Controlled release drug dispersion delivery device

Abstract: A device for the controlled delivery of a beneficial agent as a gelatinous dispersion consisting of (i) a core which contains a beneficial agent, a polymer which forms gelatinous micoroscopic particles upon hydration and if desired an agent to modulate the hydration of the polymer; and (ii) an impermeable, insoluble coating which adheres to and surrounds the core and contains apertures which provide an area for the hydration and release of a disperson comprising gelatinous microscopic particles.

Description: This invention pertains to both a useful and novel drug-delivery device for dispensing a drug to an environment of use. Particularly, the invention pertains to a system that releases a drug in a controlled fashion, by creating gelatinous microscopic particles of polymer and in so doing, generates a dispersion of drug among the microscopic particles. The dispersion then moves from the device surface into the aqueous environment of use. The device is composed of a core containing a beneficial agent such as a medicament, a polymer which provides gelatinous microscopic particles upon hydration and if desired a hydration modulating agent. The device is completely coated with an insoluble, impermeable coating. The coating contains apertures to expose discrete portions of the surface of the core. The delivery rate of the medicament is a function of the core composition as well as the number and size of the apertures. In the environment of use, biological fluid contacts the exposed portions of the core surface where hydration of the polymer at the surface begins. As the particles of polymer at the exposed surface absorb water, a gelatinous microscopic dispersion of particles results. Mixed with and dispersed in these microscopic particles are the other components of the core formulation, such as a medicament. The exposed portion of the core surface is bounded on all sides by the coating. Hydration of the polymer occurs at the exposed surface of the core, resulting in the steady-state formation of a gelatinous microscopic particle dispersion within which the drug is dispensed and which moves into the environment of use. The rate of release of the beneficial agent is not dependent upon the solubility of the beneficial agent in the biological fluid. Rather, the release rate is essentially dependent upon the rate at which the gelatinous microscopic particle dispersion forms at the exposed surface of the device core and exudes from the device carrying with it the beneficial agent and any other core excipient materials that are present. BACKGROUND OF THE INVENTION The need for systems that can deliver any drug at a controlled rate of release to an environment of use over a specified period of time is well established. U.S. Patent 4,814,182 discloses the use of rods or slabs of pre-hydrated and swelled polyethylene oxide hydrogel. The polymer is impregnated with a biologically active agent during the hydration procedure. The hydrated polymer is then dried and partially coated with an impermeable, insoluble material. When placed in an aqueous environment, the polymer swells but does not dissolve or disintegrate. The entrapped active ingredient is released from the polymer by diffusion. The mechanism of release is based on the ability of the soluble drug to diffuse through the rehydrated hydrogel and move into the aqueous environment. U.S. Patent 4,839,177 discloses the use of hydrogels compressed to defined geometric forms. In this device, the polymer is mixed with biologically active ingredients to form a core which is affixed to a "support platform" made of an insoluble polymeric material. When hydrated, the swellable, gellable hydrogel expands beyond the device and establishes a superstructure from which the active agent is released either by diffusion, if the active agent is soluble, or by erosion, if the active agent is insoluble. The generation and maintenance of the superstructure is vital to the proper operation of this device. An osmotic dosage form which utilizes a semipermeable wall containing at least one "exit means" which passes through the wall, surrounding a core containing an osmotic agent, a neutral and ionizable hydrogel and an active ingredient is taught in U.S. patent 4,971,790. The coating of this device is permeable to water from the environment of use. Water moves into the core through the semipermeable membrane. Once inside the device, the water solubilizes the osmotic agent, and hydrates the hydrogels. Pressure builds up inside the device. Ultimately, the solubilized hydrogel, containing the beneficial agent, and other core excipients are pumped out of the core, under pressure, through an exit means and into the environment of use. U.S. Patent No. 4,327,725 describes a similar dosage form comprising a semipermeable wall surrounding a compartment containing an active agent adjacent to an exit means in the wall and a layer of an expandable driving member formed of a water-swellable hydrogel positioned distant from the exit means. Fluid imbibed into the compartment expands the swellable hydrogen thereby driving the active agent out of the compartment via the exit means. Related dosage forms are described in European Patent Specification No. 0 378 404-A which relates to devices which comprise a permeable wall surrounding a compartment which contains the active agent(s) and hydrogel, said wall containing one or more holes and/or a plurality of pores. U.S. Patent No. 4,915,954 and French Patent Specification No. 2 620 025 describe dosage forms for delivering a drug at two different rates, which comprise a semipermeable wall that surrounds a compartment. The compartment comprises a first lamina comprising a beneficial agent that is released via an exit means in the wall over a short period of time. Distant from said exit means is a second lamina comprising a beneficial agent that is released over a prolonged period of time. The existing technology is limited since diffusion controlled systems are effective only when soluble active agents are dispensed. For osmotically controlled devices, the technology relies upon a wall permeable to the passage of fluid present in the environment of use. Furthermore, these devices require a wall of carefully controlled permeability. Devices which rely upon the establishment of an extra device superstructure can be altered during in vivo transit, for example, in the gastrointestinal tract. If portions of the superstructure break away,greater surface area is exposed to the environment and unpredictable release of the active agent may result. The usefulness of the above devices would be increased if a device and method were provided to improve the delivery of drugs independent of their solubility so that diffusion from a swelled polymer or through the superstructure of a polymeric matrix could be avoided. Further utility would result from a methodology which provides a device where the generation of an extra tablet structure could be avoided and the dry ingredients could be contained within a protective coating,until released from the device. This would prevent the chance of premature erosion and uncontrolled release of the active agent as well as provide enhanced stability for those active agents that are labile in the fluid of the environment of use. DESCRIPTION OF DRAWINGS Fig. 1 is a schematic representation of one embodiment of the instant invention. The device 10, has a core composition 11, comprised of a beneficial agent 12 and polymer 13 capable of forming a gelatinous microscopic particle dispersion upon hydration. The core may optionally contain a polymer hydration modulating agent 14 and other tablet forming excipients 15. The core is surrounded by an insoluble, impermeable coating 16, with a plurality of apertures 17 which expose the core surface to the environment of use. In operation, aqueous solution, from the environment of use, contacts the surface of the core that is exposed within the apertures 17. The available water begins to hydrate the polymer (13) and gelatinous microscopic particles form at the surface of the core. If present, the polymer hydration modulating agent 14, at the exposed core surface, is solubilized and establishes the environment required for controlled of polymer hydration. As the polymer particles 13 are hydrated, the gelatinous microscopic particles move from the surface. At the same time, the gelatinous microscopic particles move the beneficial agent 12 from the surrounding surface into the environment as well. These particles of beneficial agent move from the core surface into the environment of use in a dispersion with the gelatinous microscopic particles. As a result, controlling the surface area of the core which is exposed to the environment of use, effectively controls the delivery rate of medicament to the environment. The instant invention provides a novel device for delivery of an active or beneficial agent (drug), in a dispersion, and produces a beneficial effect which overcomes the disadvantages associated with prior art devices. The instant invention also provides a device for delivering an active or beneficial agent, in situ as a dispersion, at a controlled rate over a specified period of time, which delivery is controlled by selection of components of the device and not the environment surrounding the device. Further, the instant invention provides a device for controlled delivery of an beneficial agent where the release rate of the beneficial agent is neither related to the solubility of the beneficial agent nor to the in vivo establishment of an extra tablet superstructure. Additionally, the instant invention provides a device for controlled delivery of an beneficial agent where delivery occurs from the surface of the device not from within a core so that delivery rate is not dependent on diffusion of the active ingredient from inside the device to the environment of use. Other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of the invention, taken in conjunction with the drawings and accompanying claims. DETAILED DESCRIPTION OF THE INVENTION The novel device of this invention consists essentially of a drug delivery device for the controlled in situ production and release of a dispersion containing a beneficial agent, consisting essentially of: (A) a compressed core prepared from an admixture comprising (i) a therapeutically effective amount of a beneficial agent; and (ii) a polymer which upon hydration forms gelatinous microscopic particles; (B) a water insoluble, water impermeable polymeric coating, which surrounds and adheres to the core, the coating having a plurality of apertures exposing between about 1 and about 75% of the core surface. By "drug delivery device" is meant, a dosage form that provides a convenient means of delivering a drug to a subject. The subject can be a human or any other animal. The device is designed to be useful for the delivery of a drug by any pharmaceutically accepted means such as by swallowing, retaining it within the mouth until the beneficial agent has been dispensed, placing it within the buccal cavity, or the like. By "controlled" production is meant that the rate of release of the beneficial agent, that is the amount of beneficial agent released from the device to the environment of use, follows a predetermined pattern. Thus, relatively constant or predictably varying amounts of the beneficial agent can be dispensed over a specified period of time. The "gelatinous microscopic particles" are composed of discrete particles of hydrated polymer. Both size and hydration rate of these gelatinous microscopic particles are characteristics of the individual polymers. Illustrative of this type of polymer are sodium polyacrylate, particularly those compositions sold under the trade names "AQUAKEEP® J-550", "AQUAKEEP® J-400", which are trade names for sodium acrylate polymer produced by Seitetsu Kagaku Co., Ltd., Hyogo, Japan. The "AQUAKEEP®" polymers are generically described in United States Patent 4,340,706. Also illustrative of this type of polymer are carboxypolymethylenes prepared from acrylic acid cross-linked with allyl ethers of sucrose or pentaerythritol and sold under the trade names "CARBOPOL® 934P" and "CARBOPOL® 974P", which are trade names for two carbomer type polymers produced by B.F. Goodrich Chemical Company, Cleveland, Ohio. These latter polymers are generically described in United States Patent 2,909,462 and in the National Formulary XVII at p 1911, CAS Registry Number 9003-01-4. All of the forgoing references are hereby incorporated by reference. In the dry state, CARBOPOL® 974P and CARBOPOL® 934P particles range in size from about 2 to about 7 microns. When these particles are hydrated, gelatinous microscopic particles of about 20 microns are produced. When AQUAKEEP® J-550 or AQUAKEEP® J-400 particles are hydrated, the diameter of the gelatinous microscopic particles can range in size from 100 to 1000 microns. Once the drug delivery device is within the environment of use, the polymer of the compressed core which is exposed to the ambient aqueous solution at the coating apertures, begins to hydrate and produce gelatinous microscopic particles. By " in situ production and release of a dispersion" is meant that during the production of the gelatinous microscopic particles, soluble and insoluble core components located near the polymer particles become dispersed and mixed in such a manner that a gelatinous dispersion is produced. The dispersion moves from the device into the aqueous solvent, bringing the beneficial agent into the environment of use. In this novel device, the components of the compressed core move into the environment of use, carried along by the gelatinous microscopic particles, continually exposing new surfaces for further hydration and production of the dispersion. By "gelatinous" is meant a semisolid system consisting of hydrated polymer interpenetrated by the aqueous solvent of the environment of use. By "compressed core" is meant that an admixture of ingredients comprising a beneficial agent, a polymer which produces gelatinous microscopic particles when hydrated, and other ingredients that may affect any of (1) the rate of production of the dispersion; (2) the stability of the components of the dosage form; or (3) the mixing or compression characteristics of the admixture, is blended in such a way to produce a uniform material. This uniform material is then compressed, within a die, to produce a desired form, normally in the shape of a tablet, capsule or bolus. The compressed core contains a therapeutically effective amount of beneficial agent and a polymer which upon hydration results in gelatinous microscopic particles. The term "beneficial agent" broadly includes any drug or mixture thereof, that can be delivered from the system to produce a beneficial result. The drug can be soluble in the fluid that makes contact with the exposed surface of the core or it can be essentially insoluble in the fluid. In the specification and the accompanying claims, the term "drug" and its equivalents includes any physiologically or pharmacologically active substance that produces a localized or systemic effect or effects in animals. The term "animal" includes mammals, humans and primates such as domestic, household, sport or farm animals such as sheep, goats, cattle, horses and pigs, laboratory animals such as mice, rats and guinea pigs, fishes, avians, reptiles and zoo animals. The active drug that can be delivered by the novel device of this invention, includes inorganic and organic compounds without limitation, including drugs that act on the peripheral nerves, adrenergic receptors, cholinergic receptors, nervous system, skeletal muscles, cardiovascular system, smooth muscles, blood circulatory system, synaptic sites, neuroeffector junctional sites, endocrine and hormone systems, immunological system, reproductive system, skeletal systems, autocoid systems, alimentary and excretory systems, inhibitory and histamine systems, and those materials that act on the central nervous system such as hypnotics and sedatives. Examples of beneficial drugs are disclosed in Remington's Pharmaceutical Sciences , 16th Ed., 1980, published by Mack Publishing Co., Eaton, Pa.; and in The Pharmacological Basis of Therapeutics , by Goodman and Gilman, 6th Ed., 1980, published by the MacMillan Company, London; and in The Merck Index , 11th Edition, 1989, published by Merck & Co., Rahway, N.J. The dissolved drug can be in various forms, such as charged molecules, charged molecular complexes or ionizable salts. Acceptable salts include, but are not limited to hydrochlorides, hydrobromide, sulfate, laurylate, palmitate, phosphate, nitrate, borate, acetate, maleate, malate, succinate, tromethamine, tartrate, oleate, salicylate, salts of metals, and amines or organic cations, for example quaternary ammonium. Derivatives of drugs such as esters, ethers and amides without regard to their ionization and solubility characteristics can be used alone or mixed with other drugs. Also, a drug can be used in a form that upon release from the device, is converted by enzymes, hydrolyzed by body pH or other metabolic processes to the original form, or to a biologically active form. Specific examples of drugs that may be adapted for use include, Angiotensin-converting enzyme (ACE) inhibitors such as enalapril, lisinapril, and captopril; barbiturates such as pentobarbital sodium, phenobarbital, secobarbital, thiopental and mixtures thereof; heterocyclic hypnotics such as dioxopiperidines and glutarimides; hypnotics and sedatives such as amides and ureas, exemplified by diethylisovaleramide and α-bromoisovaleryl urea; hypnotic and sedative urethanes and disulfanes; psychic energizers such as isocarboxazid, nialamide, imipramine, amitryptyline hydrochloride, pargylene, and protryptyline hydrochloride; tranquilizers such as chloropromazine, promazine, fluphenzaine, reserpine, deserpidine, and meprobamate; benzodiazepines such as diazepam and chlordiazepoxide; anticonvulsants such as primidone, phenytoin, and ethosuximide; muscle relaxants and antiparkinson agents such as mephenesin, methocarbomal, cyclobenzaprine hydrochloride, trihexylphenidyl hydrochloride, levodopa/carbidopa, and biperiden; antihypertensives such as α-methyldopa and the pivaloyloxyethyl ester of α-methyldopa; calcium channel blockers such as nifedipine, felodipine, diltiazem hydrochloride, diltiazem malate and verapamil hydrochloride; analgesics such as morphine sulfate, codeine sulfate, meperidine, and nalorphine; antipyretics and antiinflammatory agents such as aspirin, indomethacin, ibuprofen, sodium indomethacin trihydrate, salicylamide, naproxen, colchicine, fenoprofen, sulindac, diflunisal, diclofenac, indoprofen and sodium salicylamide; local anesthetics such as procaine, lidocaine, tetracaine and dibucaine; antispasmodics and muscle contractants such as atropine, scopolamine, methscopolamine, oxyphenonium, papaverine; prostaglandins such as PGE 1 , PGE 2 , PGF 2a ; antimicrobials and antiparasitic agents such as penicillin, tetracycline, oxytetracycline, chlorotetracycline, chloramphenicol, thiabendazole, ivermectin, and sulfonamides; antimalarials such as 4-aminoquinolines, 8-amino-quinolines and pyrimethamine; hormonal and steroidal agents such as dexamethasone, prednisolone, cortisone, cortisol and triamcinolone; androgenic steroids such as methyltestosterone; estrogenic steroids such as 17α-estradiol, α-estradiol, estriol, α-estradiol 3-benzoate, and 17-ethynyl estradiol-3-methyl ether; progestational steroids such as progesterone; sympathomimetic drugs such as epinephrine, phenylpropanolamine hydrochloride, amphetamine, ephedrine and norepinephrine; hypotensive drugs such as hydralazine; cardiovascular drugs such as procainamide hydrochloride, amyl nitrite, nitroglycerin,dipyridamole, sodium nitrate and mannitol nitrate; diuretics such as chlorothiazide, acetazolamide, methazolamide, hydrochlorothiazide, amiloride hydrochloride and flumethiazide, sodium ethacrynate, and furosemide; antiparasitics such as bephenium, hydroxynaphthoate, dichlorophen and dapsone; antineoplastics such as mechlorethamine, uracil mustard, 5-fluorouracil, 6-thioguanine and procarbazine; β-blockers such as pindolol, propranolol, metoprolol, oxprenolol, timolol maleate, atenolol; hypoglycemic drugs such as insulin, isophane insulin, protamine zinc insulin suspension, globin zinc insulin, extended insulin zinc suspension, tolbutamide, acetohexamide, tolazamide and chlorpropamide; antiulcer drugs such as cimetidine, ranitidine, famotidine and omeprazole; nutritional agents such as ascorbic acid, niacin, nicotinamide, folic acid, choline, biotin, pantothenic acid; essential amino acids; essential fats; ophthalmic drugs such as timolol maleate, pilocarpine nitrate, pilocarpine hydrochloride, atropine sulfate, scopolamine; electrolytes such as calcium gluconate, calcium lactate, potassium chloride, potassium sulfate, sodium fluoride, ferrous lactate, ferrous gluconate, ferrous sulfate, ferrous fumurate and sodium lactate; and drugs that act on α-adrenergic receptors such as clonidine hydrochloride; analgesic drugs such as acetaminophen, oxycodone, hydrocodone, and propoxyphene; antihypercholesterolemic drugs such as simvastatin, pravastatin, lovastatin and gemfibrozil; antiinfective drugs such as cefoxitin, cefazolin, cefotaxime, ciprofloxacin, cephalexin, norfloxacin, amprolium, ampicillin, amoxicillin, cefaclor, erythromycin, nitrofurantoin, minocycline, doxycycline, cefadroxil, miconazole, clotrimazole, phenazopyridine, clorsulon, fludalanine, pentizidone, cilastin, phosphonomycin, imipenem; gastrointestinal drugs such as bethanechol, clidinium, dicyclomine, meclizine, prochlorperizine, trimethobenzamide, loperamide, diphenoxylate, and metoclopramide; anticoagulant drugs such as warfarin, phenindione, and anisindione; 5α-reductase inhibitors such as PROSCAR® and other drugs such as trientine, cambendazole, ronidazole, rafoxinide, dactinomycin, asparaginase, nalorphine, rifamycin, carbamezapine, metaraminol bitartrate, allopurinol, probenecid, diethylpropion, dihydrogenated ergot alkaloids, nystatin, pentazocine, phenylpropanolamine, phenylephrine, pseudoephedrine, trimethoprim, and ivermectin. The above list of drugs is not meant to be exhaustive. Many other drugs will certainly work in the instant invention. By "therapeutically effective amount" is meant that the quantity of beneficial agent, contained in the core, which can be delivered to the environment of use, has been demonstrated to be sufficient to induce the desired effect during studies utilizing the beneficial agent. Other excipients such as lactose, magnesium stearate, microcrystalline cellulose, starch, stearic acid, calcium phosphate, glycerol monostearate, sucrose, polyvinylpyrrolidone, gelatin, methylcellulose, sodium carboxymethylcellulose, sorbitol, mannitol, polyethylene glycol and other ingredients commonly utilized as stabilizing agents or to aid in the production of tablets may also be present in the core. The drug can be in the core as a dispersion, particle, granule, or powder. Also, the drug can be mixed with a binder, dispersant, emulsifier or wetting agent and dyes. The active agent may comprise from about 0.01% to about 75% of the core weight. Generally, the device can house from about 0.05 ng to about 50 grams of active agent or more, with individual devices containing, for example, about 25 ng, about 1 mg, about 5 mg, about 250 mg, about 500 mg, about 1.5 g, about 5 g, or the like. The "polymer which upon hydration forms gelatinous microscopic particles" useful in the novel device of this invention broadly encompasses any polymer that upon hydration, is capable of producing discrete gelatinous microscopic particles which support a dispersion, including the beneficial agent, as it forms. The gelatinous forming polymer used also must move from the core surface in such a way that the beneficial agent is carried into the environment of use. Upon hydration, the gelatinous microscopic particles must be predisposed to leave the surface taking the drug with it. This assures a constant surface area exposed to the solvent of the environment of use and maintains the appropriate rate of release. Polymers that form usable gelatinous microscopic particles, include the superabsorbant polymers such as AQUAKEEP® J550, AQUAKEEP® J400, CARBOPOL® 974P and CARBOPOL® 934P and their pharmaceutically acceptable salts. By "pharmaceutically acceptable salts" of the polymers is meant the acid form of the polymer neutralized by converting all or a portion of the free acid functional groups to their salt form. The core of the device contains from about 5% to about 75% by weight of the dry gelatinous microscopic particle polymer. The "polymer hydration modulator" useful in the novel device of this invention broadly encompasses any water soluble compound that can inhibit or enhance the rate of hydration of the gelatinous forming polymer of the core. Among the groups of compounds that can exert this effect are acids, bases, and the salts of acids and bases such as adipic acid, citric acid, fumaric acid, tartaric acid, succinic acid, sodium carbonate, sodium bicarbonate, betaine hydrochloride, sodium citrate, arginine, meglamine, sodium acetate, sodium phosphates, potassium phosphates, calcium phosphate, ammonium phosphate, magnesium oxide, magnesium hydroxide, sodium tartrate and tromethamine. Other compounds that can be used as polymer hydration modifiers include sugars such as lactose, sucrose, mannitol, sorbitol, pentaerythritol, glucose and dextrose. Polymers such as microcrystalline cellulose and polyethylene glycol as well as surfactants and other organic and inorganic salts can also be used to modulate polymer hydration. The hydration modulating agents are solubilized by the aqueous media of the environment and establish an environment such that the pH, ionic strength or hydrophilic character is appropriate for the desired polymer gelatinous microscopic particle hydration rate. For example, these hydration modulating agents can enhance or retard the neutralization of acidic functional groups on the polymer which affects the rate of hydration. The core compartment containing the drug, hydration modulator, and gelatinous microscopic particle polymer as described herein, is typically in the form of a solid conventional tablet. Generally, the core is compressed into its final shape using a standard tablet compressing machine. The core may contain compressing aids and diluents such as lactose that assist in the production of compressed tablets. The core can be comprised of a mixture of agents combined to give the desired manufacturing and delivery characteristics. The number of agents that may be combined to make the core is substantially without an upper limit with the lower limit equalling two components: the gelatinous forming polymer and the beneficial agent. The preferred specifications for the core are summarized below and include: 1. Core Drug Loading (size) : about 0.01% to about 75% by weight of the total core mass or about 0.05 nanogram to about 50 grams or more (includes dosage forms for humans and animals). 2. Polymer Hydration Modulator : 0% to about 75% by weight of the total core mass. 3. Gel Forming Polymer : about 5% to about 75% by weight of the total core mass. In cases where the drug, the gelatinous forming polymer and polymer hydration modulating agent exhibit the desired release rate, stability, and manufacturing characteristics, there is no critical upper or lower limit as to the amount of drug that can be incorporated into a core mass. The ratio of drug to excipient is dictated by the desired time span and profile of release, and the pharmacological activity of the drug. Generally the core will contain 1% to 50% by weight, of a beneficial agent admixed with other solute(s). Representative of compositions of matter that can be released from the device and can function as a solute are, without limitation, those compositions as described. The coating, applied to the core of the invention, is a material that is impermeable and insoluble in the fluid of the environment of use, can form films, and does not adversely affect the drug, animal body, or host. The coating is impermeable to water and also impermeable to the selected product, drugs, polymer hydration modulating agents, or to other compounds in the device. This impermeable material is insoluble in body fluids and non-erodible or it can be bioerodible after a predetermined period with bioerosion following the end of the active drug release period. In each instance it is impermeable to solvent and solute(s) and is suitable for construction of the device. By "impermeable" is meant that the influx of water across the coating is de minimus. Flux of water into the device is via the apertures placed in the coating. The polymeric coating is applied to and adheres to the entire surface of the core. Apertures are produced in the coating to expose the core, using either a drill, a coring device or any other pharmaceutically accepted means. The apertures allow liquids from the environment of use to make contact only with exposed portions of the core when in use. The number, size and configuration of the apertures is chosen to provide the release rate required to suit a pharmacologically recognized requirement since the gelatinous dispersion can form only where the apertures allow such core-liquid contact. The coating can be applied by dipping the cores into a solution of the polymer or by coating the cores using a pharmaceutically acceptable polymer coating process. Among the groups of polymers that can provide this type of protection are cellulose acetate, cellulose acetate butyrate, ethylcellulose, polyvinylacetate, polyvinyl chloride and polymers of acrylic and methacrylic acid esters. In addition, other materials may be included with the coating to enhance its stability, color, elasticity, ease of application or opacity. These include plasticizers such as dibutylsebacate, diethylphthalate, triethylcitrate and polyethylene glycol. The coating is applied to a thickness of from about 1 to about 1000 microns but preferably about 10 to about 500 microns typically, although thinner and thicker coatings fall within the scope of the invention. The expression "aperture" as used herein, refers to ports through the coating which expose the surface of the core to the environment. The size and number of apertures is chosen to effect the desired release rate. Exposure of from about 1% to about 75% of the core surface is contemplated by this invention. The apertures are generally positioned in a regular pattern on both faces of the device although they can be positioned anywhere on the core including the edges or all on one face. The apertures are generally circular but may be of any design that results in the proper release rate. When the aperture is circular, its diameter ranges from about 0.1 mm to about 20 mm with diameters of about 0.2 to about 3.5 mm typical. The number of apertures in each device may range from about 2 to about 1000 or more. Typically, the number of apertures in each dosage form ranges from about 5 to about 100. The apertures may be made by drilling the appropriate size hole through the coating using a mechanical or laser-based process. In the preferred embodiment, a digital laser marking system is used to drill the holes required. This system allows for an array of apertures to be drilled on both faces of a dosage form simultaneously and at rates suitable for production of dosage forms. The process utilizes a digital laser marking system (for example the DigiMark® variable marking system, available from Directed Energy, Inc.) to produce an unlimited number of holes through the surface or coating of the dosage form, at rates practically suitable for production of dosage forms. The steps involved in this laser drilling process are as follows: a digital laser marking system is focused at a laser stage; the dosage form is moved onto the laser stage of the digital laser marking system; the digital laser marking system is pulsed to energize those laser tubes needed to drill the desired apertures along a linear array on the dosage form; the dosage form is moved forward on the laser stage and the digital laser marking system is again pulsed as needed to produce an additional linear array of apertures; The dosage form is then removed from the laser stage. Additional, preferred specifications for the impermeable wall include: a mixture of eight parts by weight of cellulose acetate butyrate, two parts by weight of cellulose acetate and one part by weight of diethylphthalate. This mixture is dissolved in a solution of methylene chloride and methanol (about 3:1 v/v) and sprayed onto the cores to a thickness of about 250 microns. Another preferred coating consists of five parts by weight of cellulose acetate butyrate and one part by weight of triethyl citrate dissolved in a mixture of acetone and methanol (about 3:1 v/v). This mixture is sprayed on the core or dipped into the mixture so that a coating thickness of about 100 microns is applied. The polymers used in the coating which are herein described are known to the art or can be prepared according to the procedures in Encyclopedia of Polymer Science and Technology , Vol. 3, published by Interscience Publishers, Inc., New York, in Handbook of Common Polymers by Scott, J. R. and Roff, W. J., 1971, published by CRC Press, Cleveland, Ohio. In a preferred aspect of the present invention, there is provided a drug delivery device for the controlled in s itu production and release of a dispersion containing lovastatin, consisting essentially of: (A) a compressed core prepared from an admixture comprising (i) a therapeutically effective amount of lovastatin; (ii) a polymer which upon hydration forms gelatinous microscopic particles; (iii) an effective amount of sodium citrate as a polymer hydration modulating agent; (B) a water insoluble, water impermeable polymeric coating comprising cellulose acetate butyrate which surrounds and adheres to the core, the coating having apertures, exposing between about 1 and about 75% of the core surface, wherein the release rate of lovastatin from the device is a function of the number and size of the apertures. In this aspect of the present invention, the polymer which upon hydration forms gelatinous microscopic particles is preferably a carboxypolymethylene prepared from acrylic acid cross-linked with allylethers of sucrose or pentaerythritol. In a drug delivery device of this preferred aspect of the present invention, the water insoluble, water impermeable polymeric coating preferably contains from about three to about 100 apertures. The following examples illustrate the preparation of the drug delivery device of this invention and their controlled release of one or more therapeutically active ingredients into an environment of use. EXAMPLES In the following examples the hydroxymethyl-glutarylcoenzyme A reductase inhibitors (HMG CoA reductase inhibitors) simvostatin and lovastatin are used as model drugs. These drugs are highly effective in the reduction of serum cholesterol levels in humans. The aqueous solubilities of simvastatin and lovastatin are 0.03 mg/ml and 0.00044 mg/ml respectively, at 20°C. The generation of a dispersion, in situ , from the components of a solid core is disclosed. The anti-arthritic, indomethacin and the analgesic, acetaminophen serve as examples of beneficial agents which are deliverable with this device. This permits the successful formulation of poorly aqueous soluble (simvastatin, lovastatin, indomethacin), moderately soluble (acetominophren) and freely water soluble drugs into a delivery device. EXAMPLE 1 Tablets for the controlled release of the drug indomethacin were made as follows, utilizing a 1:1 weight ratio of drug:J-550 polymer. Core Component Weight (g) AQUAKEEP® J-550 2 Indomethacin 2 Avicel PH 101 400 mg Povidone (K29-32) 60 mg in 6 ml EtOH Indomethacin, J-550 and Avicel were mixed thoroughly and granulated with the polyvinylpyrrolidone as a 1% by weight solution in ethyl alcohol. The solvated mass was passed through a sieve of standard mesh size 18 then dried overnight at 45°C. Tablet cores were prepared from the resulting granulation by taking approximately 115 mg of the granules and compressing them on a Carver® press using 1/4" standard concave punches. The tablet cores prepared as above were coated with polyvinyl chloride (PVC) coating by dip coating 5 times in diluted clear polyvinyl chloride cement. These tablets were rolled on edge each time on a teflon sheet to prevent sticking. Each tablet was allowed to dry approximately one hour between subsequent coatings and the tablets were dried for approximately 8 hours after the fifth coat was applied. Five 1.5 mm diameter circular openings were drilled through the coating on each face of the tablets. The release of indomethacin from the coated, drilled tablets into 900 ml of pH 7.5 phosphate buffer at 37°C with 100 rpm stirring was then determined (USP Apparatus 2). The absorbance of indomethacin was measured at 320 nm using a Cary-14 spectrophotometer. Indomethacin release profiles for the coated, drilled dosage forms are shown in Fig. 2. EXAMPLE 2 Tablets were prepared according to the procedure of Example 1 except that the core mixture comprised indomethacin and J-550 polymer in the weight ratio of 1:3. Indomethacin release rates were determined as in Example 1 and are shown in Fig. 2. EXAMPLES 3 AND 4 Tablets were prepared according to the procedures of Examples 1 and 2. Core compositions of indomethacin and J-550 in a weight ratio of 1:1 and 1:3 were spray coated with cellulose acetate butyrate CAB 381-20 (Eastman Fine Chemicals) in a Freund® Model HCT-Mini Hi-Coater (8-inch pan) from a methylene chloride:methanol (1:1) solution at 4% by weight solids. Coating thicknesses were 250 microns for the 1:1 indomethacin:J-550 core composition and 400 microns for the 1:3 core composition. The indomethacin release rates were determined as in Example 1 and are shown in Fig. 2. EXAMPLE 5 Tablets for the controlled release of simvastatin were prepared from the following formulation: Ingredient mg/Tab Simvastatin 100 AQUAKEEP® J-550 100 Avicel PH101 100 Povidone (K29-32) 7.8 Magnesium Stearate 1.5 Total 309.3 The dry ingredients with the exception of magnesium stearate were thoroughly mixed and granulated with absolute alcohol. The solvated mass was passed through a No. 18 stainless steel sieve and then dried for twenty-four hours at 37°C. The dried granules were forced through a No. 35 mesh stainless steel sieve before lubricating with magnesium stearate. This homogeneous mixture was compressed into tablets using 3/8 inch standard concave round punches. The tablets were compressed to a hardness of 19 kg. The tablets were coated in a Freund® Model HCT-Mini Hi-Coater (8-inch pan) to a thickness of 250 microns using the following coating formulation: Ingredient Amount Cellulose Acetate Butyrate CAB 381-20 48 g Cellulose Acetate CA 435-75S 12 g Methylene Chloride 2250 ml Methanol 750 ml Diethylphthalate 6 g Circular openings in the coating were made using a tubular boring tool with an i.d. of 2.80 mm which provided openings of nearly 3.0 mm. The in vitro release of simvastatin from tablets with three circular openings of 3.0 mm diameter on each face was carried out at 37°C using USP Apparatus 2 into pH 7.4 phosphate buffer with 0.5% by weight sodium dodecyl sulfate at 100 rpm. The results are shown in Fig. 3. EXAMPLE 6 Tablets for the controlled release of lovastatin were prepared from the following formulation: Ingredient mg/Tablet Lovastatin 20 CARBOPOL® 974P 13.4 Sodium Citrate Dihydrate 13.3 Lactose Hydrous (spray dried) 13.3 Povidone (K29-32) 3.0 Total 63.0 The ingredients were combined and thoroughly mixed in a mortar and pestle, then granulated with 90% alcohol: 10% by volume water. This wet mass was passed through a No. 20 stainless steel sieve and dried overnight at 40°C. The resulting mixture was compressed into tablets using 1/4 inch standard concave punches. The tablets were compressed to a thickness of 2.33 mm and a hardness of 9 kg. The tablets were coated to a thickness of 250 microns with the following formulation using a Freund® Model HCT-Mini H-Coater (8-inch pan). Ingredient Amount Cellulose Acetate Butyrate CAB 381-20 64 g Cellulose Acetate CA 435-75S 16 g Methylene Chloride 3000 ml Methanol 1000 ml Diethylphthalate 8 g In vitro release tests were carried out at 37°C using USP Apparatus 2 into pH 7.4 phosphate buffer containing 0.2% sodium dodecyl sulfate at 50 rpm. The drug released was monitored by flow-through UV spectrophotometry. The drug released from coated tablets with 1.75 mm diameter circular openings bored through the coating on each face is shown in Fig. 4. EXAMPLE 7 Simvastatin tablets were prepared from the following formulation: Ingredients mg/Tablet Simvastatin 40 CARBOPOL® 974P 26.7 Sodium Citrate Dihydrate (milled to 100-200 mesh) 26.7 Lactose Hydrous NF (spray dried) 26.6 Povidone USP (K29-32) 6.0 Butylated Hydroxyanisole (BHA) NF 0.04 Magnesium Stearate NF 0.6 Total 126.64 The simvastatin, CARBOPOL®, milled sodium citrate, lactose and polyvinyl-pyrrolidone were combined, mixed thoroughly and granulated with 10% by weight water in alcohol containing the required BHA. The wet mass was forced through a No. 18 sieve and dried overnight. The dry granulation was lubricated with magnesium stearate and the homogeneous mixture compressed using 1/4 inch standard concave round tooling and a compression force of 1000 lbs. The compressed tablets had a thickness of 3.89 mm and a hardness of 10 kg. The tablets were spray coated to a coat thickness of 100 microns in a Freund® HCT-Mini Hi-Coater (8-inch pan) using the following coating formulation: Ingredient Amount Cellulose Acetate Butyrate CAB 381-20 80 g Triethyl Citrate 16 g Acetone 3000 ml Methanol 1000 ml In vitro release tests were carried out at 37°C using USP Apparatus 2 into pH 7.4 phosphate buffer containing 0.4% by weight sodium dodecyl sulfate at 50 rpm. The drug released was monitored by flow-through UV spectrophotometry. The results for tablets with one 2.8 mm diameter circular opening per tablet face are shown in Fig. 5 EXAMPLE 8 Tablets for the controlled release of lovastatin were prepared from the following formulation: Ingredient mg/Tablet Lovastatin 40 CARBOPOL® 974P NF 16 Sodium Citrate USP (dihydrate) 32 Lactose Hydrous NF (spray dried) 16 Povidone USP (K29-32) 5.2 Butylated Hydroxyanisole NF 0.04 Magnesium Stearate NF 0.55 Total 109.79 The granular sodium citrate dihydrate was reduced in particle size such that 90% by weight passed through a No. 120 mesh sieve. The milled sodium citrate dihydrate was combined with lovastatin, CARBOPOL®, lactose and polyvinylpyrrolidone, mixed thoroughly then granulated using Alcohol USP. The solvated mass was passed through a #10 screen then dried overnight at 50°C. The dried granulation was milled, then lubricated with magnesium stearate. The homogeneous mixture was compressed into tablets using 1/4 inch standard concave tooling. The tablets were compressed to a thickness of 3.43 mm and a hardness of 10.5 kg. The tablets were coated to a thickness of 100 microns with the following coating formulation using a Glatt WSG-3 fluidized bed column spray coater. Ingredients Amount Cellulose Acetate Butyrate CAB 381-20 80 g Triethyl Citrate NF 16 g Acetone NF 3000 ml Alcohol USP 1000 ml In vitro release tests were carried out as in Example 7 for tablets with bored circular openings of 1.5 mm diameter and three per tablet face. The results are shown in Fig. 6. EXAMPLE 9 Tablets for the controlled release of acetaminophen were prepared according to the following formulation: Ingredient mg/Tablet Acetaminophen 20 CARBOPOL® 974P 10 Sodium Citrate Dihydrate 20 Lactose Hydrous (spray dried) 10 Povidone (K29-32) 3 Total 63 The ingredients above were combined, mixed thoroughly then granulated with alcohol. The solvated mass was passed through a No. 20 mesh sieve and dried overnight at 40°C. The dried granulation was compressed into tablets using 1/4 inch standard concave tooling. The tablets were compressed to a thickness of 2.31 mm and a hardness of 6-7 kg. The tablets were coated as in Example 6. In vitro release tests were carried out at 37°C using USP Apparatus 2 into pH 7.4 phosphate buffer at 50 rpm. The drug released was monitored by flow-through UV spectrophotometry. The results for tablets with one 2.75 mm diameter circular opening per tablet are shown in Fig. 7. EXAMPLE 10 Tablets cores containing lovastatin, CARBOPOL® 974P, trisodium citrate and lactose in rations of 5:2:4:2 were prepared using the procedure described in Example 8. Varying numbers of apertures were mechanically drilled in each face of the coated tablets. The diameter of the apertures ranged from about 0.23 mm to about 3 mm in diameter as measured by microscopic imaging using an Analytical Imaging Concepts IM4000. In vitro release tests were carried out at 37°C using USP Apparatus 2 in pH 7.4 phosphate buffer containing 0.4% sodium dodecyl sulfate at 50 rpm. The drug released was monitored by flow-through UV spectrophotometry. The results of the study are shown in Table I. EXAMPLE 11 Twenty-four (24) apertures of 0.35 mm in diameter were drilled in each face of the coated tablets prepared for the study in Example 10 using the DIGIMARK™ digital laser marking system. The apertures were measured by microscopic imaging using an Analytical Imaging Concepts IM4000. Release rates were studied as in Example 10. The results are shown in Table II. Number of holes Initial Drug Release Rate(mg/h) (mg/h) Hole Diameter (mm) Hole Surface Area (mm 2 ) Release Rate/Hole Surface Area (mm/h)/mm 2 5 0.4 0.23 0.42 1.06 10 0.91 0.23 0.83 1.10 20 2.14 0.23 1.66 1.29 40 3.57 0.23 3.32 1.07 1 0.35 0.53 0.44 0.79 3 1.03 0.53 1.32 0.78 5 1.92 0.53 2.21 0.87 10 3.36 0.53 4.41 0.76 5 4.28 1.07 8.99 0.48 7 5.80 1.07 12.59 0.46 1 1.96 1.6 4.02 0.49 2 3.55 1.6 8.04 0.44 3 5.07 1.6 12.06 0.42 1 2.22 2.0 6.28 0.35 1 2.73 2.4 9.05 0.30 1 4.17 3.0 14.14 0.29 Number of holes Initial Drug Release Rate (mg/h) Hole Surface Area (mm 2 ) Release Rate/Hole Surface Area (mg/h)/mm 2 24 3.96 4.62 0.86

Claims: A drug delivery device (10) for the controlled in situ production and release of a dispersion containing a beneficial agent (12), consisting essentially of: (A) a compressed core prepared from an admixture (11) comprising (i) a therapeutically effective amount of a beneficial agent (12); and (ii) a polymer (13) which upon hydration forms gelatinous microscopic particles; (B) a water insoluble, water impermeable polymeric coating (16) comprising a polymer and a plasticizer, which surrounds and adheres to the core, the coating having apertures (17), exposing between 1 and 75% of the core surface, wherein the release rate of drug from the device is a function of the number and size of the apertures. A device as claimed in Claim 1 wherein the polymer (13) which upon hydration forms gelatinous microscopic particles is selected from sodium polyacrylate and carboxypolymethylenes prepared from acrylic acid cross-linked with allylethers of sucrose or pentaerythritol and the pharmaceutically acceptable salts thereof. A device as claimed in Claim 1 wherein the polymer component of the coating (16) is selected from cellulose acetate, cellulose acetate butyrate, ethylcellulose, polyvinyl acetate, polyvinyl chloride and polymers of acrylic and methacrylic acid esters. A device as claimed in Claim 1 wherein the plasticizer component of the coating (16) is selected from dibutyl sebacate, diethyl phthalate, triethyl citrate and polyethylene glycol. A device as claimed in any one of Claims 1 to 4 wherein the amount of beneficial agent (12) in the core comprises from 0.01% to 75% by weight of the core mixture. A device as claimed in any one of claims 1 to 5 wherein the coating (16) comprises five parts by weight of cellulose acetate butyrate, and one part by weight of triethyl citrate. A device as claimed in any one of Claims 1 to 6 wherein the beneficial agent (12) is an HMG CoA reductase inhibitor. A device as claimed in Claim 7 wherein the HMG CoA reductase inhibitor is selected from lovastatin, pravastatin and simvastatin. A device as claimed in any one of Claims 1 to 6 wherein the beneficial agent (12) is a calcium channel blocker. A device as claimed in Claim 9 wherein the calcium channel blocker is nifedipine. The device as claimed in any one of Claims 1 to 6 wherein the beneficial agent (12) is an anti-inflammatory agent. A device as claimed in Claim 11 wherein the anti-inflammatory agent is indomethacin. A device as claimed in any one of Claims 1 to 12 wherein the core mixture further comprises a polymer hydration modulating agent (14) is selected from acids, bases, salts, sugars, surfactants and soluble polymers. A device as claimed in any one of Claims 1 to 13 wherein the number of apertures ranges from 2 to 100 and the apertures range from 0.1 mm to 20 mm at their widest point. A drug delivery device (10) as claimed in Claim 1, for the controlled in situ production and release of a dispersion containing lovastatin, consisting essentially of: (A) a compressed core prepared from an admixture comprising (i) a therapeutically effective amount of lovastatin; (ii) a polymer (13) which upon hydration forms gelatinous microscopic particles; (iii) an effective amount of sodium citrate as a polymer hydration modulating agent (14); (B) a water insoluble, water impermeable polymeric coating (16) comprising cellulose acetate butyrate which surrounds and adheres to the core, the coating having apertures (17), exposing between 1 and 75% of the core surface, wherein the release rate of lovastatin from the device (10) is a function of the number and size of the apertures. A drug delivery device as claimed in Claim 15, wherein the polymer (13) which upon hydration forms gelatinous microscopic particles is a carboxypolymethylene prepared from acrylic acid cross-linked with allylethers of sucrose or pentaerythritol. A drug delivery device as claimed in Claim 15, wherein the water insoluble, water impermeable polymeric coating (16) contains from three to 100 apertures. A process for the preparation of a device (10) as claimed in Claim 1 for the controlled release of a beneficial agent (12) wherein: (A) the core is prepared by either dry mixing or wet granulating the polymer (13) which upon hydration produces gelatinous microscopic particles, the beneficial agent (12) and other excipients required in the preparation of tablets and compressing the mixture into cores; (B) coating the entire core with the coating (16) material; and (C) drilling apertures (17) through the coating (16) using a laser or mechanical drilling device.

Inventors: PIPKIN JAMES D, RORK GERALD S, PIPKIN, JAMES D., RORK, GERALD S.
Applicants: MERCK & CO INC, MERCK & CO., INC.
Application year: 1992
Main classification: A61K9
IPC codes: A61K31, A61K9, A61K47