodium salt), N-(hydroxy-ethyl)ethylenediaminetriacetic acid, nitrilotriacetic acid (NIA), ethylene-bis(oxyethylene-nitrilo)tetraacetic acid, 1,4,7,10-tetraazacyclodo-decane-N,N′,N″,N′″-tetraacetic acid, 1,4,7,10-tetraaza-cyclododecane-N,N′,N″-triacetic acid, 1,4,7-tris(carboxymethyl)-10-(2′-hydroxypropyl)-1,4,7,10-tetraazocyclodecane, 1,4,7-triazacyclonane-N,N′,N″-triacetic acid, 1,4,8,11-tetraazacyclotetra-decane-N,N′,N″,N′″-tetraacetic acid; diethylenetriamine-pentaacetic acid (DTPA), ethylenedicysteine, bis(aminoethanethiol)carboxylic acid, triethylenetetraamine-hexaacetic acid, and 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid. The chelating agent may be present in the IR layer in an amount that is about 0.01 wt % to about 0.10 wt % or about 0.02 to about 0.08 wt % of the tablet. Alternatively, the tablet may comprise about 0.01 wt %, 0.02 wt %, 0.03 wt %, 0.04 wt %, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt % or 0.10 wt % of the chelating agent. 
     In one embodiment, the IR layer of the dosage form comprises an anti-oxidant which is ascorbic acid, citric acid, ascorbyl palmitate, butylated hydroxyanisole, a mixture of 2 and 3 tertiary-butyl-4-hydroxyanisole, butylated hydroxytoluene, sodium isoascorbate, dihydroguaretic acid, potassium sorbate, sodium bisulfate, sodium metabisulfate, sorbic acid, potassium ascorbate, vitamin E, 4-chloro-2,6-ditertiarybutylphenol, alphatocopherol, or propylgallate. In another embodiment, the antioxidant is present in the IR layer of the dosage form at a wt % ranging from about 0.10 wt % to about 0.20 wt %, or from about 0.05 wt % to about 0.30 wt %. In yet another embodiment, the antioxidant is present in the IR layer of the dosage form at a wt % of about 0.01 wt %, 0.05 wt %, 0.10 wt %, 0.15 wt %, 0.20 wt %, 0.25 wt %, 0.35 wt %, 0.50 wt %, 0.75 wt %, 1.00 wt %, 2.00 wt %, 3.00 wt % or 4.00 wt % of the ER layer. 
     In one embodiment, a gastric retentive dosage form comprising an IR layer with a first dose of acetaminophen and an ER layer with a second dose of acetaminophen is provided. In another embodiment, the first dose of acetaminophen is about 200 mg, 250 mg, 300 mg, 350 or 400 mg and the second dose of acetaminophen is about 400 mg, 450 mg, 500 mg, 550 mg, 600 mg, 650 mg, 700 mg, 750 mg, or 800 mg. In yet another embodiment, the total dose of acetaminophen in the gastric retentive dosage form is about 500 mg, 550 mg, 600 mg, 650 mg, 700 mg, 750 mg, 800 mg, 850 mg, 900 mg, 950 mg, or 1000 mg. 
     In one embodiment, the gastric retentive dosage is a tablet. In another embodiment, the tablet has a total weight ranging from about 1000 mg to about 1450 mg, or from about 1100 mg to about 1300 mg or from about 1175 mg to about 1250 mg. In yet another embodiment, the tablet has a total weight of about 1200 mg, 1225 mg, 1250 mg, 1275 mg, 1300 mg, 1325 mg, 1350 mg, 1375 mg, 1400 mg, 1425 mg, or 1450 mg. 
     In one embodiment, the dosage form is a pharmaceutical tablet, such as a gastric retentive tablet for the extended release of acetaminophen. In another embodiment, the tablet is a monolithic tablet comprising an ER layer. In another embodiment, the tablet is a monolithic tablet comprising an ER layer and an IR layer. In another embodiment, the tablet is a bilayer tablet, comprising an ER layer and an IR layer. The bilayer tablet is typically a monolithic tablet. In another embodiment, the dosage form is a capsule comprising an ER layer. In another embodiment, the dosage form is a capsule comprising ER layer and an IR layer. 
     In some embodiments, the bilayer tablet has a friability of no greater than about 0.1%, 0.2% 0.3%, 0.4%, 0.5%, 0.7% or 1.0%. 
     In some embodiments, the bilayer tablet has a hardness of at least about 10 kilopond (also known as kilopons) (kp). In some embodiments, the tablet has a hardness of about 9 kp to about 25 kp, or about 12 kp to about 20 kp. In further embodiments, the tablet has a hardness of about 11 kp, 12 kp, 13 kp, 14 kp, 15 kp, 16 kp, 17 kp, 18 kp, 19 kp, 20 kp, 21 kp, 22 kp, 23 kp, 24 kp, or 25 kp. 
     In some embodiments, the tablets have a content uniformity of from about 85 to about 115 percent by weight or from about 90 to about 110 percent by weight, or from about 95 to about 105 percent by weight. In other embodiments, the content uniformity has a relative standard deviation (RSD) equal to or less than about 3.5%, 3.0%, 2.5%, 2.0%, 1.5%, 1.0% or 0.5%. 
     In one embodiment, about 90% to about 100% of the first dose of acetaminophen is released within 15 minutes, 30 minutes, 45 minutes or 60 minutes after oral administration. 
     In one embodiment, the ER layer swells upon imbibition of fluid to a size which is about 15%, 20%, 25%, 30%, 35% 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% larger than the size of the ER layer prior to imbibition of fluid. In another embodiment, the ER layer swells upon imbibition of fluid to a size at least about 25% larger than the size of the ER layer prior to imbibition of fluid within about 15 minutes of the start of fluid imbibition. In still another embodiment, the ER layer swells upon imbibition of fluid to a size at least about 100% larger than the size of the ER layer prior to imbibition of fluid within about 45 min, 50 min, 75 min, or 90 min of the start of fluid imbibition. 
     In one embodiment, the dosage form provides a dissolution profile wherein about 20 to about 65%, about 35 to about 55% or about 40% to about 50% of the second dose of acetaminophen remains in the ER layer between about 1 and 2 hours after administration. In one embodiment, not more than 50% of the second dose of acetaminophen is released within about the first hour. In a further embodiment, not more than 45% or not more than 40% of the second dose of acetaminophen is released within about the first hour. In another embodiment, not more than 85% of the second dose of acetaminophen is released within about 4 hours. In yet another embodiment, not less than 50% is released after about 6 hours. In yet another embodiment, not less than 60% is released after about 6 hours. 
     In one embodiment, the second dose of acetaminophen is released over a time period of about 6 to 12, about 8 to 10, or about 9 to 10 hours in vitro. In another embodiment, the second dose of acetaminophen is released over a time period of about 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours in vitro. In another embodiment, at least 90% or 95% of the second dose of acetaminophen is released over a time period of about 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours in vitro. 
     In one aspect, a method of making a gastric retentive dosage form comprising acetaminophen and at least one hydrophilic polymer is provided. 
     In one embodiment, the method of making the dosage form comprises granulating acetaminophen powder with at least one hydrophilic polymer. In another embodiment, the granulating is fluid bed or high shear granulation. In another embodiment, the method comprises direct compression of the at least one hydrophilic polymer with a pregranulated acetaminophen composition. In yet another embodiment, the granulated acetaminophen composition contains acetaminophen granulated with starch or povidone. 
     In one embodiment, a gastric retentive dosage form comprising acetaminophen and made by the process of directly compressing a pregranulated acetaminophen with one or more hydrophilic polymers is provided. 
     In one embodiment, a gastric retained dosage form comprising acetaminophen and at least one swellable polymer is administered to a subject suffering from or diagnosed with a pain state. In other embodiments, the subject is suffering from chronic pain. In yet another embodiment, the subject is suffering from acute pain. In yet other embodiments, the subject is suffering from both chronic and acute pain. 
     In one embodiment, a gastric retained dosage form is administered to a subject in a fed mode. In another embodiment, the dosage form is administered with a meal to a subject once in a 24 hour period. In other embodiments, the dosage form is administered with a meal to the subject twice in a 24 hour period. In yet another embodiment, the dosage form is administered with a meal to a subject once or twice in a 24 hour period for 2, 3, 4, 5, 6, 7, 8 or more days. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph comparing dissolution release profiles for gastric retentive (GR) dosage forms identified herein as GR-6 and GR-8 tablets containing 650 mg acetaminophen with the dissolution profile of Tylenol® ER 8 Hour Caplets. 
         FIG. 2  is a graph showing disintegration and dissolution release profiles for GR-6 and GR-8 tablets containing 650 mg acetaminophen. 
         FIG. 3  is a graph showing disintegration release profiles for tablets having both immediate release and gastric retentive extended release drug layers. 
         FIG. 4  is a graph showing dissolution and disintegration release profiles for various tablet formulations containing polyethylene oxide and 1000 mg acetaminophen. The legend descriptors refer only to the hydrophilic polymer component in the ER layer and are trademarks of the Dow Chemical Company of Midland, Mich. 
         FIG. 5  is a schematic for simulation of pharmacokinetic profiles. 
         FIG. 6  is a graph showing simulated pharmacokinetic plasma profiles determined for GR8 tablet formulations. 
         FIGS. 7 and 8  are graphs comparing simulated pharmacokinetic plasma profiles for a GR8 acetaminophen formulation and an immediate release acetaminophen formulation. 
         FIG. 9  is a graph showing simulated pharmacokinetic plasma profiles determined for GR9 tablet formulations. 
         FIGS. 10 and 11  are graphs comparing simulated pharmacokinetic plasma profiles for a GR8 acetaminophen formulation and an immediate release acetaminophen formulation. 
         FIG. 12  is a graph showing simulated pharmacokinetic plasma profiles from various gastric retentive extended release formulations. 
     
    
    
     DETAILED DESCRIPTION 
     The various aspects and embodiments will now be fully described herein. These aspects and embodiments may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided so the disclosure will be thorough and complete, and will fully convey the scope of the present subject matter to those skilled in the art. 
     All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety. 
     I. DEFINITIONS 
     It must be noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. 
     Compounds useful in the compositions and methods include those described herein in any of their pharmaceutically acceptable forms, including isomers such as diastereomers and enantiomers, salts, solvates, and polymorphs, as well as racemic mixtures and pure isomers of the compounds described herein, where applicable. 
     “Optional” or “optionally,” as used herein, means that the subsequently described element, component or circumstance may or may not occur, so that the description includes instances where the element, component, or circumstance occurs and instances where it does not. 
     The terms “subject,” “individual” or “patient” are used interchangeably herein and refer to a vertebrate, preferably a mammal. Mammals include, but are not limited to, humans. 
     The term “about,” particularly in reference to a given quantity, is meant to encompass deviations of plus or minus five percent. 
     The gastric retentive oral dosage forms presented herein provide an immediate and extended release dose of acetaminophen that is released into the stomach of a subject in a fed mode. 
     The term “fed mode,” as used herein, refers to a state which is typically induced in a patient by the presence of food in the stomach, the food giving rise to two signals, one that is said to stem from stomach distension and the other a chemical signal based on food in the stomach. It has been determined that once the fed mode has been induced, larger particles are retained in the stomach for a longer period of time than smaller particles; thus, the fed mode is typically induced in a patient by the presence of food in the stomach. The fed mode is initiated by nutritive materials entering the stomach upon the ingestion of food. Initiation is accompanied by a rapid and profound change in the motor pattern of the upper GI tract, over a period of 30 seconds to one minute. The change is observed almost simultaneously at all sites along the GI tract and occurs before the stomach contents have reached the distal small intestine. Once the fed mode is established, the stomach generates 3-4 continuous and regular contractions per minute, similar to those of the fasting mode but with about half the amplitude. The pylorus is partially open, causing a sieving effect in which liquids and small particles flow continuously from the stomach into the intestine while indigestible particles greater in size than the pyloric opening are retropelled and retained in the stomach. This sieving effect thus causes the stomach to retain particles exceeding about 1 cm in size for about 4 to 6 hours. Administration of a dosage form “with a meal,” as used herein, refers to administration before, during or after a meal, and more particularly refers to administration of a dosage form about 1, 2, 3, 4, 5, 10, 15 minutes before commencement of a meal, during the meal, or about 1, 2, 3, 4, 5, 10, 15 minutes after completion of a meal. 
     A drug “release rate,” as used herein, refers to the quantity of drug released from a dosage form or pharmaceutical composition per unit time, e.g., milligrams of drug released per hour (mg/hr). Drug release rates for drug dosage forms are typically measured as an in vitro rate of dissolution, i.e., a quantity of drug released from the dosage form or pharmaceutical composition per unit time measured under appropriate conditions and in a suitable fluid. The specific results of dissolution tests claimed herein are performed on dosage forms or pharmaceutical compositions in a USP Type II apparatus and immersed in 900 ml of simulated intestinal fluid (SIF) at pH 6.8 and equilibrated in a constant temperature water bath at 37° C. Suitable aliquots of the release rate solutions are tested to determine the amount of drug released from the dosage form or pharmaceutical composition. For example, the drug can be assayed or injected into a chromatographic system to quantify the amounts of drug released during the testing intervals. 
     The terms “hydrophilic” and “hydrophobic” are generally defined in terms of a partition coefficient P, which is the ratio of the equilibrium concentration of a compound in an organic phase to that in an aqueous phase. A hydrophilic compound has a P value less than 1.0, typically less than about 0.5, where P is the partition coefficient of the compound between octanol and water, while hydrophobic compounds will generally have a P greater than about 1.0, typically greater than about 5.0. The polymeric carriers herein are hydrophilic, and thus compatible with aqueous fluids such as those present in the human body. 
     The term “polymer” as used herein refers to a molecule containing a plurality of covalently attached monomer units, and includes branched, dendrimeric, and star polymers as well as linear polymers. The term also includes both homopolymers and copolymers, e.g., random copolymers, block copolymers and graft copolymers, as well as uncrosslinked polymers and slightly to moderately to substantially crosslinked polymers, as well as two or more interpenetrating cross-linked networks. 
     The term “swellable polymer,” as used herein, refers to a polymer that will imbibe a fluid, preferably water, and become enlarged or engorged. A polymer is swellable due, at least in part, to a structural feature of the polymer. Whether or not a swellable polymer when incorporated into a dosage form or matrix containing other components swells in the presence of fluid will depend upon a variety of factors, including the specific type of polymer and the percentage of that polymer in a particular formulation. For example, the term “polyethylene oxide” or “PEO” refers to a polyethylene oxide polymer that has a wide range of molecular weights. PEO is a linear polymer of unsubstituted ethylene oxide and has a wide range of viscosity-average molecular weights. Examples of commercially available PEOs and their approximate molecular weights are: POLYOX® NF, grade WSR coagulant, approximate molecular weight 5 million, POLYOX® grade WSR 301, approximate molecular weight 4 million, POLYOX® grade WSR 303, approximate molecular weight 7 million, POLYOX® grade WSR N-60K, approximate molecular weight 2 million, and POLYOX® grade N-80K, approximate molecular weight 200,000. An oral dosage form which comprises a swellable polymer as used herein intends that the polymer when incorporated into the dosage form will swell upon imbibition of water or fluid from gastric fluid. 
     The terms “swellable” and “bioerodible” (or simply “erodible”) are used to refer to the polymers used in the present dosage forms, with “swellable” polymers being those that are capable of absorbing water and physically swelling as a result, with the extent to which a polymer can swell being determined by the molecular weight or degree of crosslinking (for crosslinked polymers), and “bioerodible” or “erodible” polymers referring to polymers that slowly dissolve and/or gradually hydrolyze in an aqueous fluid, and/or that physically disentangle or undergo chemical degradation of the chains themselves, as a result of movement within the stomach or GI tract. 
     The term “friability,” as used herein, refers to the ease with which a tablet will break or fracture. The test for friability is a standard test known to one skilled in the art. Friability is measured under standardized conditions by weighing out a certain number of tablets (generally 20 tablets or less), placing them in a rotating Plexiglas drum in which they are lifted during replicate revolutions by a radial lever, and then dropped about 8 inches. After replicate revolutions (typically 100 revolutions at 25 rpm), the tablets are reweighed and the percentage of formulation abraded or chipped is calculated. The friability of the tablets, of the present invention, is preferably in the range of about 0% to 3%, and values about 1%, or less, are considered acceptable for most drug and food tablet contexts. Friability which approaches 0% is particularly preferred. 
     The term “tap density” or “tapped density,” as used herein, refers to a measure of the density of a powder. The tapped density of a pharmaceutical powder is determined using a tapped density tester, which is set to tap the powder at a fixed impact force and frequency. Tapped density by the USP method is determined by a linear progression of the number of taps. 
     The term “bulk density,” as used herein, refers to a property of powders and is defined as the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume and internal pore volume. 
     The term “capping,” as used herein, refers to the partial or complete separation of top or bottom crowns of the tablet main body. For multilayer tablets, capping refers to separation of a portion of an individual layer within the multilayer tablet. Unintended separation of layers within a multilayer tablet prior to administration is referred to herein as “splitting.” 
     The term “content uniformity,” as used herein refers to the testing of compressed tablets to provide an assessment of how uniformly the micronized or submicron active ingredient is dispersed in the powder mixture. Content uniformity is measured by use of USP Method (General Chapters, Uniformity of Dosage Forms), unless otherwise indicated. A plurality refers to five, ten or more tablet compositions. 
     The terms “effective amount” or a “therapeutically effective amount” refer to the amount of drug or pharmacologically active agent to provide the desired effect without toxic effects. The amount of an agent that is “effective” may vary from individual to individual, depending on the age, weight, general condition, and other factors of the individual. An appropriate “effective” amount in any individual may be determined by one of ordinary skill in the art using routine experimentation. An “effective amount” of an agent can refer to an amount that is either therapeutically effective or prophylactically effective or both. 
     By “pharmaceutically acceptable,” such as in the recitation of a “pharmaceutically acceptable carrier,” or a “pharmaceutically acceptable acid addition salt,” is meant a material that is not biologically or otherwise undesirable, i.e., the material may be incorporated into a pharmaceutical composition administered to a patient without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the composition in which it is contained. The term “pharmacologically active” (or simply “active”) as in a “pharmacologically active” derivative, refers to a derivative having the same type of pharmacological activity as the parent compound and/or drug and about equivalent in degree. When the term “pharmaceutically acceptable” is used to refer to a derivative (e.g., a salt) of an active agent, it is to be understood that the compound is pharmacologically active as well. When the term, “pharmaceutically acceptable” is used to refer to an excipient, it implies that the excipient has met the required standards of toxicological and manufacturing testing or that it is on the Inactive Ingredient Guide prepared by the FDA, or comparable agency. 
     The terms “drug,” “active agent,” “therapeutic agent,” and/or “pharmacologically active agent” are used interchangeably herein to refer to any chemical compound, complex or composition that is suitable for oral administration and that has a beneficial biological effect, preferably a therapeutic effect in the treatment or prevention of a disease or abnormal physiological condition. The terms also encompass pharmaceutically acceptable, pharmacologically active derivatives of those active agents specifically mentioned herein, including, but not limited to, salts, esters, amides, prodrugs, active metabolites, analogs, and the like. When the terms “active agent,” “pharmacologically active agent,” and “drug” are used, then, or when a particular active agent is specifically identified, it is to be understood that applicants intend to include the active agent per se as well as pharmaceutically acceptable, pharmacologically active salts, esters, amides, prodrugs, metabolites, analogs, etc. 
     The term “dosage form” refers to the physical formulation of the drug for administration to the patient. Dosage forms include without limitation, tablets, capsules, caplets, liquids, syrups, lotions, lozenges, aerosols, patches, enemas, oils, ointments, pastes, powders for reconstitution, sachets, solutions, sponges, and wipes. Within the context of the present invention, a dosage form comprising an acetaminophen formulation will generally be administered to patients in the form of tablets or capsules, although a liquid formulation is also contemplated within this disclosure. 
     The term “dosage unit” refers to a single unit of the dosage form that is to be administered to the patient. The dosage unit will be typically formulated to include an amount of drug sufficient to achieve a therapeutic effect with a single administration of the dosage unit although where the size of the dosage form is at issue, more than one dosage unit may be necessary to achieve the desired therapeutic effect. For example, a single dosage unit of a drug is typically, one tablet, one capsule, or one tablespoon of liquid. More than one dosage unit may be necessary to administer sufficient drug to achieve a therapeutic effect where the amount of drug causes physical constraints on the size of the dosage form. 
     “Delayed release” dosage forms are a category of modified release dosage forms in which the release of the drug is delayed after oral administration for a finite period of time after which release of the drug is unhindered. Delayed release dosage forms are frequently used to protect an acid-labile drug from the low pH of the stomach or where appropriate to target the GI tract for local effect while minimizing systemic exposure. Enteric coating is frequently used to manufacture delayed release dosage forms. 
     The terms “sustained release,” and “extended release” are used interchangeably herein to refer to a dosage form that provides for release of a drug over an extended period of time. With extended release dosage forms, the rate of release of the drug from the dosage form is reduced in order to maintain therapeutic activity of the drug for a longer period of time or to reduce any toxic effects associated with a particular dosing of the drug. Extended release dosage forms have the advantage of providing patients with a dosing regimen that allows for less frequent dosing, thus enhancing compliance. Extended release dosage forms can also reduce peak-related side effects associated with some drugs and can maintain therapeutic concentrations throughout the dosing period thus avoiding periods of insufficient therapeutic plasma concentrations between doses. 
     The term “modified release” refers to a dosage form that includes both delayed and extended release drug products. The manufacture of delayed, extended, and modified release dosage forms are known to ordinary skill in the art and include the formulation of the dosage forms with excipients or combinations of excipients necessary to produce the desired active agent release profile for the dosage form. 
     The “gastric retentive” oral dosage forms described herein are a type of extended release dosage form. Gastric retentive dosage forms are beneficial for the delivery of drugs with reduced absorption in the lower GI tract or for local treatment of diseases of the stomach or upper GI tract. For example, in certain embodiments of gastric retentive oral dosage forms of the present invention, the dosage form swells in the gastric cavity and is retained in the gastric cavity of a patient in the fed med so that the drug may be released for heightened therapeutic effect. See, Hou et al., Crit. Rev. Ther. Drug Carrier Syst. 20(6):459-497 (2003). 
     The in vivo “release rate” and in vivo “release profile” refer to the time it takes for the orally administered dosage form, or the active agent-containing layer of a bilayer or multilayer tablet (administered when the stomach is in the fed mode) or the content of the active ingredient to be reduced to 0-10%, preferably 0-5%, of its original size or level, as may be observed visually using NMR shift reagents or paramagnetic species, radio-opaque species or markers, or radiolabels, or determined mathematically, such as deconvolution, upon its plasma concentration profiles. 
     The term “AUC” (i.e., “area under the curve,” “area under the concentration curve,” or “area under the concentration-time curve”) is a pharmacokinetic term used to refer a method of measurement of bioavailability or extent of absorption of a drug based on a plot of an individual or pool of individual&#39;s blood plasma concentrations sampled at frequent intervals; the AUC is directly proportional to the total amount of unaltered drug in the patient&#39;s blood plasma. For example, a linear curve for a plot of the AUC versus dose (i.e., straight ascending line) indicates that the drug is being released slowly into the blood stream and is providing a steady amount of drug to the patient; if the AUC versus dose is a linear relationship this generally represents optimal delivery of the drug into the patient&#39;s blood stream. By contrast, a non-linear AUC versus dose curve indicates rapid release of drug such that some of the drug is not absorbed, or the drug is metabolized before entering the blood stream. 
     The term “Cmax” (i.e., “maximum concentration”) is a pharmacokinetic term used to indicate the peak concentration of a particular drug in the blood plasma of a patient. The term “Cmin” (i.e., “minimum concentration”) is a pharmacokinetic term used to indicate the minimum concentration of a particular drug in the blood plasma of a patient. 
     The term “Tmax” (i.e., “time of maximum concentration” or “time of Cmax”) is a pharmacokinetic term used to indicate the time at which the Cmax is observed during the time course of a drug administration. 
     “Preventing,” in reference to a disorder or unwanted physiological event in a patient, refers specifically to inhibiting or reducing the occurrence of symptoms associated with the disorder and/or the underlying cause of the symptoms. 
     “Therapeutically effective amount,” in reference to a therapeutic agent, refers to an amount that is effective to achieve a desired therapeutic result. Therapeutically effective amounts of a given agent will typically vary with respect to factors such as the type and severity of the disorder or disease being treated and the age, gender, weight and other factors of the patient. 
     “Treating,” “treat,” and “treatment” refer to reduction in severity and/or frequency of symptoms, elimination of symptoms and/or underlying cause, prevention of the occurrence of symptoms and/or their underlying cause, and improvement or remediation of damage. 
     All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entireties. However, where a patent, patent application, or publication containing express definitions is incorporated by reference, those express definitions should be understood to apply to the incorporated patent, patent application, or publication in which they are found, and not to the present disclosure or its claims. 
     II. GASTRIC RETENTIVE DOSAGE FORM FOR THE EXTENDED RELEASE OF ACETAMINOPHEN 
     The pharmaceutical compositions described herein, i.e., gastric retained dosage forms comprising acetaminophen, provide extended or sustained release of acetaminophen to the upper gastrointestinal tract. The dosage forms may also be formulated to include an immediate release (“IR”) layer or portion with a separate dose of acetaminophen to provide immediate pain relief. The presently described dosage forms provide for extended release of acetaminophen in the stomach wherein the dosage forms are comprised of a polymer matrix that swells upon imbibition of fluid to a size sufficient for gastric retention. Thus, in formulating the dosage forms, properties which simultaneously allow: a) an extent of swelling to provide gastric retention over an extended period, and b) a rate of swelling and erosion that allows release of the acetaminophen over a time period of about 8 to 12 hours, are preferably provided. 
     The dosage forms described herein for the extended or extended and immediate release of acetaminophen may also be formulated to include a second active ingredient. The second active ingredient may be an active agent having solubility properties similar to that of acetaminophen. Alternatively, the second active ingredient may be more or less soluble than acetaminophen. Opioids are examples of pharmaceutical agents having greater solubility in water than acetaminophen. Other active agents to be combined in the dosage form with acetaminophen include barbituates such as butalbitol or non-steroidal anti-inflammatory drugs such as ibuprofen. 
     The formulation of these pharmaceutical oral dosage forms preferably result in final products that meet the requirements of regulatory agencies such as the Food and Drug Administration. For example, final dosage forms are preferably stable such that they do not fracture during storage and transport. This is measured for tablets, in part, in terms of friability and hardness. Dosage forms preferably also meet requirements for content uniformity, such that dispersion of the active ingredient(s) is uniform throughout the mixture used to make the dosage form, such that the composition of tablets formed from a particular formulation does not vary significantly from one tablet to another. The FDA requires a content uniformity within a range of 95% to 105%. 
     The dosage form as described here is capable of swelling dimensionally unrestrained in the stomach upon contact with gastric fluid due to the hydrophilic polymer(s) component, such as, polyethylene oxide and/or hypromellose (also known as hydroxypropyl methylcellulose or HPMC), in the formulation, and increase to a size sufficient to be retained in the stomach in a fed mode. 
     Water-swellable, erodible polymers suitable for use herein are those that swell in a dimensionally unrestrained manner upon contact with water, and gradually erode over time. Examples of such polymers include polyalkylene oxides, such as polyethylene glycols, particularly high molecular weight polyethylene glycols; cellulose polymers and their derivatives including, but not limited to, hydroxyalkyl celluloses, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethylcellulose, microcrystalline cellulose; polysaccharides and their derivatives; chitosan; poly(vinyl alcohol); xanthan gum; maleic anhydride copolymers; poly(vinyl pyrrolidone); starch and starch-based polymers; maltodextrins; poly(2-ethyl-2-oxazoline); poly(ethyleneimine); polyurethane; hydrogels; crosslinked polyacrylic acids; and combinations or blends of any of the foregoing. 
     Further examples are copolymers, including block copolymers and graft polymers. Specific examples of copolymers are PLURONIC® and TECTONIC®, which are polyethylene oxide-polypropylene oxide block copolymers available from BASF Corporation, Chemicals Div., Wyandotte, Mich., USA. Further examples are hydrolyzed starch polyacrylonitrile graft copolymers, commonly known as “Super Slurper” and available from Illinois Corn Growers Association, Bloomington, Ill., USA. 
     Preferred swellable, erodible hydrophilic polymers suitable for forming the gastric retentive portion of the dosage forms described herein are poly(ethylene oxide), hydroxypropyl methyl cellulose, and combinations of poly(ethylene oxide) and hydroxypropyl methyl cellulose. Poly(ethylene oxide) is used herein to refer to a linear polymer of unsubstituted ethylene oxide. The molecular weight of the poly(ethylene oxide) polymers can range from about 9×10 5  Daltons to about 8×10 6  Daltons. A preferred molecular weight poly(ethylene oxide) polymer is about 5×10 6  Daltons and is commercially available from The Dow Chemical Company (Midland, Mich.) referred to as SENTRY® POLYOX® water-soluble resins, NF (National Formulary) grade WSR Coagulant. The viscosity of a 1% water solution of the polymer at 25° C. preferably ranges from 4500 to 7500 centipoise. 
     Dosage forms prepared for oral administration according to the present disclosure will generally contain other inactive additives (excipients) such as binders, lubricants, disintegrants, fillers, stabilizers, surfactants, coloring agents, and the like. 
     Binders are used to impart cohesive qualities to a tablet, and thus ensure that the tablet or tablet layer remains intact after compression. Suitable binder materials include, but are not limited to, starch (including corn starch and pregelatinized starch), gelatin, sugars (including sucrose, glucose, dextrose and lactose), polyethylene glycol, waxes, and natural and synthetic gums, e.g., acacia sodium alginate, polyvinylpyrrolidone, cellulosic polymers (including hydroxypropyl cellulose, hydroxypropyl methylcellulose, methyl cellulose, microcrystalline cellulose, ethyl cellulose, hydroxyethyl cellulose, and the like), and Veegum. Examples of polyvinylpyrrolidone include povidone, copovidone and crospovidone. 
     Lubricants are used to facilitate tablet manufacture, promoting powder flow and preventing particle capping (i.e., particle breakage) when pressure is relieved. Useful lubricants are magnesium stearate (in a concentration of from 0.25 wt % to 3 wt %, preferably 0.2 wt % to 1.0 wt %, more preferably about 0.3 wt %), calcium stearate, stearic acid, and hydrogenated vegetable oil (preferably comprised of hydrogenated and refined triglycerides of stearic and palmitic acids at about 1 wt % to 5 wt %, most preferably less than about 2 wt %). Disintegrants are used to facilitate disintegration of the tablet, thereby increasing the erosion rate relative to the dissolution rate, and are generally starches, clays, celluloses, algins, gums, or crosslinked polymers (e.g., crosslinked polyvinyl pyrrolidone). Fillers include, for example, materials such as silicon dioxide, titanium dioxide, alumina, talc, kaolin, powdered cellulose, and microcrystalline cellulose, as well as soluble materials such as mannitol, urea, sucrose, lactose, lactose monohydrate, dextrose, sodium chloride, and sorbitol. Solubility-enhancers, including solubilizers per se, emulsifiers, and complexing agents (e.g., cyclodextrins), may also be advantageously included in the present formulations. Stabilizers, as well known in the art, are used to inhibit or retard drug decomposition reactions that include, by way of example, oxidative reactions. 
     The gastric retentive dosage form may be a single layer, bilayer, or multilayer tablet or it may be a capsule. The tablet comprises a gastric retentive layer comprised of acetaminophen dispersed in a matrix of at least one hydrophilic polymer which swells upon imbibition of fluid. 
     III. ACETAMINOPHEN 
     Acetaminophen (N-(4-hydroxyphenyl)acetamine) is a white, crystalline powder, which is poorly soluble in water, and has a molecular weight of about 151. As acetaminophen powder does not possess properties conducive to direct compression to form a tablet, the acetaminophen may first be granulated with one or more excipients using a method such as fluid bed or dry granulation. Alternatively, tablets as described herein may be manufactured using a pregranulated composition such as COMPAP®, COMPAP® L, COMPAP® COARSE L, COMPAP® WSE, or COMPAP® PVP, all of which are manufactured by Mallinckrodt, Inc. The pregranulated compositions have been specially processed to yield an active agent that has flow properties, particle size distribution, and compression characteristics that enhance the ability to manufacture a stable tablet. 
     IV. METHODS FOR MAKING THE DOSAGE FORMS 
     In one embodiment, manufacture of a pharmaceutical oral dosage form that both delivers a therapeutically effective ingredient over a desired period of time and satisfies criteria for commercial and regulatory approval is provided. 
     In the case of gastric retentive tablets containing acetaminophen, as disclosed herein, tablets may be made by direct compression or by a granulation procedure. Direct compression is used with a group of ingredients that can be blended, placed onto a tablet press, and made into a perfect tablet without any of the ingredients having to be changed. Powders that can be blended and compressed are commonly referred to as directly compressible or as direct-blend formulations. When powders do not compress correctly, they must be granulated. 
     Granulation is a manufacturing process that increases the size and homogeneity of active pharmaceutical ingredients and excipients in a solid dosage formulation. The granulation process, which is often referred to as agglomeration, changes physical characteristics of the dry formulation, with the aim of improving manufacturability, and therefore, product quality. 
     Granulation technology can be classified into one of two basic types: wet granulation and dry granulation. Wet granulation is the more prevalent agglomeration process utilized within the pharmaceutical industry. Most wet granulation procedures follow some basic steps; the drug(s) and excipients are mixed together, and a binder solution is prepared and added to the powder mixture to form a wet mass. The moist particles are then dried and sized by milling or by screening through a sieve. In some cases, the wet granulation is “wet milled” or sized through screens before the drying step. There are four basic types of wet granulation; high shear granulation, fluid bed granulation, extrusion and spheronization and spray drying. 
     A. Fluid Bed Granulation 
     The fluid bed granulation process involves the suspension of particulates within an air stream while a granulation solution is sprayed down onto the fluidized bed. During the process, the particles are gradually wetted as they pass through the spray zone, where they become tacky as a result of the moisture and the presence of binder within the spray solution. These wetted particles come into contact with, and adhere to, other wetted particles resulting in the formation of larger particles. 
     A fluid bed granulator consists of a product container into which the dry powders are charged, an expansion chamber which sits directly on top of the product container, a spray gun assembly, which protrudes through the expansion chamber and is directed down onto the product bed, and air handling equipment positioned upstream and downstream from the processing chamber. 
     The fluidized bed is maintained by a downstream blower that creates negative pressure within the product container/expansion chamber by pulling air through the system. Upstream, the air is “pre-conditioned” to target values for humidity, temperature and dew point, while special product retention screens and filters keep the powder within the fluid bed system. 
     As the air is drawn through the product retention screen it “lifts” the powder out of the product container and into the expansion chamber. Since the diameter of the expansion chamber is greater than that of the product container, the air velocity becomes lower within the expansion chamber. This design allows for a higher velocity of air to fluidize the powder bed causing the material to enter the spray zone where granulation occurs before loosing velocity and falling back down into the product container. This cycle continues throughout the granulation process. 
     The fluid bed granulation process can be characterized as having three distinct phases; pre-conditioning, granulation and drying. In the initial phase, the process air is pre-conditioned to achieve target values for temperature and humidity, while by-passing the product container altogether. Once the optimal conditions are met, the process air is re-directed to flow through the product container, and the process air volume is adjusted to a level that will maintain sufficient fluidization of the powder bed. This pre-conditioning phase completes when the product bed temperature is within the target range specified for the process. 
     In the next phase of the process, the spraying of the granulating solution begins. The spray rate is set to a fall within a pre-determined range, and the process continues until all of the solution has been sprayed into the batch. It is in this phase where the actual granulation, or agglomeration, takes place. 
     Once the binder solution is exhausted, the product continues to be fluidized with warm process air until the desired end-point for moisture content is reached. This end-point often correlates well with product bed temperature, therefore in a manufacturing environment, the process can usually be terminated once the target product bed temperature is reached. A typical fluid bed process may require only about thirty to forty-five minutes for the granulation step, plus ten to fifteen minutes on either side for pre-conditioning and drying. 
     As with any of the wet granulation processes, one variable is the amount of moisture required to achieve successful agglomeration. The fluid bed granulation process requires a “thermodynamic” balance between process air temperature, process air humidity, process air volume and granulation spray rate. While higher process air temperature and process air volume add more heat to the system and remove moisture, more granulating solution and a higher solution spray rate add moisture and remove heat via evaporative cooling. These are the process parameters which must be evaluated as a manufacturing process is developed, and the key is understanding the interdependency of each variable. 
     Additional factors affecting the outcome of the fluid bed granulation process are the amount and type of binder solution, and the method by which the binder is incorporated within the granulation. Other process variables are the total amount of moisture added through the process, and the rate at which the moisture content is increased. These parameters can have an effect on the quality and the characteristics of the granulation. For instance, a wetter fluid bed granulation process tends to result in a stronger granule with a higher bulk density. However, an overly aggressive process, where moisture is added too rapidly, can loose control over achieving the final particle size and particle size distribution objectives. 
     B. High Shear Granulation 
     Many pharmaceutical products manufactured by wet granulation utilize a high shear process, where blending and wet massing are accomplished by the mechanical energy generated by an impeller and a chopper. Mixing, densification and agglomeration are achieved through the “shear” forces exerted by the impeller; hence the process is referred to as high shear granulation. 
     The process begins by adding the dry powders of the formulation to the high shear granulator, which is a sealed “mixing bowl” with an impeller which rotates through the powder bed, and a chopper blade which breaks up over-agglomerates which can form during the process. There are typically three phases to the high shear process; dry mixing, solution addition, or wet massing and high shear granulation. 
     In the first phase, dry powders are mixed together by the impeller blade which rotates through the powder bed. The impeller blade is positioned just off the bottom of the product container. There is a similar tolerance between the tips of the impeller blade and the sides of the container. The impeller blades rotation trough the powder bed creates a “roping” vortex of powder movement. The dry mixing phase typically lasts for only a few minutes. 
     In the second phase of the process, a granulating liquid is added to the sealed product container, usually by use of a peristaltic pump. The solution most often contains a binder with sufficient viscosity to cause the wet massed particles to stick together or agglomerate. It is common for the solution addition phase to last over a period of from three to five minutes. While the impeller is rotating rather slowly during this step of the process, the chopper blade is turning at a fairly high rate of speed, and is positioned within the product container to chop up over-sized agglomerates, while not interfering with the impellers movement. 
     Once the binder solution has been added to the product container, the final stage of the granulation process begins. In this phase, high shear forces are generated as the impeller blades push through the wet massed powder bed, further distributing the binder and intimately mixing the ingredients contained therein. The impeller and chopper tool continue to rotate until the process is discontinued when the desired granule particle size and density end-points are reached. This end-point is often determined by the power consumption and/or torque on the impeller. 
     Once the high shear granulation process has been completed, the material is transferred to a fluid bed dryer, or alternatively, spread out onto trays that are then placed in a drying oven, where the product is dried until the desired moisture content is achieved, usually on the order of 1-2% as measured by Loss On Drying (LOD) technique. 
     A variable that affects the high shear process is the amount of moisture required to achieve a successful granulation. A key to the process is having the right amount of moisture to allow for agglomeration to occur. Too little moisture will result in an under-granulated batch, with weak bonds between particles and smaller, to non-existent particles, with properties similar to those of the dry powder starting materials. On the other hand, excess moisture can result in a “crashed” batch with results varying from severe over-agglomeration to a batch that appears more like soup. 
     Other formulation parameters affecting the outcome of the high shear granulation process are the amount and type of binder solution, and the method by which the binder is incorporated within the granulation. For example, it is possible to include some of the binder in the dry powder mixture as well as in the granulating solution, or it may be incorporated only in the granulating solution or only in the dry powder, as is the case where water is used as the granulating solution. 
     The high shear granulation process parameters which are variable include impeller and chopper speeds, the solution addition rate, and the amount of time allocated to the various phases of the process. Of these, preferred variables for consideration are the solution addition rate and the amount of time the wet massed product is under high shear mixing. 
     C. Extrusion and Spheronization 
     This specialized wet granulation technique involves multiple processing steps and was developed to produce very uniform, spherical particles ideally suited for multi-particulate drug delivery of delayed and sustained release dosage forms. 
     Similar to high shear granulation initially, the first step involves the mixing and wet massing of the formulation. Once this step is complete, the wet particles are transferred to an extruder that generates high forces used to press the material out through small holes in the extruder head. The extrudate is of uniform diameter and is then transferred onto a rotating plate for spheronization. The forces generated by the rotating plate initially break up the extruded formulation strands into uniform lengths. Additional dwell time within the spheronizer creates particles that are round and uniform in size. These pellets or spheres are then dried to the target moisture content, usually within a fluid bed system. 
     Particles produced in this manner tend to be dense, and have a capacity for high drug loading, approaching 90% or more in some cases. The particle size is uniform, and the size distribution is narrow, as compared to other granulation approaches. This quality assures consistent surface area within and between batches, which is desired when functional coatings are subsequently applied to create sustained release formulations, delayed release formulations and formulations designed to target a specific area within the body. 
     Uniform surface area is desired because the pharmaceutical coating process endpoint is determined not by coating thickness, but by the theoretical batch weight gain of the coating material. If the batch surface area is consistent, then the coating thickness will also be consistent for a given weight gain, and coating thickness is the primary variable in determining the functionality of the coating system, whether the goal is controlling the duration of sustained release formulations or imparting an acid resistant characteristic to “beads” necessary to protect certain compounds which would otherwise be severely degraded in the presence of the acidic environment of the stomach. 
     D. Spray Drying 
     Spray drying is a unique and specialized process that converts liquids into dry powders. The process involves the spraying of very finely atomized droplets of solution into a “bed” or stream of hot process air or other suitable gas. Not typically utilized for the conventional granulation of dosage form intermediates, spray drying has gained acceptance within the industry as a robust process that can improve drug solubility and bioavailability. 
     Spray drying can be used to create co-precipitates of a drug/carrier that can have improved dissolution and solubility characteristics. In addition, the process can also be useful as a processing aid. For example, it is much more difficult to maintain the uniformity of a drug in suspension, as compared to the same compound in solution. One may have a need to develop an aqueous coating or drug layering process utilizing a drug that is otherwise not soluble in water. By creating a co-precipitate of the drug and a suitable water soluble carrier, often a low molecular weight polymer, the co-precipitate will remain in solution throughout the manufacturing process, improving uniformity of the spray solution and the dosage form created by the coating process. Uniformity is particularly desired where lower doses of potent compounds are intended to be coated onto beads or tablet cores. 
     This same process may be used to enhance the solubility and bioavailability of poorly soluble drugs. By complexing certain excipients and the active ingredient within a solvent system which is then spray dried, it is possible to enhance the drugs absorption within the body. Selection of the solvent system, the complexing agent(s) and the ratios utilized within the formulation are formulation variables that influence the effectiveness of solubility enhancement utilizing the spray drying technique. Other process parameters with an effect on drug solubility are the temperatures of the spray solution and process gas, the spray rate and droplet size and the rate of re-crystallization. The spray dried granulations created by these techniques can then be incorporated into capsules or tablets by conventional manufacturing processes. 
     E. Dry Granulation 
     The dry granulation process involves three basic steps; the drug(s) and excipients(s) are mixed (along with a suitable binder if needed) and some form of lubrication, the powder mixture is compressed into dry “compacts,” and then the compacts are sized by a milling step. The two methods by which dry granulation can be accomplished are slugging and roller compaction. 
     V. METHODS OF MAKING THE EXTENDED RELEASE GASTRIC RETENTIVE DOSAGE FORMS DISCLOSED HEREIN 
     In one aspect, a method of making a gastric retentive extended-release dosage form as a single layer tablet comprising wet granulation of the acetaminophen with the binder is provided. The wet granulation can be a fluid-bed or high shear granulation method. The granulated particles are then blended with additional excipients as needed to form a mixture which is then compressed to form tablets. 
     Extended release polymer matrices comprising acetaminophen are made using either POLYOX® 1105 (approximate molecular weight of 900,000 Daltons), POLYOX® N-60K (approximate molecular weight of 2,000,000 Daltons), or POLYOX® WSR-301 (approximate molecular weight of 4,000,000 Daltons). Prior to compression, components are granulated using a top spray fluid bed granulator A solution of povidone (PVP) in water is sprayed onto the acetaminophen and fluid-bed granulated. 
     After fluid bed granulation and drying of the resultant particles, batches are characterized with respect to properties such as final Loss on Drying (LOD), bulk density, tap density, and particle size. 
     Loss on Drying (LOD) is determined after each granulation using the Moisture Analyzer. A 1 gram (g) samples are taken and loaded into the moisture analyzer. The sample is run for 5 minutes at a temperature of 105° C. 
     Bulk and tap densities can be determined as follows. A graduated cylinder is filled with a certain amount of material, and the volume recorded to determine the material bulk density. Tap density can be determined with a help of a Tap Density Tester by exposing the material to 100 taps per test and recording the new volume. 
     Particle size determination is performed immediately after granulation, after sieving through 20 mesh screen to remove agglomerates. Particle diameter is determined with a sieve-type particle diameter distribution gauge using sieves with openings of 44, 53, 75, 106, 150, and 250 mesh. Fractions are weighed on Mettler balance to estimate size distribution. This provides determination of the quantitative ratio by particle diameter of composition comprising extended release particles. Sieve analysis according to standard United States Pharmacopoeia methods (e.g., USP-23 NF 18), may be done such as by using a Meinzer II Sieve Shaker. 
     The granulated mixture can be blended with the polymer, filler and lubricant in a V-blender. The resultant mixture can be compressed into monolithic, single-layer tablets using a Manesty® BB4 press, with a modified oval 0.3937″ width×0.6299″ length×0.075″ cup depth tool. Tablets may be prepared at a rate, for example, of about 800 tablets per minute. 
     Tablets are then characterized for disintegration and dissolution release profiles, hardness, friability and content uniformity. 
     The dissolution profiles for the tablets are determined in USP apparatus (40 mesh baskets), 100 revolutions per minute (rpm), in pH 5.8 phosphate buffer (0.1 N HCl), 37° C. Samples of 5 milliliters (ml) at each time-point, are taken without media replacement at 1, 2, 4, 6, 8 and 12 hours. The resulting cumulative dissolution profiles for the tablets are based upon a theoretical percent active added to the formulations. 
     A disintegration tester measures the time it takes a tablet to break apart in solution. The tester suspends tablets in a solution bath for visual monitoring of the disintegration rate. Both the time to disintegration and the disintegration consistency of all tablets are measured. The disintegration profile is determined in a USP Disintegration Tester in pH 5.8 phosphate buffer. Samples, 1 ml at each time-point, may be taken, for example, without media replacement at 0.5, 1, 2, 3, 4, 5, 6, 7 and 8 hours. The resulting cumulative disintegration profiles are based upon a theoretical percent active added to the formulation is determined. 
     Tablet hardness changes rapidly after compression as the tablet cools. In the case of the presently disclosed gastric retentive dosage forms, a tablet that is too hard may not be able to imbibe fluid rapidly enough to prevent passage through the pylorus in a stomach in a fed mode. A tablet that is too soft may break apart, not handle well, and can create other defects in manufacturing. A soft tablet may not package well or may not stay together in transit. 
     After tablets are formed by compression, it is desired that the tablets have a strength of at least 9-25 Kiloponds (Kp)/cm 2 , preferably at least about 12-20 (Kp)/cm 2 . A hardness tester is used to determine the load required to diametrically break the tablets (crushing strength) into two equal halves. The fracture force may be measured using a Venkel Tablet Hardness Tester, using standard USP protocols. 
     Friability is a well-known measure of a tablet&#39;s resistance to surface abrasion that measures weight loss in percentage after subjecting the tablets to a standardized agitation procedure. Friability properties are especially relevant during any transport of the dosage form as any fracturing of the final dosage form will result in a subject receiving less than the prescribed medication. Friability can be determined using a Roche Friability Drum according to standard USP guidelines that specify the number of samples, the total number of drum revolutions and the drum rpm to be used. Friability values of from 0.8 to 1.0% are regarded as constituting the upper limit of acceptability. 
     The prepared tablets are tested for content uniformity to determine if they meet the pharmaceutical requirement of &lt;6% relative standard deviation (RSD). Each tablet is placed in a solution of 1.0 N HCl and stirred at room temperature until all fragments have visibly dissolved. The solution containing the dissolved tablet is analyzed by HPLC. 
     In another aspect, a method of making a bilayer tablet comprising a gastric retentive extended-release layer and an immediate release layer is provided. In a further aspect, the gastric retentive extended-release layer is wet-granulated using the fluid bed or high shear granulation process. In yet a further aspect, the immediate release layer is wet-granulated using the fluid bed or high shear granulation process. 
     VI. METHODS OF TREATING PAIN 
     In another aspect, a subject suffering from pain or at risk of experiencing pain is treated by oral administration of a gastric retentive extended release dosage form as described above. Treatment of both acute pain and chronic pain are contemplated. 
     The gastric retentive dosage forms described herein are useful for treating numerous pain states that are currently being treated with conventional immediate formulations comprising acetaminophen. These and additional pain states include, by way of illustration and not limitation, headache pain, pain associated with migraine, neuropathic pain selected from the group consisting of diabetic neuropathy, HIV sensory neuropathy, post-herpetic neuralgia, post-thoracotomy pain, trigeminal neuralgia, radiculopathy, neuropathic pain associated with chemotherapy, reflex sympathetic dystrophy, back pain, peripheral neuropathy, entrapment neuropathy, phantom limb pain, and complex regional pain syndrome, dental pain, pain associated with a surgical procedure and or other medical intervention, bone cancer pain, joint pain associated with psoriatic arthritis, osteoarthritic pain, rheumatoid arthritic pain, juvenile chronic arthritis associated pain, juvenile idiopathic arthritis associated pain, Spondyloarthropathies (such as ankylosing spondylitis (Mb Bechterew) and reactive arthritis (Reiter&#39;s syndrome)) associated pain, pain associated with psoriatic arthritis, gout pain, pain associated with pseudogout (pyrophosphate arthritis), pain associated with systemic lupus erythematosus (SLE), pain associated with systemic sclerosis (scleroderma), pain associated with Behcet&#39;s disease, pain associated with relapsing polychondritis, pain associated with adult Still&#39;s disease, pain associated with transient regional osteoporosis, pain associated with neuropathic arthropathy, pain associated with sarcoidosis, arthritic pain, rheumatic pain, joint pain, osteoarthritic joint pain, rheumatoid arthritic joint pain, juvenile chronic arthritis associated joint pain, juvenile idiopathic arthritis associated joint pain, Spondyloarthropathies (such as ankylosing spondylitis (Mb Bechterew) and reactive arthritis (Reiter&#39;s syndrome)) associated joint pain, gout joint pain, joint pain associated with pseudogout (pyrophosphate arthritis), joint pain associated with systemic lupus erythematosus (SLE), joint pain associated with systemic sclerosis (scleroderma), joint pain associated with Behcet&#39;s disease, joint pain associated with relapsing polychondritis, joint pain associated with adult Still&#39;s disease, joint pain associated with transient regional osteoporosis, joint pain associated with neuropathic arthropathy, joint pain associated with sarcoidosis, arthritic joint pain, rheumatic joint pain, acute pain, acute joint pain, chronic pain, chronic joint pain, inflammatory pain, inflammatory joint pain, mechanical pain, mechanical joint pain, pain associated with the fibromyalgia syndrome (FMS), pain associated with polymyalgia rheumatica, monarticular joint pain, polyarticular joint pain, nociceptive pain, psychogenous pain, pain of unknown etiology, pain mediated by IL-6, IL-6 soluble receptor, or IL-6 receptor, pain associated with a surgical procedure in a patient with a clinical diagnosis of OA, pain like static allodynia, pain like dynamic allodynia, pain associated with Crohn&#39;s disease, and/or pain associated with completion of a large number of patent applications within a limited interval of time. 
     Generally, the frequency of administration of a particular dosage form is determined to provide the most effective results in an efficient manner without overdosing and varies according to the following criteria: (1) the characteristics of the particular drug(s), including both its pharmacological characteristics and its physical characteristics, such as solubility; (2) the characteristics of the swellable matrix, such as its permeability; and (3) the relative amounts of the drug and polymer. In most cases, the dosage form is prepared such that effective results are achieved with administration once every eight hours, once every twelve hours, or once every twenty-four hours. As previously discussed, due to the physical constraints placed on a tablet or capsule that is to be swallowed by a patient, most dosage forms can only support a limited amount of drug within a single dosage unit. 
     In one embodiment, the dosage form allows a dosing frequency of two times a day (b.i.d.) or three times a day (t.i.d.) to result in sustained plasma concentration of both drugs as compared to current immediate release products that require more frequent administration for effective sustained pain relief. The total daily dose may be about 500 mg, 750 mg, 1000 mg, 1250 mg, 1500 mg, 1750 mg, 2000 mg, 2250 mg, 2500 mg, 2750 mg, 3000 mg, 3250 mg or 3500 mg. In another embodiment, the total daily dose is about 500 mg to 4000 mg, about 1000 mg to 3000 mg or about 1500 mg to 3000 mg. It is understood that the total daily dose may be administered as a single dose, wherein a number of acetaminophen tablets providing the full daily dose are administered at a single time, e.g, with a morning, afternoon or evening meal. Alternatively, the total daily dose may be administered in two or three separate times. For example, a total daily dose of 3000 mg may be administered by oral ingestion of 1500 mg two times per day (24 hours) or 1000 mg three times per day. Additionally, when a total daily dose is administered two or three times per day, asymmetrical dosing may be carried out such that unequal doses are provided at the separate times. 
     Within the context of the present disclosure, the gastric retentive dosage forms have the advantage of improving patient compliance with administration protocols because the drugs may be administered in a once-daily or twice-daily dosing regimen, rather than the multiple dosing administrations necessary for the immediate release dosage forms of acetaminophen in order to maintain a desired level of pain relief. One embodiment of the invention relates to a method of administering a therapeutically effective amount of acetaminophen to a patient in need thereof, comprising administering the acetaminophen or pharmaceutically acceptable salts thereof, in a gastric retentive dosage form once in the morning or evening in a once a day daily regime. Another embodiment comprises administering the gastric retentive dosage form twice a day, for example once in the morning and once in the evening in a twice a day daily dosage regime. 
     For all modes of administration, the gastric retentive dosage forms described herein are preferably administered in the fed mode, i.e., with or just after consumption of a small meal (see U.S. Publication No. 2003/0104062, herein incorporated by reference). When administered in the evening fed mode, the gastric retentive dosage form may provide the subject with continued relief from pain through the night and into the next day. The gastric retentive dosage form of the present invention is able to provide pain relief for an extended period of time because the dosage form allows for both extended release of the acetaminophen and the superior absorption of the drug in the GI tract. 
     In some aspects, the postprandial or fed mode can also be induced pharmacologically, by the administration of pharmacological agents that have an effect that is the same or similar to that of a meal. These fed-mode inducing agents may be administered separately or they may be included in the dosage form as an ingredient dispersed in the shell, in both the shell and the core, or in an outer immediate release coating. Examples of pharmacological fed-mode inducing agents are disclosed in U.S. Pat. No. 7,405,238, entitled “Pharmacological Inducement of the Fed Mode for Enhanced Drug Administration to the Stomach,” inventors Markey, Shell, and Berner, the contents of which are incorporated herein by reference. 
     The ability to treat a subject suffering from a pain state though a once- or twice-daily dosing schedule has a distinct advantage over the currently needed thrice-daily dosing of current marketed forms of extended release acetaminophen. This advantage involves both convenience and more stable drug levels in the blood. This once- or twice-daily dosage form requires that the dosage form contains enough acetaminophen to provide pain relief over an extended period approximating twelve hours. The extended release dosage form must contain sufficient amounts of acetaminophen and must release the drug upstream of the primary site of absorption, the small intestine. The applicants have overcome obstacles in formulating a stable dosage form that contains both high amounts of acetaminophen and extended release which allows once- or twice-daily dosing. 
     EXAMPLES 
     The following examples illustrate certain aspects and advantages of the present invention, however, the present invention is in no way considered to be limited to the particular embodiments described below. 
     Example 1 
     Formulation of Gastric Retentive Tablets Having 650 mg Acetaminophen 
     Prototype gastric retentive (GR) tablets containing 650 mg acetaminophen in a gastric retentive layer were developed as follows. 
     A granulation of acetaminophen (Acetaminophen USP; Spectrum Chemical Mfg. Corp.) and binder (Plasdone K29/32; ISP Technologies) was dry blended in a glass jar with the other excipients listed in the table below. Tablets were then hand made on a Carver Auto C Press (Fred Carver, Inc., Ind.), compressing the granulation mixture into a tablet using a 0.3937″×0.7086″ Modified Oval die (Natoli Engineering, St. Charles, Mo.). The parameters for the operation of the Carver Auto C Press were as follows: 3000 lbs. force, 0 second dwell time (the setting on the Carver Press), and 100% press speed The formulation for two tablet prototypes (Samples 1 and 2) is set forth in Table 1 below. The numbers in Table 1 reflect the amount of acetaminophen active ingredient present in each tablet. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Sample 1 
                 Sample 2 
               
               
                   
                   
                 GR-6 
                 GR-8 
               
               
                   
                 Ingredient 
                 Mg (wt %) 
                 Mg (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Acetaminophen 
                 650 (72.7)  
                 650 (72.7) 
               
               
                   
                 POLYOX ® 1105 
                 89 (10.0) 
                 179 (20.0) 
               
               
                   
                 POLYOX ® N80 
                 89 (10.0) 
                 — 
               
               
                   
                 Plasdone ® K29/32 
                 56 (6.3)  
                 56 (6.3) 
               
               
                   
                 Magnesium Stearate 
                 9 (1.0) 
                  9 (1.0) 
               
               
                   
                   
               
            
           
         
       
     
     Release rate characteristics of the GR tablets were investigated and compared to commercially available Tylenol® ER 8 Hour Caplets, using a USP Dissolution Apparatus 1 containing pH 5.8 phosphate buffer. The results are presented in Table 2 below and illustrated in  FIG. 1 . 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Cumulative 
                   
               
               
                   
                 Cumulative Release (%) 
                 Release (%) 
                 Cumulative 
               
               
                 Time 
                 Sample 1 
                 Sample 2 
                 Release (%) 
               
               
                 (hours) 
                 GR-6 
                 GR-8 
                 Tylenol ® ER 
               
               
                   
               
             
            
               
                 0.5 
                 12.00 
                   
                 57.20 
               
               
                 1.0 
                 21.72 
                 17.46 
                 66.06 
               
               
                 2.0 
                 41.51 
                 30.45 
                 78.38 
               
               
                 4.0 
                 72.98 
                 55.35 
                 93.52 
               
               
                 6.0 
                 91.51 
                 74.92 
                 96.80 
               
               
                 8.0 
                 98.31 
                 87.42 
                 97.27 
               
               
                   
               
            
           
         
       
     
     Example 2 
     Prototype tablets were then formulated using a direct compression grade of acetaminophen, Acetaminophen DC90 Fine (Zhejiang Kangle Pharmaceutical Co., Ltd., Wenzhou, China), which contains 90% by weight acetaminophen and 10% by weight excipients, to contain different blends of hydrophilic polymers. This granular powder of acetaminophen and associated excipients was dry blended with other excipients in amounts detailed in Table 3, and tablets were hand made on a Carver Press as described in Example 1. Samples 3-5 were pressed into single GR layer tablets, whereas Samples 6 and 7 were bilayer tablets in which the GR layers were compressed with an immediate release layer having the formulations presented in Table 4. As with the GR layers, the IR layer was generated by dry blending direct compression grade acetaminophen with other excipients prior to compression into a bilayer tablet. The percent weight composition of the GR layer in Samples 6 and 7 are the same as that of Sample 4. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 R86-88-1 
                 R86-88-2 
                 R86-88-3 
                 R86-88-4 
                 R86-88-5 
               
               
                   
                 Sample 3 
                 Sample 4 
                 Sample 5 
                 Sample 6* 
                 Sample 7* 
               
               
                 Ingredient 
                 Mg (wt %) 
                 Mg (wt %) 
                 Mg (wt %) 
                 Mg (wt %) 
                 Mg (wt %) 
               
               
                   
               
             
            
               
                 Acetaminophen 
                 722 (74.0) 
                 722 (74.0) 
                 722 (74.0) 
                 614 (74.0) 
                 507 (74.0) 
               
               
                 DC90 Fine 
               
               
                 POLYOX ® 
                 244 (25.0) 
                 — 
                 — 
                 — 
                 — 
               
               
                 WSR-301 
               
               
                 POLYOX ® N60K 
                 — 
                 244 (25.0) 
                 — 
                 208 (25.0) 
                 171 (25.0) 
               
               
                 POLYOX ® 
                 — 
                 — 
                 244 (25)     
                 — 
                 — 
               
               
                 N-1105 
               
               
                 Magnesium 
                 10 (1.0) 
                 10 (1.0) 
                 10 (1.0) 
                  8 (1.0) 
                  7 (1.0) 
               
               
                 Stearate 
               
               
                   
               
               
                 *Bi-layer tablets 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 R86-88-4 
                 R86-88-5 
               
               
                   
                   
                 Sample 6 
                 Sample 7 
               
               
                   
                 Ingredient 
                 Mg (wt %) 
                 Mg (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Acetaminophen 
                 110 (68.8) 
                 220 (74.0) 
               
               
                   
                 DC90 Fine 
               
               
                   
                 Microcrystalline 
                  50 (31.2) 
                  50 (18.5) 
               
               
                   
                 Cellulose 
               
               
                   
                   
               
            
           
         
       
     
     Release rate characteristics of the Samples 4 and 5 were investigated using a USP Disintegration Apparatus and Dissolution Apparatus 1 containing pH 5.8 phosphate buffer. The results are presented in Tables 5 and 6 below and are presented as graphs in  FIGS. 2 and 3 . 
     
       
         
           
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Cumulative 
                 Cumulative 
               
               
                   
                 Release (%) 
                 Release (%) 
               
               
                   
                 Sample 4 
                 Sample 5 
               
               
                 Time (hours) 
                 GR8 
                 GR6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1.0 
                 16.1 
                 22.7 
               
               
                 2.0 
                 27.0 
                 40.4 
               
               
                 4.0 
                 47.2 
                 66.8 
               
               
                 6.0 
                 65.0 
                 83.9 
               
               
                 8.0 
                 80.1 
                 94.2 
               
               
                 12.0 
                 98.2 
                 98.1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Cumulative 
                 Cumulative 
               
               
                   
                 Release (%) 
                 Release (%) 
               
               
                   
                 Sample 4 
                 Sample 5 
               
               
                 Time (hours) 
                 GR8 
                 GR6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1.0 
                 12.4 
                 13.2 
               
               
                 2.0 
                 19.2 
                 22.7 
               
               
                 4.0 
                 30.8 
                 39.9 
               
               
                 6.0 
                 41.2 
                 54.7 
               
               
                 8.0 
                 50.5 
                 66.7 
               
               
                 12.0 
                 66.0 
                 81.8 
               
               
                   
               
            
           
         
       
     
     Release rate characteristics of the Samples 6 and 7 (bi-layer tablets) were investigated using a USP Disintegration Apparatus containing pH 5.8 phosphate buffer. The results are presented in Tables 7 and 8 below and are presented as a graph in  FIG. 3 . The release from the GR layers was calculated by subtraction of the nominal amount of acetaminophen in the IR layer of tablet. 
     
       
         
           
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                 Sample 6 
                 Sample 7 
               
               
                   
                 100 mg IR/550 mg 
                 200 mg IR/450 mg 
               
               
                 Time (hours) 
                 GR8 
                 GR6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 0.5 
                 23.7 
                 37.8 
               
               
                 1.0 
                 29.6 
                 43.5 
               
               
                 2.0 
                 39.8 
                 53.1 
               
               
                 4.0 
                 59.4 
                 71.9 
               
               
                 6.0 
                 75.4 
                 88.8 
               
               
                 8.0 
                 89.2 
                 96.4 
               
               
                 12.0 
                 98.2 
                 98.6 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Sample 6 
                 Sample 7 
               
               
                   
                 100 mg IR/550 mg 
                 200 mg IR/450 mg 
               
               
                 Time (hours) 
                 GR8 
                 GR6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 0.5 
                 21.6 
                 34.9 
               
               
                 1.0 
                 25.5 
                 39.2 
               
               
                 2.0 
                 31.6 
                 45.5 
               
               
                 4.0 
                 42.1 
                 55.6 
               
               
                 6.0 
                 51.5 
                 64.4 
               
               
                 8.0 
                 59.9 
                 72.0 
               
               
                 12.0 
                 73.1 
                 83.1 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Erosion Studies for the 650 mg Gastric Retentive Tablet 
     This was a study in 5 healthy female beagle dogs weighing between 12-16 kg to determine the erosion time of acetaminophen gastric retentive extended-release tablets. Following an overnight fast of at least 14 hours, the dogs were fed 100 g of canned dog food (Pedigree® Traditional ground Dinner with Chunky Chicken). Within 15 minutes of the dog consuming the meal they were administered an acetaminophen gastric retentive extended-release tablet. 
     Erosion of the gastric retentive extended-release acetaminophen tablets was assessed using fluoroscopy. Each tablet contained two radio-opaque strings in the shape of an “X”. Separation of the strings was considered to signify complete erosion of the tablets. Images were obtained every 30 min until the strings separated. The results showed that the erosion time for the 650 mg GR tablets was 4.6±0.5 hours. This predicts an erosion time of about 8 hours in humans. 
     Example 4 
     Formulation of Gastric Retentive Tablets Having 1000 mg Acetaminophen 
     Prototype tablets having both an immediate release (IR) layer and a gastric retained (GR) extended release layer were formulated as described below. The IR layer contained 300 mg acetaminophen and the GR layer contained 700 mg acetaminophen. The tablets were formulated using acetaminophen in the form of COMPAP® PVP3 (Mallinckrodt, Inc.) which is a pregranulated composition having about 97% acetaminophen and 3% povidone USP. 
     The GR layer contained 700 mg acetaminophen via the pregranulated COMPAP® PVP3 product (wherein about 4 wt % PVI is the binder), magnesium stearate, and poly(ethylene oxide), the types and amounts of which are provided in Table 9 below. Amounts and wt % of acetaminophen refer to amounts and wt % of the active agent, not of the pregranulated COMPAP® composition. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                   
                   
                 Sample 10 
                   
                   
               
               
                   
                   
                 Sample 9 
                 10% 60K/10% 
                 Sample 11 
                 Sample 12 
               
               
                   
                   
                 20% N-60K 
                 WSR-301 
                 15% WSR-301 
                 20% WSR-301 
               
               
                 Ingredient 
                 Function 
                 Mg (wt %) 
                 Mg (wt %) 
                 Mg (wt %) 
                 Mg (wt %) 
               
               
                   
               
             
            
               
                 COMPAP ® 
                 Active Agent 
                 729 (79.5) 
                  729 (79.5) 
                 729 (84.5) 
                 729 (79.5) 
               
               
                 PVP3 
               
               
                 POLYOX ® 
                 Swellable, erodible 
                 183 (20)     
                 92 (10) 
                 — 
                 — 
               
               
                 N60K 
                 polymer 
               
               
                 POLYOX ® 
                 Swellable, erodible 
                 — 
                 92 (10) 
                 129 (15)     
                 183 (20)     
               
               
                 WSR-301 
                 polymer 
               
               
                 Magnesium 
                 Lubricant 
                  5 (0.5) 
                     5 (0.5) 
                  5 (0.5) 
                  5 (0.5) 
               
               
                 Stearate 
                   
                   
                   
                   
               
               
                   
                 Total GR layer 
                 917 mg 
                 917 mg 
                 863 mg 
                 863 mg 
               
               
                   
                 weight 
               
               
                   
               
            
           
         
       
     
     The IR layer contained 300 mg acetaminophen via the pregranulated COMPAP® PVP3 product (wherein about 4 wt % PVI is the binder) dry blended with a disintegrant, and a lubricant as shown in Table 10 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 Ingredient 
                 Function 
                 Mg (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 COMPAP ® 
                 Pregranulated 
                 312.7 (96.5) 
               
               
                   
                 PVP3 
                 Active Agent 
               
               
                   
                 Polyplasdone 
                 Disintegrant 
                  9.7 (3.0) 
               
               
                   
                 XL 
               
               
                   
                 Magnesium 
                 Lubricant 
                  1.6 (0.5) 
               
               
                   
                 Stearate 
                   
                   
               
               
                   
                   
                 Total IR layer 
                 324 mg 
               
               
                   
                   
                 weight 
               
               
                   
                   
               
            
           
         
       
     
     After dry blending the ingredients for each of the GR and IR layers, the bilayer tablets were tableted on a Carver Auto C Press (Fred Carver, Inc., Ind.) using an 11×19 mm concave cup, modified oval tooling (Natoli Engineering, Saint Charles, Mo.). 
     The acetaminophen cumulative release profiles for each of the bilayer tablets was determined by both dissolution and disintegration methods. The dissolution was determined in a USP apparatus (40 mesh baskets), 100 rpm, in 900 ml of 0.1 N HCl at 37.4° C. Samples, 5 ml at each time point, were taken without media replacement at 1, 3, 6, 9, 12, and 15 hours. 
     Disintegration profiles were determined in a USP Disintegration Tester in 800 ml of 0.1N HCl at 37.4° C. Samples, 1 ml at each time point, were taken without media replacement at 1, 2, 4, 6, 7 and 8 hours. The final volume of the media was measured after 8 hours and an estimation of the evaporation rate was calculated into the cumulative acetaminophen release. 
     Results of the dissolution tests for the four tablets having the formulations set forth in Tables 8 and 9 are presented in Table 11. Results of the disintegration tests for the four tablets are presented in Table 12. Graphical representation of the data is provided in  FIG. 4 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 11 
               
               
                   
               
               
                 Time (hr) 
                 Sample 9 
                 Sample 10 
                 Sample 11 
                 Sample 12 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 52.7 
                 42.0 
                 40.2 
                 39.3 
               
               
                 3 
                 64.3 
                 52.3 
                 50.9 
                 50.9 
               
               
                 6 
                 76.1 
                 62.4 
                 60.5 
                 60.5 
               
               
                 9 
                 85.5 
                 70.3 
                 67.6 
                 67.6 
               
               
                 12 
                 92.0 
                 76.5 
                 73.3 
                 73.3 
               
               
                 15 
                 96.3 
                 81.6 
                 78.0 
                 78.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 12 
               
               
                   
               
               
                 Time (hr) 
                 Sample 9 
                 Sample 10 
                 Sample 11 
                 Sample12 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 52.9 
                 46.1 
                 44.8 
                 41.3 
               
               
                 2 
                 61.9 
                 55.8 
                 54.2 
                 49 
               
               
                 4 
                 76.7 
                 71.4 
                 70.3 
                 62.3 
               
               
                 6 
                 84.2 
                 84.2 
                 83.9 
                 74.4 
               
               
                 7 
                 89.3 
                 89.3 
                 89.5 
                 80.2 
               
               
                 8 
                 93.8 
                 93.8 
                 84.3 
                 85.2 
               
               
                   
               
            
           
         
       
     
     Example 5 
     Pharmacokinetic Simulation of Gastric Retentive Acetaminophen Dosage Forms 
     Pharmacokinetic simulation analysis was performed to predict a one-compartment model with first order absorption and elimination was used. The upper gastrointestinal tract was treated as a “mixing tank” (shown in  FIG. 5 ). 
     Pharmacokinetic (PK) parameters for acetaminophen (paracetamol) oral immediate release were obtained from Rawlins et al., 1977 (“Pharmacokinetics of Paracetamol (Acetaminophen) After Intravenous and Oral Administration.” Eur. J. Clin. Pharmacol. 11:283-286) and Divoll et al., 1982 (“Effect of Food on Acetaminophen Absorption in Young and Elderly Subjects.” J. Clin. Pharmacol. 22:571-576). Equations for the analytical solutions of the model were used to calculate the predicted acetaminophen plasma concentration time profiles. As acetaminophen is sparingly soluble in water, the release mechanism from the gastric retentive systems is by tablet matrix erosion (zero-order release). Plasma concentrations of acetaminophen due to the immediate release (IR) portion of the dose were calculated using Equation 2 (Eq. (2)) shown below, and that due to the extended release portion was calculated using Equation 3 (Eq. (3)) shown below. These were added to obtain the resulting plasma concentration profile. Plasma concentrations under multiple dose administration was obtained by superposition of the single dose profiles. 
     Equations for Pharmacokinetic Model for Acetaminophen GR (IR+ER): 
     Plasma Concentration 
         C ( t )= C   IR ( t )+ C   ER ( t )  (1)
 
     Immediate-Release Portion 
     
       
         
           
             
               
                 
                   
                     C 
                     IR 
                   
                   = 
                   
                     
                       
                         
                           FD 
                           IR 
                         
                         V 
                       
                        
                       
                         ( 
                         
                           
                             
                                
                               
                                 - 
                                 Kt 
                               
                             
                             - 
                             
                                
                               
                                 - 
                                 kat 
                               
                             
                           
                           
                             
                               k 
                               a 
                             
                             - 
                             K 
                           
                         
                         ) 
                       
                        
                       
                           
                       
                        
                       t 
                     
                     &gt; 
                     0 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Extended-Release Portion 
     
       
         
           
             
               
                 
                   
                     C 
                     ER 
                   
                   = 
                   
                     
                       
                         A 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                        
                       
                           
                       
                        
                       0 
                     
                     &lt; 
                     t 
                     ≤ 
                     τ 
                   
                 
               
               
                 
                   ( 
                   
                     3 
                      
                     a 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     
                       C 
                       ER 
                     
                     = 
                     
                       
                         
                           A 
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                         - 
                         
                           
                             B 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                            
                           
                               
                           
                            
                           t 
                         
                       
                       &gt; 
                       τ 
                     
                   
                    
                   
                     
 
                   
                    
                   where 
                 
               
               
                 
                   ( 
                   
                     3 
                      
                     b 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     A 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         FR 
                         0 
                       
                       VK 
                     
                      
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             
                               K 
                                
                               
                                   
                               
                                
                               
                                  
                                 
                                   - 
                                   kat 
                                 
                               
                             
                             - 
                             
                               
                                 k 
                                 a 
                               
                                
                               
                                  
                                 
                                   - 
                                   Kt 
                                 
                               
                             
                           
                           
                             
                               k 
                               a 
                             
                             - 
                             K 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     B 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         FR 
                         0 
                       
                       VK 
                     
                      
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             
                               K 
                                
                               
                                   
                               
                                
                               
                                  
                                 
                                   - 
                                   
                                     ka 
                                      
                                     
                                       ( 
                                       
                                         t 
                                         - 
                                         τ 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             - 
                             
                               
                                 k 
                                 a 
                               
                                
                               
                                  
                                 
                                   - 
                                   
                                     K 
                                      
                                     
                                       ( 
                                       
                                         t 
                                         - 
                                         τ 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                           
                           
                             
                               k 
                               a 
                             
                             - 
                             K 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 13 
               
               
                   
                   
               
               
                   
                 Input Parameter 
                 Value 
                 Units 
               
               
                   
                   
               
             
            
               
                   
                 Dose - IR + ER 
                 1000 × 2  
                 mg 
               
               
                   
                 D = D IR  +D ER   
                   
                   
               
               
                   
                 Dose - IR Portion D IR   
                 300 × 2 
                 mg 
               
               
                   
                 Dose - ER Portion D ER   
                 700 × 2 
                 mg 
               
               
                   
                 Duration of Delivery τ 
                 8 or 9* 
                 hr 
               
               
                   
                   
               
               
                   
                 
                   
                     
                       
                         
                           
                             
                               
                                 Zero 
                                  
                                 
                                     
                                 
                                  
                                 Order 
                                  
                                 
                                     
                                 
                                  
                                 Delivery 
                                  
                                 
                                     
                                 
                                  
                                 Rate 
                               
                             
                           
                           
                             
                               
                                 
                                   R 
                                   0 
                                 
                                 = 
                                 
                                   
                                     D 
                                     ER 
                                   
                                   τ 
                                 
                               
                             
                           
                         
                           
                       
                     
                   
                 
                 175 × 10 3  or 156 × 10 3   
                 μg/hr 
               
               
                   
                   
               
               
                   
                 1st Order Absorption 
                 0.912 
                 hr −1   
               
               
                   
                 Constant (under fed 
                   
                   
               
               
                   
                 mode - with food) k a   
                   
                   
               
               
                   
                 (Absorption Half-life) 
                 (0.76)  
                 (hr) 
               
               
                   
                 1st Order Elimination 
                 0.257 
                 hr −1   
               
               
                   
                 Constant K 
                   
                   
               
               
                   
                 (Half-life) 
                 (2.7)  
                 (hr) 
               
               
                   
                 Volume of Distribution V 
                 78.8 × 10 3   
                 ml 
               
               
                   
                 Oral Bioavaiability F 
                 0.89  
                 — 
               
               
                   
                   
               
               
                   
                 *GR8: 8-hour duration of release 
               
               
                   
                 GR9: 9-hour duration of release 
               
            
           
         
       
     
     All immediate release pharmacokinetic parameters used were obtained from Rawlins et al., 1977 (“Pharmacokinetics of Paracetamol (Acetaminophen) After Intravenous and Oral Administration.” Eur. J. Clin. Pharmacol. 11:283-286)), except the absorption constant for administration under the fed mode which was from Divoll et al., 1982 (“Effect of Food on Acetaminophen Absorption in Young and Elderly Subjects.” J. Clin. Pharmacol. 22:571-576). 
     Pharmacokinetic simulation of an acetaminophen extended-release dosage form having 1000 mg acetaminophen for twice-daily administration was performed for the GR8 formulation, which provides release over 8 hours. The results are shown below. 
     In  FIG. 6 , the simulation represents twice-daily dosing, in which a tablet having 300 mg acetaminophen in the immediate release layer and 700 mg acetaminophen in the gastric retentive extended release layer is administered at 12 hour intervals. 
       FIGS. 7 and 8  compares simulated plasma concentration profiles resulting from twice-daily administration of the GR8 dosage form and administration every 6 hours of an immediate release dosage form having 1000 mg acetaminophen. 
     Pharmacokinetic simulation of an acetaminophen extended-release dosage form having 1000 mg acetaminophen for twice-daily administration was performed for the GR9 formulation, which provides release over 9 hours. The results are shown below in  FIGS. 9-11 .  FIGS. 10 and 11  compare plasma concentration profiles predicted to result from twice-daily administration of the GR9 formulation or administration every 6 hours of the immediate release formulation, each having 1000 mg acetaminophen. 
     Results of the simulation studies show that gastric retentive tablets having 300 mg acetaminophen in the immediate release layer and 700 mg in the extended release gastric retentive layer, when administered every 12 hours, are predicted to provide similar onset to standard immediate release acetaminophen tablet in a fed state. Plasma acetaminophen levels are above 4 μg/ml in one hour or less after taking the dose. In addition, the plasma acetaminophen levels are slightly above or close to 4 μg/ml 12 hours after administration of the dose. A Cmin of 3.9 μg/ml was predicted for the GR8 dosage form, while a Cmin of 4.4 μg/ml was predicted for the GR9 dosage form. The data show that the AUC and Cmin values predicted to result from twice-daily dosing of the gastric retentive acetaminophen dosage formulations are similar to those that would be obtained from administration of an immediate release dosage form having 1000 mg acetaminophen when taken every 6 hours. 
     Pharmacokinetic simulation was performed for various gastric retentive extended-release dosage forms having 1000 mg acetaminophen for twice-daily administration as described herein. Plasma concentrations were predicted based on in vitro release profiles (disintegration testing) of four tablet prototypes. Simulation was performed for dosage forms in which the extended release drug layers contains (a) 20 wt % Polyox N-60 k, (b) 10 wt % Polyox N-60 k/10 wt % Polyox WSR-301, (c) 15 wt % Polyox WSR-301, or (c) 20 wt % Polyox WSR-301. The plasma concentrations were compared to that of an ideal GR9 formulation having 300 mg acetaminophen in the IR layer and 700 mg acetaminophen in the ER layer. The simulated plasma profiles are shown in  FIG. 12 .