A MOISTURE STABLE SOLID VALPROIC ACID FORMULATION AND A METHOD OF PREPARING THE SAME

Abstract: A moisture stable solid valproic acid formulat­ ion capable of being compressed into tablets is provided. It comprises: a) 55 to 65 weight percent of valproic acid, b) 10 to 25 weight percent of at least one filler, c) 10 to 20 weight percent of at least one disintegrant, d) 3 to 6 weight percent of at least one binder, and e) 0.5 to 1.2 weight percent of at least one lubricant. The most preferred formulation comprises: a) 60 ± 5 weight percent of valproic acid, b) 20 ± 5 weight percent of magnesium oxide, c) 15 ± 1 weight percent of corn starch, d 1 ) 3 ± 0.2 weight percent of polyvinylpyrrolidone, d 2 ) 1 ± 0.4 weight percent of sodium carboxymethylcellu­ lose, and e) 1 ± 0.2 weight percent of magnesium stearate.

Description: This invention relates to the formulation of valproic acid, which is a liquid, into solid pharmaceutical form, in particular tablets. The formulations of the invention provide valproic acid in a solid, moisture stable form without resort to protective coatings. Valproic acid or its salts have known utility as anticonvulsants. However, a number of problems are associated with formulating them in solid form. Valproic acid is disclosed in US-A-3,325,361. According to the Merck Index it is a liquid having anticonvulsant and antiepileptic activity. As a liquid it suffers from the difficulty attendant any liquid formulation; that is, it is inconvenient to use since the precise volume necessary to result in administration of the proper dose must be measured for each administration and it is less easily portable than solid dosage forms. Efforts have been made to address the problems of administering valproic acid by converting it to its salt forms. However, as noted in US-A-4,301,176, the sodium salt of valproic acid is hygroscopic, therefore precluding production of a compacted tablet formulation. This patent suggests resort to calcium valproate as a chewable tablet to overcome the problems associated with tabletting sodium valproate. In US-A-4,558,070 the liquid form of valproic acid and the hygroscopic character of the sodium salt are again noted as limiting the utility of these materials as oral dosage forms. In that patent a stable non-hygroscopic compound is made by combining equimolar amounts of the acid and its sodium or calcium salt to form an oligomer. The present invention provides valproic acid as a moisture stable, solid formulation capable of being compressed into tablets. In DE-A-1 938 108 it is noted that oily or liquid glucofuranosides can be converted to a granular material by treating them with a considerable amount of magnesium trisilicate, whereby the glucofuranosides are adsorbed on the latter. The big amount of magnesium trisilicate necessary for the adsorption of the active ingredient is inappropriate in cases where the active ingredient has to be administered in high amounts to reach therapeutic levels as is the case for valproic acid. By means of the method of the invention valproic acid can be formulated into a dry, non-hygroscopic powder. The powder is suitable for use in forming compacted tablets or for filling capsules. No protective coatings or other special packaging or protective measures are required to maintain the stability of the formulation against moisture. The invention relates to a moisture stable valproic acid formulation comprising: a) 55 to 65 weight percent of valproic acid, b) 10 to 25 weight percent of at least one filler, c) 10 to 20 weight percent of at least one disintegrant d) 3 to 6 weight percent of at least one binder, and e) 0.5 to 1.2 weight percent of at least one lubricant. Fillers useful in the invention include alkaline earth metal oxides such as magnesium oxide and calcium oxide, earth metal oxides such as aluminium oxide, zinc oxide, clays such as magnesium silicates and aluminium silicates, and amorphous silicon dioxide. The preferred filler is magnesium oxide. It is preferred that the filler be present at a 15 to 20 weight percent level. Disintegrants are present in the formulation to facilitate disintegration in the stomach. Polysaccharides, such as corn starch, potato starch, dextrins and sugars, which swell thereby promoting disintegration are preferred. Preferred disintegrants are corn starch or potato starch, preferably at levels of 10 to 20 weight percent. Corn starch at a level of 15 weight percent is most preferred. Binders used in the formulation are preferably water soluble hydrophilic gel forming polymers. Hydrophilic cellulose gums such as methylcellulose and carboxymethylcellulose, polyvinylpyrrolidone and xanthan gum are suitable binders. The preferred binder is a combination of polyvinylpyrrolidone and sodium carboxymethylcellulose. These compounds are preferably combined in a 3:1 ratio, and the combination is preferably present in the formulation at a level of 3 to 6 weight percent. Lubricants which are useful include talc, preferably talc USP, fatty acids such as stearic and salts of fatty acids such as magnesium stearate and calcium stearate. In preferred practice, the lubricants are used at a level of 0.5 to 1.2 weight percent. The most preferred lubricant is magnesium stearate at a level of 1 weight percent. The most preferred formulation comprises: a) 60 ± 5 weight percent of valproic acid, b) 20 ± 5 weight percent of magnesium oxide, c) 15 ± 1 weight percent of corn starch, d 1 ) 3 ± 0.2 weight percent of polyvinylpyrrolidone, d 2 ) 1 ± 0.4 weight percent of sodium carboxymethylcellulose, and e) 1 ± 0.2 weight percent of magnesium stearate. The formulations are prepared as follows: Valproic acid is mixed with a solvent, preferably ethyl alcohol. The filler is slowly added with mixing and the resulting mass is dried and then milled. The disintegrant is then added with mixing. The resulting mixture is wet granulated with an alcoholic solution of the binder. The granules are dried and sized. Lubricants, optionally along with additional disintegrant and/or binder, are then mixed with the dried granules. The resultant lubricated mixture may be compressed into tablets or placed in capsules in amounts appropriate to a unit dosage - commonly 500 mg or less per tablet or capsule. As an example of the manufacture of the formulation of the invention, the preferred formulation set forth above may be made as follows. The ingredients are used in the following proportions by weight: valproic acid, 500 parts; magnesium oxide, 140 parts; ethyl alcohol, 100 parts; corn starch, 122 parts; polyvinylpyrrolidone, 25 parts; sodium carboxymethylcellulose, 5 parts; and magnesium stearate, 5 parts. The valproic acid is mixed with the ethyl alcohol (optimally in a 5:1 ratio). The magnesium oxide is added slowly while stirring, preferably with a planetary mixer. The wet mass produced is dried, for example, at 50°C in an oven for 16 hours. The dried material is milled, preferably by means of a mesh screen, most preferably a 16 or 32 mesh screen. To the milled mixture, the corn starch is added with mixing, preferably by means of a high shear mixer. The mixture is wet granulated with 25% polyvinylpyrrolidone solution in ethyl alcohol. The granules are dried, by way of example, in an oven at 60°C for 10 to 12 hours. The dried granules are sized, preferably by means of a 16 mesh screen. The sodium carboxymethylcellulose and magnesium stearate, optimally with some corn starch, are added and mixed, for example in a V-blender for ten minutes. The resulting lubricated granulation can be formed into stable solid unit dosage forms. For example, the granulation can be placed in gelatin capsules or it can be compacted into tablets. The amount of material used in each tablet or capsule is dependent on the dosage desired. As a rule, unit dosage forms contain 500 mg or less per tablet. Dosage levels and schedules would be in accordance with known practice. The formulation is moisture stable and needs no protective coating. The following examples are illustrative of the invention. Mesh data are ASTM mesh. Example 1 Manufacture of a valproic acid formulation 26 kg of valproic acid were mixed with 5 kg of ethyl alcohol. 7.5 kg of magnesium oxide were then slowly added while mixing with a planetary mixer. The wet mass was transferred to trays and dried in an oven at 50°C for 16 hours. The dried materials were sized through a 30 mesh screen and then transferred to a high shear mixer. 6.4 kg of corn starch were added with five minutes mixing. The resultant mixture was wet granulated with 5.2 kg of a 25% solution of polyvinylpyrrolidone in ethanol. Mixing was effected for 10 minutes. The wet mass was dried in an oven at 60°C for 12 hours. The dried granulation was sized through a 16 mesh sieve and transferred to a V-blender. 0.25 kg of sodium carboxymethylcellulose and 0.25 kg of magnesium stearate were added with mixing for fifteen minutes. The resulting lubricated granulation was compressed using a conventional tablet press to a tablet hardness within the range of 6 to 8 kg (Scheleuniger hardness tester). The foregoing batch provides one hundred thousand 250 mg or fifty thousand 500 mg valproic acid tablets. The granulation can be filled into hard gelatin capsules in the alternative. Example 2 Stability of the valproic acid formulation of Example 1 Tablets manufactured in accordance with Example 1 were stability tested at drastic and normal temperature and humidity conditions. The tablets were packaged in PVC blisters and then stored under three different conditions: 45°C dry oven 37°C and 75% R.H. 25°C - 28°C (room temperature) Periodically the tablets were tested for physical appearance, physico-chemical properties and valproic acid content. The following table shows the valproic acid content as percentage of the amount given on the label after storage for 6 months in drastic conditions and for three years at room temperature: The tablets disintegration time upon stability testing was as follows: Example 3 Bioavailability of valproic acid for the formulation of Example 1 Valproic acid 500 mg tablets prepared according to Example 1 were tested for bioavailability in a randomized, 3-period cross-over study, using valproic acid syrup as a control and comparing with commercially available sodium valproate enteric coated tablets. Nine healthy adult volunteers aged 18 to 35 years old were selected for the experiment. The products were randomly administered to the fasted subjects at a dose equivalent to 500 mg of valproic acid. Blood samples were withdrawn at 0.25, 0.50, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 25 and 56 hours after dosing. A waiting period of one week was allowed between treatments. Plasma samples were kept frozen until the time of analysis. Valproic acid plasma concentrations were determined by E.M.I.T. assay method (a homogeneous enzyme immunoassay commonly used to measure valproic acid concentration in biological fluids). The table below represents average values of valproic acid concentration in plasma found for the three products. The table below represents the pharmacokinetic parameters calculated for each of three products.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, LI, LU, IT, NL, SE A moisture stable solid valproic acid formulation comprising: a) 55 to 65 weight percent of valproic acid, b) 10 to 25 weight percent of at least one filler selected from alkaline earth metal oxides, earth metal oxides, zinc oxide, clays and amorphous silicon dioxide, c) 10 to 20 weight percent of at least one disintegrant selected from polysaccharides having disintegrant properties, d) 3 to 6 weight percent of at least one binder selected from hydrophilic gel forming polymers, and e) 0.5 to 1.2 weight percent of at least one lubricant selected from talc, fatty acids and salts of fatty acids. The formulation of claim 1 comprising: a) 55 to 65 weight percent of valproic acid, b) 10 to 25 weight percent of at least one filler selected from magnesium oxide, calcium oxide, aluminium oxide and zinc oxide, c) 10 to 20 weight percent of at least one disintegrant selected from corn starch and potato starch, d) 3 to 6 weight percent of at least one binder selected from hydrophilic cellulose gums, polyvinylpyrrolidone and xanthan gum, and e) 0.5 to 1.2 weight percent of at least one lubricant selected from talc, magnesium stearate and calcium stearate. The formulation of claim 1 or 2 wherein the filler is magnesium oxide. The formulation of any one of claims 1 to 3 wherein the disintegrant is corn starch. The formulation of any one of claims 1 to 4 wherein the binder is a combination of polyvinylpyrrolidone and sodium carboxymethyl cellulose. The formulation of claim 5 wherein the polyvinylpyrrolidone and the sodium carboxymethylcellulose are combined in a 3:1 ratio. The formulation of any one of claims 1 to 6 wherein the lubricant is magnesium stearate or calcium stearate. The formulation of claim 1 comprising: a) 60 weight percent of valproic acid b) 20 weight percent of magnesium oxide c) 15 weight percent of corn starch or potato starch d₁) 3 weight percent of polyvinylpyrrolidone, d₂) 1 weight percent of sodium carboxymethylcellulose, and e) 1 weight percent of magnesium stearate A method for compounding valproic acid as a moisture stable powder comprising: a) mixing valproic acid and a solvent b) slowly adding filler to the mixture resulting from step a) while mixing, c) drying the wet mass resulting from step b), d) sizing the dried material resulting from step c) e) adding a suitable disintegrant to the product of step d) and mixing, f) thereafter wet granulating the mixture resulting from step e) with an alcoholic solution of a hydrophilic water soluble polymer, and g) drying the wet granulate resulting from step f) and combining with a lubricant. Claims for the following Contracting States : GR, ES A method for compounding valproic acid as a moisture stable powder comprising: a) mixing 55-65 weight percent of valproic acid and a solvent b) slowly adding 10-25 weight percent of at least one filler selected from alkaline earth metal oxides, earth metal oxides, zinc oxide, clays and amorphous silicon dioxide to the mixture resulting from step a) while mixing, c) drying the wet mass resulting from step b), d) sizing the dried material resulting from step c) e) adding 10-20 weight percent of a disintegrant selected from polysaccharides having disintegrant properties to the product of step d) and mixing, f) thereafter wet granulating the mixture resulting from step e) with an alcoholic solution of 3-6 weight percent of at least one binder selected from hydrophilic gel forming polymers , and g) drying the wet granulate resulting from step f) and combining with 0.5 to 1.2 weight percent of at least one lubricant selected from talc, fatty acids and salts of fatty acids. A method according to claim 1, wherein: a) 55 to 65 weight percent of valproic acid, b) 10 to 25 weight percent of at least one filler selected from magnesium oxide, calcium oxide, aluminium oxide and zinc oxide, c) 10 to 20 weight percent of at least one disintegrant selected from corn starch and potato starch, d) 3 to 6 weight percent of at least one binder selected from hydrophilic cellulose gums, polyvinylpyrrolidone and xanthan gum, and e) 0.5 to 1.2 weight percent of at least one lubricant selected from talc, magnesium stearate and calcium stearate are present. A method according to claim 1 or 2 wherein the filler is magnesium oxide. A method according to any one of claims 1 to 3 wherein the disintegrant is corn starch. A method according to any one of claims 1 to 4 wherein the binder is a combination of polyvinylpyrrolidone and sodium carboxymethyl cellulose. A method according to claim 5 wherein the polyvinylpyrrolidone and the sodium carboxymethylcellulose are combined in a 3:1 ratio. A method according to any one of claims 1 to 6 wherein the lubricant is magnesium stearate or calcium stearate. A method according to claim 1, wherein: a) 60 weight percent of valproic acid b) 20 weight percent of magnesium oxide c) 15 weight percent of corn starch or potato starch d₁) 3 weight percent of polyvinylpyrrolidone, d₂) 1 weight percent of sodium carboxymethylcellulose, and e) 1 weight percent of magnesium stearate are present.

Inventors: DE PEREZ, PILAR MARTIN, DR., ORTEGA, ARACELIS M., DR.
Applicants: FARVALSA AG
Application year: 1987
Main classification: A61K31
IPC codes: A61K9, A61K31