Controlled Release Formulation

The present invention relates to a controlled release formulation, preferably in the form of a tablet, for slowly releasing medicament, such as the cardiac depressant (anti-arrhythmic) procainamide hydrochloride.

It is of great advantage to both the patient and clinician that medication be formulated so that it may be administered in a minimum number of daily doses from which the drug is uniformly released over a desired extended period of time. Until now, this has been accomplished in several different ways. Medicinal agents are either coated with varying thicknesses of a relatively insoluble material or are embedded into a rigid lattice of resinous material. The medicinal agent is continuously made available for absorption into the blood stream to replace the amount eliminated while the dosage form is passing through the gastrointestinal tract of the patient. However, certain types of medicinal agents are not suited to absorption during passage through the gastrointestinal tract. For example, most acidic medicinals are principally absorbed from the stomach, whereas most basic medicinals are absorbed primarily from the intestines.

U.S. Pat. No. 3,458,622 to Hill discloses a controlled release tablet for the administration of medicinal agents over a prolonged period of up to about eight hours. This patent discloses a compressed tablet for the prolonged release of a medicament containing that medicament in a core formed from a polymeric vinyl pyrrolidone, preferably polyvinyl pyrrolidone (PVP), and a carboxyvinyl hydrophilic polymer (hydrocolloid) such as those marketed under the trademark Carbopol. The core material formed from the two polymeric substances provides the controlled release effect by forming a complex under the action of water or gastric fluid. This complex is gel-like in consistency and retards the diffusion of active ingredient from the tablet. The controlled release rate of the drug is dependent upon the interaction of the two principal ingredients, the polymer and the hydrocolloid, in the presence of water to form a gummy complex of low solubility. Since little of the gummy complex is present initially, the drug at or near the surface dissolves fairly rapidly and there is an initial surge wherein a relatively large amount of drug is released in the beginning for a period of about one hour. As the colloid complex is formed, once aqueous solution penetrates the surface of the tablet, the gel retards the dissolution of the drug out of the tablet.

U.S. Pat. No. 4,252,786 to Weiss et al recognizes the initial surge problem in the Hill patent and resolves same by applying a rupturable relatively water-insoluble water-permeable film formed of a combination of hydrophobic and hydrophilic polymers over an insoluble swelling type delayed release matrix or core containing the medicament which core includes a blend of polyvinyl pyrrolidone and a carboxyvinyl hydrophilic polymer. Weiss et al in Column 2 states as follows:

"Initially, while the film is intact, the release of the drug contained in the matrix is primarily controlled by diffusion of solvent and solute molecules through the film. As water or gastric fluid permeates through the film, the gummy complex forms and the slight swelling of the complex causes the film to rupture or erode. The release rate is then controlled by the gummy complex. The application of a relatively water insoluble, water permeable film primarily controls the drug release rate while the matrix gel is being generated and a smoother, gradual, more uniform release rate is achieved during the entire period of about eight to twelve hours, approaching a zero order release pattern. The release pattern of the core, upon application of the film, can be varied over a range by varying the composition and amount of film-forming mixture."

U.S. Pat. No. 4,140,755 to Sheth et al discloses a sustained release formulation in the form of sustained release tablets which are hydrodynamically balanced to have a bulk density (specific gravity) of less than 1 in contact with gastric fluid and which will therefore remain floating in gastric fluid which has a specific gravity of between 1.004 and 1.010. The Sheth et al sustained release formulation contains a homogeneous mixture of one or more medicaments with one or more hydrophilic hydrocolloids, such as hydroxypropyl methyl cellulose having a viscosity of 4000 cps. The hydrocolloids when contacted with gastric fluid at body temperatures form a sustained gelatinous mix on the surface of the tablet causing the tablet to enlarge and acquire a bulk density of less than 1. The medicament is slowly released from the surface of the gelatinous mix which remains buoyant in the gastric fluid.

All of the medicament in the tablet disclosed in the Sheth et al patent is released in the stomach.

U.S. Pat. Nos. 4,309,404 and 4,248,857 to DeNeale et al disclose slow release formulations for many different drugs and classes of drugs including propranolol and other antihypertensives which formulations are formed of a core material containing the active drug (31-53%), carboxypolymethylene (7-14.5%), zinc oxide (0-3%), stearic acid (4.5 to 10%) and mannitol (3 to 30%); a seal coating surrounding the core; and a sugar coating surrounding the seal coating.

U.S. Pat. No. 4,309,405 to Guley et al discloses a sustained release tablet similar to that disclosed in DeNeale et al (U.S. Pat. No. 4,309,404) except that the core contains 20 to 70% drug, 30 to 72% of a mixture of a water-soluble polymer such as hydroxypropylmethyl cellulose or hydroxypropyl cellulose and water-insoluble polymer (ethylcellulose alone or in admixture with carboxypolymethylene, hydroxypropyl cellulose and the like).

Each of the DeNeale et al and Guley et al patents disclose that their compositions provide substantially zero order release of the core contained drug for about 12 hours following the first hour of administration. Thus, zero order release is only obtained after the initial surge of release of drug in the first hour.

U.S. Pat. No. 4,259,314 to Lowey discloses a controlled long-acting dry pharmaceutical composition which includes a dry carrier which contains less than 1% moisture and is formed from a mixture of 80 to 95% hydroxypropylmethyl cellulose (viscosity of 50 to 4000 cp in 2% aqueous solution at 20.degree. C.) and 20 to 5% hydroxypropyl cellulose (viscosity of 4000 to 6500 cp for a 2% aqueous solution at 25.degree. C.) which dry carrier is employed with a therapeutic agent among which include aspirin, ascorbic acid and nitroglycerin.

U.S. Pat. Nos. 3,065,143 to Christenson et al, 3,147,137 to Playfair, 3,444,290 to Wal et al, 3,427,378 to Henderson et al, 3,555,151 to Kaplan et al, 3,574,820 to Johnson et al, and 3,976,764 to Watanabe and 4,173,626 to Dempski et al disclose various sustained release tablets which include gelling agents.

U.S. Pat. No. 4,389,393 to Schor et al discloses a carrier base material to be combined with a therapeutically active medicament into a solid dosage form. The carrier base material is one or more hydroxypropylmethyl celluloses, or a mixture of one or more hydroxypropylmethyl celluloses and up to 30% by weight of the mixture of methyl cellulose, sodium carboxymethyl cellulose and/or other cellulose ether, wherein at least one of the hydroxypropylmethyl celluloses has a methoxy content of 16 to 24% and an average molecular weight of at least 50,000, the carrier base material constituting less than one-third of the weight of the solid unit dosage form.

In accordance with the present invention, a controlled release formulation for the time release of medicament, preferably in the form of a tablet, is provided, which is exceptional in that it is capable of high drug loading and as a release mechanism for substantially near zero order release of medicaments, such as procainamide hydrochloride, over a period of 10 to 12 hours or more substantially starting from ingestion of the tablet. The controlled release formulation of the invention is in the form of a coated tablet which includes a core containing the medicament, one or more water-soluble or water-swellable primary hydrocolloid gelling agents which is a hydroxypropylmethyl cellulose having a methoxyl content of 28 to 30% and having a viscosity of within the range of from about 1,000 to about 6,000 centipoises, preferably 3,000 to 5,000 centipoises, optimally about 4,000 centipoises, in 2% aqueous solution at 20.degree. C., optionally one or more secondary hydrocolloid gelling agents as defined hereinafter, optionally one or more non-swellable binders and/or waxes where the medicament and/or hydrocolloid gelling agent is non-compressible, and one or more lubricants, and optionally one or more anti-adherents, and optionally water and/or other conventional additives. In preferred embodiments, the core will contain less than 4% by weight moisture. The core will be coated with a unique pharmaceutically acceptable coating which will include a combination of water-insoluble film-former and water-soluble film-former, one or more plasticizers, one or more solvents and other conventional ingredients.

The term "non-compressible" as employed herein refers to the inability of medicament and/or hydrocolloid gelling agent to form a compact with a hardness of 8 Strong-Cobb units (SCU) under a pressure of 1000 or more newtons of force.

Upon oral ingestion of the sustained release tablet of the invention, the tablet coating first slowly peels off up to 2-4 hours after ingestion, leaving the core contents in contact with gastrointestinal fluid. Upon contact with gastrointestinal fluid, the core very slowly erodes; the outermost hydrocolloid particles hydrate and swell to form a gelatinous mass which acts as a protective barrier. Medicament is released by diffusion or leaching through the gel layer. In fact, the medicament is released practically uniformly over a period of 10 to 12 hours or more in a substantially linear or near zero order release essentially starting from ingestion to provide substantially the same therapeutic efficacy for the drug as provided by the identical dosage of drug administered in divided doses.

It has been found that near zero order release of the medicament from the uncoated core is not possible but it is only through the presence of the unique coating in combination with the unique core formulation that near zero order or linear release is obtained.

In addition, it has also been found that the controlled release formulation of the invention, for example, in the form of a tablet, allows for surprisingly high drug loading. Thus, until now whereas in conventional procainamide hydrochloride formulations, due to the high water-solubility of the drug, it has been possible to include a core formulation containing at most 65% procainamide hydrochloride based on the weight of the core through the use of the unique combination of coating and core of the present invention, it is now possible to achieve a core formulation containing 75 to 95% procainamide hydrochloride based on the weight of the core. Thus, in effect, the controlled release formulations of the invention may contain from about 14 to 28% or more procainamide hydrochloride than prior art formulations thereby allowing for a reduction in number of daily doses and longer release rates as compared to prior art formulations.

As indicated, the unique core-coating combination in the tablets of the invention allow for unexpectedly high drug loading, Thus, the medicament may be present in the core in an amount of more than about 70% by weight of the core and preferably in an amount within the range of from more than about 75 to about 93% and more preferably, of from about more than 75 to about 85% by weight of the core.

A wide variety of medicaments which are orally administered in tablet form can be used in the form of tablets prepared according to this invention. These include, for example, adrenergic agents such as ephedrine, desoxyephedrine, phenylephrine, epinephrine and the like, cholinergic agents such as physostigmine, neostigmine and the like, antispasmodic agents such as atropine, methantheline, papaverine and the like, curariform agents such as chlorisondamine and the like, tranquilizers and muscle relaxants such as fluphenazine, chlorpromazine, triflupromazine, mephenesin, meprobamate and the like, antidepressants like amitriptyline, nortriptyline, and the like, antihistamines such as diphenhydramine, dimenhydrinate, tripelennamine, perphenazine, chlorprophenazine, chlorprophenpyridamine and the like, hypotensive agents such as rauwolfia, reserpine and the like, cardioactive agents such as bendroflumethiazide, flumethiazide, chlorothiazide, aminotrate, propranolol, nadolol, procainamide and the like, angiotensin converting enzyme inhibitors such as captopril and enalapril, bronchodialators such as theophylline, steroids such as testosterone, prednisolone, and the like, antibacterial agents, e.g., sulfonamides such as sulfadiazine, sulfamerazine, sulfamethazine, sulfisoxazole and the like, antimalarials such as chloroquine and the like, antibiotics such as the tetracyclines, nystatin, streptomycin, cephradine and other cephalosporins, penicillin, semi-synthetic penicillins, griseofulvin and the like, sedatives such as chloral hydrate, phenobarbital and other barbiturates, glutethimide, antitubercular agents such as isoniazid and the like, analgesics such as aspirin, acetominophen, propoxyphene, meperidine and the like, etc. These substances are frequently employed either as the free compound or in a salt form, e.g., acid addition salts, basic salts like alkali metal salts, etc. Other therapeutic agents having the same or different physiological activity can also be employed in pharmaceutical preparations within the scope of the present invention.

The invention is particularly adapted for controlled release tablets containing the antiarrhythmic agent procainamide (usually formulated in the form of its hydrochloride).

The primary hydrocolloid gelling agent, which is hydroxypropylmethyl cellulose, may be of the compressible or non-compressible type, and is esential to the practice of the invention in that it absorbs water, swells and forms a gel. The primary hydrocolloid, namely the hydroxypropylmethyl cellulose, will have a methoxyl content of 28 to 30%, a methoxyl degree of substitution of 1.78-2.03, a hydroxypropoxyl molar substitution of 0.18 to 0.34% and a hydroxypropoxy content of 7 to 12%, a viscosity of 1,000 to 6,000 centipoises in a 2% aqueous solution at 20.degree. C., and a molecular weight ranging from about 50,000 to about 120,000, and preferably from about 70,000 to about 110,000, and will be present in an amount small enough to ensure that a near zero order release is obtained, at a sufficient rate, not only after the first hour, but substantially immediately after ingestion. Thus, the hydroxypropylmethyl cellulose is provided in an amount within the range of from about 5 to about 15% by weight of the core (including medicament) and preferably from about 5 to about 12% of the core (including medicament) and from about 30 to about 50% by weight of the core (exclusive of medicament) and preferably from about 35 to about 45% by weight of the core (exclusive of medicament). Although amounts of such hydroxypropylmethyl cellulose of higher than 15% by weight of the core (including medicament) may be employed, the rate of release of medicament may be undesirably slowed down and the coated tablet may become too large in size to be suitable for oral ingestion.

The hydroxypropylmethyl cellulose for used in the core may be employed alone or in conjunction with a secondary hydrocolloid which includes cellulose ethers such as methyl cellulose, cellulose alkyl hydroxylates such as hydroxypropylmethyl cellulose (of the same type as described above or of other conventional type), hydroxypropyl cellulose, hydroxymethyl cellulose or hydroxyethyl cellulose, cellulose alkyl carboxylates such as carboxymethyl cellulose and carboxyethyl cellulose, and alkali metal salts of cellulose alkyl carboxylates, such as sodium carboxymethyl cellulose and sodium carboxyethyl cellulose, as well as carboxypolymethylene (molecular weight 2.5 to 3.5 million) as well as gum acacia, guar gum, gum tragacanth, gum xanthan, an alkali metal or alkaline earth metal carageenate, alginates, such as alginic acid, ammonium or sodium alginate or mixtures thereof. Preferred secondary hydrocolloids include hydroxypropyl cellulose, having a viscosity of 1,500 to 2,500 centipoises for a 1% aqueous solution or 4,000 to 6,000 centipoises for a 2% aqueous solution at 25.degree. C., sodium carboxymethyl cellulose, methyl cellulose, hydroxypropylmethyl cellulose and carboxypolymethylene.

Other examples of suitable secondary hydrocolloids are set out in U.S. Pat. No. 4,140,755 to Sheth et al.

The secondary hydrocolloid gelling agent will be present to impart a supportive matrix and will act as a binder for and impart hardness to the finished tablets of the invention.

Where employed in the core, the secondary hydrocolloid will be present in an amount within the range of from about 2.5 to about 7.5% by weight of the core (including medicament) and preferably from about 2.5 to about 5% by weight of the core (including medicament), and from about 15 to about 25% by weight of the core (excluding medicament), and preferably from about 17 to about 23% by weight of the core (excluding medicament). The hydroxypropylmethyl cellulose will be employed in a weight ratio to the secondary hydrocolloid (where present) in the range of from about 0.5:1 to about 4:1, and preferably from about 1:1 to about 3:1.

Where both the medicament and/or the primary and/or secondary hydrocolloid gelling agent are non-compressible, it is preferred that the core also include one or more non-swellable binders which bind the core ingredients to prevent premature core disintegration and promote proper release rate. The binders will be present in the core in an amount within the range of from 0 to about 8% and preferably from about 2 to about 5% by weight of the core. Examples of such binders suitable for use herein include, but are not limited to, polyvinylpyrrolidone (molecular weight ranging from 5000 to 80,000 and preferably about 40,000), lactose, gelatin, starches such as corn starch, modified corn starch, sugars, gum acacia and the like.

In addition to, or in lieu of, the above described non-swellable binders, the core may contain a wax binder in finely powdered form of average particle size of, for example, less than 500 microns and preferably within the range of from about 150 to about 500 microns, in an amount within the range of from 0 to about 8% and preferably from about 2 to about 5% by weight of the core. Examples of such wax binders suitable for use herein include, but are not limited to carnauba wax, paraffin, spermaceti, polyethylenes or microcrystalline wax.

It will be appreciated that at least one of the non-swellable binders, preferably, polyvinylpyrrolidone and/or one of the wax binders, preferably carnauba wax, will be present in the core where neither the medicament nor the primary and/or secondary hydrocolloid gelling agent is compressible and such binder together with the primary hydrocolloid will form a water-insoluble matrix.

In a preferred core formulations, the primary hydrocolloid gelling agent will be employed in a weight ratio to non-swellable binder and/or wax binder of within the range of from about 5:1 to about 0.2:1 and more preferably from about 3:1 to about 0.3:1, and the secondary hydrocolloid gelling agent (where present) will be employed in a weight ratio to such binder of within the range of from about 2.5:1 to about 0.1:1 and preferably from about 1.5:1 to about 0.2:1.

The sustained release tablets will also include additional edible non-toxic ingredients as conventionally employed in solid medicinal dosage forms. Thus, the core of the tablets of the invention may include one or more excipients in an amount within the range of from about 1% to about 25% by weight and preferably from about 1% to about 10% weight such as lactose, sugar, mannitol, sorbitol, inorganic salts such as calcium carbonate, one or more tableting lubricants in an amount within the range of from about 0.5 to about 8% by weight of the core, and preferably from about 1 to about 4% by weight of the core, such as magnesium stearate, stearic acid, palmitic acid, calcium stearate, talc, carnauba wax and the like. Other conventional ingredients which may optionally be present include preservatives, stabilizers, anti-adherents or silica flow conditioners or glidants, such as Syloid brand silicon dioxide as well as FD&C colors.

The coating layer which is applied over the core, as indicated hereinbefore, will include one or more water-soluble hydrophilic film-formers, binders or barrier materials and one or more relatively water-insoluble hydrophobic barrier materials.

The coating or film layer which is applied over the core will be formed of a mixture of one or more water-soluble hydrophilic polymeric film-formers in an amount within the range of from about 10 to about 90% and preferably from about 10 to about 60% by weight based on the weight of the coating layer and one or more relatively water-insoluble hydrophobic polymeric barrier materials in an amount within the range of from about 10 to about 90% and preferably from about 20 to about 70% by weight of the coating layer. The above mixture of polymers forming the coating layer permits entry of water and hydration of the matrix so that there is not a large initial surge in the release of medicament.

The hydrophilic polymers are water-soluble polymers. They include cellulose methyl ethers like methyl cellulose, hydroxypropylmethyl cellulose, hydroxymethyl cellulose phthalate, also hydroxypropyl cellulose, cellulose acetate phthalate or polyvinyl alcohol.

The hydrophobic polymers are slightly soluble in water. (By slightly soluble is meant the definition in USP XXI, polymers up to 3% soluble in water can be used.) They include cellulose ethyl esters like ethyl cellulose, also cellulose acetate, polyvinyl alcohol-maleic anhydride copolymers, .beta.-pinene polymers (Piccolyte), glycerol esters of wood resins like glycerol ester of partially dimerized rosin, glycerol ester of partially hydrogenated wood rosin, glycerol ester of polymerized rosin, hydroxypropyl methyl cellulose phthalate, etc.

Preferred are combinations of methyl cellulose and ethyl cellulose, or hydroxypropylmethyl cellulose (preferably, the same type as the primary hydrocolloid as discussed above) and ethyl cellulose, the ethyl cellulose containg about 42 to 49.5% ethoxyl groups.

One or more members of each class of polymer can be used in forming the coating material. The weight ratio of hydrophilic polymer or polymers to hydrophobic polymer or polymers is within the range of about 4:1 to about 1:4 (by weight), preferably from about 2:1 to about 1:2, and optimally about 1.5:1 to 1:1. These polymers are best combined in a proportion which results in rupture in about three hours. A film of about 1 to 15 mil. (0.001 to 0.015 inches) preferably 3 to 7 mil., in thickness is sufficient to achieve the purpose.

The combined weight of the components of the core (with the exclusion of the medicament) and coating layer is below about 30% of the weight of the medicament or active drug ingredient present in the core. Finished tablets having a total weight of up to 1 gm or even more can be prepared. Of this total weight, the core will comprise from about 85 to about 98% by weight of the tablet, the coating layer will comprise from about 15 to about 2% by weight of the tablet, with the medicament comprising from about 70 to about 90% or more by weight of the tablet.

The coating or film forming layer will also include one or more plasticizers, such as triethyl citrate, diethyl phthalate, polyethylene glycol (molecular weight 300 to 4000), propylene glycol, glycerin, butyl phthlate, castor oil and the like.

The film formers are applied from a solvent system containining one or more solvents including water, alcohols like methyl alcohol, ethyl alcohol or isopropyl alcohol, ketones like acetone, or ethylmethyl ketone, chlorinated hydrocarbons like methylene chloride, dichloroethane, and 1,1,1-trichloroethane.

Where a color is employed, the color will be applied together with the film former, plasticizer and solvent composition.

A preferred sustained release tablet in accordance with the present invention will inlucde a core containing from about 70 to about 90% by weight procainamide hydrochloride, from about 8 to about 15% by weight of the primary hydrocolloid gelling agent, which is hydroxypropylmethyl cellulose having a methoxyl content of 28 to 30%, from about 2 to about 6% by weight of polyvinyl pyrrolidone, from about 2 to about 7% by weight of secondary hydrocolloid, preferably hydroxypropyl cellulose, from about 1 to about 5% by weight of an excipient which preferably is lactose, and from about 1 to about 4% by weight of one or more tabletting lubricants which preferably is a mixture of magnesium stearate and stearic acid (all of such % being based on the weight of the core) and a coating which contains a mixture of film formers, namely, ethyl cellulose and hydroxypropylmethyl cellulose (preferably the same type as the primary hydroxypropylmethyl cellulose), and a plasticizer such as triethyl citrate.

The sustained release tablets of the invention may be prepared as follows.

Procainamide hydrochloride, primary hydrocolloid such as hydroxypropylmethyl cellulose, and excipient such as lactose are mixed in a planetary mixer. The mixture is then granulated with a portion of polyvinyl pyrrolidone or other binder, water and ethanol solution. The granulation is dried in an oven and mill granulated, for example in a tornado mill. Remaining binder is milled into the granulation, the secondary hydrocolloid, if any, is mixed into the blend and tabletting lubricant such as magnesium stearate and/or stearic acid are mixed into the blend. The mixture is thoroughly mixed and then compressed into tablet cores. The coating solution formed of film formers, plasticizers and one or more solvents is then sprayed on the cores to form the tablets of the invention.

The following Examples represent preferred embodiments of the present invention.

A sustained release formulation capable of slowly releasing the antiarrhythmic agent procainamide hydrochloride for a period of up to 10 to 12 hours or more and having the following composition was prepared as described below.

The q.s. ingredients were for processing purposes only and do not appear in the final product.

The q.s. ingredients were for processing purposes only and do not appear in the final product.

The procainamide hydrochloride, hydroxypropylmethyl cellulose and lactose were mixed together in a planetary mixer. The mix was then granulated with about one-half of the polyvinylpyrrolidone, water and ethanol. The granulation was dried and mill granulated in a tornado mill. The remaining polyvinyl pyrrolidone and hydroxypropyl cellulose were mixed therein and the magnesium stearate and stearic acid were added thereto. The so-formed mixture was then thoroughly mixed and compressed into tablet cores each weighing 1300 mg.

A coating solution formed of a mixture of hydroxypropylmethyl cellulose (Methocel E-5), ethyl cellulose and triethyl citrate dissolved in a mixture of ethyl alcohol and methylene chloride was sprayed on the cores.

Thereafter, a secondary coating solution (to provide color and sheen) formed of a mixture of hydroxypropylmethyl cellulose (Methocel E-5), triethyl citrate and Opaspray 371 colorant dissolved in a mixture of ethyl alcohol and methylene chloride was sprayed on the core to form the sustained release tablets of the invention each weighing about 1350 mg and containing 1000 mg procainamide hydrochloride (core=1300 mg).

The so-formed sustained release tablet of the invention was found to undergo substantially zero order release so that it slowly and uniformly releases drug over a 10-12 hour period.

In a manner similar to that described in Example 1, 1062 mg tablets each containing 750 mg procainamide hydrochloride and 675 mg tablets each containing 500 mg procainamide hydrochloride were prepared.

The release rates of active drug determined for the uncoated cores and the film coated tablets prepared according to the procedure of Example 1 by the U.S.P. XX method using Apparatus 1 (basket) at 50 rpm with 0.9 liter of 0.1N HCl at 37.degree. C. as the medium are set out below.

A sustained release formulation capable of slowly releasing the antiarrhythmic agent procainamide hydrochloride for a period of up to 1 to 12 hours or more and having the following composition is prepared as described below.

The q.s. ingredients are for processing purposes only.

The water is added to procainamide hydrochloride while mixing in a planetary (Hobart) mixer until granulated. Then the methyl cellulose, polyvinyl pyrrolidone and carnauba wax are added and the mass is mixed for 5 minutes. The mixture is passed through a 40 mesh screen and thereafter the silica flow agent and magnesium stearate are added thereto. The so-formed mixture is then thoroughly mixed and compressed into tablet cores each weighing 1226 mg.

A coating solution formed of a mixture of hydroxypropylmethyl cellulose, ethyl cellulose and triethyl citrate dissolved in a mixture of ethyl alcohol and methylene chloride is sprayed on the cores to form the sustained release tablets of the invention each weighing 1226 mg and containing 1000 mg procainamide hydrochloride (core=1221 mg).

The so-formed sustained release tablet of the invention was found to undergo substantially zero order release so that it slowly and uniformly releases drug over a 10-12 hour period.

Following the procedure of Example 1, tablets of the following composition are prepared.

The coating composition for each of the cores of Examples 5 to 10 is similar to that described in Example 1.

Sustained release formulations capable of slowly releasing the antiarrhythmic agent procainamide hydrochloride for a period of up to 10 to 12 hours or more and having the following composition are prepared as described below.

The water was added to procainamide while mixing in a planetary (Hobart) mixer until granulated. Then the carboxypolymethylene was added with mixing. The mixture was passed through a 40 mesh screen and then other hydrocolloid gelling agents were added. The mixture was again passed through a 40 mesh screen and thereafter the silica flow agent and magnesium stearate were added. The so-formed mixture was then thoroughly mixed and compressed into tablet cores each weighing 1226 mg. The tablet cores were then coated as described in Example 1.

A captopril tablet in accordance with the present invention is prepared following the procedure of Example 1 except substituting 0.5 kg (50 mg per unit) captopril for the procainamide hydrochloride.

A propranolol tablet in accordance with the present invention is prepared following the procedure of Example 6 except substituting 0.8 kg (40 mg per unit) of propranolol for the procainamide hydrochloride.

A fluphenazine HCl tablet in accordance with the present invention is prepared following the procedure of Example 8 except substituting 0.5 kg (10 mg per unit) of fluphenazine HCl for the procainamide hydrochloride.

An aspirin tablet in accordance with the present invention is prepared following the procedure of Example 10 except substituting 0.7 kg (325 mg per unit) of aspirin for the procainamide hydrochloride.

A theophylline tablet in accordance with the present invention is prepared following the procedure of Example 12 except substituting 0.6 kg (200 mg per unit) of theophylline for the procainamide hydrochloride.