Abstract:
New bendroflumethiazide formulations in solid form are provided which are characterized by excellent disintegration and dissolution capabilities even after long periods of storage. The new bendroflumethiazide formulations, for example, in the form of tablets, are formed of one or more excipients and a dry granulation containing one or more fillers, such as lactose and starch, and a preformed partial coprecipitate of bendroflumethiazide and a wetting agent therefor, such as polyvinyl pyrrolidone which converts the bendroflumethiazide into a more hydrophilic form.

Description:
FIELD OF THE INVENTION 
     The present invention relates to bendroflumethiazide formulations, in solid form, especially tablets, which have improved disintegration properties and dissolution properties even after storage for long periods of time, and to a method for preparing such formulations. 
     BACKGROUND OF THE INVENTION 
     Bendroflumethiazide (the generic name for 3-benzyl-3,4-dihydro-7-sulfamoyl-6-trifluoromethyl-1,2,4-benzothiadiazine 1,1-dioxide) is known as a diuretic and antihypertensive agent as disclosed in U.S. Pat. No. 3,265,573. However, bendroflumethiazide has a dissolution problem due to its hydrophobic nature and low solubility. Its in vivo bioavailability is compromised due to its poor dissolution from tablets. Reduction in particle size and selection of a fast dissolving polymorphic form improves its dissolution but not to a desired acceptable level. 
     When formulated as a tablet, bendroflumethiazide is usually in admixture with gum acacia which serves as a binder, corn starch which serves as a disintegrant, together with a lactose diluent, lubricant and water-soluble dyes. 
     The prior art bendroflumethiazide tablets are prepared by first dissolving part of the gum acacia binder and water-soluble dyes in water, adding lactose to the resulting solution, drying the mixture, reducing the resulting particles to fine granules, and then mixing such granules with the bendroflumethiazide, cornstarch and remainder of the gum acacia, and compressing the mixture into tablets. Such tablet formulations disintegrate in water after about 9 minutes and have good dissolution properties upon aging. However, tablet formulations which have improved disintegration properties and dissolution properties and are faster and cheaper to manufacture would still be most desirable. 
     DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, a unique bendroflumethiazide formulation in solid oral dosage form, especially in tablet form, is provided wherein gum acacia is not employed and therefore water is not mixed with any of the formulation ingredients. Accordingly, the bendroflumethiazide formulation of the invention is faster and less expensive to manufacture than prior art formulations, and is more stable, and has faster disintegration and dissolution times than prior art formulations. The bioavailability of bendroflumethiazide from the above type of dosage form is at a maximum equivalent to a solution form. In addition, since water is not employed in the formulation of the invention, the risk of drug degradation due to water is eliminated. 
     The solid bendroflumethiazide formulation of the invention contains one or more excipients substantially uniformly mixed with a dry granulation including one or more fillers and a preformed partial coprecipitate formed of bendroflumethiazide and a wetting or granulating agent therefor for converting the bendroflumethiazide into a more hydrophilic form. 
     In addition, the bendroflumethiazide formulation of the invention may contain an anti-hypertensive agent and/or a beta-blocking agent (which itself may or may not be an anti-hypertensive agent), such as nadolol, propranolol, or timolol, as well as anti-hypertensive drugs, such as captopril. 
     Further, in accordance with the present invention, a method is provided for preparing the new hydrophilic bendroflumethiazide formulation of the invention, which method includes the steps of forming a wet granulation of bendroflumethiazide including one or more fillers, such as lactose, starch and/or microcrystalline cellulose; wetting or granulating agent for bendroflumethiazide, such as polyvinyl pyrrolidone; and a solvent for bendroflumethiazide, such as ethanol; drying the wet granulation, for example, by use of fluid-bed or tray dryers causing the solvent to evaporate and the bendroflumethiazide and wetting agent to form a partial coprecipitate, thereby forming a dry granulation, reducing the average particle size of the dry granulation to below about 500 microns, and mixing the dry granulation with excipients to form the solid bendroflumethiazide formulation of the invention. 
     The afore-described wet granulation is formed by mixing bendroflumethiazide and fillers to form a bendroflumethiazide composition, dissolving wetting or granulating agent in the solvent to form a granulating mixture, and mixing the granulating mixture with the bendroflumethiazide composition. 
     Where it is desired to include an anti-hypertensive agent or a beta-blocking agent in the bendroflumethiazide formulation of the invention, the anti-hypertensive agent or beta-blocking agent will be separately granulated with filler and precompacted and mixed with the dry bendroflumethiazide formulation before mixing with the excipients. 
     By means of the above method, dissolution of bendroflumethiazide from the oral dosage form is substantially improved. It is believed that the improved dissolution of bendroflumethiazide is achieved by means of the wet granulation technique using the wetting agent and solvent described above which aids in wetting, dispersing and partially forming coprecipitates of the bendroflumethiazide and wetting or granulating agent. 
     In carrying out the method of the invention, in forming the wet granulation, the bendroflumethiazide will first be mixed with one or more fillers, such as starch (of the gelatinized type such as Sta Rx brand starch made by Colorcon, Inc.), lactose, microcrystalline cellulose, dicalcium phosphate, sucrose, calcium sulphate or sodium starch glycolate or mixtures thereof, with a mixture of lactose and starch being preferred, in a weight ratio of bendroflumethiazide:filler of within the range of from about 1:40 to about 1:8 and preferably from about 1:30 to about 1:15, to form the bendroflumethiazide composition. 
     The bendroflumethiazide composition is mixed with a mixture of the wetting agent and solvent employing a weight ratio of bendroflumethiazide to wetting agent of within the range of from about 0.5:1 to about 5:1 and preferably from about 0.7:1 to about 1.5:1, and a weight to volume ratio of bendroflumethiazide to solvent of within the range of from about 1:15 to about 1:45, and preferably from about 1:20 to about 1:30. The wetting agent is employed in a weight to volume ratio to the solvent of within the range of from about 1:15 to about 1:45, and preferably from about 1:20 to about 1:30. 
     Examples of wetting or granulating agents for bendroflumethiazide suitable for use herein include, but are not limited to, polyvinyl pyrrolidone, hydroxypropylmethyl cellulose, hydroxypropyl cellulose or methyl cellulose, with polyvinyl pyrrolidone being preferred. 
     Examples of solvent for bendroflumethiazide suitable for use herein include, but are not limited to, ethanol, methylene chloride, isopropanol, methanol, acetone or water, with ethanol being preferred. 
     The excipients which may be included in the bendroflumethiazide formulation of the invention include one or more disintegrants, such as sodium carboxymethyl starch, modified cellulose, cross-linked polyvinyl pyrrolidone, or corn starch, with sodium carboxymethyl starch being preferred, in an amount within the range of from about 0 to about 10% and preferably from about 1 to about 6% by weight, fillers such as any of those mentioned above, with microcrystalline cellulose being preferred, in an amount within the range of from about 0 to about 80% and preferably from about 10 to about 50%, optional colorants in an amount of from about 0 to about 6% and preferably from about 0.5 to about 2%. 
     The excipients may also include a tabletting lubricant which may comprise conventional type tabletting lubricants, such as magnesium stearate, cornstarch, talc, stearic acid or mixtures thereof with magnesium stearate being preferred, present in an amount within the range of from about 0 to about 3% and preferably from about 0.1 to about 2% by weight. All of the above percents are based upon the weight of the total bendroflumethiazide formulation. 
    
    
     Preferred table formulations in accordance with the present invention are set out below. 
     
         ______________________________________                 Most PreferredIngredient            % by Weight______________________________________Bendroflumethiazide   2.5 to 10Wetting agent(preferably polyvinyl pyrrolidone)                 2 to 6Fillers(preferably Lactose   20 to 80Starch (gelatinized)) 10 to 30ExcipientsDisintegrant (preferablySodium carboxymethyl starch and/or                 1 to 6Microcrystalline cellulose)                 10 to 50Lubricant (preferablymagnesium stearate)   0.1 to 2Color                   0 to 1.5Nadolol               11 to 36______________________________________ 
    
     The solid bendroflumethiazide formulation of the invention may comprise a tablet, capsule, pill, powder and preferably, a tablet which may take any conventional shape or size, such as square, round, oblong, pill-shape and the like. These solid forms may contain from about 0.01 to about 0.2 mg bendroflumethiazide per kg of body weight and may be formulated in dosages of 1-20 mg amounts. 
     Even in the case of the high dosage forms, the solid formulations of the invention will quickly disintegrate in water after only 1 to 5 minutes and will dissolve to 90% in 0.1 HCl within 20 minutes. 
     An anti-hypertensive compound or beta blocker, such as nadolol, may be present in amounts of from about 0.5 to about 2 mg per kg of body weight and may be formulated (with the bendroflumethiazide) in dosages of 20 to 160 mg amounts. 
     The following Examples represent preferred embodiments of the present invention. 
     EXAMPLE 1 
     A bendroflumethiazide tablet having the following composition is prepared as described below. 
     
         ______________________________________               AmountComposition         Parts by Weight______________________________________Bendroflumethiazide 2.5Polyvinyl pyrrolidone               2.5Lactose, Fast Flo (Foremost)               40Pregelatinized starch(StaRx-1500 Starch, USP)               20Microcrystalline cellulose(Avicel PH 101, NF) 33Sodium carboxymethyl starch(Explotab)          2F.D.C. Green Lake Blend               1Magnesium Stearate, USP               0.3______________________________________ 
    
     A wet granulation of bendroflumethiazide is formed as follows. Bendroflumethiazide; lactose and pregelatinized starch are mixed to form a bendroflumethiazide composition. 
     In a separate vessel, polyvinyl pyrrolidone and ethanol (in a weight to volume ratio of bendroflumethiazide to ethanol of 1:25) are mixed to form a granulating mixture. 
     The granulating mixture is then mixed with the bendroflumethiazide composition to form the wet granulation of bendroflumethiazide. 
     The wet bendroflumethiazide granulation is dried either by tray drying or fluid bed drying thereby causing the ethanol to evaporate and the bendroflumethiazide and polyvinyl pyrrolidone to form a partial coprecipitate (also referred to as a &#34;dry granulation&#34;). The resulting dry granulation is reduced in average particle size, by screening, to below about 500 microns and is then mixed with the microcrystalline cellulose, sodium carboxymethyl starch, magnesium stearate and color to form a solid bendroflumethiazide formulation which is compressed into bendroflumethiazide tablets. 
     The bendroflumethiazine tablets formed as described below allow for rapid dissolution of bendroflumethiazide therefrom. It is found that bendroflumethiazide bioavailability from these tablets, prepared using the wet granulation, is equivalent to that from solution form. 
     EXAMPLE 2 
     A bendroflumethiazide tablet having the following composition is prepared as described in Example 1. 
     
         ______________________________________               AmountComposition         Parts by Weight______________________________________Bendroflumethiazide 5Polyvinyl pyrrolidone               5Pregelatinized starch(StaRx-1500 Starch, USP)               25Microcrystalline cellulose(Avicel PH 101)     30Lactose, Fast Flo (Foremost)               80Sodium carboxymethyl starch(Explotab)          3Color               1Magnesium Stearate, USP               0.5______________________________________ 
    
     The bendroflumethiazide tablets of the above composition formed as described in Example 1 allow for rapid dissolution of bendroflumethiazide therefrom so that bioavailability of bendroflumethiazide from these tablets is equivalent to that from solution form. 
     EXAMPLE 3 
     A bendroflumethiazide tablet having the following composition is prepared as described in Example 1. 
     
         ______________________________________                    AmountComposition              Parts by Weight______________________________________Bendroflumethiazide      10Polyvinyl pyrrolidone    10Pregelatinized starch (StaRx-1500 Starch, USP)                    29Microcrystalline cellulose (Avicel PH 101)                    32Lactose, Fast Flo (Foremost)                    160Sodium carboxymethyl starch(Explotab)               5Color                    3Magnesium stearate, USP  0.8______________________________________ 
    
     The bendroflumethiazide tablets of the above composition formed as described in Example 1 allow for rapid dissolution of bendroflumethiazide therefrom so that bioavailability of bendroflumethiazide from these tablets is equivalent to that from solution form. 
     EXAMPLES 4 TO 8 
     The following bendroflumethiazide-nadolol combination tablet formulations are prepared as described below. 
     
         ______________________________________Example No.  4       5       6     7     8______________________________________Ratio Nadolol:Bendro-flumethiazide        160:5   80:5    40:5  60:5  120:5Ingredient   Parts by WeightBendroflumethiazidegranulation* 100     100     100   100   100Nadolol granulation**        240     120     60    90    180Microcrystallinecellulose (AvicelPH 102,NF)   65      95.5    58    75.5  80Sodium carboxymethylstarch (Explotab)        13.5    10      12    10.5  12Blue #2 Nu-Pariels        27      21      17.5  21    24Magnesium stearate        4.5     3.5     2.5   3     4______________________________________ *Bendroflumethiazide granulation (prepared as described in Example 1) 
    
     
         Ingredient       Parts by WeightBendroflumethiazide            5Polyvinyl pyrrolidone            5Pregelatinized starch(Sta Rx-1500 Starch, U.S.P.)            10Lactose, anhydrous            80Ethyl alcohol (is not presentin final tablet - removedduring drying)   0 **Nadolol granulationIngredient       Parts by WeightNadolol          2 partsMicrocrystalline cellulose(Avicel PH 102, NF)            1 part______________________________________ 
    
     Therefore, in the 160:5 microcrystalline cellulose:nadolol combination tablet (Example 4), in 240 parts of the nadolol granulation, 160 parts will be nadolol and 80 parts will be microcrystalline cellulose. 
     The above ingredients including bendroflumethiazide granulation and nadolol granulation and the other excipients are mixed together and compressed into tablets. 
     The above nadolol:bendroflumethiazide tablets are tested for comparative bioavailability against a 5 mg bendroflumethiazide solution in dogs employing the following test. 
     Four formulations are employed in a four-way crossover study, namely, 5 mg solution in water/ethanol (99.5:0.5 v/v) (A); 5 mg aqueous suspension (B); 5 mg reformulated tablet (C); and 5 mg bendroflumethiazide-40 mg nadolol combination tablet (D). Six female dogs each receive a single 5 mg dose of each formulation with a 7-day washout period between doses. Sequential blood samples are withdrawn for up to 12 hours after dosing. Plasma is collected from each blood sample and is analyzed by a gas chromatographic method. 
     The bioavailability results obtained indicate that the bendroflumethiazide from the combination tablet is bioequivalent to bendroflumethiazide solution.