Patent Publication Number: US-8110226-B2

Title: Drug formulations having inert sealed cores

Description:
BACKGROUND 
     The subject matter disclosed herein relates generally to pharmaceutical dosage forms comprising a drug. The pharmaceutical dosage forms generally relate to immediate release, controlled release, and/or combinations of both immediate and controlled release dosage forms. The subject matter additionally relates to formulations containing said controlled release beads, and to methods of preparing said beads. The subject matter further relates to stabilized tolterodine tartrate formulations. 
     Controlled release dosage forms, may include particles or beads containing a drug or active agent, where the particles or beads are coated with a release-controlling polymer. Controlled release beads may comprise an inert core, coated with an inner drug-containing layer and an outer membrane layer controlling drug release from the inner layer. The inert core may be a sphere or bead of sugar, a hydrophilic cellulosic polymer, or a crosslinked hydrophilic synthetic polymer. 
     Examples of controlled release beads may comprise a core unit of an inert material; an active ingredient-containing layer on the core unit, which may also contain a hydrophilic polymer; and a polymeric outer membrane layer effective for controlled release of the active ingredient. The membrane modifying and controlling the drug release can be a pH-dependent enteric coating, or a pH-independent permeable coating. Either the enteric coatings or the pH-independent permeable coatings may be used in combination with a water-soluble polymer or non-polymer as a pore forming agent to adjust the permeability of the coating layer. 
     In some controlled release beads interaction between the core layer and the active-ingredient containing layer may lead to drug degradation. For example, solid oral dosage forms containing water-soluble drugs, such as tolterodine tartrate, can undergo a slow topochemical degradation, leading to a reduction in the purity of the active ingredient and in the potency of the dosage form. Such solid oral dosage forms include tablets and solid-filled capsules. 
     Tolterodine tartrate is a muscarinic receptor antagonist that is used to treat urinary incontinence. Tolterodine acts on M2 and M3 subtypes of muscarinic receptors whereas most antimuscarinic treatments for overactive bladder only act on M3 receptors making them more selective. Tolterodine, although it acts on two types of receptors, has fewer side effects than other antimuscarinics, such as oxybutynin (which is selective for M3 receptors only) as tolterodine targets the bladder more than other areas of the body. This means that less active agents need to be given daily (due to efficient targeting of the bladder) and so there are fewer side effects. Common side effects of tolterodine tartrate include hyposalivation, constipation, and decreased gastric motility. 
     SUMMARY 
     Various exemplary embodiments disclosed herein include controlled release drug compositions including a bead or a plurality of beads. Each bead includes an inert core, and a seal layer or seal coat positioned on the core layer. The seal layer is formed from a non-polymeric hydrophobic material. A layer containing at least one active ingredient is then positioned on the seal layer; and at least one layer or membrane of at least one release-controlling polymer, with or without a pore forming agent, is positioned on the active ingredient-containing layer. In various exemplary embodiments, the active ingredient is an antimuscarinic agent, such as tolterodine. 
     In various exemplary embodiments, the release-controlling polymer is a water-insoluble, non-pH dependent polymer, with or without a pore-forming agent which becomes permeable in an aqueous environment, thereby allowing release of the active ingredient. Alternatively, the release-controlling polymer is a pH dependent enteric polymer which is insoluble in the acidic gastric juices in the stomach (pH=1-3), but which is soluble in the more neutral environment of the small intestine (pH=6-8). In various exemplary embodiments, a composite release-controlling polymer membrane may include an inner layer of a water-insoluble, non-pH dependent polymer, and an outer layer of a pH dependent enteric polymer. 
     Various exemplary embodiments include controlled release dosage forms including a plurality of beads. Each bead includes an inert core, a seal layer or seal coat positioned on the core layer, a layer containing at least one active ingredient is positioned on the seal layer; and at least one outer layer or membrane of at least one release-controlling polymer, with or without a pore forming agent, positioned on the active ingredient-containing layer. In various exemplary embodiments, the dosage forms are tablets. In various exemplary embodiments, the dosage forms are capsules. The tablets or capsules are coated with a polymer layer if desired. In various exemplary embodiments, the release-controlling polymer in the outer layer of the beads is a water-insoluble, non-pH dependent polymer, and the tablets or capsules are coated with a pH dependent enteric polymer. 
     Various exemplary embodiments disclosed herein include methods of making a controlled release drug-containing bead. These methods include a step of depositing a seal layer on an inert core. The seal layer being formed from a non-polymeric hydrophobic material. The methods also include a step of depositing a layer containing at least one active ingredient on the seal layer; and depositing a layer of at least one release-controlling polymer, with or without a pore forming agent, on the active ingredient-containing layer. 
     Various exemplary embodiments disclosed herein include methods of treating a mammal with bladder control problems, including but not limited to a human. The methods include the step of administering a controlled release dosage form comprising a plurality of controlled release beads to the patient. Each bead includes an inert core, and a seal layer or seal coat positioned on the core layer. A layer containing at least one active ingredient is then positioned on the seal layer. In various exemplary embodiments, the active ingredient includes an antimuscarinic agent, such as oxybutynin, tolterodine, or darifenacin. At least one layer or membrane of at least one release-controlling polymer, with or without a pore forming agent, is then positioned on the active ingredient-containing layer. 
     Various exemplary embodiments disclosed herein include solid oral dosage forms comprising an effective amount of a stabilized tolterodine L-tartrate and pharmaceutically acceptable excipients. The tolterodine L-tartrate is stabilized with a pharmaceutically acceptable pH-modifying acid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand various exemplary embodiments, reference is made to the accompanying drawings. 
         FIG. 1  shows a first exemplary embodiment of a controlled release bead. 
         FIG. 2  shows a second exemplary embodiment of a controlled release bead. 
         FIG. 3  shows a third exemplary embodiment of a controlled release bead. 
         FIG. 4  shows a fourth exemplary embodiment of a controlled release bead. 
         FIG. 5  shows a fifth exemplary embodiment of a controlled release bead. 
         FIG. 6  shows a sixth exemplary embodiment of an immediate release bead. 
         FIG. 7  shows a flow chart depicting the process by which various exemplary embodiments discussed herein are manufactured. 
         FIG. 8  shows dissolution of active ingredient from tolterodine tartrate capsules containing various exemplary embodiments of the controlled release beads discussed herein. 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EXEMPLARY EMBODIMENTS 
     Referring now to the drawings, in which like numerals refer to like components or steps, there are disclosed broad aspects of various exemplary embodiments. 
       FIG. 1  is a cross-sectional view of a first exemplary embodiment of a controlled release bead  10  which allows for gradual release of the drug. The exemplary bead  10  includes an inert core  1  made of a water-soluble or water-swellable material. In various exemplary embodiments, the core  1  is made of a low molecular weight sugar, such as maltose, lactose, dextrose, or sucrose. Alternatively, the core  1  is made of a hydrophilic polysaccharide, such as starch, microcrystalline cellulose, carboxymethylcellulose, croscarmellose, hydroxyethylcellulose, or hydroxypropyl methylcellulose. In various exemplary embodiments, the core  1  is made of a partially or completely water-soluble pharmaceutically acceptable inorganic salt. In various exemplary embodiments, the core  1  is made of a water-swellable synthetic polymer, such as crosslinked acrylic or methacrylic acid polymers and copolymers or crospovidone. 
     A coating  3  of a non-polymeric water-insoluble material is positioned on core  1 . The non-polymeric water-insoluble material prevents water from entering into the core  1  and causing the core  1  to dissolve or swell. In various exemplary embodiments, the non-polymeric hydrophobic material is a fatty alcohol, a fatty carboxylic acid, a fatty carboxylic acid ester, a hydrogenated oil, a triglyceride fat, a wax, or a mixture thereof. In various exemplary embodiments, the non-polymeric hydrophobic material is a C 12 -C 20  fatty alcohol, a C 12 -C 20  fatty carboxylic acid, an ester of a C 12 -C 20  fatty carboxylic acid, a hydrogenated vegetable oil, a triglyceride fat, or a mixture thereof. In various exemplary embodiments, the non-polymeric hydrophobic material is stearyl alcohol; cetyl alcohol; stearic acid; an ester of stearic acid with a lower alcohol or polyol, such as glyceryl monostearate; an ester of cetyl alcohol; hydrogenated castor oil; and a mixture thereof. 
     In various exemplary embodiments, a drug-containing coating  5  is positioned on non-polymeric water-insoluble material layer  3 . In various exemplary embodiments, coating  5  includes a drug and, optionally, a binder. In various exemplary embodiments, the drug is a water-soluble drug. Suitable water-soluble drugs include tolterodine tartrate, diltiazem hydrochloride, verapamil hydrochloride, bupropion hydrochloride, metformin hydrochloride, propranolol hydrochloride, dextromethorphan hydrobromide, diphenhydramine hydrochloride, disopyramide hydrochloride, tramadol, fluoxetine hydrochloride, paroxetine hydrochloride, pentoxifylline hydrochloride and the like. 
     In various exemplary embodiments, the drug in coating  5  is an antimuscarinic, such as synthetic or semisynthetic muscarinic receptor antagonists. Such muscarinic receptor antagonists act on one or both of the M2 and M3 subtypes of muscarinic receptors. Suitable muscarinic receptor antagonists include dicyclomine, flavoxate, ipratropium, oxybutynin, pirenzepine, tiotropium, tolterodine, tropicamide, solifenacin, darifenacin, and combinations thereof. 
     In various exemplary embodiments, the drug in coating  5  is a synthetic or semisynthetic muscarinic receptor antagonists suitable for treating human or non-human mammalian patients with bladder control problems, such as urinary incontinence or enuresis. Suitable muscarinic receptor antagonists for treatment of patients with bladder control problems include oxybutynin, tolterodine, darifenacin, salts thereof, stereoisomers thereof, prodrugs thereof, and mixtures thereof. 
     In various exemplary embodiments, the drug in coating  5  is the (R)-enantiomer of tolterodine, the (R)-enantiomer of the 5-hydroxymethyl metabolite of tolterodine, the (S)-enantiomer of tolterodine, the 5-hydroxymethyl metabolite of the (S)-enantiomer of tolterodine, the racemate of tolterodine, a prodrug form of tolterodine, a pharmacologically acceptable salt of tolterodine, or a mixture thereof. In various exemplary embodiments, drug in coating  5  is tolterodine L-tartrate. 
     In various exemplary embodiments, dosage forms containing, as the drug in coating  5 , a stabilized tolterodine L-tartrate composition are disclosed. Solid oral pharmaceutical compositions containing tolterodine tartrate as the active pharmaceutical ingredient (API) are found to be stabilized using at least one organic or mineral acid excipient. The use of one or more of these additives in a tablet or capsule pharmaceutical composition has been shown to decrease the formation of degradants and increase the stability of the composition. 
     Under certain conditions, such as those found in pharmaceutical tablets and capsules stored over time, tolterodine tartrate can undergo slow topochemical degradation, leading to a reduction in the potency and purity of the dosage form. The addition of at least one acidifying agent to tableted or encapsulated dosage forms of tolterodine tartrate can lead to a dramatic reduction of degradation, thereby providing improved quality and a longer useful shelf-life of the pharmaceutical dosage form. The inclusion of a pharmaceutically acceptable amount of a pH modifying compound into pharmaceutical compositions of tolterodine tartrate for the purpose of reducing the apparent pH of the composition improves the stability of the active pharmaceutical ingredient in the composition. In various exemplary embodiments, the pH modifying compound is an organic acid, a mineral acid, or a mixture thereof. 
     In various exemplary embodiments, the pH modifying compound within drug layer  5  would be one or more of the acidifying agents commonly used in the preparation of solid oral pharmaceutical compositions. These pH modifying compounds may be organic or mineral acids. In various exemplary embodiments, the pH modifying compounds are non-polymeric acids having at least a first pK a  of less than 5.0, as shown in Table 1. In various exemplary embodiments, the pH modifying compounds may be acetic acid, benzoic acid, fumaric acid, lactic acid, malic acid, propionic acid, hydrochloric acid, phosphoric acid, sulfuric acid, stereoisomers thereof, or mixtures thereof. In various exemplary embodiments, the pH modifying compounds may be a solid acidifying agent selected from the group including tartaric acid, citric acid, ascorbic acid, stereoisomers thereof, or mixtures thereof. Pharmaceutically acceptable levels of these pH modifiers range from 0.1% to 10.0% of the pharmaceutical composition by weight. In various exemplary embodiments, the pH modifying acids are present in a range of from 0.4% to 2.5% by weight of the composition. In various exemplary embodiments, the pH modifying acids are present in a range of from 0.8% to 1.5% by weight. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Exemplary pH Modifying Acids 
               
            
           
           
               
               
               
            
               
                   
                 Acid 
                 pK a   
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Acetic Acid 
                 4.76 
               
               
                   
                 Benzoic Acid 
                 4.19 
               
               
                   
                 Fumaric Acid 
                 3.03 
               
               
                   
                 Lactic Acid 
                 4.14 
               
               
                   
                 Malic Acid 
                 3.40 
               
               
                   
                 Propionic Acid 
                 4.88 
               
               
                   
                 Tartaric Acid 
                 2.93 
               
               
                   
                 Citric Acid 
                 3.13 
               
               
                   
                 Ascorbic Acid 
                 4.17 
               
               
                   
                 Hydrochloric Acid 
                 −8 
               
               
                   
                 Sulfuric Acid 
                 −3 
               
               
                   
                 Phosphoric Acid 
                 2.15 
               
               
                   
                   
               
            
           
         
       
     
     In various exemplary embodiments, dosage forms containing stabilized tolterodine L-tartrate within drug layer  5  contain tolterodine L-tartrate stabilized with from 0.1 to 10 wt % of the dosage form of a pH modifying compound. In various exemplary embodiments, dosage forms contain tolterodine L-tartrate within drug layer  5 , where tolterodine L-tartrate is stabilized with from 0.8 to 1.5 wt % of the dosage form of a pH modifying compound. In various exemplary embodiments, the pH modifying compound may be L-(+)-tartaric acid, D-(−)-tartaric acid, meso-tartaric acid, racemic tartaric acid, or a mixture thereof. 
     If desired, coating  5  may include a binder in addition to the drug. Suitable binders are typically water-soluble polymers. In various exemplary embodiments, water soluble binders include polyvinyl alcohol, polymers and copolymers of hydroxyalkyl acrylates and hydroxyalkyl methacrylates, polyvinylpyrrolidone, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, polyethylene glycols, and combinations thereof. In various exemplary embodiments, water soluble binders include hydroxypropylmethylcellulose binders sold under the brand names Opadry II® Clear, Opadry® Clear, or a mixture thereof. Opadry II® Clear and Opadry® Clear, manufactured by Colorcon, Inc, USA, are used as an aqueous mixture containing hydroxypropylmethylcellulose. 
     In various exemplary embodiments, a controlled release coating  7  is positioned on drug-containing layer  5 . In various exemplary embodiments according to  FIG. 1 , the controlled release coating  7  is a layer of at least one pH-independent water-insoluble non-enteric polymer with or without a pore forming agent. The polymeric membrane in coating  7  becomes permeable upon exposure to aqueous environments within the human body, allowing the drug within underlying layer  5  to gradually leach through the release controlling coating  7 . In various exemplary embodiments, the water-insoluble non-enteric polymer includes polyacrylic resins and cellulose derivatives such as cellulose ethers and cellulose esters. Suitable polymers include acrylic resins, preferably insoluble polymers or copolymers of alkyl acrylates or alkyl methacrylates, or water-insoluble celluloses such as ethylcellulose and cellulose acetate. In addition to the water-insoluble polymers, water-soluble polymers or non polymers may optionally be used in coating  7  in amounts of up to 50 wt. % as a pore forming agent to increase the permeability of the membrane and therefore increase the release rate of the active substance. In various exemplary embodiments, these pore forming agents are hydroxypropylmethylcellulose, hydroxyethyl cellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, or polyvinyl alcohol. Opadry® Clear and Opadry II® Clear may be used as pore forming agents to increase the release rate of the active substance. Water-soluble non-polymeric pore-forming agents such as, for example, sucrose, lactose, mannitol, NaCl, and maltose may also be present in the release-controlling layer  7  of water-insoluble polymers to increase the release rate of the active substance. 
     In various exemplary embodiments, the release-controlling layer or membrane is comprised of at least one water-insoluble, non-pH dependent polymer with or without a pore forming agent. The release controlling membrane becomes permeable in an aqueous environment, thereby allowing release of the active ingredient. The pore former may be a water soluble or water mobile polymer or non polymer, organic or inorganic. In various exemplary embodiments, the release-controlling layer or membrane is comprised of two water-insoluble non-pH dependent polymers of different permeability with or without a pore forming agent. Alternatively, the release-controlling polymer is a pH dependent enteric polymer which is insoluble in the acidic gastric juices in the stomach (pH=1-3), but which is soluble in the more neutral environment of the small intestine (pH=6-8). In various exemplary embodiments, a composite release-controlling polymer membrane may include an inner layer of a water-insoluble, non-pH dependent polymer, and an outer layer of a pH dependent enteric polymer. In another exemplary embodiments, a composite release-controlling polymer membrane may include both water-insoluble, non-pH dependent polymer and pH dependent polymer with the later functioning as a pore forming agent. 
     If desired, the release rate of the active substance may be slowed in the acidic environment of the stomach by adding pH-sensitive enteric polymers to release controlling layer  7 . These polymers do not dissolve until the bead enters the neutral environment of the small intestine. Suitable enteric polymers useful for this purpose include cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, cellulose acetate trimellitate, polymethacrylates, and an ammonium salt of a copolymer of methacrylic acid and methacrylic acid alkyl ester. 
       FIG. 2  is a cross-sectional view of an exemplary embodiment of a controlled release bead  20  which prevents release of drug in the stomach. The exemplary bead  20  includes an inert core  1  made of a water-soluble or water-swellable material. A coating  3  of a non-polymeric water-insoluble material is positioned on core  1 . A drug-containing coating  5  is positioned on non-polymeric water-insoluble material layer  3 . A controlled release coating  11  is positioned on drug-containing layer  5 . The constitution of core  1  and of coatings  3  and  5  is substantially identical to the constitution of core  1  and of coatings  3  and  5  in previously described bead  10 , as shown in  FIG. 1 . However, controlled release coating  11 , unlike the controlled release coating  7  on bead  10 , is not a layer of a pH-independent water-insoluble non-enteric polymer. Rather, controlled release coating  11  on bead  20  is a layer of a pH-dependent enteric polymer. Accordingly, in the acidic environment of the stomach (pH 1-3), the pH-dependent enteric polymers in release controlling layer  11  are insoluble. These enteric polymers do not dissolve until the bead enters a neutral environment. Therefore, release controlling layer  11  remains intact in the stomach, but dissolves in the intestine (pH 6-8). This prevents the drug in layer  5  from being released until bead  20  enters the intestine. Once the bead is in the intestine, the dissolution of the release controlling layer rapidly releases the drug. Suitable enteric polymers useful for this purpose include cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, cellulose acetate trimellitate, polymethacrylates, and an ammonium salt of a copolymer of methacrylic acid and methacrylic acid alkyl ester. 
       FIG. 3  is a cross-sectional view of an exemplary embodiment of a controlled release bead  30  which both prevents release of drug in the stomach and allows for gradual release of the drug in the intestine. The exemplary bead  30  includes an inert core  1  made of a water-soluble or water-swellable material. A coating  3  of a non-polymeric water-insoluble material is positioned on core  1 . A drug-containing coating  5  is positioned on non-polymeric water-insoluble material layer  3 . A controlled release coating  21  is positioned on drug-containing layer  5 . The constitution of core  1  and of coatings  3  and  5  is substantially identical to the constitution of core  1  and of coatings  3  and  5  in previously described beads  10  and  20 , as shown in  FIGS. 1 and 2 . However, controlled release coating  21 , unlike the controlled release coating  7  on bead  10  and the controlled release coating  11  on bead  20 , is not a single layer of a controlled release polymer. Rather, coating  21  includes an inner controlled release layer  7  of a water-insoluble non-enteric polymer, and an outer layer  11  of a pH-dependent enteric polymer. The pH-dependent enteric polymers in outer layer  11  are insoluble in the acidic environment of the stomach (pH 1-3), thereby preventing any release of the drug in the stomach. These enteric polymers do not dissolve until the bead enters the neutral environment of the intestines (pH 6-8). After release controlling layer  11  dissolves in the intestine, the water-insoluble non-enteric polymer in layer  7  of bead  30  gradually erodes, allowing the drug in layer  5  to gradually escape from the bead by leaching through the inner release controlling layer  7 . 
     In various exemplary embodiments, the enteric polymer in layer  11  of bead  30  is cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, cellulose acetate trimellitate, polymethacrylates, or an ammonium salt of a copolymer of methacrylic acid and methacrylic acid alkyl ester. In various exemplary embodiments, the water-insoluble non-enteric polymer in layer  7  of bead  30  includes polyacrylic resins and cellulose derivatives such as cellulose ethers and cellulose esters. Suitable polymers include acrylic resins, preferably insoluble polymers or copolymers of alkyl acrylates or alkyl methacrylates, or water-insoluble celluloses such as ethylcellulose and cellulose acetate. In addition to the water-insoluble non-enteric polymers, coating  7  of bead  30  may include water-soluble polymers in order to increase the release rate of the active substance in the intestine. 
       FIG. 4  is a cross-sectional view of an exemplary embodiment of a controlled release bead  40  which allows for gradual release of a first drug in the intestine. The exemplary bead  40  includes an inert core  1  made of a water-soluble or water-swellable material. A coating  3  of a non-polymeric water-insoluble material is positioned on core  1 . A drug-containing coating  5  is positioned on non-polymeric water-insoluble material layer  3 . A controlled release coating  7  is positioned on drug-containing layer  5 . The constitution of core  1  and of coatings  3 ,  5  and  7  is substantially identical to the constitution of core  1  and of coatings  3 ,  5  and  7  in previously described bead  10 , as shown in  FIG. 1 . On top of controlled release coating  7  is deposited one or more additional layers  31  of water-soluble polymer. Such polymers may be a non-thermoplastic soluble polymer to decrease tackiness of the beads for subsequent processing, such as curing of the beads and/or filling the beads into capsules. Optionally, such an additional layer  31  of water soluble polymers may contain one or more second drugs for immediate release, where the second drugs may be the same as or different from the drug in the drug-containing layer  5 . Suitable soluble polymers for layer  31  include hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol. Opadry® Clear or Opadry II® Clear may be used to form water soluble polymer coatings  31  in bead  40 . 
       FIG. 5  is a cross-sectional view of an exemplary embodiment of a controlled release bead  45  which allows for gradual release of a first drug in the intestine. In various exemplary embodiments, bead  45  includes an inert core  1 ; a coating of a non-polymeric water-insoluble material positioned on core  3 ; and a drug-containing coating positioned on layer  5 . An enteric coating  11  may be positioned on the drug-containing layer. On top of the enteric coating  11  is deposited one or more layers of water-soluble polymer  31 , which may serve to reduce tackiness of the beads. Alternatively, the water-soluble polymer may contain an active ingredient for immediate release. 
       FIG. 6  is a cross-sectional view of an exemplary embodiment of an immediate release bead  47 . The exemplary bead  47  includes an inert core  1  made of a water-soluble or water-swellable material. A coating  3  of a non-polymeric water-insoluble material is positioned on core  1 . A drug-containing coating  5  is positioned on non-polymeric water-insoluble material layer  3 . The constitution of core  1  and of coatings  3  and  5  is substantially identical to the constitution of core  1  and of coatings  3  and  5  in previously described bead  10 , as shown in  FIG. 1 . Since no controlled release polymer is present, the drug is released rapidly when exposed to an aqueous solution at physiological pH. If desired, an additional coating of a water-soluble or water-swellable polymer may be deposited on drug-containing coating  5 . This additional coating may include polyvinyl alcohol, polymers and copolymers of hydroxyalkyl acrylates and hydroxyalkyl methacrylates, polyvinylpyrrolidone, hydroxyethylcellulose, hydroxypropyl methyl cellulose, polyethylene glycols, and combinations thereof. 
     In various exemplary embodiments, controlled release dosage forms comprising a plurality of beads are provided. Each of these beads includes an inert water-soluble or water-swellable core; a seal layer formed from a non-polymeric hydrophobic material positioned on said core layer; a layer containing at least one active ingredient positioned on said seal layer; and a layer of a release-controlling polymer positioned on said layer containing at least one active ingredient. In various exemplary embodiments, the beads may be beads  10 , beads  20 , beads  30 , beads  40 , beads  45 , or mixtures thereof. In various exemplary embodiments, the controlled release dosage forms may be tablets. These controlled release tablets may be formed by compressing the plurality of beads in a mold. Prior to compression, the beads may be combined with various pharmaceutically acceptable tabletting excipients. Suitable tabletting excipients include binders such as croscarmellose sodium, crospovidone, gellan gum, hydroxypropyl cellulose, hydroxypropylmethylcellulose, povidone, sodium starch glycolate, and starch. Additional excipients may include calcium carbonate, dextrose, fructose, lactose, microcrystalline cellulose, maltodextrin, maltose, mannitol, microcrystalline cellulose, guar gum, sorbitol, and sucrose. In various exemplary embodiments, the controlled release tablets are coated with an enteric coating subsequent to molding. In various exemplary embodiments, controlled release tablets are coated with an enteric coating contain non-enteric coated beads; these non-enteric coated beads may be beads  10 , beads  40 , or mixtures thereof. 
     In various exemplary embodiments, the controlled release tablets contain at least one active ingredient in the controlled release beads, where the at least one active ingredient is a water-soluble drug. Suitable water-soluble drugs include tolterodine tartrate, diltiazem hydrochloride, verapamil hydrochloride, bupropion hydrochloride, metformin hydrochloride, propranolol hydrochloride, dextromethorphan hydrobromide, diphenhydramine hydrochloride, disopyramide hydrochloride, tramadol, fluoxetine hydrochloride, paroxetine hydrochloride, pentoxifylline hydrochloride and the like. In various exemplary embodiments, the drug in the controlled release beads is an antimuscarinic, such as synthetic or semisynthetic muscarinic receptor antagonists. Suitable muscarinic receptor antagonists include Dicyclomine, Flavoxate, Ipratropium, Oxybutynin, Pirenzepine, Tiotropium, Tolterodine, Tropicamide, Solifenacin, Darifenacin, and combinations thereof. In various exemplary embodiments, the drug in the controlled release beads is tolterodine tartrate. 
     In various exemplary embodiments, controlled release capsules containing a plurality of beads are provided. Each of these beads includes an inert water-soluble or water-swellable core; a seal layer formed from a non-polymeric hydrophobic material positioned on said core layer; a layer containing at least one active ingredient positioned on said seal layer; and a layer of a release-controlling polymer positioned on said layer containing at least one active ingredient. In various exemplary embodiments, the beads may be beads  10 , beads  20 , beads  30 , beads  40 , beads  45 , or mixtures thereof. These controlled release capsules may be formed by filling a plurality of controlled release beads into a gelatin shell. In various exemplary embodiments, the controlled release capsules are sealed with a polymeric coating subsequent to filling of beads into the shells; the polymeric coating may be made from a hydrophilic polymeric material, a hydrophilic polymeric material, or an enteric polymeric material. In various exemplary embodiments, controlled release capsules are coated with an enteric coating and contain non-enteric coated beads; these non-enteric coated beads may be beads  10 , beads  40 , or mixtures thereof. 
     In various exemplary embodiments, the controlled release capsules contain at least one active ingredient in the controlled release beads, where the at least one active ingredient is a water-soluble drug. Suitable water-soluble drugs include tolterodine tartrate, diltiazem hydrochloride, verapamil hydrochloride, bupropion hydrochloride, metformin hydrochloride, propranolol hydrochloride, dextromethorphan hydrobromide, diphenhydramine hydrochloride, disopyramide hydrochloride, tramadol, fluoxetine hydrochloride, paroxetine hydrochloride, pentoxifylline hydrochloride and the like. In various exemplary embodiments, the drug in the controlled release beads is an antimuscarinic, such as synthetic or semisynthetic muscarinic receptor antagonists. Suitable muscarinic receptor antagonists include Dicyclomine, Flavoxate, Ipratropium, Oxybutynin, Pirenzepine, Tiotropium, Tolterodine, Tropicamide, Solifenacin, Darifenacin, and combinations thereof. In various exemplary embodiments, the drug in the controlled release beads is tolterodine tartrate. 
     In various exemplary embodiments, the capsules or tablets containing the immediate release beads  47  or controlled release beads  10 , beads  20 , beads  30 , beads  40 , beads  45 , or mixtures thereof may be used to treat a human or other mammal with enuresis, urinary incontinence, or other types of bladder control problems. This is done by administering one or more controlled release tablets or capsules containing an effective amount of an antimuscarinic agent approved for treatment of bladder control problems to the patient. Each controlled release tablet or capsule comprises a plurality of controlled release beads  10 , controlled release beads  20 , controlled release beads  30 , controlled release beads  40 , controlled release beads  45 , or mixtures thereof. In various exemplary embodiments, each of the controlled release beads includes at least one antimuscarinic may include Oxybutynin, Tolterodine, Darifenacin, salts thereof, stereoisomers thereof, prodrugs thereof, metabolites thereof, and mixtures thereof. In various exemplary embodiments, the at least one active ingredient may include the (R)-enantiomer of tolterodine, the (R)-enantiomer of the 5-hydroxymethyl metabolite of tolterodine, the (S)-enantiomer of tolterodine, the 5-hydroxymethyl metabolite of the (S)-enantiomer of tolterodine, the racemate of tolterodine, prodrug forms of tolterodine, pharmacologically acceptable salts thereof, and mixtures thereof. In various exemplary embodiments, the at least one active ingredient is tolterodine tartrate. 
     Various exemplary embodiments of methods of making a controlled release drug-containing bead will now be described with reference to the flow diagram of  FIG. 7 . The process begins with uncoated inert cores  50 . The cores  50  may be made of a hydrophilic polysaccharide, such as starch, microcrystalline cellulose, carboxymethylcellulose, croscarmellose, hydroxyethylcellulose, or hydroxypropyl methylcellulose. In various exemplary embodiments, the bead may be made of a partially or completely water-soluble pharmaceutically acceptable inorganic salt. In various exemplary embodiments, the bead may be made of a water-swellable synthetic polymer, such as crosslinked acrylic or methacrylic acid polymers and copolymers or crospovidone. In a first step  55 , a seal layer is deposited on inert core  50  to produce seal-coated cores  60 . The seal layer is formed from a non-polymeric hydrophobic material. In various exemplary embodiments, the non-polymeric hydrophobic material may be a fatty alcohol, a fatty carboxylic acid, a fatty carboxylic acid ester, a hydrogenated oil, a triglyceride fat, a wax, or a mixture thereof. In various exemplary embodiments, the non-polymeric hydrophobic material may be a C 12 -C 20  fatty alcohol, a C 12 -C 20  fatty carboxylic acid, an ester of a C 12 -C 20  fatty carboxylic acid, a hydrogenated vegetable oil, a triglyceride fat, or a mixture thereof. In various exemplary embodiments, the non-polymeric hydrophobic material may be stearyl alcohol; cetyl alcohol; stearic acid; an ester of stearic acid with a lower alcohol or polyol, such as glyceryl monostearate; an ester of cetyl alcohol; hydrogenated castor oil; and a mixture thereof. 
     In various exemplary embodiments, step  55  of depositing a seal layer on said inert core  50  is performed by treating the inert core  50  with a non-aqueous solution or dispersion of the non-polymeric hydrophobic material. Suitable solvents for the non-aqueous solution or dispersion include ethanol, isopropyl alcohol, acetone, and lower alkanes or cycloalkanes. In various exemplary embodiments, step  55  of depositing a seal layer on said inert core  50  is performed by treating the inert core  50  with an aqueous solution or dispersion of the non-polymeric hydrophobic material. In various exemplary embodiments, step  55  of depositing a seal layer on said inert core  50  is performed by treating inert core  50  with a low-melting non-polymeric hydrophobic material in a molten state. This may be done by spraying the non-polymeric hydrophobic molten material onto core  50 , or dipping core  50  into a pool of molten non-polymeric hydrophobic material. 
     Referring again to  FIG. 7 , in a second step  65 , a layer containing an active ingredient is deposited on seal-coated core  60  to produce active ingredient-coated beads  70 . In various exemplary embodiments, the layer deposited in step  65  includes a drug and, optionally, a binder. In various exemplary embodiments, the drug is a water-soluble drug. Suitable water-soluble drugs include tolterodine tartrate, diltiazem hydrochloride, verapamil hydrochloride, bupropion hydrochloride, metformin hydrochloride, propranolol hydrochloride, dextromethorphan hydrobromide, diphenhydramine hydrochloride, disopyramide hydrochloride, tramadol, fluoxetine hydrochloride, paroxetine hydrochloride, pentoxifylline hydrochloride and the like. In various exemplary embodiments, the drug deposited in step  65  is an antimuscarinic. Suitable muscarinic receptor antagonists include dicyclomine, flavoxate, ipratropium, oxybutynin, pirenzepine, tiotropium, tolterodine, tropicamide, solifenacin, darifenacin, and combinations thereof. 
     In various exemplary embodiments, the drug deposited in step  65  is a synthetic or semisynthetic muscarinic receptor antagonists suitable for treating human or non-human mammalian patients with bladder control problems, such as urinary incontinence or enuresis. Suitable muscarinic receptor antagonists for treatment of patients with bladder control problems include oxybutynin, tolterodine, darifenacin, salts thereof, stereoisomers thereof, prodrugs thereof, and mixtures thereof. In various exemplary embodiments, the drug in coating  5  is the (R)-enantiomer of tolterodine, the (R)-enantiomer of the 5-hydroxymethyl metabolite of tolterodine, the (S)-enantiomer of tolterodine, the 5-hydroxymethyl metabolite of the (S)-enantiomer of tolterodine, the racemate of tolterodine, a prodrug form of tolterodine, a pharmacologically acceptable salt of tolterodine, or a mixture thereof. The drug deposited in step  65  may be tolterodine L-tartrate. In various exemplary embodiments, the drug deposited in step  65  is acid-stabilized tolterodine L-tartrate, where the acid-stabilized tolterodine L-tartrate is prepared by mixing tolterodine L-tartrate with a stabilizing amount of a non-polymeric pH modifying acid having a pK a  of less than 5.0. The tolterodine L-tartrate may be mixed with the acid prior to deposition or during deposition. 
     If desired, the binder deposited in step  65  in addition to the drug may be a water-soluble polymer. In various exemplary embodiments, water soluble binders include polyvinyl alcohol, polymers and copolymers of hydroxyalkyl acrylates and hydroxyalkyl methacrylates, polyvinylpyrrolidone, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, polyethylene glycols, and combinations thereof. 
     In various exemplary embodiments, step  65  of depositing a layer containing at least one active ingredient is performed by coating the seal-coated cores  60  with a non-aqueous solution or dispersion of said at least one active ingredient and, optionally, a binder; or coating the seal-coated cores  60  with an aqueous solution or dispersion of said at least one active ingredient and, optionally, a binder. 
     In various exemplary embodiments, beads  70  are used as immediate-release drug-containing beads. Alternatively, active ingredient-coated beads  70  containing a water-soluble binder in the layer containing the active ingredient may be segregated into two groups. If desired, a first group of beads  70  may be set aside and reserved for use as immediate release drug containing beads, where the active ingredient is released upon dissolution of the water-soluble binder. A second group of beads  70  is coated with a controlled release polymer. These portions may then be recombined and used to produce dosage forms having a first portion of drug which undergoes immediate release, and a second portion of drug which undergoes controlled release. 
     Referring again to  FIG. 7 , the process of making controlled release beads  80  having non-enteric coatings from active ingredient-coated beads  70  will now be described. In a third step  75 , a layer of a non-enteric release-controlling polymer is deposited on active-ingredient-coated beads  70  to produce controlled release beads  80 . Step  75  of depositing a layer of a non-enteric release-controlling polymer is performed by coating said layer containing at least one active ingredient with a non-aqueous solution or dispersion of said release-controlling polymer; or coating said seal layer with an aqueous solution or dispersion of said release-controlling polymer. Controlled release beads  80  may be used in preparation of controlled release tablets or capsules, as previously described. If desired, controlled release beads  80  may be combined with active ingredient-coated beads  70 , which have been held in reserve for use as immediate release beads, prior to preparation of tablets or capsules. This allows preparation of a dosage form which allows immediate release of one portion of the drug, and release of a second portion of the drug over an extended period of time. 
     In various exemplary embodiments, the non-enteric release-controlling polymer deposited in step  75  is a water-insoluble non-enteric polymer that includes polyacrylic resins and/or cellulose derivatives such as cellulose ethers and cellulose esters. Suitable polymers include acrylic resins, preferably insoluble polymers or copolymers of alkyl acrylates or alkyl methacrylates, or water-insoluble celluloses such as ethylcellulose and cellulose acetate. In step  75 , water-soluble polymers may be combined with the water-insoluble non-enteric polymer in amounts of up to 30 wt. %. These soluble polymers may be hydroxypropylmethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, or polyvinyl alcohol. 
     Referring again to  FIG. 7 , the process of making controlled release beads  90  having enteric coatings from ingredient-coated beads  70  will now be described. In a third step  77 , a layer of an enteric polymer is deposited on active-ingredient-coated beads  70  to produce enteric coated beads  90 . Suitable enteric polymers useful for this purpose include cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, cellulose acetate trimellitate, polymethacrylates, and an ammonium salt of a copolymer of methacrylic acid and methacrylic acid alkyl ester. Step  77  of depositing a layer of an enteric polymer on the layer containing the active ingredient is performed by coating the layer containing the active ingredient with a non-aqueous solution or dispersion of the enteric polymer; coating the layer containing the active ingredient with an aqueous dispersion of enteric polymer; or coating the layer containing the active ingredient with a solution of the enteric polymer in aqueous acid, and then treating the enteric coated beads with aqueous base to neutralize the enteric polymer. Enteric coated beads  90  may be used in preparation of controlled release tablets or capsules, as previously described. If desired, enteric coated beads  90  may be combined with active ingredient-coated beads  70 , which have been held in reserve for use as immediate release beads, prior to preparation of tablets or capsules. This allows preparation of a dosage form which allows immediate release of one portion of the drug, and subsequent release of a second portion of the drug, after the beads pass from the stomach into the intestine. 
     Referring again to  FIG. 7 , an alternate method of making controlled release beads having enteric coatings from ingredient-coated beads  70  will now be described. This method produces controlled release beads having enteric shells. In a step  75 , a layer of a non-enteric release-controlling polymer is deposited on active-ingredient-coated beads  70  to produce controlled release beads  80 , as previously described. Next, in step  87 , a layer of an enteric polymer is deposited on controlled release beads  80  to produce enteric coated beads  115 . Deposition of the enteric polymer in step  87  is carried out in essentially the same manner as deposition of the enteric polymer in step  77 . The resulting beads have enteric coatings on top of water-insoluble controlled release coatings. The enteric coatings do not dissolve in the stomach, but remain intact until the bead enters the neutral environment of the intestine (pH 6-8). After the enteric coatings dissolve in the intestine, the water-insoluble non-enteric polymer layer beneath gradually erodes, allowing the drug in the bead to gradually escape by leaching through the water-insoluble non-enteric polymer layer. Enteric coated beads  115  may be used in preparation of controlled release tablets or capsules, as previously described. 
     Referring again to  FIG. 7 , a method of making controlled release beads having water-soluble polymeric coatings will now be described. This method produces controlled release beads having soluble shells. In step  85 , a layer of a water-soluble polymer is deposited on controlled release beads  80  to produce controlled release beads having water soluble shells  100 . Similarly, in step  95 , a layer of a water-soluble polymer is deposited on enteric coated beads  90  to produce enteric coated beads with water-soluble shells  110 . Deposition of the water-soluble polymer in step  95  is carried out in essentially the same manner as deposition of the water-soluble polymer in step  85 . The polymers in the soluble shells may be used as binders for immediate release drug containing layers, or for polymers used to reduce tackiness of the finished beads. The layer of water soluble polymer may contain immediate release drugs, which may be the same as or different from the drug in the drug-containing layer deposited in step  65 . Suitable soluble polymers for the layer of water soluble polymer include hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol. Beads  110  and  110  may be used in preparation of controlled release tablets or capsules, as previously described. 
     Additional exemplary embodiments of pharmaceutical dosage forms contain stabilized tolterodine L-tartrate. These exemplary embodiments are solid oral dosage forms comprising an effective amount of tolterodine L-tartrate and pharmaceutically acceptable excipients, wherein the tolterodine L-tartrate is stabilized with a pharmaceutically acceptable non-polymeric pH-modifying acid having a pK a  of less than 5.0. The acid may be hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, benzoic acid, fumaric acid, lactic acid, malic acid, propionic acid, tartaric acid, citric acid, ascorbic acid, stereoisomers thereof, or mixtures thereof. 
     In various exemplary embodiments, solid oral dosage forms containing stabilized tolterodine L-tartrate are controlled release dosage forms. These controlled release dosage form comprise acid-stabilized tolterodine L-tartrate and a release-controlling polymer. In various exemplary embodiments, the acid-stabilized tolterodine L-tartrate is dispersed in the release-controlling polymer, where the release-controlling polymer is a pH-insensitive water-insoluble polymer. The drug is released by erosion of the polymer upon exposure to an aqueous environment under physiological conditions. The polymer may be a polymer or copolymer of alkyl acrylates or alkyl methacrylates, a cellulose ether such as ethylcellulose, or a cellulose ester. 
     In various exemplary embodiments, the acid-stabilized tolterodine L-tartrate present in a core layer of the dosage form. The drug-containing core layer is coated by a layer of a release-controlling polymer, where the release-controlling polymer is a pH-insensitive water-insoluble polymer or an enteric polymer. In dosage forms where the release-controlling polymeric coating is a pH-insensitive water-insoluble polymer, the drug is released by erosion of the polymer upon exposure to an aqueous environment under physiological conditions. The pH-insensitive water-insoluble polymer may be a polymer or copolymer of alkyl acrylates or alkyl methacrylates, a cellulose ether such as ethylcellulose, or a cellulose ester. The enteric polymer may be cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, cellulose acetate trimellitate, polymethacrylates, or an ammonium salt of a copolymer of methacrylic acid and methacrylic acid alkyl ester. In dosage forms where the release-controlling polymeric coating is an enteric polymer, the drug is released upon dissolution of the enteric coating in the intestines. 
     In various exemplary embodiments, solid oral dosage forms containing stabilized tolterodine L-tartrate are immediate release dosage forms. These immediate release dosage forms contain acid-stabilized tolterodine L-tartrate and a water-swellable or water-soluble polymer. In various exemplary embodiments, the acid-stabilized tolterodine L-tartrate is dispersed in said water-swellable or water-soluble polymeric binder. Non-limiting examples of water-swellable or water-soluble polymers which may be used in such exemplary embodiments include hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol. Hydroxypropylmethyl cellulose is a useful water-swellable or water-soluble polymer which may be used in a commercially available form, such as Opadry® Clear or Opadry II® Clear. The acid-stabilized tolterodine L-tartrate and the water-swellable or water-soluble polymeric binder may be provided as a homogeneous composition. This composition may be prepared by mixing the tolterodine L-tartrate with a stabilizing amount of an acid, such as tartaric acid; mixing the resulting acid-stabilized tolterodine L-tartrate with a water-swellable or water-soluble polymeric binder; and compressing the mixture to form tablets or filling the mixture into a capsule shell. The total amount of tolterodine L-tartrate in the final dosage form may range 0.5 to 4 mg. 
     In various exemplary embodiments, the immediate release solid oral dosage form may be a non-homogeneous dosage form including a core layer containing the acid-stabilized tolterodine L-tartrate and a layer containing a water-swellable or water-soluble polymer. The layer containing the acid-stabilized tolterodine L-tartrate is surrounded by the layer of said water-swellable or water-soluble polymer. The layer containing the acid-stabilized tolterodine L-tartrate contains, in addition to the drug, disintegrants such as microcrystalline cellulose, carboxymethylcellulose, sodium starch glycolate, or mixtures thereof. The outer layer of a water-swellable or water-soluble polymer contains hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, or a mixture thereof. The layer containing the acid-stabilized tolterodine L-tartrate may be a core layer of said dosage form, and the layer containing said water-swellable or water-soluble polymer surrounds the core layer. This composition may be prepared by mixing the tolterodine L-tartrate with a stabilizing amount of an acid, such as tartaric acid; mixing the resulting acid-stabilized tolterodine L-tartrate with a disintegrant; and compressing the resulting mixture to form tolterodine L-tartrate containing cores. The cores are then coated with a water-swellable or water-soluble polymeric binder. 
     In various exemplary embodiments, the solid oral dosage form may be a non-homogeneous dosage form including an inert core, a layer containing the acid-stabilized tolterodine L-tartrate surrounding the core, and a layer containing a water-swellable or water-soluble polymer. The layer containing said water-swellable or water-soluble polymer surrounds the acid-stabilized tolterodine L-tartrate layer. This composition may be prepared by mixing the tolterodine L-tartrate with a stabilizing amount of an acid, such as tartaric acid, and coating the inert cores with the resulting acid-stabilized tolterodine L-tartrate. The drug-coated cores may be coated with a water-swellable or water-soluble polymeric binder to produce an immediate release dosage form, or with a controlled release polymer to produce a controlled release dosage form. 
     In various exemplary embodiments, a seal layer may be deposited on the inert cores prior to coating the inert cores with the acid-stabilized tolterodine L-tartrate. The seal layer, if used in the acid-stabilized tolterodine L-tartrate dosage form, may be prepared from a hydrophilic polymer, a hydrophobic polymer, or a water-insoluble non-polymeric material. The water-insoluble non-polymeric material may include a fatty alcohol, a fatty carboxylic acid, a fatty carboxylic acid ester, a hydrogenated oil, a triglyceride fat, a wax, and mixtures thereof. In various exemplary embodiments, the non-polymeric hydrophobic material in the seal layer may include stearyl alcohol, cetyl alcohol, stearic acid, an ester of stearic acid with a lower alcohol or polyol, an ester of cetyl alcohol, hydrogenated castor oil, and mixtures thereof. 
     In various exemplary embodiments, tablets containing acid stabilized tolterodine-L-tartrate may be prepared. The method of preparing tablets includes a first step of mixing tolterodine-L-tartrate with a pharmaceutically acceptable pH-modifying acid to obtain an acid-stabilized tolterodine-L-tartrate. The acid-stabilized tolterodine-L-tartrate is then combined with at least one pharmaceutically acceptable excipient to form an acid-stabilized mixture. The pharmaceutically acceptable excipients usable with acid-stabilized tolterodine-L-tartrate include microcrystalline cellulose, sucrose, hydroxypropylmethylcellulose, sodium starch glycolate, starch, xylitol, fructose, sorbitol, calcium phosphate, calcium sulfate, magnesium stearate, oleic acid, stearic acid, stearyl alcohol, calcium carbonate, dextrose, lactose, polyvinylpyrrolidone, crosslinked polyvinylpyrrolidone, silica, titanium dioxide, gelatin, triglycerides, or a mixture thereof. The acid-stabilized mixture is then compressed to form a tablet. In a further step, the tablet may be coated with a polymer. The polymer may be a hydrophilic polymer, such as hydroxypropylmethylcellulose, or a hydrophobic controlled release polymer, such as ethylcellulose. 
     In various exemplary embodiments, capsules containing acid stabilized tolterodine-L-tartrate may be prepared. The method of preparing capsules includes a first step of mixing tolterodine-L-tartrate with a pharmaceutically acceptable pH-modifying acid to obtain an acid-stabilized tolterodine-L-tartrate. The acid-stabilized tolterodine-L-tartrate is then combined with at least one pharmaceutically acceptable excipient to form an acid-stabilized mixture. The pharmaceutically acceptable excipients usable with acid-stabilized tolterodine-L-tartrate include microcrystalline cellulose, sucrose, hydroxypropylmethylcellulose, sodium starch glycolate, starch, xylitol, fructose, sorbitol, calcium phosphate, calcium sulfate, magnesium stearate, oleic acid, stearic acid, stearyl alcohol, calcium carbonate, dextrose, lactose, polyvinylpyrrolidone, crosslinked polyvinylpyrrolidone, silica, titanium dioxide, gelatin, triglycerides, or a mixture thereof. The acid-stabilized mixture is then filled into a capsule shell. In a further step, the capsule may be coated with a polymer. The polymer may be a hydrophilic polymer, such as hydroxypropylmethylcellulose, or a hydrophobic controlled release polymer, such as ethylcellulose. 
     The invention will now be described in more detail by the following non-limiting Examples. 
     Example 1 
     An exemplary capsule containing 4 mg/unit acid-stabilized tolterodine L-tartrate as active ingredient comprises a plurality of beads. Each bead includes as an inert core, a sugar sphere, 20-25 mesh (20/25). As a first seal layer, stearyl alcohol is deposited on the sugar sphere. Next, a layer containing Tolterodine L-tartrate, tartaric acid, and an Opadry II Clear dispersion containing hydroxypropylmethylcellulose (HPMC) is deposited on the seal layer. Finally, a third layer of Surelease® and Opadry Clear is deposited on the Tolterodine L-tartrate layer as a release-controlling layer. The ratio of Surelease® solids:Opadry Clear is 80:20. Surelease® is an aqueous film-coating dispersion, about 25% solids, consisting primarily of ethylcellulose plasticized with fractionated coconut oil, and is manufactured by Colorcon, Inc, USA. 
     Beads with a three-layer coating having the above characteristics were prepared as follows: 
     2900 g of sugar spheres, 20-25 mesh, were charged into a rotor fluid bed coater and sprayed with a solution of 725 g of stearyl alcohol dissolved in isopropyl alcohol to produce stearyl alcohol coated beads. In the same rotor, 983.6 g of the stearyl alcohol coated beads were sprayed with a solution of 26 g Tolterodine L-tartrate, 8.21 g tartaric acid, and 8.55 g Opadry® Clear (Opadry® Clear, manufactured by Colorcon, Inc, USA, includes hydroxypropylmethylcellulose) in a mixed solvent containing water and isopropyl alcohol in a 4:1 ratio. The beads are then coated with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear in a ratio of 80:20 w/w solids. 
     After drying, the coated spheres were filled into gelatin capsules to obtain 4 mg tolterodine L-tartrate capsules. Each capsule contained 180 mg beads, giving capsules of the composition shown in Table 2; the final composition contained 0.8 wt. % tartaric acid. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Formulation of Tolterodine Tartrate Capsules 
               
            
           
           
               
               
               
            
               
                   
                 Component 
                 mg/unit 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Sugar Spheres 20/25 
                 121.06 
               
               
                   
                 Stearyl Alcohol 
                 30.26 
               
               
                   
                 Tolterodine L-tartrate 
                 4.00 
               
               
                   
                 Tartaric Acid 
                 1.26 
               
               
                   
                 Opadry II ® Clear 
                 1.32 
               
               
                   
                 Surelease Ethylcellulose Suspension 
                 17.68 
               
               
                   
                 Opadry ® Clear 
                 4.42 
               
               
                   
                 Total 
                 180.0 
               
               
                   
                   
               
            
           
         
       
     
     In an analogous manner to the procedure described in Example 1 above, other exemplary bead formulations containing tolterodine L-tartrate as the active ingredient were prepared as described in Examples 2, 3, and 4 below. 
     Example 2 
     Tolterodine L-tartrate capsules were prepared by the process described in Example 1, except for the step of coating the beads with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear. In this Example, the ethylcellulose aqueous suspension was composed of Surelease® and Opadry® Clear in a ratio of 85:15 w/w solids. 
     Example 3 
     Tolterodine L-tartrate capsules were prepared by the process described in Example 1, except for the step of coating the beads with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear. In this Example, the ethylcellulose aqueous suspension was composed of Surelease® and Opadry® Clear in a ratio of 75:25 w/w solids. 
     Example 4 
     Tolterodine L-tartrate capsules were prepared by the process described in Example 1, except for the step of coating the beads with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear. In this Example, the ethylcellulose aqueous suspension was composed of Surelease® and Opadry® Clear in a ratio of 82.5:17.5 w/w solids. 
     Example 5 
     A study of the effect of the composition of the controlled release layer was performed. The effect of the controlled release layer on drug release was tested as follows. Four lots of Tolterodine L-tartrate capsules according to Examples 1 through 4. In the first lot, prepared according to Example 1, the ratio of Surelease® solids:Opadry Clear solids in the controlled release layer is 80:20. In the second lot, prepared according to Example 2, the ratio of Surelease® solids:Opadry Clear solids in the controlled release layer is 85:15. In the third lot, prepared according to Example 3, the ratio of Surelease® solids:Opadry Clear solids in the controlled release layer is 75:25. In the fourth lot, prepared according to Example 4, the ratio of Surelease® solids:Opadry Clear solids in the controlled release layer is 82.5:17.5. 
     The in vitro drug release rate was measured at 37° C. in a phosphate buffer of pH 6.8. The USP dissolution test apparatus I was used at 100 rpm. The results are shown in the diagrams in  FIG. 8 . As shown in  FIG. 8 , as the percentage of plasticized ethylcellulose (Surelease®) in the controlled release layer increases, the drug release rate decreases. For the capsules of Example 3, where Surelease® makes up 75% of the controlled release layer, essentially 100% of the Tolterodine L-tartrate was released after 7 hr. For the capsules of Example 2, where Surelease® makes up 85% of the controlled release layer, only 50% of the Tolterodine L-tartrate was released after 7 hr. Additionally, the capsules of Example 2 exhibit nearly linear, zero order release of Tolterodine L-tartrate over a range of time beginning approximately 2 hr after the start of the test to at least a time of 7 hr after the start of the test. Further, it is seen that the capsules of Example 4, where Surelease® makes up 82.5% of the controlled release layer, also exhibit nearly linear, zero order release of Tolterodine L-tartrate over a range of time of 1 hr after the start of the test to at least a time of 7 hr after the start of the test. 
     Example 6 
     An exemplary capsule containing 4 mg/unit tolterodine L-tartrate as active ingredient comprises a plurality of beads; no organic stabilizing acid was included in the drug layer. Each bead includes as an inert core, a sugar sphere, 20-25 mesh (20/25). As a first seal layer, stearyl alcohol is deposited on the sugar sphere. Next, a layer of Tolterodine L-tartrate and hydroxypropylmethylcellulose (HPMC) is deposited on the seal layer. Finally, a third layer of Surelease® and HPMC is deposited on the Tolterodine L-tartrate layer as a release-controlling layer. Surelease® is an aqueous film-coating dispersion, about 25% solids. 
     Beads with a three-layer coating having the above characteristics were prepared as follows: 
     Sugar spheres, 20-25 mesh, were charged into a rotor fluid bed coater and sprayed with a solution of stearyl alcohol dissolved in isopropyl alcohol (20 wt. % stearyl alcohol) to produce stearyl alcohol coated beads. In the same rotor, stearyl alcohol coated beads were coated with Tolterodine L-tartrate and Opadry® Clear. This is done in by spray coating in three stages, with an initial coating of aqueous Opadry® Clear; a second coating of a solution of 26 g Tolterodine L-tartrate and Opadry® Clear; and a third coating of Opadry® Clear. The resulting Tolterodine L-tartrate/Opadry® Clear coating contains Tolterodine L-tartrate and Opadry® Clear solids in a 4:1 ratio. The beads are then coated with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear in a ratio of 85:15 w/w solids. 
     After drying, the coated spheres were filled into gelatin capsules to obtain 4 mg tolterodine L-tartrate capsules. Each capsule contained 180 mg beads, giving capsules of the composition shown in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Formulation of Tolterodine Tartrate Capsules 
               
            
           
           
               
               
               
            
               
                   
                 Component 
                 mg/unit 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Sugar Spheres 20/25 
                 120.83 
               
               
                   
                 Stearyl Alcohol 
                 24.17 
               
               
                   
                 Tolterodine L-tartrate 
                 4.00 
               
               
                   
                 Tartaric Acid 
                 0.00 
               
               
                   
                 Opadry ® Clear (in drug layer) 
                 1.00 
               
               
                   
                 Surelease Ethylcellulose Suspension 
                 25.50 
               
               
                   
                 Opadry ® Clear (in sustained release coating) 
                 4.50 
               
               
                   
                 Total 
                 180.0 
               
               
                   
                   
               
            
           
         
       
     
     Example 7 
     A study of the effect of a stabilizing amount of tartaric acid on the degradation of the tolterodine L-tartrate was performed. The effect of the tartaric acid was tested by exposing capsules prepared according to Example 6, with no acid stabilizer, and capsules of Example 1, containing 0.8 wt. % tartaric acid stabilizer, to elevated temperate and humidity (40° C. and 75% relative humidity). Concentrations of total degradation products, an unknown degradation product, and tolterodine monomer were monitored over time. Tolterodine dimer and tolterodine tartrate 4B are other known degradation products; however, since concentrations of these products were essentially constant over the course of stability experiments, they were not individually reported. As a comparison, formation of degradation products in the commercially available tolterodine tartrate extended release formulation Detrol® LA was also monitored. 
     As seen in Table 4, Detrol® LA has an initial impurity level of 0.37 wt. %. After three months of exposure to elevated temperate and humidity, the impurity level has increased to 1.27 wt. %. The formulation of Example 6, which has no acid stabilizer, and the formulation of Example 1, which has 0.8 wt. % acid stabilizer, each exhibit very low initial concentrations of impurities. In each case, the initial impurity level is 0.05 wt. %. After three months of exposure to elevated temperate and humidity, Example 6 has a significantly increased level of impurities, with an impurity level of 1.17 wt. %. Acid-stabilized Example 1, on the other hand, has a much lower level of impurities, with an impurity level of 0.16 wt. %. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Tolterodine Capsule Formulations - Accelerated Stability 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Stability 
                 Monomer 
                 Unknown 
                 Total Impurity 
               
               
                 Lot 
                 Timepoint 
                 Degradant (%) 
                 Degradant (%) 
                 Level (%) 
               
               
                   
               
               
                 Detrol ® LA 
                 Initial 
                 0.05 
                 0.25 
                 0.37 
               
               
                 Commercially available 
                 1 month 
                 0.12 
                 0.50 
                 0.70 
               
               
                 formulation 
                 2 month 
                 0.26 
                 0.96 
                 1.29 
               
               
                   
                 3 month 
                 0.26 
                 0.93 
                 1.27 
               
               
                 Example 6 
                 Initial 
                 0.05 
                 LT 0.07 
                 0.05 
               
               
                 Bead formulation 
                 1 month 
                 0.19 
                 0.55 
                 0.74 
               
               
                 without acid stabilizer 
                 3 month 
                 0.28 
                 0.89 
                 1.17 
               
               
                 Example 1 
                 Initial 
                 0.05 
                 LT 0.05 
                 0.05 
               
               
                 Bead formulation with 
                 1 month 
                 LT 0.05 
                 LT 0.05 
                 LT 0.05 
               
               
                 0.8 wt % tartaric acid 
                 2 month 
                 0.05 
                 LT 0.05 
                 0.05 
               
               
                   
                 3 month 
                 0.05 
                 0.11 
                 0.16 
               
               
                   
               
            
           
         
       
     
     Example 8 
     An exemplary capsule containing 4 mg/unit tolterodine L-tartrate as active ingredient comprises a plurality of beads. Each bead includes as an inert core, a sugar sphere, 20-25 mesh (20/25). As a first seal layer, stearic acid is deposited on the sugar sphere. Next, a layer of Tolterodine L-tartrate and hydroxypropylmethylcellulose (HPMC) is deposited on the seal layer. Finally, a third layer of Surelease® and HPMC is deposited on the Tolterodine L-tartrate layer as a release-controlling layer. The ratio of Surelease® solids:HPMC is 75:25. 
     Beads with a three-layer coating having the above characteristics were prepared as follows: 
     1047.3 g of sugar spheres, 20-25 mesh, were charged into a rotor fluid bed coater and sprayed with a solution of 104.7 g of stearic acid dissolved in isopropyl alcohol/water (9:1) to produce stearic acid coated beads. In the same rotor, 1045 g of the stearic acid coated beads were sprayed with a solution of 29.03 g Tolterodine L-tartrate and 14.51 g Opadry® Clear in a mixed solvent containing water and isopropyl alcohol in a 4:1 ratio. The HPMC is obtained as Opadry® Clear. The beads are then coated with a sustained release coating liquid of an ethylcellulose aqueous suspension composed of Surelease® and Opadry® Clear in a ratio of 75:25 w/w solids. 
     After drying, the coated spheres were filled into gelatin capsules to obtain 4 mg tolterodine L-tartrate capsules. Each capsule contained 180 mg beads, giving capsules of the composition shown in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Formulation of Tolterodine Tartrate Capsules 
               
            
           
           
               
               
               
            
               
                   
                 Component 
                 mg/unit 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Sugar Spheres 20/25 
                 130.91 
               
               
                   
                 Stearic Acid 
                 13.09 
               
               
                   
                 Tolterodine L-tartrate 
                 4.00 
               
               
                   
                 Opadry ® Clear in drug layer 
                 2.00 
               
               
                   
                 Surelease Ethylcellulose Suspension 
                 22.50 
               
               
                   
                 Opadry ® Clear in sustained release coating 
                 7.50 
               
               
                   
                 Total 
                 180.0 
               
               
                   
                   
               
            
           
         
       
     
     Although various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the subject matter disclosed herein is capable of other different embodiments, and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be affected while remaining within the spirit and scope of the disclosure. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only, and do not in any way limit the invention, which is defined only by the claims.