Abstract:
A process for preparing divalproex sodium tablets is provided. The process comprises preparing a neutralized divalproex sodium solution by combining divalproex sodium, having a sodium valproate and a valproic acid moiety, with an aqueous solvent and a base, e.g., sodium hydroxide, the base being in sufficient amount to ensure neutralization of the valproic acid moiety of the divalproex sodium. The neutralized divalproex sodium solution is sprayed onto a pharmaceutically acceptable carrier, and processed to obtain divalproex sodium tablets.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 10/465,702, filed on Jun. 19, 2003; which is a continuation of U.S. patent application Ser. No. 09/785,069, filed Feb. 16, 2001, now U.S. Pat. No. 6,610,326, issued on Aug. 26, 2003, the disclosures of which are hereby incorporated by reference in their entireties. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention is related to a process for formulating divalproex sodium solid oral dosage forms. The process comprises preparing a neutralized divalproex sodium solution, wherein the valproic acid moiety of the divalproex sodium is neutralized by addition of a strong base. The neutralized divalproex sodium solution is subsequently processed into a solid dosage form, such as divalproex sodium tablets.  
         BACKGROUND OF THE INVENTION  
         [0003]    Valproic acid, or 2-propylpentanoic acid, and its salts and derivatives are compounds with anticonvulsant properties. Of these, valproic acid and its sodium salt (sodium valproate) are the most well known. U.S. Pat. No. 3,325,361 describes the use of valproic acid, sodium valproate and other salts and derivatives of valproic acid as anti-convulsants.  
           [0004]    It has been recognized by those skilled in the art that both valproic acid and sodium valproate are difficult to formulate into solid oral dosage forms. Valproic acid, for example, is an oily liquid. Sodium valproate is known to be very hygroscopic and to liquify rapidly, and is, therefore, difficult to formulate into tablets.  
           [0005]    Efforts have been made to address the problems associated with formulating valproic acid and sodium valproate into solid oral dosage forms. U.S. Pat. No. 5,049,586 (Ortega, et al.) describes valproic acid tablets having a specific composition, which tablets are said to be stable. The tablets contain valproic acid, magnesium oxide, corn starch, poyvinylpyrrolidone, sodium carboxymethylcellulose, and magnesium stearate in specific proportions.  
           [0006]    U.S. Pat. No. 5,017,613 (Aubert, et al.) describes a process for preparing a composition containing valproic acid in combination with valproate sodium, wherein the process does not use any binder or granulating solvent. In the process, a mixture of valproic acid and ethylcellulose is prepared and valproate sodium is added to the mixture to form drug granules in the absence of any binder or granulating solvent. Precipitated silica is added to the granules before the compression into tablets.  
           [0007]    Efforts have also been made to overcome the limited utility of valproic acid and sodium valproate in formulating solid dosage forms by creating a different salt form or a derivative of valproic acid. U.S. Pat. No. 4,895,873 (Schafer) describes a crystalline calcium salt of valproic acid, in which five valproic acid radicals are associated with one calcium ion. The crystalline salt, called calcium pentavalproate, is said to be non-hygroscopic.  
           [0008]    U.S. Pat. No. 4,558,070 (Bauer, et al.) describes potassium, cesium or rubidium salt of valproic acid, which is prepared by combining 4 moles of valproic acid with 1 mole of the potassium, cesium or rubidium. U.S. Pat. No. 4,699,927 (Deboeck) describes arginine, lysine, histidine, ornithine or glycine salts of valproic acid.  
           [0009]    U.S. Pat. Nos. 5,212,326 and 4,988,731 (Meade) describe divalproex sodium and its preparation. Divalproex sodium is described as an ionic oligomer in which one mole each of the valproic acid form coordinate bonds with the sodium of the sodium valproate molecule, where the valproate ion is ionically bonded to the sodium ion. Meade also describes the oligomeric compound as having better physical properties than either monomer from which it is made in that the oligomer is a crystalline, non-hygroscopic, stable solid compound.  
           [0010]    Some patents describe sustained release dosage forms for divalproex sodium, valproic acid, its salts, amides, or other derivatives. U.S. Pat. No. 5,980,943 (Ayer, et al.) describes a sustained release delivery device for administering divalproex sodium, valproic acid, and its salts and derivatives. The device comprises a semipermeable wall containing drug granules that are microencapsulated with polyalkylene oxide or carboxymethylcellulose polymer.  
           [0011]    U.S. Pat. No. 4,913,906 (Friedman, et al.) describes a controlled release dosage form containing divalproex sodium, valproic acid, valpromide and other valproic acid salts and derivatives. The composition is prepared by mixing the drug with hydroxypropyl cellulose, ethylcellulose, or esters of acrylic and methacrylic acid, and by applying high pressure to the mixture of the ingredients.  
           [0012]    U.S. Pat. No. 5,807,574 (Cheskin, et al.) describes a controlled release dosage form containing divalproex sodium and a process for its preparation. The process involves melting divalproex sodium and mixing it with a molten wax to form a divalproex sodium-wax composite. The drug-wax mixture is formulated into a capsule.  
           [0013]    U.S. Pat. No. 5,169,642 (Brinker, et al.) describes a sustained release dosage form containing granules of divalproex sodium, valproic acid or amides or esters or salts thereof and a polymeric viscosity agent. The drug is coated with a sustained release composition comprising specified portions of ethylcellulose or a methacrylic methylester, plasticizer, and detactifying agent.  
           [0014]    U.S. Pat. No. 5,068,110 (Fawzi, et al.) describes various delayed-release tablets and capsules currently marketed, including the delayed-release divalproex sodium tablets manufactured by Abbott Laboratories, and states that the stability of an enteric coated capsules is increased by the application of thicker, higher levels of the enteric coating having a thickness of 14 mg/cm 2  to 24 mg/cm 2 , alone or in combination with a hydroxypropylcellulose, hydroxymethylcellulose or hydroxypropylmethyl cellulose coating.  
           [0015]    Divalproex sodium is a oligomer having a 1:1 molar ratio of sodium valproate and valproic acid. The oligomer is described as a stable crystalline solid and is designated as sodium hydrogen bis (2-propyl pentanoate).  
           [0016]    Upon administration, divalproex dissociates into valproate ion in the gastrointestinal tract, and in that form exerts its pharmacological effect. Divalproex sodium is indicated for the treatment of patients with complex partial seizures, as well as for the treatment of mania associated with bipolar disorders and for prophylaxis of migraine headaches.  
           [0017]    U.S. Pat. No. 4,558,070 (Bauer, et al.) indicates that divalproex sodium is a highly stable, non-hygroscopic, crystalline compound. Bauer also discusses a theory behind the stability of divalproex sodium, stating that it is not a mixture of the two precursors but a chemical entity, and that in the oligomer, the outer shell of electrons of the sodium atom is filled by coordination to the oxygen atoms of both valproic acid and valproate ions, resulting in a stable complex where the sodium ion is completely surrounded by oxygen. Bauer, et al., therefore, appears to indicate that the particular oligomeric structure and the molar ratio of divalproex sodium accounts for the stability of the compound.  
           [0018]    Applicants have discovered that divalproex sodium may be formulated into stable solid oral dosage forms, even in the absence of the oligomeric structure and the equimolar ratio of sodium valproate and valproic acid.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0019]    It is an object of the invention to provide a process for preparing a divalproex sodium composition.  
           [0020]    It is a further object of the invention to provide a process for preparing a divalproex sodium composition, wherein the process comprises preparing a neutralized divalproex sodium solution by combining divalproex sodium, having a valproic acid moiety and a sodium valproate moiety, with a base (e.g., sodium hydroxide) and an aqueous solvent. The base is added in sufficient amount to ensure neutralization of the valproic acid moiety of the divalproex sodium. In the neutralized divalproex sodium solution, divalproex sodium is not present as its oligomeric structure or the 1:1 molar ratio of sodium valproate and valproic acid. The valproic acid of the divalproex sodium is neutralized. Preferably the neutralized divalproex sodium solution contains from about 20 to about 60% valproic acid activity.  
           [0021]    It is a further object of the invention to provide an oral solid dosage form containing a therapeutically effective amount of divalproex sodium wherein the divalproex sodium is not present as an oligomeric structure or a 1:1 molar ratio of sodium valproate to valproic acid. It is a further object to provide a new divalproate formulation which provides a delayed release of valproate ion when the dosage form is orally administered to human patients, which dosage form is bioavailable and provides a therapeutic effect which is considered bioequivalent to delayed release divalproex sodium tablets, manufactured by Abbot Laboratories (Depakote®).  
           [0022]    The neutralized divalproex sodium solution is sprayed onto a pharmaceutically acceptable carrier, and the resulting mixture may be processed to obtain a divalproex sodium tablet.  
           [0023]    In one embodiment of the invention, the pharmaceutically acceptable carrier comprises a plurality of particles of a material such as, for example, anhydrous lactose or microcrystalline cellulose. A granulate is formed by spraying the neutralized divalproex sodium solution onto the carrier. Additional processing steps may then be undertaken to prepare a uniform granulate suitable for formulating into tablets. Sufficient quantities of pharmaceutically necessary tableting excipients may then be admixed with the divalproex granulate, and the resulting mixture may be compressed into tablets.  
           [0024]    The divalproex sodium tablets may be coated with an enteric coating to produce delayed-release divalproex sodium tablets. Optionally, a seal coating may also be applied to the tablets before the enteric coating is provided. The enteric coated divalproex sodium tablets may be further overcoated with a film-coating.  
           [0025]    In accordance with the invention, the pharmaceutically acceptable carrier may comprise a plurality of inert beads, for example, sugar beads or nonpareil seeds. The neutralized divalproex sodium solution is sprayed onto the inert beads to produce divalproex sodium coated beads, which can then be formulated into solid dosage forms, such as capsules or tablets.  
           [0026]    In one embodiment of the invention, the divalproex sodium coated beads may additionally be coated with an enteric coating. In yet another embodiment, a seal coating may be applied to the drug containing beads prior to the application of the enteric coating. After the coatings are applied, the beads may be admixed with sufficient quantities of pharmaceutically necessary tableting excipients. Pharmaceutical tableting excipients include but are not limited to a lubricant, disintegrant, binder, glidant and/or inert diluent. The tablets thus formulated may further be coated with a film-coating.  
           [0027]    The invention is further related to a process for preparing divalproex sodium delayed release tablets, wherein the process comprises preparing a neutralized divalproex sodium solution by combining divalproex sodium, having a sodium valproate moiety and a valproic acid moiety, with sodium hydroxide and an aqueous solvent. The base (e.g., sodium hydroxide) is added in sufficient amount to ensure neutralization of the valproic acid moiety of the divalproex sodium. In the neutralized divalproex sodium solution, divalproex sodium does not retain its oligomeric structure or the 1:1 molar ratio of sodium valproate and valproic acid.  
           [0028]    The process further comprises spraying the neutralized divalproex sodium solution on a pharmaceutically acceptable carrier and processing the carrier sprayed with the neutralized divalproex sodium solution to obtain divalproex sodium granules. The granules are further processed to obtain divalproex sodium tablet cores, and an enteric coating is applied to the cores to produce divalproex sodium delayed-release tablets. In one example of the invention, a seal coating is applied to the tablet cores prior to the application of the enteric coating. The delayed-release divalproex sodium tablets may also be coated with a film-coating.  
           [0029]    In processing the divalproex sodium granules into tablets, as described above, the granules may be admixed with at least one pharmaceutically necessary excipient and compressed into the tablets. Pharmaceutically acceptable excipients include but are not limited to a lubricant, a disintegrant, a binder, a glidant and/or an inert diluent.  
           [0030]    In certain embodiments, the invention is directed to an oral solid dosage form comprising a therapeutically effective amount of neutralized divalproex sodium which provides a delayed release of valproate ion when the neutralized divalproex sodium dosage form is orally administered to human patients, said dosage form being bioavailable and providing a therapeutic effect which is bioequivalent to a reference standard which is a delayed release divalproex sodium tablet manufactured by Abbott Laboratories (Depakote®).  
           [0031]    In certain embodiments, the invention is directed to an oral solid dosage form comprising a therapeutically effective amount of neutralized divalproex sodium which provides a delayed release of valproate ion when the neutralized divalproex sodium dosage form is orally administered to human patients, said dosage form being bioavailable and providing a therapeutic effect, and said dosage form providing a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 1.8 to about 13.15 hours after oral administration.  
           [0032]    In certain embodiments, the invention is directed to an oral solid dosage form comprising a therapeutically effective dose of neutralized divalproex sodium and a pharmaceutically acceptable carrier, said dosage form providing a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 1.8 to about 13.15 hours after oral administration.  
           [0033]    The invention is also directed to a method of treating human patients, comprising administering to human patients an effective amounts of the divalproex sodium formulations prepared in accordance with the invention.  
           [0034]    The invention is further related to a method of treating complex partial seizures, mania associated with bipolar disorders, and/or migraine headaches in humans comprising orally administering an effective dose of the divalproex sodium formulations prepared in accordance with the invention.  
           [0035]    The term “neutralized divalproex sodium,” as used in the present invention, refers to divalproex sodium in which the valproic acid moiety has been neutralized by addition of a strong base, e.g., sodium hydroxide. Neutralized divalproex sodium is not an oligomer. Neutralized divalproex sodium also does not exhibit a 1:1 molar ratio of sodium valproate and valproic acid.  
           [0036]    Divalproex sodium tablet prepared using neutralized divalproex sodium solution, therefore, does not contain oligomeric divalproex sodium, nor does it exhibit 1:1 molar ratio of sodium valproate and valproic acid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims.  
         [0038]    [0038]FIG. 1 is a linear plot comparison of the 500 mg test and 500 mg reference products mean plasma valproic acid concentrations vs time of Example 13.  
         [0039]    [0039]FIG. 2 is semi-logarithmic plot comparison of the 500 mg test and 500 mg reference products mean plasma valproic acid concentrations vs time of Example 13.  
         [0040]    [0040]FIG. 3 is a linear plot comparison of the mean plasma valproic acid concentrations vs time for the 500 mg test product in the fasting and fed states, and the 500 mg reference product in the fed state of Example 14.  
         [0041]    [0041]FIG. 4 is semi-logarithmic plot comparison of the mean plasma valproic acid concentrations vs time for the 500 mg test product in the fasting and fed states, and the 500 mg reference product in the fed state of Example 14.  
         [0042]    [0042]FIG. 5 is a linear plot comparison of the 250 mg test and reference products mean plasma valproic acid concentrations vs time of Example 15.  
         [0043]    [0043]FIG. 6 is semi-logarithmic plot comparison of the 250 mg test and reference products mean plasma valproic acid concentrations vs time of Example 15.  
         [0044]    [0044]FIG. 7 is a linear plot comparison of the 125 mg test and reference products mean plasma valproic acid concentrations vs time of Example 16.  
         [0045]    [0045]FIG. 8 is semi-logarithmic plot comparison of the 125 mg test and reference products mean plasma valproic acid concentrations vs time of Example 16. 
     
    
     DETAILED DISCLOSURE OF THE INVENTION  
       [0046]    The present invention provides a process for preparing divalproex sodium solid oral dosage forms, where the process comprises preparing a neutralized divalproex sodium solution by combining divalproex sodium with an aqueous solvent and a base, the base added in sufficient quantities to ensure neutralization of the valproic acid moiety of the divalproex sodium. The pH of the neutralized divalproex sodium solution is preferably 10.8±1.0, most preferably ±0.5. In a preferred embodiment, the aqueous solvent is water.  
         [0047]    In an embodiment of the invention, the neutralized divalproex sodium solution may be prepared by dissolving divalproex sodium in a basic solution (e.g. sodium hydroxide and water). Additional sodium hydroxide may be added to ensure that the valproic acid moiety of divalproex sodium is neutralized. In a preferred embodiment, additional water is added to the neutralized divalproex sodium solution so that the resulting solution has 20-60%, most preferably 50±3%, valproic acid activity.  
         [0048]    In accordance with the present invention, the neutralized divalproex sodium solution is sprayed onto a pharmaceutically acceptable carrier, and the resulting mixture may then be processed to obtain divalproex sodium tablets.  
         [0049]    In one embodiment, the pharmaceutically acceptable carrier comprises a plurality of particles of a material that is an inert diluent, and the divalproex sodium solution is sprayed onto the carrier and dried to produce divalproex sodium granules. In another embodiment of the invention, a binder may also be combined with the neutralized divalproex sodium solution and the pharmaceutically acceptable carrier.  
         [0050]    In a preferred embodiment of the invention, the neutralized divalproex sodium solution is sprayed onto the pharmaceutically acceptable carrier in a fluid bed processor with a Wurster apparatus. In one embodiment, this process occurs at a product temperature of 42-48° C., with a spray rate of 40-80 ml/min. The divalproex sodium granules may then be dried and then sifted using a mesh screen, e.g., with a 16 mesh screen, to produce divalproex sodium granules.  
         [0051]    In a preferred embodiment, the neutralized divalproex sodium solution is diluted, e.g., with isopropyl alcohol before it is sprayed onto the carrier.  
         [0052]    The base used in the present invention can be any pharmaceutically acceptable base such as sodium carbonate, sodium bicarbonate, sodium phosphate dibasic, sodium phosphate tribasic, sodium citrate, magnesium hydroxide, magnesium carbonate, calcium carbonate, calcium phosphate, sodium hydroxide and mixtures thereof. A preferred base is sodium hydroxide.  
         [0053]    Examples of pharmaceutically acceptable carriers include, but are not limited to, calcium phosphate dihydrate, calcium sulfate dihydrate, microcrystalline cellulose, cellulose derivatives, dextrose, lactose, anhydrous lactose, spray-dried lactose, lactose monohydrate, mannitol, starches, sorbitol and sucrose. Further examples of the carrier include hydroxypropylmethylcellulose, hydroxypropylcellulose, methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethyleneglycol, cellulose acetate butyrate, hydroxyethyl cellulose, ethyl cellulose, polyvinyl alcohol, polypropylene, dextrans, dextrins, hydroxypropyl-beta-cyclodextrin, chitosan, copolymers of lactic and glycolic acid, lactic acid polymers, glycolic acid polymers, polyorthoesters, polyanyhydrides, polyvinyl chloride, polyvinyl acetate, ethylene vinyl acetate, lectins, carbopols, silicon elastomers, polyacrylic polymers, maltodextrins, fructose, inositol, trehalose, maltose raffinose, and alpha-, beta-, and gamma-cyclodextrins, and suitable mixtures of the foregoing. A preferred pharmaceutically acceptable carrier is anhydrous lactose.  
         [0054]    In certain embodiments, optional pharmaceutical excipients are added to the divalproex sodium granules in the process of formulating the granules into tablets. Such pharmaceutical excipients may include but are not limited to a lubricant, disintegrant, binder, glidant and/or diluent.  
         [0055]    Examples of lubricants include magnesium stearate, calcium stearate, oleic acid, caprylic acid, stearic acid, magnesium isovalerate, calcium laurate, magnesium palmitate, behenic acid, glyceryl behenate, glyceryl stearate, sodium stearyl fumarate, potassium stearyl fumarate, and zinc stearate.  
         [0056]    Suitable disintegrants include crospovidone, alginates, cellulose and its derivatives, clays, polyvinylpyrrolidone, polysaccharides, such as corn and potato starch, dextrins and sugars. Disintegrants, when used in the formulation, facilitates disintegration when the tablet contacts water in the gastrointestinal tract.  
         [0057]    Binders, when added to the formulation, promote granulation and/or promote cohesive compact during the direct compression into tablets. Examples of binders include acacia, cellulose derivatives, gelatin, glucose, polyvinylpyrrolidone, sodium alginate and alginate derivatives, sorbitol, and starch. Binders also include hydrophillic cellulose gums, such as methylcellulose and carboxymethylcellulose, and xanthan gum.  
         [0058]    Examples of glidants include but are not limited to corn starch, silica derivatives, and talc.  
         [0059]    Examples of inert diluents can include, but are not limited to, calcium phosphate dihydrate, calcium sulfate dihydrate, microcrystalline cellulose, cellulose derivatives, dextrose, lactose, anhydrous lactose, spray-dried lactose, lactose monohydrate, mannitol, starches, sorbitol and sucrose. Further examples of the carrier include hydroxypropylmethylcellulose, hydroxypropylcellulose, methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethyleneglycol, cellulose acetate butyrate, hydroxyethyl cellulose, ethyl cellulose, polyvinyl alcohol, polypropylene, dextrans, dextrins, hydroxypropyl-beta-cyclodextrin, chitosan, copolymers of lactic and glycolic acid, lactic acid polymers, glycolic acid polymers, polyorthoesters, polyanyhydrides, polyvinyl chloride, polyvinyl acetate, ethylene vinyl acetate, lectins, carbopols, silicon elastomers, polyacrylic polymers, maltodextrins, fructose, inositol, trehalose, maltose raffinose, and alpha-, beta-, and gamma-cyclodextrins, and suitable mixtures of the foregoing. A preferred pharmaceutically acceptable carrier is anhydrous lactose.  
         [0060]    The tablet cores described above may be coated with an enteric coating to obtain delayed-release divalproex sodium tablets that remain intact in the stomach and release the active ingredient in the intestine. Suitable enteric coating may comprise cellulose acetate phthalate, polyvinyl acetate phthalate, acrylic resins such as Eudragit L.RTM., shellac, cellulose acetate butyrate, hydroxypropyl methylcellulose phthalate or combinations thereof.  
         [0061]    Additional materials suitable for use in the enteric coating include phthalates including cellulose acetyl phthalate, cellulose triacetyl phthalate, sodium cellulose acetate phthalate, cellulose ester phthalate, cellulose ether phthalate, methylcellulose phthalate, cellulose ester-ether phthalate, hydroxy propyl cellulose phthalate, alkali salts of cellulose acetate phthalate, alkaline earth salts of cellulose acetate phthalate, calcium salt of cellulose acetate phthalate, ammonium salt of hydroxypropyl methylcellulose phthalate, cellulose acetate hexahydrophthalate, hydroxypropyl methylcellulose hexahydrophthalate, and polyvinyl acetate phthalate. The enteric materials are discussed in Remington&#39;s Pharmaceutical Sciences, 17th Ed., page 1637 (1985).  
         [0062]    The enteric coating may be applied by press coating, molding, spraying, dipping and/or air-suspension or air tumbling procedures. A preferred method of applying the enteric coating is by pan coating, where the enteric coating is applied by spraying the enteric composition onto the tablet cores accompanied by tumbling in a rotating pan. The enteric coating material may be applied to the tablet cores by employing solvents, including an organic , aqueous or a mixture of an organic and aqueous solvent. Examplary solvents suitable in applying the enteric coating include an alcohol, ketone, ester, ether, aliphatic hydrocarbon, halogenated solvents, cycloaliphatic solvents, aromatic, heterocyclic, aqueous solvents, and mixtures thereof. In a preferred embodiment, the enteric coating comprises cellacefate and diethyl phthalate in isopropyl alcohol and acetone. In preferred embodiments, the coating has a thickness from about 6% to about 8% of the final dosage form.  
         [0063]    In accordance with the invention, the divalproex sodium tablet cores may further be coated with a seal coating. In a preferred embodiment, the seal coating occurs between the tablet core and the enteric coating. The seal coating may comprise a hydrophilic polymer. Examples include but are not limited to hydroxypropyl cellulose, hydroxypropylmethylcellulose, methoxypropyl cellulose, hydroxypropylisopropylcellulose, hydroxypropylpentylcellulose, hydroxypropylhexylcellulose and any mixtures thereof.  
         [0064]    The seal coating, like the enteric coating, may be applied by press coating, molding, spraying, dipping and/or air-suspension or air tumbling procedures. A preferred method of applying the seal coating is by pan coating, where the seal coating is applied by spraying it onto the tablet cores accompanied by tumbling in a rotating pan. The seal coating material may be applied to the tablets as a suspension by employing solvents, e.g., an organic, aqueous, or a mixture of an organic and aqueous solvent. Examplary solvents suitable in applying the seal coating include aqueous-based solutions, an alcohol, ketone, ester, ether, aliphatic hydrocarbon, halogenated solvents, cycloaliphatic solvents, aromatic, heterocyclic, aqueous solvents, and mixtures thereof. In a preferred embodiment, the seal coating comprises hydroxypropyl cellulose and hydroxypropylmethylcellulose, and is delivered as a suspension using ethanol as a solvent.  
         [0065]    The divalproex sodium tablets may be overcoated with a pharmaceutically acceptable film coating, e.g., for aesthetic purposes (e.g., including a colorant), for stability purposes (e.g., coated with a moisture barrier), for taste-masking purposes, etc. For example, the tablets may be overcoated with a film coating, preferably containing a pigment and a barrier agent, such as hydroxypropylmethycellulose and/or a polymethylmethacrylate. An example of a suitable material which may be used for such overcoating is hydroxypropylmethylcellulose (e.g., Opadry®, commercially available from Colorcon, West Point, Pa.). In a preferred embodiment, an overcoating is applied to the divalproex sodium tablets that have already been coated with a seal coating and an enteric coating. The overcoat may be applied using a coating pan or a fluidized bed, and may be applied by using a solvent, preferably an aqueous solvent.  
         [0066]    The final product is optionally subjected to a polishing step to improve the appearance of the final product and also to facilitate the manipulation of the formulation post manufacture. For example, the slippery nature of the polished dosage form aids in filling printer carrier bars with the formulation and facilitates final packaging of the product. Suitable polishing agents are polyethylene glycols of differing molecular weight or mixtures thereof, talc, surfactants (e.g., Brij types, Myrj types, glycerol mono-stearate and poloxamers), fatty alcohols (e.g., stearyl alcohol, cetyl alcohol, lauryl alcohol and myristyl alcohol) and waxes (e.g., carnauba wax, candelilla wax and white wax). Preferably, polyethylene glycols having molecular weight of 3,000-20,000 are employed.  
         [0067]    In certain embodiments of the present invention, the pharmaceutically acceptable carrier onto which the neutralized divalproex sodium solution is sprayed comprises a plurality of inert beads, e.g., sugar beads. The divalproex sodium coated beads thus obtained may be coated with an enteric coating. The beads may also be coated with a seal coating, preferably the seal coating being applied before the enteric coating. The suitable enteric coating and the seal coating materials are set forth above.  
         [0068]    The divalproex sodium beads may be formulated into solid oral dosage forms. For example, the beads made be formulated into tablets by admixing them with sufficient quantities of a pharmaceutically necessary tableting excipient and compressing the resulting mixture. The pharmaceutically necessary tableting excipient is selected from the group consisting of a lubricant, a disintegrant, a binder, a glidant, an inert diluent and mixtures thereof. Suitable tableting excipients are set forth above.  
         [0069]    In certain preferred embodiments, the present invention provides a process for preparing divalproex sodium delayed-release tablets. The process comprises preparing a neutralized divalproex sodium solution by combining divalproex sodium, having a sodium valproate moiety and a valproic acid moiety, with an aqueous solvent and a base, e.g., sodium hydroxide, the bases being added in sufficient amount to ensure neutralization of the valproic acid moiety of the divalproex sodium. The process further comprises spraying the neutralized divalproex sodium solution onto a pharmaceutically acceptable diluent, processing the resulting mixture to obtain divalproex sodium granules, and processing the granules to obtain tablet cores. An enteric coating is applied to the divalproex sodium tablet cores to produce divalproex sodium delayed-release tablets. Preferably, the delayed-release tablet further comprises a seal coating, applied between the core and the enteric coating. Suitable material for the seal coating and the enteric coating, as well as the procedures for application of these coatings, are set forth above. The tablet thus produced does not contain divalproex sodium that is an oligomeric compound and does not have a 1:1 molar ratio of sodium valproate and valproic acid. Rather, the tablets of the present invention contain divalproex sodium in which the valproic acid moiety has been neutralized.  
         [0070]    The pH of the neutralized divalproex sodium solution is preferably about 10.8±0.5, and the neutralized divalproex sodium solution preferably has about 50±3% valproic acid activity. A preferred aqueous solvent for preparation of the neutralized divalproex sodium solution is water.  
         [0071]    In a preferred embodiment, the processing of the divalproex sodium granules to obtain tablets comprises drying and then screening the divalproex sodium granules, and admixing the screened divalproex sodium granules with pharmaceutically necessary excipients and compressing the resulting mixture into tablets. The pharmaceutically acceptable excipients are selected from the group consisting of a lubricant, a disintegrant, a binder, a glidant, an inert diluent and mixtures thereof. Examples of suitable excipients are listed above.  
         [0072]    In a preferred embodiment, the neutralized divalproex sodium solution is diluted with isopropyl alcohol before it is sprayed onto anhydrous lactose in a fluid bed processor with a Wurster apparatus at product temperature of, e.g., 42-48° C. and a spray rate of, e.g., 40-80 ml/min to form granules. The granules are sized through an appropriate sized screen, e.g., a 16 mesh screen. The sized granules are blended with crospovidone, anhydrous lactose, colloidal silicon dioxide and magnesium stearate and compressed into tablets. The tablets are coated with a seal coating in a coating pan with a suspension of hydroxypropylmethylcellulose, hydroxypropylethylcellulose, hydroxypropyl cellulose and magnesium stearate in ethanol. An enteric coating is then applied, also in a coating pan. The enteric coating comprises cellacefate and diethyl phthalate in isopropyl alcohol and acetone. As an optional final step, the enteric coated tablet is film coated and subjected to a polishing step.  
         [0073]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 1.8 to about 13.15 hours after oral administration.  
         [0074]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 2.6 to about 9.1 hours after oral administration.  
         [0075]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 3.7 to about 9.1 hours after oral administration.  
         [0076]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 2.7 to about 13.15 hours after oral administration.  
         [0077]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 2.7 to about 4.8 hours after oral administration in the fasted state.  
         [0078]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 5 to about 13.15 hours after oral administration in the fed state.  
         [0079]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 1.8 to about 3.5 hours after oral administration.  
         [0080]    In certain embodiments, the oral solid dosage form of the present invention provides a mean time to maximum plasma concentration (TMAX) of valproic acid at from about 2.4 to about 4 hours after oral administration.  
         [0081]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 38 to about 67 mcg/ml, based on oral administration of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0082]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 49 to about 59 mcg/ml, based on oral administration of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0083]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 46 to about 67 mcg/ml, based on oral administration in the fasted state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0084]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 38 to about 59 mcg/ml, based on oral administration in the fed state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0085]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 23 to about 33 mcg/ml, based on oral administration of a 250 mg delayed release dose of neutralized divalproex sodium.  
         [0086]    In certain embodiments, the oral solid dosage form of the present invention provides a mean maximum plasma concentration (CMAX) of valproic acid of from about 11 to about 15 mcg/ml, based on oral administration of a 125 mg delayed release dose of neutralized divalproex sodium.  
         [0087]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 763 to about 1154 mcg·hr/ml, based on oral administration of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0088]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 925 to about 976 mcg·hr/ml, based on oral administration of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0089]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 771 to about 1154 mcg·hr/ml, based on oral administration in the fasted state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0090]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 763 to about 1087 mcg·hr/ml, based on oral administration in the fed state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0091]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 323 to about 509 mcg·hr/ml, based on oral administration of a 250 mg delayed release dose of neutralized divalproex sodium.  
         [0092]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to last quantifiable concentration (AUCTLQC) of valproic acid of from about 127 to about 231 mcg·hr/ml, based on oral administration of a 125 mg delayed release dose of neutralized divalproex sodium.  
         [0093]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of 1062±227 mcg·hr/ml based on oral administration in the fasted state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0094]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of about 988 to about 1062 mcg·hr/ml based on oral administration in the fasted state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0095]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of 1038±192 mcg·hr/ml based on oral administration in the fasted state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0096]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of 988±173 mcg·hr/ml based on oral administration in the fed state of a 500 mg delayed release dose of neutralized divalproex sodium.  
         [0097]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of 471±100 mcg·hr/ml based on oral administration of a 250 mg delayed release dose of neutralized divalproex sodium.  
         [0098]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC from time zero to infinity (AUCINF) of valproic acid of 235±63 mcg·hr/ml based on oral administration of a 125 mg delayed release dose of neutralized divalproex sodium.  
         [0099]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC to last quantifiable concentration (AUCTLQC) of valproic acid which is from about 80% to about 125% of the AUC to last quantifiable concentration (AUCTLQC) of valproic acid provided by oral administration of a reference standard over the same time interval.  
         [0100]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC to last quantifiable concentration (AUCTLQC) of valproic acid which is from about 80% to about 125% of the AUC to last quantifiable concentration (AUCTLQC) of valproic acid provided by oral administration of a reference standard over the same time interval, and wherein the dosage form and the reference standard are orally administered in a fasted state.  
         [0101]    In certain embodiments, the oral solid dosage form of the present invention provides a mean AUC to last quantifiable concentration (AUCTLQC) of valproic acid which is from about 80% to about 125% of the AUC to last quantifiable concentration (AUCTLQC) of valproic acid provided by oral administration of a reference standard over the same time interval, and wherein the dosage form and the reference standard are orally administered in a fed state.  
         [0102]    In certain embodiments, the oral solid dosage form of the present invention provides provides a mean half-life (THALF) of valproic acid of about 10.9 to about 21.3 hours.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0103]    The following example illustrate various aspects of the present invention. It is not to be construed to limit the claims in any manner whatsoever.  
       EXAMPLE 1  
     Divalproex Sodium Delayed Release Tablets  
       [0104]    1. Preparation of Neutralized Divalproex Sodium Solution  
         [0105]    Neutralized divalproex sodium solution is prepared by dissolving 260 kg of divalproex sodium in about 189.49 kg purified water with 33.51 kg of sodium hydroxide. The solution is adjusted to pH 10.8±0.3 with 20% sodium hydroxide solution and adjusted to 483 kg with additional purified water to yield divalproex sodium solution with 50±3% valproic acid activity.  
         [0106]    2. Preparation Divalproex Sodium Granules  
         [0107]    11.52 kg of the neutralized divalproex sodium solution is diluted with 14.57 kg of isopropyl alcohol. The diluted solution is then sprayed onto 5.15 kg anhydrous lactose in a fluid bed processor with a Wurster apparatus at product temperature of 42-48° C. and spray rate of 40-80 ml/min to form divalproex sodium granules. The granules are sized through a sifter equipped with 16 mesh screen.  
         [0108]    3. Blending and Tableting  
         [0109]    The sifted divalproex sodium granules, 102.51 kg, are blended with 3.987 kg crospovidone, 5.695 kg anhydrous lactose, 0.57 kg colloidal silicon dioxide and 1.139 magnesium stearate to yield divalproex sodium blend. The divalproex sodium blend is then compressed to yield divalproex sodium tablets having a weight of 871 to 983 mg, with 500 mg valproic acid activity.  
         [0110]    4. Seal Coating and Enteric Coating  
         [0111]    The divalproex sodium tablet cores, 108.3 kg, are seal coated in a coating pan with a suspension of 1.34 kg hydroxypropylmethylcellulose, 1.34 kg hydroxypropylcellulose and 0.67 kg magnesium stearate in 30.15 kg ethanol. The seal coated tablets, 110.71 kg, are coated in a coating pan with a solution of 7.181 kg cellacefate (CAP) and 1.795 kg diethyl phthalate in 31.42 kg ispropyl alcohol and 31.42 kg acetone to yield enteric coated, delayed-release divalproex sodium tablets.  
         [0112]    5. Color Coating and Polishing  
         [0113]    The enteric coated tablets, 118.51 kg, are color coated with a solution of 3.291 kg Opadry Blue and 0.037 kg Vanillin in 29.62 kg water. The color coated tablets are then polished by sprinkling 0.037 kg candelilla wax powder onto the tablets while the pan is rotating to yield color-coated divalproex sodium delayed-release tablets, with 500 mg valproic acid activity.  
         [0114]    The example provided above is not meant to be exclusive. Many other variations of the present invention would be obvious to those skilled in the art, and are contemplated to be within the scope of the appended claims. For example, it will be recognized by those skilled in the art that a wide variety of pharmaceutically acceptable excipients may be utilized for their intended purpose in the process for preparing divalproex sodium tablets as described herein.  
         [0115]    The percent (%) ingredients for tablets prepared in accordance with Example 1 are listed in Table 1 below:  
                             TABLE 1                       Ingredient   Percent (%) of composition                                Divalproex Sodium Granules           Divalproex Sodium Solution   69.11       Anhydrous Lactose   30.89       Subtotal   100.00       Divalproex Sodium Blend       Divalproex Sodium Granules   90.00       Crosspovidone, NF   3.50       Anhydrous Lactose, NF   5.00       Colloidal Silicon Dioxide, NF   0.50       Magnesium Stearate, NF   1.00       Subtotal   100.00       (This total blend was compressed into tablets       as in Example 1)       Seal Coating       Divalproex Sodium tablets (compressed   97.00       blend)       Hydroxypropylmethylcellulose, USP   1.20       (Methocel E5 Premium)       Hydroxypropyl Cellulose, USP (Klucel,   1.20       EF)       Magnesium Stearate, NF   0.60       Subtotal   100.00       Enteric Coating       Divalproex Sodium(Seal Coated) Tablets   91.00       Cellacefate, NF   7.20       Diethyl Pthalate   1.80       Subtotal   100.00       Color Coat and Polishing       Divalproex Sodium (Enteric Coated)   97.24       Tablets       Opadry Blue   2.70       Vanillin, NF   0.03       Candilla Wax   0.03       Total   100.00                  
 
       EXAMPLES 2-10  
       [0116]    In Example 2, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of sodium carbonate substituted for the sodium hydroxide.  
         [0117]    In Example 3, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of sodium bicarbonate substituted for the sodium hydroxide.  
         [0118]    In Example 4, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of sodium phosphate dibasic substituted for the sodium hydroxide.  
         [0119]    In Example 5, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of sodium phosphate tribasic substituted for the sodium hydroxide.  
         [0120]    In Example 6, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of sodium citrate substituted for the sodium hydroxide.  
         [0121]    In Example 7, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of magnesium hydroxide substituted for the sodium hydroxide.  
         [0122]    In Example 8, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of magnesium carbonate substituted for the sodium hydroxide.  
         [0123]    In Example 9, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of calcium carbonate substituted for the sodium hydroxide.  
         [0124]    In Example 10, divalproex delayed release tablets were prepared in accordance with Example 1, with an equivalent amount of calcium phosphate substituted for the sodium hydroxide.  
       EXAMPLE 11  
       [0125]    In Example 11, 250 mg divalproex sodium tablets were prepared in accordance with the process of Example 1 and having the following ingredients in the respective percentages listed in the Table 2 below:  
                             TABLE 2                       Ingredient   Percent (%) of composition                                Divalproex Sodium Granules           Divalproex Sodium Solution   69.11       Anhydrous Lactose   30.89       Subtotal   100.00       Divalproex Sodium Blend       Divalproex Sodium Granules   90.00       Crosspovidone, NF   3.50       Anhydrous Lactose, NF   5.00       Colloidal Silicon Dioxide, NF   0.50       Magnesium Stearate, NF   1.00       Subtotal   100.00       (This total blend was compressed into tablets       as in Example 1)       Seal Coating       Divalproex Sodium tablets (compressed   97.00       blend)       Hydroxypropylmethylcellulose, USP   1.20       (Methocel E5 Premium)       Hydroxypropyl Cellulose, USP (Klucel,   1.20       EF)       Magnesium Stearate, NF   0.60       Subtotal   100.00       Enteric Coating       Divalproex Sodium(Seal Coated) Tablets   91.00       Cellacefate, NF   7.20       Diethyl Pthalate   1.80       Subtotal   100.00       Color Coat and Polishing       Divalproex Sodium (Enteric Coated)   97.17       Tablets       Opadry Blue   2.75       Vanillin, NF   0.04       Candilla Wax   0.04       Total   100.00                  
 
       EXAMPLE 12  
       [0126]    In Example 12, 125 mg divalproex sodium tablets were prepared in accordance with the process of Example 1 and having the following ingredients in the respective percentages listed in the Table 3 below:  
                             TABLE 3                       Ingredient   Percent (%) of composition                                Divalproex Sodium Granules           Divalproex Sodium Solution   69.11       Anhydrous Lactose   30.89       Subtotal   100.00       Divalproex Sodium Blend       Divalproex Sodium Granules   90.00       Crosspovidone, NF   3.50       Anhydrous Lactose, NF   5.00       Colloidal Silicon Dioxide, NF   0.50       Magnesium Stearate, NF   1.00       Subtotal   100.00       (This total blend was compressed into tablets       as in Example 1)       Seal Coating       Divalproex Sodium tablets (compressed   97.00       blend)       Hydroxypropylmethylcellulose, USP   1.20       (Methocel E5 Premium)       Hydroxypropyl Cellulose, USP (Klucel,   1.20       EF)       Magnesium Stearate, NF   0.60       Subtotal   100.00       Enteric Coating       Divalproex Sodium(Seal Coated) Tablets   87.00       Cellacefate, NF   10.40       Diethyl Pthalate   2.60       Subtotal   100.00       Color Coat       Divalproex Sodium (Enteric Coated)   96.97       Tablets       Opadry Blue   3.00       Vanillin, NF   0.03       Candilla Wax   —       Subtotal   100.00       Wax polish       Divalproex Sodium Color Coated Tablets   99.97       Candilla Wax   0.03       Total   100.00                  
 
       EXAMPLE 13  
       [0127]    In Example 13, a randomized, single-dose, open label, two-way crossover study design was used to compare the oral bioavailability of a 500 mg delayed release test divalproex sodium formulation prepared according to Example 1, to an equivalent oral dose of a commercially available 500 mg delayed release divalproex sodium (Depakote®, Abbott Laboratories, Lot No. 45-404-AA-21, exp. date Oct. 1, 2001), in a test population of 30 healthy adult males under fasting conditions. Sampling times were at hour 0 (within 60 minutes prior to dose), and at post-dosing hours 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, and 48. A total of 16 samples per subject were collected in each study period. All subjects consumed 240 ml (8 fl. ozs.) of room temperature tap water simultaneously, at 1.5 hours prior to each dosing, and 120 ml (4 fl. ozs.) of room temperature tap water at post-dose hours 1, 2, and 3, after each dose.  
         [0128]    The following pharmacokinetic parameters were determined from the plasma concentration data.  
         [0129]    The area under the plasma concentration versus time curve [AUCTLQC] was calculated using the linear trapezoidal rule from the zero time point to the last quantifiable concentration.  
         [0130]    The area under the plasma concentration versus time curve from zero to infinity [AUCINF] was calculated by adding C t /KELM to AUCTLQC where C t  is the last quantifiable concentration and KELM is the elimination rate constant.  
         [0131]    The maximum observed plasma concentration [CMAX] was obtained by inspection. The time to maximum plasma concentration [TMAX] was obtained by inspection.  
         [0132]    The terminal elimination rate constant [KELM] was obtained from the slope of the line, fitted by linear least squares regression, through the terminal points of the log(base e) of the concentration versus time plot for these points.  
         [0133]    The half-life [THALF] was calculated by the equation THALF=0.693/KELM.  
         [0134]    The lag time was obtained by inspection, and is the time to the first quantifiable concentration. Throughout this report the lag time will be designated as TLAG.  
         [0135]    The elimination of valproic acid from the plasma appeared to be polyphasic for most of the subjects. The elimination rate constants were estimated from the plasma valproic acid data for all subjects using the plasma concentrations of the elimination phase as determined from the plasma drug concentration vs time plots (log scale) for the individual subjects.  
         [0136]    The number of values used in the mean calculations is designated as “N”.  
         [0137]    The coefficient of variation is designated as “CV”.  
         [0138]    All concentrations are reported as mcg/ml.  
         [0139]    The mean plasma valproic acid concentration (mcg/ml) by time point values for the 500 mg test product are listed in Table 4 below:  
                                                                         TABLE 4                                   Variable*   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   30   0.000   0.000   .           C2   0.50 HR   30   0.000   0.000   .           C3   1.00 HR   30   0.000   0.000   .           C4   1.50 HR   30   1.007   4.223   419.487           C5   2.00 HR   30   6.821   16.008   234.682           C6   3.00 HR   30   35.939   25.078   69.780           C7   4.00 HR   30   53.220   13.486   25.341           C8   5.00 HR   30   53.530   8.153   15.230           C9   6.00 HR   30   48.433   6.459   13.337            C10   8.00 HR   30   41.917   6.787   16.192            C11   10.0 HR   30   36.853   6.640   18.018            C12   12.0 HR   30   32.477   6.333   19.499            C13   16.0 HR   30   25.370   5.646   22.254            C14   24.0 HR   30   16.590   4.008   24.161            C15   36.0 HR   30   9.310   2.860   30.719            C16   48.0 HR   30   5.535   2.289   41.353                                  
 
         [0140]    The mean plasma valproic acid concentration (mcg/ml) by time point values for the 500 mg reference product are listed in Table 5 below:  
                                                                         TABLE 5                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   30   0.000   0.000   .           C2   0.50 HR   30   0.000   0.000   .           C3   1.00 HR   30   0.000   0.000   .           C4   1.50 HR   30   2.411   6.805   282.222           C5   2.00 HR   30   10.666   17.813   167.010           C6   3.00 HR   30   32.770   27.142   82.826           C7   4.00 HR   30   48.193   14.491   30.069           C8   5.00 HR   30   49.414   10.230   20.703           C9   6.00 HR   30   46.633   10.055   21.562            C10   8.00 HR   30   38.970   5.182   13.297            C11   10.0 HR   30   36.117   5.734   15.875            C12   12.0 HR   30   31.997   5.484   17.139            C13   16.0 HR   30   25.177   5.263   20.904            C14   24.0 HR   30   15.816   3.859   24.397            C15   36.0 HR   30   9.348   3.090   33.057            C16   48.0 HR   30   5.219   2.354   45.108                      
 
         [0141]    The mean (arithmetic) pharmacokinetic values for the 500 mg test product are listed in Table 6 below:  
                                                                 TABLE 6                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   30   939.035   167.478   17.835           AUCINF   30   1062.032   227.412   21.413           CMAX   30   58.757   8.154   13.877           TMAX   30   3.867   0.819   21.189           KELM   30   0.051   0.010   19.526           THALF   30   14.289   3.188   22.310           TLAG   30   2.817   0.886   31.440           LAUCTLQC*   30   6.830   0.176   2.573           LAUCINF*   30   6.947   0.208   2.989           LCMAX*   30   4.064   0.135   3.318                                  
 
         [0142]    The mean (arithmetic) pharmacokinetic values for the 500 mg reference product are listed in Table 7 below:  
                                                                 TABLE 7                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   30   908.605   146.360   16.108           AUCINF   30   1023.595   221.609   21.650           CMAX   30   57.720   9.330   16.164           TMAX   30   4.267   1.760   41.258           KELM   30   0.052   0.010   19.794           THALF   30   13.959   3.338   23.912           TLAG   30   2.817   0.987   35.036           LAUCTLQC   30   6.800   0.155   2.285           LAUCINF   30   6.911   0.197   2.844           LCMAX   30   4.044   0.156   3.869                      
 
         [0143]    The results of this study indicate that the test product is bioequivalent to the reference product.  
       EXAMPLE 14  
       [0144]    In Example 14, a randomized, single-dose, open label, three-way crossover study design was used to evaluate the relative bioavailability of a 500 mg test divalproex sodium formulation prepared according to Example 11, to an equivalent dose of the commercially available 500 mg delayed release divalproex sodium (Depakote®, Abbott Laboratories, Lot No. 45-404-AA-21, exp. date Oct. 1, 2001), in a test population of 24 healthy adult males under fasted and fed conditions. Sampling times were at hour 0 (within 60 minutes prior to dose), and at post-dosing hours 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, 48, 60, 72 and 96. A total of 17 samples per subject were collected in each study period. All subjects consumed 240 ml (8 fl. ozs.) of room temperature tap water simultaneously, at 1.5 hours prior to each dosing, and 120 ml (4 fl. ozs.) of room temperature tap water at post-dose hours 1, 2, and 3, after each dose.  
         [0145]    Subjects assigned to the fed groups were given a standardized meal starting 15 minutes before their assigned dose time.  
         [0146]    Pharmacokinetic parameters were determined according to the procedure in Example 13. All concentrations are reported as mcg/ml.  
         [0147]    The mean plasma valproic acid fasting concentration (mcg/ml) by time point values for the 500 mg test product are listed in Table 8 below:  
                                                                         TABLE 8                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   22   0.000   0.000   .           C2   1.00 HR   22   0.147   0.691   469.042           C3   2.00 HR   22   15.025   19.703   131.141           C4   3.00 HR   22   42.406   20.917   49.325           C5   4.00 HR   22   46.773   16.952   36.243           C6   5.00 HR   22   50.391   11.675   23.169           C7   6.00 HR   22   44.218   5.725   12.947           C8   8.00 HR   22   40.391   10.286   25.465           C9   10.0 HR   22   35.564   10.183   28.633            C10   12.0 HR   22   31.200   8.050   25.802            C11   16.0 HR   22   24.168   5.320   22.012            C12   24.0 HR   22   14.989   3.597   23.996            C13   36.0 HR   20   9.006   2.391   26.547            C14   48.0 HR   21   5.377   2.311   42.971            C15   60.0 HR   21   3.060   1.517   49.578            C16   72.0 HR   21   1.246   1.545   124.038            C17   96.0 HR   21   0.137   0.626   458.258                      
 
         [0148]    The mean plasma valproic acid fed valproic acid fed concentration (mcg/ml) by time point values for the 500 mg test product are listed in Table 9 below:  
                                                                         TABLE 9                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   22   0.000   0.000   .           C2   1.00 HR   22   0.000   0.000   .           C3   2.00 HR   22   0.000   0.000   .           C4   3.00 HR   22   0.000   0.000   .           C5   4.00 HR   22   3.891   13.527   347.659           C6   5.00 HR   22   19.496   23.577   120.932           C7   6.00 HR   22   25.509   26.927   105.558           C8   8.00 HR   22   23.448   21.423   91.365           C9   10.0 HR   22   32.722   13.825   42.251            C10   12.0 HR   22   35.936   8.575   23.861            C11   16.0 HR   22   31.909   8.215   25.745            C12   24.0 HR   22   19.818   4.940   24.928            C13   36.0 HR   22   10.645   2.642   24.822            C14   48.0 HR   22   6.353   1.909   30.052            C15   60.0 HR   22   3.695   1.385   37.492            C16   72.0 HR   22   1.529   1.486   97.226            C17   96.0 HR   21   0.116   0.532   458.258                      
 
         [0149]    The mean plasma valproic acid fed concentration (mcg/ml) by time point values for the 500 mg reference product are listed in Table 10.  
                                                                         TABLE 10                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   22   0.000   0.000   .           C2   1.00 HR   22   0.000   0.000   .           C3   2.00 HR   22   0.000   0.000   .           C4   3.00 HR   22   2.364   11.086   469.042           C5   4.00 HR   22   2.418   11.342   469.042           C6   5.00 HR   22   13.212   20.913   158.291           C7   6.00 HR   22   21.332   27.241   127.703           C8   8.00 HR   22   16.278   20.201   124.101           C9   10.0 HR   22   19.528   19.205   98.344            C10   12.0 HR   22   26.820   16.635   62.026            C11   16.0 HR   22   30.877   10.841   35.110            C12   24.0 HR   22   22.476   7.020   31.233            C13   36.0 HR   22   12.324   3.672   29.800            C14   48.0 HR   22   7.265   2.749   37.837            C15   60.0 HR   22   4.285   1.654   38.605            C16   72.0 HR   22   2.081   1.622   77.936            C17   96.0 HR   22   0.194   0.628   324.332                      
 
         [0150]    The mean (arithmetic) pharmacokinetic values for the 500 mg test product in the fasting and fed state and the 500 mg reference product in the fed state are listed in Table 11 below:  
                                                                                                                                       TABLE 11                                   Variable   N   Mean   Std Dev   CV                                    500 mg test product fasting                AUCTLQC   21   975.674   177.522   18.195           AUCINF   21   1038.910   192.703   18.549           CMAX   22   56.159   9.937   17.695           TMAX   22   3.727   1.032   27.687           KELM   22   0.048   0.018   37.480           THALF   22   16.102   5.198   32.280           TLAG   22   2.591   0.959   37.019           LAUCTLQC   21   6.868   0.173   2.521           LAUCINF   21   6.931   0.174   2.509           LCMAX   22   4.015   0.164   4.082            500 mg test product fed                AUCTLQC   22   925.079   161.598   17.469           AUCINF   22   988.230   173.785   17.585           CMAX   22   48.718   9.948   20.420           TMAX   22   9.091   4.058   44.638           KELM   22   0.047   0.013   27.000           THALF   22   15.926   4.820   30.267           TLAG   22   6.955   2.319   33.348           LAUCTLQC   22   6.816   0.168   2.463           LAUCINF   22   6.882   0.169   2.455           LCMAX   22   3.866   0.204   5.287            500 mg reference product fed                AUCTLQC   22   913.104   184.634   20.220           AUCINF   22   977.985   191.474   19.578           CMAX   22   46.155   11.430   24.764           TMAX   22   11.909   6.148   51.626           KELM   22   0.046   0.010   21.274           THALF   22   15.839   3.344   21.111           TLAG   22   9.545   5.031   52.702           LAUCTLQC   22   6.798   0.201   2.952           LAUCINF   22   6.867   0.196   2.861           LCMAX   22   3.804   0.242   6.352                      
 
         [0151]    The results of this study indicate that the test product is bioequivalent to the reference product.  
       EXAMPLE 15  
       [0152]    In Example 15, a randomized, single-dose, open label two-way crossover study design was used to evaluate the relative bioavailability of a 250 mg test divalproex sodium formulation prepared according to Example 11, to an equivalent oral dose of the commercially available 250 mg delayed release divalproex sodium (Depakote®, Abbott Laboratories, Lot No. 44-228-AA-21, exp. date Sep. 1, 2001), in a test population of 30 healthy adult males under fasting conditions. Sampling times were at hour 0 (within 60 minutes prior to dose), and at post-dosing hours 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, 48, 60 and 72. A total of 17 samples per subject were collected in each study period. All subjects consumed 240 ml (8 fl. ozs.) of room temperature tap water simultaneously, at 1.5 hours prior to each dosing, and 120 ml (4 fl. ozs.) of room temperature tap water at post-dose hours 1, 2, and 3, after each dose.  
         [0153]    Pharmacokinetic parameters were determined according to the procedure in Example 13. All concentrations are reported as mcg/ml.  
         [0154]    The mean plasma valproic acid concentration (mcg/ml) by time point values for the 250 mg test product are listed in Table 12 below:  
                                                                         TABLE 12                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   30   0.000   0.000   .           C2   1.00 HR   30   1.896   6.337   334.264           C3   1.50 HR   30   8.014   12.102   151.013           C4   2.00 HR   30   18.034   11.489   63.707           C5   3.00 HR   30   23.559   7.579   32.171           C6   4.00 HR   30   23.903   4.320   18.073           C7   5.00 HR   30   22.063   3.874   17.560           C8   6.00 HR   30   20.137   3.447   17.120           C9   8.00 HR   30   17.067   2.878   16.862            C10   10.0 HR   30   15.040   2.769   18.413            C11   12.0 HR   30   13.147   2.291   17.425            C12   16.0 HR   30   10.464   2.201   21.031            C13   24.0 HR   30   6.981   1.752   25.100            C14   36.0 HR   30   4.047   1.220   30.153            C15   48.0 HR   30   1.690   1.521   89.993            C16   60.0 HR   30   0.572   1.089   190.432            C17   72.0 HR   30   0.086   0.473   547.723                      
 
         [0155]    The mean plasma valproic acid concentration (mcg/ml) by time point values for the 250 mg reference product are listed in Table 13 below:  
                                                                         TABLE 13                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   30   0.000   0.000   .           C2   1.00 HR   30   0.151   0.825   547.723           C3   1.50 HR   30   1.080   5.080   470.249           C4   2.00 HR   30   5.127   7.516   146.586           C5   3.00 HR   30   18.494   11.308   61.145           C6   4.00 HR   30   22.714   7.932   34.921           C7   5.00 HR   30   22.993   3.553   15.450           C8   6.00 HR   30   21.037   3.493   16.606           C9   8.00 HR   30   17.697   2.487   14.052            C10   10.0 HR   30   15.837   2.262   14.286            C11   12.0 HR   30   13.709   2.030   14.810            C12   16.0 HR   30   10.694   1.715   16.040            C13   24.0 HR   30   7.166   1.493   20.834            C14   36.0 HR   30   4.150   1.157   27.885            C15   48.0 HR   30   1.864   1.461   78.386            C16   60.0 HR   30   0.397   0.907   228.633            C17   72.0 HR   29   0.081   0.438   538.516                      
 
         [0156]    The mean (arithmetic) pharmacokinetic values for the 250 mg test product are listed in Table 14 below:  
                                                                 TABLE 14                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   30   416.079   92.598   22.255           AUCINF   30   471.240   100.583   21.344           CMAX   30   27.850   4.720   16.949           TMAX   30   2.617   0.817   31.210           KELM   30   0.050   0.009   18.460           THALF   30   14.437   2.835   19.639           LAUCTLQC   30   6.008   0.218   3.628           LAUCINF   30   6.134   0.207   3.372           LCMAX   30   3.313   0.173   5.228                      
 
         [0157]    The mean (arithmetic) pharmacokinetic values for the 250 mg reference product are listed in Table 15 below:  
                                                                 TABLE 15                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   30   406.296   82.077   20.201           AUCINF   30   460.435   84.942   18.448           CMAX   30   26.537   4.271   16.096           TMAX   30   3.617   0.887   24.539           KELM   30   0.050   0.009   17.003           THALF   30   14.228   2.491   17.506           LAUCTLQC   30   5.988   0.200   3.334           LAUCINF   30   6.116   0.181   2.963           LCMAX   30   3.266   0.164   5.034                      
 
         [0158]    The results of this study indicate that the test product is bioequivalent to the reference product.  
       EXAMPLE 16  
       [0159]    In Example 16, a randomized, single-dose, open label, two-way crossover study design was used to evaluate the relative bioavailability of a 125 mg test divalproex sodium formulation prepared according to Example 12, to an equivalent oral dose of the commercially available 125 mg delayed release divalproex sodium (Depakote®, Abbott Laboratories, Lot No. 43-099-AA-22, exp. date Aug. 1, 2001), in a test population of 30 healthy adult males under fasting conditions. Sampling times were at hour 0 (within 60 minutes prior to dose), and at post-dosing hours 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, 48, 60 and 72. A total of 17 samples per subject were collected in each study period. All subjects consumed 240 ml (8 fl. ozs.) of room temperature tap water simultaneously at 1.5 hours prior to each dosing, and 120 ml (4 fl. ozs.) of room temperature tap water at post-dose hours 1, 2, and 3, after each dose. Pharmacokinetic parameters were determined according to the procedure in Example 13. All concentrations are reported as mcg/ml.  
         [0160]    The mean plasma valproic acid concentration (mcg/ml) by time point values for the 125 mg test product are listed in Table 16 below:  
                                                                         TABLE 16                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   28   0.000   0.000   .           C2   1.00 HR   28   0.000   0.000   .           C3   1.50 HR   28   0.363   1.440   396.437           C4   2.00 HR   28   3.953   5.461   138.144           C5   3.00 HR   28   9.010   5.643   62.625           C6   4.00 HR   28   11.519   2.715   23.574           C7   5.00 HR   28   10.831   1.227   11.328           C8   6.00 HR   28   9.928   1.219   12.276           C9   8.00 HR   28   8.315   1.042   12.536            C10   10.0 HR   28   7.558   1.176   15.559            C11   12.0 HR   28   6.771   1.150   16.988            C12   16.0 HR   28   5.405   1.081   19.993            C13   24.0 HR   28   3.687   0.923   25.029            C14   36.0 HR   28   1.768   1.351   76.408            C15   48.0 HR   28   0.129   0.684   529.150            C16   60.0 HR   28   0.089   0.472   529.150            C17   72.0 HR   28   0.000   0.000   .                      
 
         [0161]    The mean values plasma valproic acid concentration (mcg/ml) by time point for the 125 mg reference product are listed in Table 17 below:  
                                                                         TABLE 17                                   Variable   Time   N   Mean   Std Dev   CV                                        C1   0.00 HR   28   0.000   0.000   .           C2   1.00 HR   28   0.709   3.070   432.773           C3   1.50 HR   28   2.240   4.482   200.085           C4   2.00 HR   28   5.220   5.485   105.076           C5   3.00 HR   28   10.204   3.905   38.266           C6   4.00 HR   28   10.891   2.636   24.204           C7   5.00 HR   28   10.001   1.692   16.915           C8   6.00 HR   28   9.388   1.172   12.489           C9   8.00 HR   28   8.134   1.065   13.093            C10   10.0 HR   28   7.340   1.217   16.575            C11   12.0 HR   28   6.689   1.173   17.532            C12   16.0 HR   28   5.381   1.200   22.307            C13   24.0 HR   28   3.637   1.240   34.096            C14   36.0 HR   28   1.615   1.392   86.154            C15   48.0 HR   27   0.160   0.829   519.615            C16   60.0 HR   28   0.107   0.567   529.150            C17   72.0 HR   28   0.000   0.000   .                      
 
         [0162]    The mean (arithmetic) pharmacokinetic values for the 125 mg test product are listed in Table 18 below:  
                                                                 TABLE 18                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   28   179.342   51.460   28.694           AUCINF   28   235.008   63.488   27.015           CMAX   28   12.930   1.442   11.150           TMAX   28   3.250   0.752   23.124           KELM   28   0.048   0.010   20.457           THALF   28   15.081   3.571   23.676           LAUCTLQC   28   5.153   0.273   5.298           LAUCINF   28   5.428   0.252   4.636           LCMAX   28   2.554   0.112   4.375                      
 
         [0163]    The mean (arithmetic) pharmacokinetic values for the 125 mg reference product are listed in Table 19 below:  
                                                                 TABLE 19                                   Variable   N   Mean   Std Dev   CV                                        AUCTLQC   28   176.864   58.355   32.994           AUCINF   28   235.357   72.420   30.770           CMAX   28   12.424   1.922   15.467           TMAX   28   3.273   1.164   35.561           KELM   28   0.049   0.012   23.995           THALF   28   14.987   3.744   24.985           LAUCTLQC   28   5.130   0.303   5.915           LAUCINF   28   5.423   0.274   5.047           LCMAX   28   2.508   0.161   6.411                      
 
         [0164]    The results of this study indicate that the test product is bioequivalent to the reference product.