the preferred delayed , sustained - release pharmaceutical preparation of the present invention is a water soluble core drug surrounded by a hydratable diffusion barrier comprising an insoluble film - forming polymer such as eudragit ne30d ( rohm pharma ), eudragit rs30d ( rohm pharma ), aquacoat ( fmc corp .) ethyl cellulose , or mixtures thereof and an additive which controls the rate of hydration and permeability of the diffusion barrier , together in microparticle form . the core drug is preferably a soluble orally administered drug . the solubility of the drug in the intestines should be greater than 10 grams per liter as drugs with lower solubility will not dissolve and diffuse through the hydrated diffusion barrier at adequate rates . examples of suitable drugs include propranolol hydrochloride , quinidine gluconate , dextromethorphan hydrobromide , diphenhydramine hydrochloride , disopyramide phosphate , and verapamil hydrochloride . most preferred is diltiazem hydrochloride . the hydratable diffusion barrier is formed by combining the film - forming polymer dispersion and an additive dispersion , and then spray coating the core drug . in one embodiment , the additive dispersion comprises from about 5 to 20 % magnesium stearate , from about 75 to 95 % water , and from about 0 to 5 % citric acid . in another embodiment , the additive dispersion comprises from about 5 to 20 % magnesium stearate , from about 80 to 95 % water , and 0 to 1 % simethicone emulsion . in yet another embodiment , the additive dispersion comprises 3 - 10 % acetyltributyl citrate ( atbc ), 7 - 20 % talc and 70 - 90 % water . the preferred process for applying the hydratable diffusion barrier to the core drug is a fluid bed spray coating process such as the wurster process or the tangential spray rotor process . other spray coating processes such as pan coating or the immersion tube process may be used . the additive comprises 5 - 40 % ( solids basis ) of the combined aqueous dispersions of additive dispersion and film - forming polymer dispersion . the drug beads are coated with the dispersion and tray dried at 35 ° c . to 60 ° c . for 8 hours to 5 days ( 120 hours ). to obtain delays of 9 hours or longer , as is found in a long delay batch of diltiazem , the diffusion barrier should be at least 20 % ( by weight ) of the coated bead and is preferably 22 - 26 % ( by weight ) of the coated bead . the upper limit of the diffusion barrier thickness is determined by the potency requirements for the long delay batch to obtain delays of about 2 hours , for the short delay batch the coating is thinner ( i . e . 11 - 18 % ( by weight ) of the coated bead and preferably 13 - 16 % ( by weight ) of the coated bead ). in each instance , the permeability of the hydrated diffusion barrier should be designed to provide the desired release rate of the drug after the delay has elapsed . in order that the invention may be more readily understood , reference is made to the following examples , which are intended to illustrate the invention , but are not to be taken as limiting the scope thereof . 60 % active propranolol hydrochloride beads were prepared by coating a solution of propranolol hydrochloride in water onto 25 - 30 mesh sugar spheres . a diffusion barrier coating formulation was prepared by combining 67 . 6 parts by weight eudragit ne30d from rohm pharma with 0 . 1 part by weight sodium lauryl sulfate . 3 . 6 parts by weight magnesium stearate was dispersed into 25 . 1 parts by weight water and added to the eudragit ne30d and sodium lauryl sulfate . 3 . 6 parts by weight eudragit rs30d from rohm pharma was then added with stirring . in a fluidized bed with a wurster insert 425 grams of the 60 % propranolol beads were coated with the coating formulation using a spray rate of 7 grams per minute and an inlet temperature of 30 ° c . samples were taken after spraying 425 grams ( 20 % coat ), 507 grams ( 25 % coat ) and 729 grams ( 30 % coat ). the coated beads were tray dried at 40 ° c for 18 hours . the dissolutions were performed by the u . s . p . basket dissolution method at 100 rpm in 1 liter of 0 . 05 m ph 6 . 8 phosphate buffer . the results of a dissolution study are set forth in table 1 below . table i______________________________________propranolol hydrochloride dissolution percent dissolvedtime ( hrs ) 20 % coat 25 % coat 30 % coat______________________________________2 1 % 0 % 0 % 4 3 % 2 % 0 % 5 7 % 2 % 0 % 6 16 % 3 % 0 % 7 32 % 6 % 0 % 8 53 % 13 % 1 % 10 83 % 36 % 3 % 12 93 % 67 % 13 % 13 98 % 79 % 21 % ______________________________________ 50 % active diltiazem hydrochloride beads were prepared by coating a solution of 27 . 3 parts by weight diltiazem , 0 . 5 parts hydroxy propyl methyl cellulose , 0 . 8 parts microcrystalline cellulose , and 1 . 4 parts magnesium stearate in 70 parts water . 425 grams of the 50 % active diltiazem beads were coated with the coating formulation described in example 1 by the wurster process . samples were taken after spraying 189 grams ( 10 % coat ), 277 grams ( 14 % coat ) and 373 grams ( 18 % coat ). the coated beads were tray dried at 40 ° c for 18 hours . the dissolutions were performed as in example i and the results are set forth in table ii below . table ii______________________________________diltiazem hydrochloride dissolution percent dissolvedtime ( hrs ) 10 % coat 14 % coat 18 % coat______________________________________2 3 % 3 % 2 % 4 16 % 4 % 2 % 6 44 % 15 % 3 % 8 73 % 38 % 11 % 10 85 % 59 % 28 % 14 96 % 82 % 59 % 18 100 % 93 % 77 % ______________________________________ 53 % active diltiazem hcl beads were prepared by coating 25 - 30 mesh sugar spheres with a solution of 27 . 8 parts diltiazem hcl in 70 parts water containing 2 . 2 parts microcrystalline cellulose . a coating formulation was prepared by dispersing 10 . 8 parts magnesium stearate in 17 . 2 parts water containing 0 . 2 parts citric acid and adding to 64 . 6 parts eudragit ne30d from rohm pharma and 7 . 2 parts aquacoat from fmc . 318 grams of this coating formulation was coated onto 450 grams of the 53 % active diltiazem hcl beads using the wurster process spraying at 5 . 5 grams per minute with an inlet temperature of 30 ° c . the coated beads were dried 18 hours at 40 ° c . the dissolution was performed as in example i and the results are set forth in table iii below . table iii______________________________________diltiazem hydrochloride dissolution percent dissolvedtime ( hrs ) 15 % coat______________________________________2 2 % 4 5 % 6 34 % 8 59 % 10 73 % 14 81 % 18 89 % ______________________________________ 65 % active disopyramide phosphate beads were prepared by coating a solution of 50 parts disopyramide phosphate , 2 . 5 parts povidone k30 , a binder available from gaf of texas city , texas , 0 . 2 parts talc , and 47 . 3 parts water onto 25 - 30 mesh sugar spheres using the wurster process . a coating formulation was prepared by dispersing 3 . 3 parts magnesium stearate in 31 parts water containing 0 . 1 part simethicone emulsion usp and adding it to 65 . 6 parts eudragit ne30d from rohm pharma . the coating formulation was applied to 3500 grams of the 65 % active disopyramide phosphate beads by the wurster process using a spray rate of 40 grams per minute and an inlet air temperature of 40 ° c . samples were taken after spraying 3454 grams ( 18 . 5 % coat ), 4292 grams ( 22 % coat ), and 5918 grams ( 28 % coat ). dissolutions were performed as in example i and are set forth in table iv - a below . table iv - a______________________________________disopyramide phosphate dissolution percent dissolvedtime ( hrs ) 18 . 5 % coat 22 % coat 28 % coat______________________________________1 1 % 0 % 0 % 2 2 % 0 % 0 % 3 5 % 0 % 0 % 5 13 % 4 % 2 % 8 29 % 14 % 8 % 12 65 % 50 % 29 % 16 87 % 81 % 49 % 20 100 % 96 % 68 % 24 100 % 99 % 85 % ______________________________________ the disopyramide phosphate beads with the 28 % coat were tested in healthy human subjects to determine the concentration of drug in plasma versus time after dosing . a single dose containing 300 mg of disopyramide was administered to four subjects . blood samples were taken over a 24 hour period and the plasma concentration of disopyramide was determined . the results presented in table iv - b show that the delayed then sustained release profile occurs in human subjects as well as during in vitro dissolution testing . drug is not detected in the plasma until 4 hours after dosing . the drug plasma concentration then increases to a plateau which is maintained from 18 to 24 hours . table iv - b______________________________________disopyramide phosphate biostudy300 mg dose , 28 % coated beadstime after dose ( hrs ) plasma disopyramide mg / l______________________________________ 2 0 4 0 . 09 8 0 . 3912 0 . 6516 1 . 0718 1 . 1622 1 . 1624 1 . 18______________________________________ this example illustrates the concentric coating of a fast release component onto the delayed sustained - release disopyramide phosphate of example iv . 500 grams of the 28 % coated beads from example iv were coated with 130 grams of a coating formula composed of 47 . 5 parts disopyramide phosphate , 2 . 5 parts talc , 2 . 5 parts povidone k30 from gaf , and 47 . 5 parts water using the wurster process with a spray rate of 4 . 5 grams per minute and an inlet temperature of 50 ° c . these beads were then coated with 118 grams of a coating formula composed of 57 parts eudragit ne30d from rohm pharma , 3 parts magnesium stearate , and 40 parts water . the dissolution procedure described in example i resulted in the release rate profile shown in table v . the concentrically coated fast release component provides drug release for the first 4 hours then release from the second slow release component initiates at about 7 hours . table v______________________________________disopyramide biphasic release percent dissolvedtime ( hrs ) disopyramide mg / l______________________________________ 1 5 % 2 10 % 4 18 % 8 27 % 12 42 % 16 61 % 20 75 % 24 87 % ______________________________________ this example illustrates combining a short delay batch ( batch a ) with a long delay batch ( batch b ). 54 % active diltiazem hydrochloride beads were prepared by coating a solution 25 parts diltiazem hydrochloride , 5 parts polyvinyl povidone , 5 parts magnesium stearate , and 65 parts water onto 35 - 45 mesh sugar spheres using the wurster process . a coating formulation was prepared by mixing for 60 minutes 47 . 9 parts eudragit rs30d suspension ( rohm pharma ) with 2 . 9 parts of acetyltributyl citrate ( atbc ) sold under the trademark citroflex a - 4 ( from morflex , inc , greensboro , n . c .) and then adding 5 . 8 parts talc and 43 . 4 parts water . 5 , 890 g of the 54 % active seeds were coated with 3 , 826 g of the coating formulation by the wurster process with an average spray rate of 54 g / min and with a product temperature maintained from 26 °- 31 ° c . a 48 . 9 g sample was dusted with 0 . 49 g of talc and cured for 72 hours at 55 ° c . the dissolution of batch a was performed as in example i and the results are set forth in table vi - a below : table vi - a______________________________________batch a diltiazem hydrochloride dissolutiontime ( hrs ) % dissolved______________________________________1 4 % 2 7 % 4 41 % 6 81 % 9 88 % 12 92 % 15 96 % 18 97 % ______________________________________ as can be seen the batch a pharmaceutical preparation releases drug from the 2nd and 9th hour of the dissolution test ( fast component ). with batch b , 57 % active diltiazem beads were prepared in the same manner as the drug beads in batch a . a coating formulation was prepared as in batch a . 6 , 405 g of 57 % active beads were coated with 8 , 318 g of coating formula using the wurster process with an average spray rate of 59 g / min and maintaining the product bed temperature at 26 °- 31 ° c . a 108 . 1 g sample was dusted with 1 . 1 g of talc and cured at 55 ° c . a dissolution of batch b was performed as in example i and the results are set forth in table vi - b below . table vi - b______________________________________batch b diltiazem hydrochloride dissolutiontime ( hrs ) % dissolved______________________________________ 1 2 % 2 2 % 4 2 % 6 5 % 9 5 % 12 14 % 15 40 % 18 68 % 21 83 % 24 87 % ______________________________________ as can be seen the batch b pharmaceutical preparation releases the majority of the drug from the 12th hour to the 24th hour of the dissolution test . a mixture containing 40 % of the drug in batch a beads ( fast component and 60 % of the drug in batch b beads ( slow component ) give a two - tiered release profile as set forth in table vi - c below : table vi - c______________________________________diltiazem hydrochloride dissolutiontime ( hrs ) % dissolved______________________________________ 1 3 % 2 4 % 4 20 % 6 33 % 9 37 % 12 44 % 15 58 % 18 74 % 21 81 % 24 85 % ______________________________________
a delayed , sustained - release pharmaceutical preparation is provided in which a water - soluble drug core is surrounded by a hydratable diffusion barrier which delays drug release for about 2 - 10 hours . the hydratable diffusion barrier comprises a film - forming polymer such as an acrylic resin , esterified acrylic resin , or ethyl cellulose or mixtures thereof and an additive which controls the rate of hydration and permeability of the hydratable diffusion barrier selected from the group consisting of lubricants , anionic surfactants , plasticizers , inert water - soluble materials , and mixtures thereof . in the preferred sustained - release pharmaceutical preparation , the film - forming polymer is combined with the additive and coated onto core drug granules to produce a diffusion barrier surrounding the core drug and form microparticles when the drug core is the preferred diltiazem hydrochloride , different coating thicknesses of the diffusion barrier are used to provide a long delay component and a short delay component .