The invention is directed to oral modified/controlled release drug formulations which provide a rapid initial onset of effect and a prolonged duration of effect. Preferably, the peak concentration is lower than that provided by the reference standard for immediate release formulations of the drug, and the duration of effect falls rapidly at the end of the dosing interval.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide new oral dosage formulations of methylphenidate or similarly acting drugs which results in improved patient compliance.

It is an object of the present invention to provide new oral dosage formulations which represent improvements over currently available preparations available for conditions such as Attention Deficit Hyperactivity Disorder (ADHD).

It is an object of the present invention to provide new oral dosage formulations of methylphenidate or similarly acting drugs which ensure adequate treatment throughout a child's school day.

It is an object of the present invention to provide new oral dosage formulations which allow a child with attention deficit disorder to be maximally treated throughout the daytime, while being administered only once, i.e., in the morning.

It is a further object of the present invention to provide new controlled/modified release oral dosage formulations which provide a rapid onset and rapid offset with an extended release of active medicaments incorporated therein.

It is yet another object of the present invention to provide new controlled/modified release oral dosage formulations which are useful in all types of pharmaceutically active ingredients and which can extend the time of release of all such ingredients.

It is yet another object of the present invention to provide an oral controlled release formulation which combines both a rapid onset and sustained plasma concentrations throughout the day, followed by a rapid drop-off of plasma concentrations of drug to below minimum effective concentrations.

It is yet another object of the present invention to provide a "multi-layer release" (MLR) technology which is useful for all types of pharmaceutically active ingredients and which can extend the duration of action for a desired length of time.

To address the above-mentioned deficiencies as well as other goals, the present invention is directed in part to a controlled release product which is intended to combined both a rapid onset and sustained plasma concentrations throughout the day. Significantly, the formulations of the present invention provide a rapid onset, a prolonged action, followed by rapid offset of effect, i.e., a "square wave" profile.

The invention is directed in part to controlled/modified release formulations based on a multi-layered release ("MLR") technology. The drug product can be in a tablet or a multiparticulate formulation contained within an oral gelatin capsule.

In the case of beads, encapsulated in a capsule, each bead contains a series of layers with different characteristics--an outer immediate release layer, a release delaying layer (enteric coat), a controlled release layer over an immediate release layer. The MLR formulation is designed such that upon oral administration, the formulation provides a rapid dissolution and absorption of the outer layer of the formulation which contains a portion of the drug in immediate release form, thereby resulting in a rapid rise of the drug to therapeutic plasma levels. This is followed by a period of no absorption (due to an enteric coating), followed thereafter by a controlled release of the drug from the formulation to maintain plasma levels. After absorption of the drug from an immediate release core, plasma levels then rapidly decrease. By virtue of the release of the drug from the MLR formulation, the plasma level of the drug, when plotted on a time/concentration curve, takes the appearance of a "square wave".

In certain further preferred embodiments, the formulation provides a time to maximum plasma concentration at about 0.5 to about 4 hours after oral administration and provides effective blood levels for at least about 6 hours after administration.

In certain further preferred embodiments, the formulation exhibits a "plateau" in the blood plasma curve which lasts from about 2 hours to about 6 hours. Other embodiments exhibit a "plateau" which lasts from about 6 hours to about 12 hours. The "plateau" is characterized by a stabilized plasma concentration, wherein the plasma level at the end of the measured interval does not differ by more than 20%, preferably by no more than 10% of the plasma concentration at the beginning of the measured interval.

In certain further preferred embodiments, the formulation exhibits a bimodal release of active agent from the dosage form. Bimodal release of the active agent is characterized by the active agent being release from the dosage form by more than one distinct release rate. In some embodiments, the release rates can be separated by a no-release or a substantially no-release interval, although this is not always necessary.

In certain further preferred embodiments, the formulation exhibits a biphasic absorption of the active agent. Biphasic absorption of the active agent is characterized by the active agent being absorbed through a natural barrier (e.g. the mucosal lining of the gastro-intestinal tract) by more than one distinct absorption rate. In some embodiments, the absorption rates can be separated by a no-absorption or a substantially no-absorption interval, although this is not always necessary. A formulation can exhibit both biphasic absorption and bimodal release of the active agent, with the biphasic absorption being a function of the bimodal release rate. However, biphasic absorption is not always attributed to release rate and can occur in a formulation not exhibiting bimodal release.

In other preferred embodiments the formulation exhibits bimodal release and/or biphasic absorption to provide a "plateau" in the blood plasma curve which lasts from about 2 hours to about 6 hours. Other embodiments exhibit bimodal release and/or biphasic absorption to provide a "plateau" which lasts from about 6 hours to about 12 hours. Other embodiments maintain effective plasma levels of the active agent for about 16 to about 18 hours after administration of the dosage form.

In certain preferred embodiments, an acrylic resin is utilized to provide the controlled slow release of therapeutically active ingredients over a predetermined or a specified period of time, the acrylic resin thereby comprising a significant part of the "base composition". Base compositions prepared from such acrylic resins provide sustained release of therapeutically active ingredients over a period of time from five hours and for as much as 24 hours after administration, generally oral administration, in humans or animals.

In other embodiments of the invention, the formulations of the invention are composed of: (i) a mixture of immediate release particles (e.g., beads) and enteric coated immediate release particles (e.g., beads); (ii) a mixture of immediate release particles (e.g., beads) and enteric coated controlled release particles (e.g., beads) or (iii) a mixture of immediate release particles (e.g., beads) and controlled release particles (e.g., beads). In each such instance, the mixture of particles possessing different release properties are blended together and filled into hard gelatin capsules.

In certain preferred embodiments, the controlled/modified release drug formulations of the invention consist of a plurality of beads, each containing an immediate-release component in combination with an enteric coated controlled-release component to produce a delay in the absorption process. The drug product is an oral capsule containing beads. Each bead contains a series of layers with different release characteristics--an outer immediate release layer; a release delaying layer; a controlled release layer; and an immediate release core. The final product is a capsule containing multi-layer release (MLR) beads which have both immediate release and controlled release components. It is made up of a controlled release bead which is enteric coated to delay dissolution until after gastric emptying. The enteric coated controlled release bead has an immediate release topcoat to provide an initial rate of absorption of the drug. In certain embodiments, the immediate release component represents 40% of the total dose per bead and the controlled release component represents 60%. This formulation is designed to produce a rapid rise to therapeutic plasma levels after oral administration, due to the rapid dissolution and absorption of the outer layer, followed by a period of reduced absorption and then controlled release of the immediate release core, to maintain therapeutic plasma levels. After absorption of the immediate release core, plasma levels would then decrease according to the elimination kinetics of the drug. The results of a bioavailability study of this formulation indicate a biphasic release profile that is consistent with the pharmaceutical rationale discussed herein.

In other embodiments of the invention, the bead size of the formulations can be adjusted in order to obtain a desired pharmacokinetic profile based on the correlation between gastric emptying and bead size. A smaller bead size exhibits faster gastric emptying as compared to a larger bead size.

DETAILED DESCRIPTION OF THE INVENTION

The drug used in the formulations of the invention may be selected from a wide variety of pharmaceutically active drugs such as diabetes drugs, attention deficit hyperactivity controlled drugs, analgesics, anti-obesity preparations, anti-inflammatories, antihistamines, antitussives, decongestants, antinausea agents, narcotics, bronchodilators, cardiovasculars, central nervous system (CNS) drugs, nicotine replacement therapy, nitrates, sleeping aids/sedatives, vitamins, etc.

The controlled/modified release preparations of the present invention may be used in conjunction with any multiparticulate system, such as granules, spheroids, beads, pellets, ion-exchange resin beads, and other multiparticulate systems in order to obtain a desired sustained-release of the therapeutically active agent. Beads, granules, spheroids, or pellets, etc., prepared in accordance with the present invention can be presented in a capsule or in any other suitable unit dosage form. An amount of the multiparticulates effective to provide the desired dose of drug over time may be placed in a capsule, may be contained in a packet and sprinkled onto food, or may be incorporated in any other suitable oral solid form, such as a tablet. On the other hand, the present invention can be in the form of a matrix tablet. With respect to all such optional formulations, it is desired that the formulation be prepared such that an initial immediate release of drug provides an early onset of effect, which onset is analogous to an immediate release formulation, and that the formulation further provide a sustained release component which maintains therapeutically effective levels of the drug in the plasma for the desired amount of time, followed by a relatively rapid drop-off in blood plasma levels relative to typical sustained release formulations. Viewed as an in vivo time/concentration plot, the plasma level of the drug from the formulations of the present invention have the appearance of a "square wave". The immediate release component preferably represents from about 30% to about 40% of the total dose and the controlled release component preferably represents from about 60% to about 70% of the total dose of methylphenidate contained in the formulations of the present invention. In certain preferred embodiments, including the MLR embodiments of the invention, the immediate release component represents about 40% of the total dose and the controlled release component represents about 60% of the total dose of methylphenidate contained in the formulation.

In the case of methylphenidate, it is desired that the onset of action occurs from about 0.5 to about 4 hours, and preferably from about 0.5 to about 2 hours after the oral dosage form is administered, and it is further desired that the dosage form no longer provides effective plasma levels of methylphenidate from about 8 to about 12, more preferably from about 8 to about 10 hours, after oral administration of the dose. In this manner, the dose of methylphenidate can be administered to a child in the morning before school begins, provides the desired effect at the start of the school day, with the pharmacologic action of the drug not waning until after the school day ends, and preferably before dinner so that the drug does not have the side effect of acting as an appetite suppressant.

The formulations of the present invention are designed to produce a rapid rise to therapeutic plasma levels after oral administration, due to the rapid dissolution and absorption of the outer layer, followed by a period of reduced absorption and then controlled release of the immediate release core, to maintain therapeutic plasma levels. After absorption of the immediate release core, plasma levels would then decrease according to the elimination kinetics of the drug.

It is generally recognized that the mere presence of an active substance in the gastrointestinal fluids does not, by itself, insure bioavailability. Bioavailability, in a more meaningful sense, is the degree, or amount, to which a drug substance is absorbed into the systemic circulation in order to be available to a target tissue site. To be absorbed, an active drug substance must be in a solution. The time required for a given proportion of an active drug substance contained in a dosage unit to enter into solution in appropriate physiological fluids is known as the dissolution time. The dissolution time for an active substance from a dosage unit is determined as the proportion of the amount of active drug substance released from the dosage unit over a specified time by a test method conducted under standardized conditions. The physiological fluids of the gastrointestinal tract are the media for determining dissolution time. The present state of the art dissolution time for pharmaceutical compositions, and these test procedures are described in official compendia world wide.

Although there are many diverse factors which influence the dissolution of a drug substance from its carrier, the dissolution time determined for a pharmacologically active substance from a specific composition is relatively constant and reproducible. Among the different factors affecting the dissolution time are the surface area of the drug substance presented to the dissolution solvent medium, the pH of the solution, the solubility of the substance in the specific solvent medium, and the driving forces of the saturation concentration of dissolved materials in the solvent medium. Thus, the dissolution concentration of an active drug substance is dynamically modified in this steady state as components are removed from the dissolution medium through absorption across the tissue site. Under physiological conditions, the saturation level of the dissolved materials is replenished from the dosage form reserve to maintain a relatively uniform and constant dissolution concentration in the solvent medium, providing for a steady state absorption.

The transport across a tissue absorption site in the gastrointestinal tract is influenced by the Donnan osmotic equilibrium forces on both sides of the membrane, since the direction of the driving force is the difference between the concentrations of active substance on either side of the membrane, i.e. the amount dissolved in the gastrointestinal fluids and the amount present in the blood. Since the blood levels are constantly being modified by dilution, circulatory changes, tissue storage, metabolic conversion and systemic excretion, the flow of active materials is directed from the gastrointestinal tract into the blood stream.

Notwithstanding the diverse factors influencing both dissolution and absorption of a drug substance, in many cases an important correlation can be established between the in vitro dissolution time determined for a dosage form and the in vivo bioavailability. This correlation is so firmly established in the art that dissolution time has become generally descriptive of bioavailability potential for many classes of active components contained in a particular dosage form. In view of this relationship, the dissolution time determined for a composition is one of the important fundamental characteristics for consideration when evaluating whether a controlled release formulation should be tested in vivo.

With the above in mind, the in-vitro dissolution of the drug at various time points for formulations in accordance with the present invention is provided below -- see Original Patent.

In certain preferred embodiments of the present invention, the in-vitro dissolution of the drug at various time points for formulations in accordance with the present invention is provided below -- see Original Patent.

Sustained Release Coatings

In certain preferred embodiments, the drug is incorporated into or onto a substrate and a sustained release coating is applied thereto. For example, the drug may be contained within or on a substrate as follows: (i) incorporated into matrix spheroids (e.g., together with a pharmaceutically acceptable spheronizing agent such as microcrystalline cellulose), (ii) coated into inert pharmaceutically acceptable beads (e.g., nonpareil beads); (iii) incorporated into a normal release tablet core; or (iv) incorporated into a tablet core which comprises a matrix including an sustained release carrier material. Thereafter, a sustained release coating is applied into substrates such as those mentioned in (i) (iv) above. The dosage forms of the present invention may optionally be coated with one or more materials suitable for the regulation of release or for the protection of the formulation. In one embodiment, coatings are provided to permit either pH-dependent or pH-independent release, e.g., when exposed to gastrointestinal fluid A pH-dependent coating serves to release the drug in desired areas of the gastrointestinal (GI) tract, e.g., the stomach or small intestine. When a pH-independent coating is desired, the coating is designed to achieve optimal release regardless of pH-changes in the environmental fluid, e.g., the GI tract. It is also possible to formulate compositions which release a portion of the dose in one desired area of the GI tract, e.g., the stomach, and release the remainder of the dose in another area of the GI tract, e.g., the small intestine.

Formulations according to the invention that utilize pH-dependent coatings to obtain formulations may also impart a repeat-action effect whereby unprotected drug is coated over the enteric coat and is released in the stomach, while the remainder, being protected by the enteric coating, is released further down the gastrointestinal tract. Coatings which are pH-dependent may be used in accordance with the present invention include shellac, cellulose acetate phthalate (CAP), polyvinyl acetate phthalate (PVAP), hydroxypropylmethylcellulose phthalate, and methacrylic acid ester copolymers, zein, and the like.

In certain preferred embodiments, the substrate (e.g., tablet core bead, matrix particle) comprising the drug is coated with a hydrophobic material selected from (i) an alkylcellulose; (ii) an acrylic polymer; or (iii) mixtures thereof. The coating may be applied in the form of an organic or aqueous solution or dispersion. The coating may be applied to obtain a weight gain from about 2 to about 25% of the substrate in order to obtain a desired sustained release profile. Such formulations are described, e.g., in detail in U.S. Pat. Nos. 5,273,760 and 5,286,493, assigned to the Assignee of the present invention and hereby incorporated by reference. The particles are preferably film coated with a material that permits release of the drug so as to achieve, in combination with the other stated properties, a desired in-vitro release rate and in-vivo plasma levels. The sustained release coating formulations of the present invention should be capable of producing a strong, continuous film that is smooth and elegant, capable of supporting pigments and other coating additives, non-toxic, inert, and tack-free.

Other examples of sustained release formulations and coatings which may be used in accordance with the present invention include Assignee's U.S. Pat. Nos. 5,324,351; 5,356,467, and 5,472,712, hereby incorporated by reference in their entirety.

Alkylcellulose Polymers

Cellulosic materials and polymers, including alkylcelluloses, provide hydrophobic materials well suited for coating the beads according to the invention. Simply by way of example, one preferred alkylcellulosic polymer is ethylcellulose, although the artisan will appreciate that other cellulose and/or alkylcellulose polymers may be readily employed, singly or in any combination, as all or part of a hydrophobic coating according to the invention.

One commercially available aqueous dispersion of ethylcellulose is Aquacoat.RTM. (FMC Corp., Philadelphia, Pa., U.S.A.). Aquacoat.RTM. is prepared by dissolving the ethylcellulose in a water-immiscible organic solvent and then emulsifying the same in water in the presence of a surfactant and a stabilizer. After homogenization to generate submicron droplets, the organic solvent is evaporated under vacuum to form a pseudolatex. The plasticizer is not incorporated in the pseudolatex during the manufacturing phase. Thus, prior to using the same as a coating, it is necessary to intimately mix the Aquacoat.RTM. with a suitable plasticizer prior to use.

Another aqueous dispersion of ethylcellulose is commercially available as Surelease.RTM. (Colorcon, Inc., West Point, Pa., U.S.A.). This product is prepared by incorporating plasticizer into the dispersion during the manufacturing process. A hot melt of a polymer, plasticizer (dibutyl sebacate), and stabilizer (oleic acid) is prepared as a homogeneous mixture, which is then diluted with an alkaline solution to obtain an aqueous dispersion which can be applied directly onto substrates.

Acrylic Polymers

The hydrophobic material comprising the controlled release coating may comprise a pharmaceutically acceptable acrylic polymer, including but not limited to acrylic acid and methacrylic acid copolymers, methyl methacrylate copolymers, ethoxyethyl methacrylates, cyanoethyl methacrylate, poly(acrylic acid), poly(methacrylic acid), methacrylic acid alkylamide copolymer, poly(methyl methacrylate), polymethacrylate, poly(methyl methacrylate)copolymer, polyacrylamide, aminoalkyl methacrylate copolymer, poly(methacrylic acid anhydride), and glycidyl methacrylate copolymers.

In certain preferred embodiments, the acrylic polymer is comprised of one or more ammonio methacrylate copolymers. Ammonio methacrylate copolymers are well known in the art, and are described in NF XVII as fully polymerized copolymers of acrylic and methacrylic acid esters with a low content of quaternary ammonium groups.

In order to obtain a desirable dissolution profile, it may be necessary to incorporate two or more ammonio methacrylate copolymers having differing physical properties, such as different molar ratios of the quaternary ammonium groups to the neutral (meth)acrylic esters.

Certain methacrylic acid ester-type polymers are useful for preparing pH-dependent coatings which may be used in accordance with the present invention. For example, there are a family of copolymers synthesized from diethylaminoethyl methacrylate and other neutral methacrylic esters, also known as methacrylic acid copolymer or polymeric methacrylates, commercially available as Eudragit.RTM. from Rohm Tech, Inc. There are several different types of Eudragit.RTM.. For example, Eudragit.RTM. E is an example of a methacrylic acid copolymer which swells and dissolves in acidic media. Eudragit.RTM. L is a methacrylic acid copolymer which does not swell at about pH<5.7 and is soluble at about pH>6. Eudragit.RTM. S does not swell at about pH<6.5 and is soluble at about pH>7. Eudragit.RTM. RL and Eudragit.RTM. RS are water swellable, and the amount of water absorbed by these polymers is pH-dependent, however, dosage forms coated with Eudragit.RTM. RL and RS are pH-independent.

In certain preferred embodiments, the acrylic coating comprises a mixture of two acrylic resin lacquers commercially available from Rohm Pharma under the Tradenames Eudragit.RTM. RL30D and Eudragit.RTM. RS30D, respectively. Eudragit.RTM. RL30D and Eudragit.RTM. RS30D are copolymers of acrylic and methacrylic esters with a low content of quaternary ammonium groups, the molar ratio of ammonium groups to the remaining neutral (meth)acrylic esters being 1:20 in Eudragit.RTM. RL30D and 1:40 in Eudragit.RTM. RS30D. The mean molecular weight is about 150,000. The code designations RL (high permeability) and RS (low permeability) refer to the permeability properties of these agents. Eudragit.RTM. RL/RS mixtures are insoluble in water and in digestive fluids. However, coatings formed from the same are swellable and permeable in aqueous solutions and digestive fluids.

The Eudragit.RTM. RL/RS dispersions of the present invention may be mixed together in any desired ratio in order to ultimately obtain a sustained release formulation having a desirable dissolution profile. Desirable sustained release formulations may be obtained, for instance, from a retardant coating derived from 100% Eudragit.RTM. RL, 50% Eudragit.RTM. RL and 50% Eudragit.RTM. Rs, and 10% Eudragit.RTM. RL: 90% Eudragit.RTM. RS. Of course, one skilled in the art will recognize that other acrylic polymers may also be used, such as, for example, Eudragit.RTM. L.

Plasticizers

In embodiments of the present invention where the coating comprises an aqueous dispersion of a hydrophobic material such as an alkylcellulose or an acrylic polymer, the inclusion of an effective amount of a plasticizer in the aqueous dispersion of hydrophobic material will further improve the physical properties of the sustained release coating. For example, because ethylcellulose has a relatively high glass transition temperature and does not form flexible films under normal coating conditions, it is preferable to incorporate a plasticizer into an ethylcellulose coating containing sustained release coating before using the same as a coating material. Generally, the amount of plasticizer included in a coating solution is based on the concentration of the film-former, e.g., most often from about 1 to about 50 percent by weight of the film-former. Concentration of the plasticizer, however, can only be properly determined after careful experimentation with the particular coating solution and method of application.

Examples of suitable plasticizers for ethylcellulose include water insoluble plasticizers such as dibutyl sebacate, diethyl phthalate, triethyl citrate, tributyl citrate, and triacetin, although it is possible that other water-insoluble plasticizers (such as acetylated monoglycerides, phthalate esters, castor oil, etc.) may be used. Triethyl citrate is an especially preferred plasticizer for the aqueous dispersions of ethyl cellulose of the present invention.

Examples of suitable plasticizers for the acrylic polymers of the present invention include, but are not limited to citric acid esters such as triethyl citrate NF XVI, tributyl citrate, dibutyl phthalate, and possibly 1,2-propylene glycol. Other plasticizers which have proved to be suitable for enhancing the elasticity of the films formed from acrylic films such as Eudragit.RTM. RL/RS lacquer solutions include polyethylene glycols, propylene glycol, diethyl phthalate, castor oil, and triacetin. Triethyl citrate is an especially preferred plasticizer for the aqueous dispersions of ethyl cellulose of the present invention.

It has further been found that the addition of a small amount of talc reduces the tendency of the aqueous dispersion to stick during processing, and acts as a polishing agent.

When the aqueous dispersion of hydrophobic material is used to coat a substrate including the drug, for example, inert pharmaceutical beads such as nu pariel 18/20 beads, a plurality of the resultant stabilized solid controlled release beads may thereafter be placed in a gelatin capsule in an amount sufficient to provide an effective controlled release dose when ingested and contacted by an environmental fluid, e.g., gastric fluid or dissolution media. Alternatively, the substrate may be a tablet core coated with the sustained release coating, and optionally a further film-forming agent or colorant, such as Opadry.RTM..

In formulations where an aqueous dispersion of an hydrophobic polymer such as an alkylcellulose is applied to the substrate, it is preferred that the coated substrate is cured at a temperature above the glass transition temperature of the plasticized polymer and at a relative humidity above ambient conditions, until an endpoint is reached at which the coated formulation attains a dissolution profile which is substantially unaffected by exposure to storage conditions, e.g., of elevated temperature and/or humidity. Generally, in such formulations the curing time is about 24 hours or more, and the curing conditions may be, for example, about 60.degree. C. and 85% relative humidity. Detailed information concerning the stabilization of such formulations is set forth in U.S. Pat. Nos. 5,273,760; 5,681,585; and 5,472,712; all of which are hereby incorporated by reference in their entireties.

In formulations where an aqueous dispersion of an acrylic polymer is applied to the substrate, it is preferred that the coated substrate is cured at a temperature above the glass transition temperature of the plasticized polymer until an endpoint is reached at which the coated formulation attains a dissolution profile which is substantially unaffected by exposure to storage conditions, e.g., of elevated temperature and/or humidity. Generally, the curing time is about 24 hours or more, and the curing temperature may be, for example, about 45.degree. C. Detailed information concerning the stabilization of such formulations is set forth in U.S. Pat. Nos. 5,286,493; 5,580,578; and 5,639,476; all of which are hereby incorporated by reference in their entireties.

The sustained release profile of the coated formulations of the invention can be altered, for example, by varying the amount of overcoating with the aqueous dispersion of hydrophobic material, altering the manner in which the plasticizer is added to the aqueous dispersion of hydrophobic material, by varying the amount of plasticizer relative to hydrophobic material, by the inclusion of additional ingredients or excipients, by altering the method of manufacture, etc. The dissolution profile of the ultimate product may also be modified, for example, by increasing or decreasing the thickness of the retardant coating.

Spheroids or beads coated with a therapeutically active agent are prepared, e.g., by dissolving the therapeutically active agent in water and then spraying the solution onto a substrate, for example, nu pariel 18/20 beads, using a Wuster insert. Optionally, additional ingredients are also added prior to coating the beads in order to assist the binding of the drug to the beads, and/or to color the solution, etc. For example, a product which includes hydroxypropylmethylcellulose, etc. with or without colorant (e.g., Opadry.RTM., commercially available from Colorcon, Inc.) may be added to the solution and the solution mixed (e.g., for about 1 hour) prior to application of the same onto the beads. The resultant coated substrate, in this example beads, may then be optionally overcoated with a barrier agent, to separate the therapeutically active agent from the hydrophobic controlled release coating. An example of a suitable barrier agent is one which comprises hydroxypropyhnethylcellulose. However, any film-former known in the art may be used. It is preferred that the barrier agent does not affect the dissolution rate of the final product.

The beads may then be overcoated with an aqueous dispersion of the hydrophobic material. The aqueous dispersion of hydrophobic material preferably further includes an effective amount of plasticizer, e.g. triethyl citrate. Pre-formulated aqueous dispersions of ethyl-cellulose, such as Aquacoat.RTM. or Surelease.RTM., may be used. If Surelease is used, it is not necessary to separately add a plasticizer. Alternatively, pre-formulated aqueous dispersions of acrylic polymers such as Eudragit can be used.

The coating solutions of the present invention preferably contain, in addition to the film-former, plasticizer, and solvent system (i.e., water), a colorant to provide elegance and product distinction. Color may be added to the solution of the therapeutically active agent instead, or in addition to the aqueous dispersion of hydrophobic material. For example, color be added to Aquacoat via the use of alcohol or propylene glycol based color dispersions, milled aluminum lakes and opacifiers such as titanium dioxide by adding color with shear to water soluble polymer solution and then using low shear to the plasticized Aquacoat. Alternatively, any suitable method of providing color to the formulations of the present invention may be used. Suitable ingredients for providing color to the formulation when an aqueous dispersion of an acrylic polymer is used include titanium dioxide and color pigments, such as iron oxide pigments. The incorporation of pigments, may, however, increase the retard effect of the coating.

The plasticized aqueous dispersion of hydrophobic material may be applied onto the substrate comprising the therapeutically active agent by spraying using any suitable spray equipment known in the art. In a preferred method, a Wurster fluidized-bed system is used in which an air jet, injected from underneath, fluidizes the core material and effects drying while the acrylic polymer coating is sprayed on. A sufficient amount of the aqueous dispersion of hydrophobic material to obtain a predetermined sustained release of the therapeutically active agent (i.e., drug) when the coated substrate is exposed to aqueous solutions, e.g. gastric fluid, is preferably applied, taking into account the physical characteristics of the therapeutically active agent, the manner of incorporation of the plasticizer, etc. After coating with the hydrophobic material, a further overcoat of a film-former, such as Opadry, is optionally applied to the beads. This overcoat is provided, if at all, in order to substantially reduce agglomeration of the beads.

The release of the drug from the sustained release formulation of the present invention can be further influenced, i.e., adjusted to a desired rate, by the addition of one or more release-modifying agents, or by providing one or more passageways through the coating. The ratio of hydrophobic material to water soluble material is determined by, among other factors, the release rate required and the solubility characteristics of the materials selected.

The release-modifying agents which function as pore-formers may be organic or inorganic, and include materials that can be dissolved, extracted or leached from the coating in the environment of use. The pore-formers may comprise one or more hydrophilic materials such as hydroxypropylmethylcellulose.

The sustained release coatings of the present invention can also include erosion-promoting agents such as starch and gums.

The sustained release coatings of the present invention can also include materials useful for making microporous lamina in the environment of use, such as polycarbonates comprised of linear polyesters of carbonic acid in which carbonate groups reoccur in the polymer chain.

The release-modifying agent may also comprise a semi-permeable polymer.

In certain preferred embodiments, the release-modifying agent is selected from hydroxypropylmethylcellulose, lactose, metal stearates, and mixtures of any of the foregoing.

The sustained release coatings of the present invention may also include an exit means comprising at least one passageway, orifice, or the like. The passageway may be formed by such methods as those disclosed in U.S. Pat. Nos. 3,845,770; 3,916,889; 4,063,064; and 4,088,864 (all of which are hereby incorporated by reference). The passageway can have any shape such as round, triangular, square, elliptical, irregular, etc.

The substrate of the present invention may be prepared by a spheronizing agent together with the active agent ingredient that can be spheronized to form spheroids. Microcrystalline cellulose is preferred. A suitable microcrystalline cellulose is, for example, the material sold as Avicel PH 101 (Trade Mark, FMC Corporation). In such embodiments, in addition to the active ingredients and spheronizing agent, the spheroids may also contain a binder. Suitable binders, such as low viscosity, water soluble polymers, will be well known to those skilled in the pharmaceutical art. However, water soluble hydroxy lower alkyl cellulose, such as hydroxypropylcellulose, are preferred. Additionally (or alternatively) the spheroids may contain a water insoluble polymer, especially an acrylic polymer, an acrylic copolymer, such as a methacrylic acid-ethyl acrylate copolymer or ethyl cellulose. In such embodiments, the sustained-release coating will generally include a water insoluble material such as (a) a wax, either alone or in admixture with a fatty alcohol; or (b) shellac or zein.

In a particular preferred embodiment of the invention, the controlled/modified release methylphenidate formulation is prepared as a multilayered release (MLR) formulation comprising coated inert beads. A summary of one method of manufacturing such a formulation is outlined as follows. First, immediate release (IR) drug-coated beads are prepared by spraying a solution of methylphenidate in water over sugar beads in a fluid bed dryer with a drug load of about 8%. The spray process is carried out in a fluid bed dryer, equipped with a Wurster column. A clear overcoat of HPMC is applied using an Opadry.RTM. material (e.g., Opadry.RTM. Clear (Formula No: YS-1-7006)), to a weight gain of about 1%. Next, a controlled release coating is applied to the IR beads, which converts the same into controlled release (CR) beads. This is accomplished by spraying a solution of Eudragit.RTM. RS 30 D, triethyl citrate (plasticizer) and talc (glidant), onto the IR beads. Next, the coated beads are cured in order to obtain a stabilized release rate of the therapeutically active agent. In preferred embodiments of the present invention where the CR coating utilizes an acrylic resin to control the release of the drug, the CR beads at this stage are subjected to oven curing at a temperature above the Tg of the plasticized acrylic polymer of the required time period, the optimum values of the temperature and time for the particular formulation being determined experimentally. In certain embodiments of the present invention, the stabilized products is obtained via oven curing conducted at a temperature of about 40 50.degree. C. for a time period of about 12 to about 24 hours or longer. An enteric coating is then applied onto the CR beads to convert the same into enteric coated CR (ECCR) beads. This is accomplished by spraying a solution of Eudragit.RTM. L 30 D-55 dispersion, triethyl citrate (plasticizer) and talc (glidant) onto the CR beads. Finally, an immediate release coating is applied onto the ECCR beads (referred to as, e.g., an IR Topcoat). This is accomplished by spraying a solution of methylphenidate in water over EC CR beads.

Results of initial studies show that this formulation is stable under room temperature (25.degree. C., 60% RH) and accelerated conditions (40.degree. C., 75% RH).

In certain preferred embodiments of the present invention, an effective amount of the drug in immediate release form is included in the drug formulation. The immediate release form of the drug is included in an amount which is effective to shorten the time to maximum concentration of the drug in the blood (e.g., plasma), such that time to T.sub.max is shortened to a time of, e.g., from about 0.5 to about 2 hours. By including an amount of immediate release drug in the formulation, the time to onset of action is significantly reduced, and is the same or earlier than that of the reference standard immediate release treatment (e.g., Ritalin IR). In such embodiments, an effective amount of the drug in immediate release form may be coated onto the substrates (e.g., multiparticulates or tablets) of the present invention. For example, where the extended release of the drug from the formulation is due to a controlled release coating, the immediate release layer can be overcoated on top of the controlled release coating. On the other hand, the immediate release layer may be coated onto the surface of substrates wherein the drug is incorporated in a controlled release matrix. Where a plurality of the sustained release substrates comprising an effective unit dose of the drug (e.g., multiparticulate systems including pellets, spheres, beads and the like) are incorporated into a hard gelatin capsule, the immediate release portion of the drug dose may be incorporated into the gelatin capsule via inclusion of the sufficient amount of immediate release drug as a powder or granulate within the capsule. Alternatively, the gelatin capsule itself may be coated with an immediate release layer of the drug. One skilled in the art would recognize still other alternative manners of incorporating the immediate release drug portion into the unit dose. Such alternatives are deemed to be encompassed by the appended claims.
 

Claim 1 of 12 Claims

1. An oral controlled release formulation which provides a rapid onset of therapeutic effect and a rapid drop in plasma concentration after a prolonged period of therapeutic effect, comprising a plurality of substrates comprising a portion of an effective dose of methylphenidate hydrochloride in immediate release form, a hydrophobic material comprising an acrylic polymer, coated onto the surface of said substrates in an amount sufficient to retard the release of said drug, an enteric coating applied over said hydrophobic coating in an amount sufficient to substantially delay the release of said drug from said substrate until after said formulation passes through the stomach, wherein said enteric coating is derived from an aqueous dispersion comprising an acrylic/methacrylic copolymer, a plasticizer and a glidant, the formulation further comprising the remaining portion of said methylphenidate hydrochloride in immediate release form, and wherein the formulation provides a time to maximum plasma concentration of said methylphenidate hydrochloride at about 0.5 to about 4 hours after oral administration.

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