Abstract:
A unit dosage form, such as a capsule or the like, for delivering a skeletal muscle relaxant, such as cyclobenzaprine hydrochloride, into the body in an extended or sustained release fashion comprising one or more populations of drug-containing particles (beads, pellets, granules, etc.) is disclosed. At least one bead population exhibits a pre-designed sustained release profile. Such a drug delivery system is designed for once-daily oral administration to maintain an adequate plasma concentration - time profile, thereby providing relief of muscle spasm associated with painful musculoskeletal conditions over a 24 hour period.

Description:
TECHNICAL FIELD 
       [0001]    A major objective of developing and commercializing controlled release dosage forms for indications such as cardiovascular diseases, chronic pain, relief of muscle spasm and associated symptoms especially in the elderly is to deliver the drug so as to maintain the drug at therapeutically effective concentrations over an extended period of time, thereby enhancing patient compliance and therapeutic efficacy, thereby reducing both cost of treatment and side effects. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many therapeutic agents are most effective when made available at a constant rate at or near the absorption site. The absorption of therapeutic agents thus made available generally results in desired plasma concentrations leading to maximum efficacy and minimum toxic side effects. Much effort has been devoted to developing matrix tablet based and multi-particulate capsule based drug delivery systems for oral applications. 
         [0003]    U.S. Pat. No. 4,839,177 to Colombo, et al, assigned to Jagotec AG, refers broadly to controlled release of active substances including medicaments and any type of substance which is to be released at a controlled rate into an aqueous fluid. The patent is directed to a system for the controlled-rate release of active substances consisting of a deposit core comprising an active substance and at least one of (a) a polymeric material having a high degree of swelling on contact with water and a gellable polymeric material or (b) a single polymeric material having both swelling and gelling properties, and a support platform applied to the deposit core wherein the support platform consists of a water insoluble polymeric material. 
         [0004]    U.S. Pat. Nos. 4,851,228 and No. 4,968,507, both to Zentner et al., assigned to Merck &amp; Company, refer to a multi-particulate osmotic pump for the controlled release of a pharmaceutically active agent, each osmotic pump element consisting essentially of a core containing an active agent and a rate controlling water insoluble wall comprising a semi-permeable polymer and at least one pH insensitive pore forming additive dispersed throughout the wall. U.S. Pat. No. 4,590,062 to Jang assigned to Tech Trade Corporation and U.S. Pat. No. 4,882,167 to Jang, are directed to a compressed product containing an active produced by dry blending with a matrix combination of a hydrophobic polymer (e.g. ethylcellulose) and a wax, fatty acid, neutral lipid or combination thereof. 
         [0005]    U.S. Pat. No. 4,996,047 to Kelleher, assigned to Richardson-Vicks, is directed to an oral pharmaceutical composition in unit dosage form of ion-exchange resin particles having a pharmacologically active drug bound thereto wherein the drug-resin complex particles have been coated with a water-impermeable diffusion barrier to provide controlled release of the active drug. U.S. Pat. No. 5,120,548 to McClelland et al., assigned to Merck &amp; Company, is directed to a controlled release drug delivery device comprising a composition of a polymer which swells upon exposure to an aqueous environment, a plurality of controlled release swelling modulators, at least one active agent and either a water insoluble polymer coating surrounding the composition or a microporous wall surrounding the composition. U.S. Pat. No. 5,350,584 to McClelland et al., assigned to Merck &amp; Company, relates to a process for the production of microcrystalline cellulose-free multiparticulates comprising a medicament and a charged resin. The resulting spheronized beads can be used in certain controlled release dosage forms. 
         [0006]    U.S. Pat. No. 5,366,738 to Rork et al., assigned to Merck &amp; Company, is directed to a drug delivery device for controlled release of an active agent. The drug delivery device includes a compressed core with an active agent and a polymer which forms gelatinous microscopic particles upon hydration and a water insoluble, water impermeable polymeric coating comprising a polymer and plasticizer which surrounds and adheres to the core. 
         [0007]    U.S. Pat. No. 5,582,838 to Rork et al., assigned to Merck &amp; Company, is related to a drug delivery device for the controlled release of a beneficial agent. The drug delivery device includes a compressed core having at least two layers: at least one layer is a mixture of a beneficial agent and a polymer which forms microscopic polymer gel beads upon hydration and at least one outer layer comprises a polymer which forms microscopic polymer gel beads upon hydration. A water insoluble, water impermeable coating is applied to the core and the coating has apertures exposing between about 5-75% of the core surface. 
         [0008]    U.S. Pat. No. 5,874,418 to Stella et al., assigned to Cydex, is directed to a pharmaceutical composition comprising a carrier and a mixture of a sulfoalkyl ether-cyclodextrin and a therapeutic agent wherein a major portion of the therapeutic agent is not complexed to the sulfoalkyl ether-cyclodextrin derivative. Delayed, sustained or controlled release formulations are also described wherein the pharmaceutical core is coated with a film coating comprising a file forming agent and a pore forming agent. U.S. Pat. No. 5,882,682 to Rork et al., assigned to Merck &amp; Company, is directed to a drug delivery process including the steps of preparing a uniform mixture of a polymer which forms gelatinous microscopic particles upon hydration, the beneficial agent and other excipients used in the preparation of the core; compressing the mixture into cores; coating the entire core with a water insoluble, water impermeable polymeric coating including a polymer and a plasticizer; and forming apertures through the coating. 
         [0009]    U.S. Pat. No. 5,952,451 to Zhao, assigned to Guilford Pharmaceuticals is directed to a process for preparing high molecular weight poly(phosphoester) compositions comprising a biologically active substance and a poly(phosphoester) and the high molecular weight compositions produced thereby. The polymers so produced are useful in prolonged released drug delivery systems. U.S. Pat. No. 6,004,582 to Faour et al., assigned to Laboratorios Phoenix U.S.A., is directed to a multi-layered osmotic device comprising a compressed core including a first active agent and an osmotic agent, a semi-permeable membrane surrounding the core and having a preformed passageway therein wherein the membrane is permeable to a fluid in the environment of use and substantially impermeable to the first active agent. The semi-permeable membrane preferably consists essentially of cellulose acetate and poly(ethylene glycol). The external coat can includes poly(vinylpyrrolidone) and poly (ethylene glycol) and can further includes materials such as HPMC, ethylcellulose, hydroxyl ethylcellulose, CMC, dimethylaminoethyl methacrylate-methacrylic acid ester copolymer, ethyl acrylate-methyl methacrylate copolymer, and combinations thereof. 
         [0010]    WO 99/18937 to Kleinbart et al., (Merck &amp; Company), is directed to a composition comprising a pharmaceutically effective amount of cyclobenzaprine and calcium phosphate dibasic hydrous, wherein the tablet releases most of the active component within an hour. WO 99/30671 to Ron, is directed to an oral delivery vehicle including an aspected particle comprising a pharmaceutically active component and excipients wherein the vehicle is formulated to provide controlled delivery of the pharmaceutically active component. The vehicle may further contain a coating to provide sustained drug delivery to the particle. WO 98/53802 to Faour et al., (Laboratorios Phoenix USA), is directed to a multi-layered osmotic device that is capable of delivering a first active agent in an outer lamina to one environment of use and a second active agent in the core to another environment of use. An erodible polymer coat between an internal semipermeable membrane and a second active agent-containing external coat comprises poly(vinylpyrrolidone)-vinyl acetate) copolymer. The active agent in the core is delivered through a pore containing an erodible plug. 
         [0011]    WO 98/18610 to Van Lengerich, is directed to particles containing an active agent, which provide controlled release of the active ingredient without substantial destruction of the matrix material. A release-rate controlling component is incorporated in a matrix to control the rate-release of the encapsulant from the particles. A hydrophobic component or a high water binding capacity component may be used for extending the release time. Release properties may also be controlled by precoating the encapsulant and/or coating the particles with a film-forming component. WO 98/06439 to Oedemoed, (Osteotech), is directed to a composition comprising a biologically active agent encapsulated in a matrix comprising a polyether ester copolymer, such as polyethylene glycol terephthalate/polybutylene-terephthalate copolymer. The polyether ester copolymer protects the active agent from degradation and thereby facilitates the drug delivery. 
         [0012]    Cyclobenzaprine hydrochloride, a skeletal muscle relaxant, is a centrally acting drug which reduces or abolishes excessive tonic muscle activity in hypertonic as opposed to hyperphasic disorders. Flexeril IR (immediate release) tablets containing 10 mg of cyclobenzaprine HCl are-administered three times a day to relieve skeletal muscle spasm of local origin without interfering with muscle function. The oral administration thrice daily is an issue of patient compliance, especially with the elderly. Hence, there is a need for modified release skeletal muscle relaxant suitable for a single administration. More particularly, there is a need for modified release (MR) cyclobenzaprine hydrochloride capsules, 15 and 30 mg, which would substantially minimize intersubject variability and improve the quality of life, especially in the elderly population. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention provides a modified release, multi-particulate dosage form of a skeletal muscle relaxant comprising one or more bead populations which provides an extended release profile of the active under in vitro conditions closely mimicking the profile simulated from pharmaco-kinetic modeling. One of the bead populations is an ER (extended release) Bead population typically comprising a coating of a water insoluble polymer alone, or in combination with a water soluble polymer, applied onto active containing cores. The active core of the dosage form of the present invention may comprise an inert particle such as a sugar sphere, or an acidic or alkaline buffer crystal, which is coated with a skeletal muscle relaxant such as cyclobenzaprine hydrochloride-containing film-forming formulation, preferably a water-soluble film forming composition. The first coating formulation may contain, in addition to the active, a binder such as hydroxypropyl cellulose. The drug layered beads may be coated with a protective seal coating of OPADRY® Clear to produce IR Beads. Alternatively, the core particle may be formed by granulating and dry milling and/or by extrusion and spheronization of a pharmaceutical composition containing the active. The amount of drug in the core will depend on the dose required and typically varies from about 5 to about 60% by weight. 
         [0014]    ER Beads can be produced by applying a functional membrane comprising a water insoluble polymer alone or in combination with a water soluble polymer onto IR Beads. The capsule formulation for once a day, oral administration of a skeletal muscle relaxant prepared in accordance with the present invention comprises ER Beads containing the active substance and optionally IR Beads. IR (immediate release) Beads allow immediate release of the active while ER Beads allow an extended release profile of the active over several hours. Upon oral administration, such a capsule formulation provides for therapeutically effective plasma profiles over an extended period of time, thereby resulting in improved patient compliance. 
         [0015]    In accordance with one embodiment of the invention a pharmaceutical dosage form of a skeletal muscle relaxant is provided. The dosage form includes one or more bead populations and provides a modified release profile. At least one of the bead populations includes extended release (ER) beads wherein the ER beads include a core particle (IR (immediate release) bead) containing a skeletal muscle relaxant and an ER (extended release) coating comprising a water insoluble polymer surrounding the core. The dosage form, in accordance with certain embodiments, when dissolution tested using United States Pharmacopoeia Apparatus 2 (paddles @ 50 rpm) in 900 mL of 0.1N HCl (or a suitable dissolution medium) at 37° C. exhibits a drug release profile substantially corresponding to the following pattern:
       after 2 hours, no more than about 40% of the total active is released;   after 4 hours, from about 40-65% of the total active is released;   after 8 hours, from about 60-85% of the total active is released; and   after 12 hours, from about 75- 85% of the total active is released.       
 
         [0020]    The dosage form thereby provides a therapeutically effective plasma concentration over an extended period of time, typically over a period of 24 hours to treat muscle spasm associated with painful musculoskeletal conditions in humans. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    The invention will be described in further detail with reference to the accompanying Figures wherein: 
           [0022]      FIG. 1  shows the proposed target release profile for cyclobenzaprine hydrochloride MR (modified release) capsules, 15 and 30 mg. 
           [0023]      FIG. 2  shows the simulated Day 1 plasma level following dosing of 1×10 mg Flexeril® given. 3 times a day and 1×30 mg cyclobenzaprine HCl MR capsule given once-daily. 
           [0024]      FIG. 3  shows the drug release profiles for cyclobenzaprine HCl ER (extended release) beads of Example 2. 
           [0025]      FIG. 4  compares the drug release profiles as a function of membrane coating of Example 3. 
           [0026]      FIG. 5  shows the drug release profiles for cyclobenzaprine HCl ER beads of Example 3 stored in induction sealed HDPE bottles on accelerated stability. 
           [0027]      FIG. 6  shows the drug release profiles for 30 mg cyclobenzaprine HCl MR capsules of Example 4. 
           [0028]      FIG. 7  shows the plasma levels for cyclobenzaprine HCl MR capsules, 15 and 30 mg of Example 5. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    All documents cited are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. 
         [0030]    The active core of the dosage form of the present invention may be comprised of an inert particle or an acidic or alkaline buffer crystal, which is coated with a drug-containing film-forming formulation and preferably a water-soluble film forming composition to form a water-soluble/dispersible particle. Alternatively, the active may be prepared by granulating and milling and/or by extrusion and spheronization of a polymer composition containing the drug substance. The amount of drug in the core will depend on the dose that is required, and typically varies from about 5 to 60 weight %. Generally, the polymeric coating on the active core will be from about 4 to 20% based on the weight of the coated particle, depending on the type of release profile required and/or the polymers and coating solvents chosen. Those skilled in the art will be able to select an appropriate amount of drug for coating onto or incorporating into the core to achieve the desired dosage. In one embodiment, the inactive core may be a sugar sphere or a buffer crystal or an encapsulated buffer crystal such as calcium carbonate, sodium bicarbonate, fumaric acid, tartaric acid, etc. which alters the microenvironment of the drug to facilitate its release. 
         [0031]    The drug-containing particle may be coated with an extended release (ER) coating comprising a water insoluble polymer or a combination of a water insoluble polymer and a water soluble polymer to provide ER beads. In accordance with certain embodiments, the water insoluble polymer and the water soluble polymer may be present at a weight ratio of from 100/0 to 65/35, more particularly from about 95/5 to 70/30, and still more particularly at a ratio of from about 85/15 to 75/25. The extended release coating is applied in an amount necessary to provide the desired release profile. The extended release coating typically comprises from about 1% to 15%, more particularly from about 7% to 12%, by weight of the coated beads. 
         [0032]    The present invention also provides a method of making a modified release dosage form including a mixture of two bead populations. In accordance with one embodiment, the method includes the steps of:
       1. preparing a drug-containing core by coating an inert particle such as a non-pareil seed, an acidic buffer crystal or an alkaline buffer crystal with a drug and a polymeric binder or by granulation and milling or by extrusion/spheronization to form an immediate release (IR) bead;   2. coating the IR bead with a plasticized water-insoluble polymer alone such as ethylcellulose or in combination with a water soluble polymer such as hydroxypropylmethylcellulose to form an Extended Release (ER) bead;   3. filling into hard gelatin capsules ER Beads alone or in combination with IR Beads at a proper ratio to produce MR (modified release) capsules providing the desired release profile.       
 
         [0036]    IR beads when tested in accordance with the following procedure release at least about 70%, more specifically at least about 90% of the active within 30 minutes. 
         [0037]    Dissolution Procedure: 
         [0038]    Dissolution Apparatus: USP Apparatus 2 (Paddles at 50 rpm), dissolution medium: 900 mL 0.1N HCl (or a suitable dissolution medium) at 37° C. and Drug Release determination by HPLC). 
         [0039]    An aqueous or a pharmaceutically acceptable solvent medium may be used for preparing drug-containing core particles. The type of film forming binder that is used to bind the drug to the inert sugar sphere is not critical but usually water soluble, alcohol soluble or acetone/water soluble binders are used. Binders such as polyvinylpyrrolidone (PVP), polyethylene oxide, hydroxypropyl methylcellulose (HPMC), hydroxypropylcellulose (HPC), polysaccharides such as dextran, corn starch may be used at concentrations from about 0.5 to 5 weight %, although other concentrations may be useful. The drug substance may be present in this coating formulation in the solution form or may be dispersed at a solid content up to about 35 weight % depending on the viscosity of the coating formulation. 
         [0040]    In accordance with certain embodiments, the drug substance, optionally a binder such as PVP, a dissolution rate controlling polymer (if used), and optionally other pharmaceutically acceptable excipients are blended together in a planetary mixer or a high shear granulator such as Fielder and granulated by adding/spraying a granulating fluid such as water or alcohol. The wet mass can be extruded and spheronized to produce spherical particles (beads) using an extruder/marumerizer. In these embodiments, the drug load could be as high as 90% by weight based on the total weight of the extruded/spheronized core. 
         [0041]    Representative muscle relaxants include cyclobenzaprine, dantrolene sodium, methocarbamol, metaxalone, carisoprodol, diazepam and pharmaceutically acceptable salts or derivatives thereof. Cyclobenzaprine hydrochloride is a particularly useful muscle relaxant. As used herein, the useful muscle relaxants include the base, pharmaceutically acceptable salts thereof such as hydrochloride, stereoisomers thereof and mixtures thereof. 
         [0042]    Representative examples of water insoluble polymers useful in the ER coating include ethylcellulose powder or an aqueous dispersion (such as AQUACOAT® ECD-30), cellulose acetate, polyvinyl acetate (Kollicoat SR#30D from BASF), neutral copolymers based on ethyl acrylate and methylmethacrylate, copolymers of acrylic and methacrylic acid esters with quaternary ammonium groups such as Eudragit NE, RS and RS30D, RL or RL30D and the like. Representative examples of water soluble polymers useful herein include low molecular weight hydroxypropyl methylcellulose (HPMC), methylcellulose, hydroxypropylcellulose, polyvinylpyrrolidone, polyethylene glycol (PEG of molecular weight&gt;3000) and mixtures thereof. The extended release coating will typically be applied at a thickness ranging from about 1 weight % up to 15 weight % depending on the solubility of the active in water and the solvent or latex suspension based coating formulation used. 
         [0043]    The coating compositions used in forming the membranes are usually plasticized. Representative examples of plasticizers that may be used to plasticize the membranes include triacetin, tributyl citrate, triethyl citrate, acetyl tri-n-butyl citrate diethyl phthalate, polyethylene glycol, polypropylene glycol, castor oil, dibutyl sebacate, acetylated monoglycerides and the like or mixtures thereof. The plasticizer may comprise about 3 to 30 wt. % and more typically about 10 to 25 wt. % based on the polymer. The type of plasticizer and its content depends on the polymer or polymers, nature of the coating system (e.g., aqueous or solvent based, solution or dispersion based and the total solids). 
         [0044]    In general, it is desirable to prime the surface of the particle before applying an extended release membrane coating or to separate the different membrane layers by applying a thin hydroxypropyl methylcellulose (HPMC) (OPADRY® Clear) film. While HPMC is typically used, other primers such as hydroxypropylcellulose (HPC) can also be used. 
         [0045]    The membrane coatings can be applied to the core using any of the coating techniques commonly used in the pharmaceutical industry, but fluid bed coating is particularly useful. 
         [0046]    The present invention is applied to multi-dose forms, i.e., drug products in the form of multi-particulate dosage forms (pellets, beads, granules or mini-tablets) or in other forms suitable for oral administration. As used herein, these terms are used interchangeably to refer to multi-particulate dosage forms. 
         [0047]    The invention also provides a method of making an extended release dosage form which includes a mixture of two or more bead populations. In accordance with one aspect of the present invention, the method includes the steps of:
       (a) coating an inert particle such as a non-pareil seed, an acidic buffer crystal or an alkaline buffer crystal with a drug and polymeric binder to form an active drug particle (IR beads), which may be present in the unit dosage form to act as a bolus dose;   (b) coating the active drug particle with a solution or suspension of a water insoluble polymer or a mixture of water soluble and water insoluble polymers to form an extended release coated drug particle (ER beads);   (c) filling into a hard gelatin capsule ER beads alone and optionally, in combination with IR beads at a proper ratio ranging from 95/5 to 70/30 (ER beads/IR beads) to produce a MR (modified release) capsule exhibiting a target drug release profile.       
 
         [0051]    The following non-limiting examples illustrate the capsule dosage forms manufactured in accordance with the invention using cyclobenzaprine hydrochloride as a test case, which exhibit in vitro drug release profiles, similar to that predicted by performing modeling exercises. Such dosage forms when orally administered, would enable maintaining drug plasma concentrations at therapeutically effective levels over extended periods of time, thereby significantly improving patient compliance. 
       Example 1 
       [0052]    Cyclobenzaprine is well absorbed after oral administration, but there is a large intersubject variation in plasma levels. It is eliminated quite slowly with a half-life as long as one to three days. The present treatment regimen of 10 mg three times daily is an issue of patient compliance, especially the elderly. Hence, a modified release dosage form (capsule) was designed with a release profile shown in  FIG. 1 . To determine if this is the proper release profile, the pharmacokinetics data of cyclobenzaprine following a single dose of 10 mg Flexeril® tablets administered 3 times a day was taken from the literature. A pharmacokinetic model was developed from this data using WinNonlin™ Version 1.5. 
         [0053]    The resulting model parameters are listed below: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Model Parameter 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 Volume of Distribution/F 
                 429 L 
               
               
                   
                 K01 
                 0.2031 hr − 1   
               
               
                   
                 K10 
                 0.1004 hr −1   
               
               
                   
                 K12 
                 0.0828 hr −1   
               
               
                   
                 K21 
                 0.0398 hr −1   
               
               
                   
                 Tlag 
                 0 hr 
               
               
                   
                 Dose 
                 2 × 10 mg Tablets 
               
               
                   
                   
               
             
          
         
       
     
         [0054]    Theoretical plasma levels were simulated using the pharmacokinetic model given above and the target release rate given in  FIG. 1 .  FIG. 2  shows the simulated plasma levels for day one following dosing of 1×10 mg Flexeril® Tablet given 3 times a day and the proposed Cyclobenzaprine HCl MR Capsule, 30 mg given once a day. 
       Example 2  
       [0055]    Cyclobenzaprine Hydrochloride (1,200 g) was slowly added to an aqueous solution of polyvinylpyrrolidone such as Povidone USP (K-29/32, 80 g) and mixed well. #25-30 mesh sugar spheres (2,640 g) were coated with the drug solution in a Glatt fluid bed coater, equipped with a 9″ bottom spray Wurster insert to provide IR beads with a coating weight of about 9%. The drug containing particles were dried, and a seal coat of OPADRY® Clear (2% w/w) was first applied and dried in the Glatt fluid bed unit as a precautionary measure to drive off excessive surface moisture. The composition and batch quantities of the IR Beads were given in 5 to 10 kg. Following the second coating process the IR Beads were passed through 14 and 25 mesh screens. Beads remaining on the 14-mesh screen were discarded as oversized beads and beads passing through the 25-mesh screen were discarded as undersized beads. 
         [0056]    The next step in the process was to apply an extended release polymer membrane by spraying AQUACOAT® ECD 30, an aqueous dispersion of ethylcellulose with dibutyl sebacate (76:24), onto the IR Beads for a weight gain of approximately 10%. The same fluid bed equipment was used to produce ER (extended release) Beads by further coating the AQUACOAT® coated beads with OPADRY® Clear for a weight gain of 2% w/w prior to curing at 60° C. in a conventional oven for a period of 24 hours. The batch size was 5 to 10 kg. The drug release profiles are shown in  FIG. 3 . The figure also shows the drug release profiles from ER Beads stored in induction sealed HDPE bottles at 25° C./60% RH for 6 months. 
       Example 3 
       [0057]    Cyclobenzaprine Hydrochloride (2.5 kg) was dissolved in 50/50 acetone/purified water. 25-30 mesh Sugar spheres, (7.3 kg) were coated with the drug solution in a Glatt fluid bed coater, equipped with a 9″ bottom spray Wurster insert. The drug containing particles were dried, and a seal coat of OPADRY® Clear (2% w/w) was first applied and dried in the Glatt fluid bed unit as a precautionary measure to drive off excessive surface moisture. 910 g of ethylcellulose (Ethocel Premium Standard 10 cps) and 90 g of diethyl phthalate were dissolved in 98/02 acetone/purified water and applied onto the IR Beads (9 kg) in the Glatt GPCG 5 in accordance with the present invention. The release rates of the ER Beads will vary depending upon the film weight of the ER coating. One batch of IR Beads was coated for a final weight gain of 7% based on the weight of coated beads wherein samples of the ER Beads were removed during the ER coating process to yield beads with increasing coating weights. Another batch was coated for 10% weight gain and all the coated bead batches were cured at 60° C. for 4 hours in a conventional oven.  FIG. 4  shows the relationship between the ER coating weights and the release rate of the finished ER coated Beads. 
         [0058]    A batch was coated with a 7% ER coating and cured at 60° C. for 4 hours. No changes were noted in the release rates, assay values or impurity levels after storage in HDPE bottles at 40° C./75% RH for a period of 6 months. The release rates for the samples are shown in  FIG. 5 . 
       Example 4  
       [0059]    The drug layering, seal coating, and ER Coating processes were scaled-up to Glatt GPCG 120 equipped with an 18″ bottom spray Wurster insert (batch size: 80 kg for IR Beads and 85 kg for ER Beads). The process parameters of each of the processes were optimized. The drug layering solution (9% weight gain), seal coating solution, and the ER coating solution (9% weight gain) were sprayed onto the sugar spheres or IR Beads while maintaining the product temperature between narrow limits. Following the seal or ER coating the beads were passed through 14 and 25 mesh screens discarding any beads remaining on the 14 mesh screen. The ER Beads were also cured at 60° C. for a period of 4 hours. The Extended Release Beads were then filled into size 4 capsules to produce Cyclobenzaprine HCl MR Capsules, 15 and 30 mg. The drug release profiles of 30 mg capsules of one pivotal clinical and three registration stability batches are presented in  FIG. 6 . 
       Example 5 
       [0060]    A Randomized double-blind two-period crossover study to assess the safety and bioavailability of Cyclobenzaprine HCl Modified-release (CMR) 15 mg and 30 mg in healthy male and female volunteers (N=14 or 15) was performed. Each subject received one 15 mg or 30 mg capsule of CMR in the morning, separated by a 14-day washout period between doses. The results are presented in Table 1 and  FIG. 7  wherein AUC 0-168  refers to the area under the plasma concentration-time curve to the last measurable time point (168 hrs) calculated by the linear trapezoidal rule, AUC 0-∞  refers to area under the concentration-time curve to infinity, C max  refers to the maximum blood plasma concentration and T max  refers to the time to maximum plasma levels of cyclobenzaprine. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Pharmacokinetic Results: Mean (±SD) pharmacokinetic parameters are 
               
               
                 presented for subjects in the Safety population in the following table 
               
             
          
           
               
                   
                 CMR 15 mg 
                 CMR 30 mg 
               
               
                   
                 N = 15 
                 N = 14 
               
               
                   
                   
               
             
          
           
               
                 AUC 0-168  (ng · hr/mL) 
                 318.30 ± 114.657 
                  736.60 ± 259.414 
               
               
                 AUC 0-∞  (ng · hr/mL) 
                 354.075 ± 119.8037 
                  779.889 ± 277.6349 
               
               
                 C max  (ng/mL) 
                 8.315 ± 2.1635 
                 19.851 ± 5.8765 
               
               
                 Time to Peak, T max  (hr) 
                 8.1 ± 2.94 
                  7.1 ± 1.59 
               
               
                 Elimination Half-life, 
                 33.401 ± 10.2882 
                  31.977 ± 10.1310 
               
               
                 t 1/2  (hr) 
               
               
                   
               
             
          
         
       
     
         [0061]    The treatments were significantly different from each other as values for AUCs and C max  were higher for CMR 30 mg than those for CMR 15 mg. The bioavailability of CMR 30 mg was approximately twice that of CMR 15 mg as shown by the AUCs. The adjusted mean ratio of CMR 30 mg to CMR 15 mg was greater than about 2 for each of the AUCs and C max , specifically the calculated values were 2.42 for AUC 0-168  (p&lt;0.001), 2.286 for AUC 0-∞  (p&lt;0.001), and 2.424 for C max  (p&lt;0.001). Overall, both CMR 15 mg and 30 mg were well tolerated during the study. 
         [0062]    Accordingly, one aspect of the invention relates to a dosage form containing cyclobenzaprine hydrochloride as a skeletal muscle relaxant wherein the pharmaceutical dosage form provides a maximum blood plasma concentration (C max ) within the range of about 80% to 125% of about 20 ng/mL of cyclobenzaprine HCl, an AUC 0-168  within the range of about 80% to 125% of about 740 ng.hr/mL and a T max  within the range of about 80% to 125% of about 7 hours following oral administration of a single 30 mg cyclobenzaprine HCl MR Capsule. 
         [0063]    While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made without departing from the spirit and scope thereof.