an important aspect of the invention is the release module and its manufacture . for reasons of ease and versatility of the product , using classical techniques and ordinary compressing machines , it has been possible to produce a release module having the shape of a cylindrical polymer matrix with one concave base and the other convex ( fig1 and 2 ). one of the reasons for this new geometry is that it favors the assembly of the release modules , to obtain a system that cannot be made directly , in which to change the kinetics according to the type of assembly . to increase the capacity of the release modules to remain assembled together and to control drug release , a component may be introduced into the composition such as a swelling and gelling hydrophilic polymer , generally , but not necessarily , with a high molecular weight . in this case the composition of the module is that of a hydrophilic matrix . these types of polymer are easily available on the market , for example , as illustration without limitation , hydroxypropylmethylcellulose , known by the commercial name methocel ® hydroxypropyl methylcellulose in grades k4m , k15m and k100m ( dow chemical company ); or other polymers such as xanthan gum , pectin , carrageenans , guar gum . the quantity of these polymers used to obtain the control of the release of active principle by the release module is that commonly described in the literature , and varies preferably between 20 and 60 % weight / weight referred to the total composition of the matrix which may also comprise excipients generally considered safe as well as the active principle which may be any one of the active principles contemplated by the pharmacopoeia for oral administration . with respect to the total composition , the contribution of the active principle varies preferably between 80 % and 0 . 0001 % weight / weight . the inventors of the present patent application have found that the assembly of the release modules making up the finished system (“ assembly ”) can be easily obtained , including in the release module a polymer with strong adhesive properties such as sodium carboxymethylcellulose , carboxypolymethylene , hydroxypropylcellulose , hydroxypropylmethylcellulose , methylcellulose , polymethacrylate or others . in this way , the release system can be obtained by inserting the release modules in a hard gelatine capsule , in the sequence concave face against convex face , so that they are in close contact with each other in forming the assembly . when the gelatine capsule is immersed in the gastric fluid at 37 ° c ., the gelatine component softens and dissolves , creating , around the pile of modules inserted in the capsule , a layer of sticky material which holds them together for a brief period due to the complete dissolving of the gelatine . during this period the gastric fluid also comes in contact with the modules included in the capsule . they are thus able to gel on the outside , giving rise to a sticky layer which welds them very firmly together . a cylindrical assembly is thus obtained ( with one concave base and the other convex , as in fig4 ), having the same base area as the modules of which it is composed , with a height smaller than the sum of the individual heights of the single modules . this cylinder , which possesses an unusual geometry for pharmaceutical forms , may ( in the case of polymers with a low apparent density ), but need not , show the capacity to float due to the intrinsic property of the modules of which it is composed . it is subject to a very slow phenomenon of swelling and dissolving , which guarantees slow drug release and self - destruction only at the end of the drug release period . since the individual modules are assembled to obtain various release systems , in some situations it is preferable that they are assembled in such a way as to produce an assembly in which the various individual modules are even more firmly fitted and stuck together . in this case the gluing of the modules fitted convex face into concave face ( fig4 ) is further strengthened with a solution or suspension of a biocompatible polymer such as ethylcellulose , cellulose acetate phthalate or other polymers , but also with an aqueous solution of water - soluble polymers such as high - viscosity carboxymethylcellulose . alternatively , the welding of the modules may also be obtained by means of thermal welding or ultrasound welding . moreover , the inventors of the present patent application have found that , in the case where the modules are welded two by two , concave face against concave face , the resulting assembly , due to the formation of an insulated internal cavity ( fig5 ), besides presenting a varied release kinetics , shows the immediate capacity to float in water ( that is even if the apparent density of the polymer matrix exceeds the density of water ). this gluing is achieved : by placing in contact the concave faces of the cylindrical modules , on which a small amount of adhesive polymer solution has been applied , or by means of thermal welding or ultrasound welding . the inventors of the present patent application have also discovered the possibility of creating a floating release system by combining cylindrical modules with one concave and one convex base ( or with one concave base and the other flat , or with two concave bases ), with other “ simple ” cylindrical elements with flat bases . the modules with a concave and a convex base according to the invention are intended to give floating capacity ( and therefore so - called “ auxiliary ” modules can , but need not , be used , that is to say modules without active principle , that is composed of biocompatible polymers possibly mixed with excipients generally recognized as safe ), whereas the cylindrical elements with flat bases are intended for drug release . this can be achieved by stacking the release element between two or more floating modules depending on its weight . in fact , by placing both flat faces of the release element in contact with a concave base of the floating module , two float chambers are created which are able to develop a total buoyancy able to render floating the new assembly thus obtained . in particular , for the functioning of the finished assembly the release element must be firmly glued to two or more floating modules . in this case the swelling of the two or more floating modules does not interfere with drug release , which takes place through the exposed surface of the release element . after the floating phase , the whole system is slowly destroyed . in this variation , to further strengthen the floating power , the floating module may be composed of a mixture of a hydrophilic polymer and a low - density hydrophobic component ( that is one that reduces the apparent density of the overall polymer matrix ). by contact with the gastric fluid or with water , it rapidly reaches a stable floating situation . in order to ensure the correct functioning of the floating element , the composition of the mixture that must provide the hydrostatic thrust is essential . the inventors of the present patent application have found that the maximum result can be obtained by mixing a hydrophobic substance with a hydrophilic one , so as to give the module the lowest possible true density , together with a certain hydrophobia which favors the immediate floating of the element . as a hydrophilic substance for making the floating layer it is possible to use gellable and soluble biocompatible polymers such as : polyvinylpyrrolidone , hydroxypropylmethylcellulose , carboxymethyl cellulose , hydroxypropylcellulose , hydroxyethylcellulose , carboxypolymethylene , gums such as guar gum , xanthan gum , chitosanes , gum arabic , gum tragacanth , sodium and calcium alginates , gelatine , pectins . the hydrophobic substances that can be used may be : hydrogenated oils , cetyl , myristic and stearyl alcohol , esters of fatty acids such as glyceryl mono - or distearate . to further increase the buoyancy of the floating module it is also possible to include a mixture of salts able to develop co 2 by contact with gastric fluid : in this case the swelling of the polymer determines the formation of a gelled structure which retains the bubbles of co 2 that have formed , further reducing the apparent density of the polymer matrix . the effervescent mixture may be composed of substances that produce co 2 such as : calcium carbonate , calcium bicarbonate , sodium carbonate , sodium bicarbonate , potassium carbonate , potassium bicarbonate , magnesium carbonate . lastly , as concerns the composition of the drug release element ( cylindrical or polyhedric , with flat bases / faces ), as in the case of the release modules provided by the present invention , it can be given by a mixture of active principle , possible excipients generally recognized as safe and a biocompatible polymer , preferably gellable such as polyvinylpyrrolidone , hydroxypropylmethylcellulose , carboxymethyl - cellulose , sodium and calcium alginates , gum arabic , gum tragacanth . the first example describes the manufacture and operation of a release module containing acyclovir . it is intended for the preparation of a system composed of a capsule containing various modules stacked in such a way as to give an assembly containing a total quantity of 400 mg of acyclovir . x 1 module ( mg ) acyclovir 100 hydroxypropylmethylcellulose 29 . 5 sodium carboxymethylcellulose 29 . 5 nahco 3 12 . 3 talc 6 . 2 mg stearate 1 . 8 125 g of acyclovir are blended with about 33 ml of a solution 8 % p / v of sodium carboxymethylcellulose ( blanose 7lf ). the granulate is obtained by forcing the mixture through the 500μ mesh of the net of an oscillating granulator . the granules are stove - dried with air circulating at 35 ° c . for about 8 hours . the remaining components of the formula are added to the acyclovir granulate and the whole is mixed in a turbula for about 40 minutes . the production of the module by compression is carried out with an alternative tablet press , using special punches with diameter 7 . 4 mm , the drawing of which is shown in fig3 . the weight of each module was 191 . 5 mg , the diameter 7 . 5 mm and the mean height 5 . 5 mm . the speed at which acyclovir is released from the release module was determined at 37 ° c . in artificial gastric fluid with the apparatus 2 usp 24 , vane 50 rpm . the profile of the release of acyclovir from the release module is shown in fig6 ( circles ). about 30 % of the drug was released after 120 minutes and about 70 % after 500 minutes . the kinetics of release from this module , which has one concave and one convex face , was faster than that of a cylindrical matrix with flat faces ( fig6 , rhombi ) having the same composition , prepared with a set of punches with diameter 7 . 4 mm from the same quantity of mixture . such comparative result is shown in fig6 . four release modules , prepared according to the technique described in example 1 , were stacked one on another , with the convex faces fitted into the concave faces and stuck with a 0 . 5 % hydroalcoholic solution ( 2 : 8 ) of hydroxypropylmethylcellulose phthalate ( fig4 ). the speed at which acyclovir is released from the capsule was determined at 37 ° c . in artificial gastric fluid with the apparatus 2 usp 24 , vane 50 rpm . the release of acyclovir from this stacked system of four modules is shown in fig7 ( rhombi ), in comparison with the release from the individual modules ( circles ). in the first 500 minutes the drug release from the four stacked and glued modules was slower and more linear than the release presented by the individual modules . four release modules , prepared according to the technique described in example 1 , were glued two by two , concave face against concave face , wetting the edges of these faces with a 5 % hydroalcoholic solution ( 2 : 8 ) p / v of hydroxypropylmethylcellulose phthalate and joining them with a light pressure , to form two assemblies of two modules ( fig5 ). these assemblies float immediately in the dissolving fluid . the release of acyclovir from these two assemblies ( fig7 , squares ) was faster and more linear than that obtained with the four stacked and glued modules ( fig7 , rhombi ). the example illustrates the preparation of a floating release system which contains the float modules separate from the release elements . for the preparation of 500 floating systems , the following substances are used in the quantities indicated : aluminium hydroxide 95 g polyvinylpyrrolidone 4 g magnesium stearate 1 g hydroxypropylmethylcellulose 75 g ( methocel ® k 100m ) hydrogenated castor oil ( cutina hr ) 15 g sodium carbonate 5 g tartaric acid 5 g granulate the aluminium hydroxide and the active principle with a 1 % aqueous solution of polyvinylpyrrolidone . dry , calibrate on sieve 25 # . mix with magnesium stearate and compress the mixture with a tablet press equipped with flat punches with diameter 7 . 4 mm . mix the components according to the quantities indicated in a turbula ® mixer for 15 minutes and compress the mixture with a tablet press equipped with punches with a concave and a convex face with diameter 7 . 4 mm . for the preparation of the finished assembly , rigid gelatine capsules are used , of the type snap fit ™ 00 , with internal diameter 8 mm and a total closed capsule height of 23 . 4 mm . the floating modules and the release elements are stuck together by means of a 12 . 5 % solution of cellulose acetate phthalate in acetone , before being inserted in the capsule in the following sequence : a thin film of adhesive solution is applied on the concave base of a floating module ; the flat base of the release element is stuck onto this . the gluing operation is repeated , sticking a second floating module onto the second flat base of the release element . for the preparation of 500 floating systems , the following substances are used in the quantities indicated : aluminium hydroxide 95 g polyvinylpyrrolidone 4 g magnesium stearate 1 g crospovidone ( kollidon ® cl ) 96 g tartaric acid 20 g sodium carbonate 24 g hydroxypropylmethylcellulose 54 g ( methocel ® k4m ) talc 4 g magnesium stearate 2 g let half the dose of kollidon ® cl absorb a quantity equal to its own weight of a 1 % aqueous solution of methocel ® k4m hydroxypropyl methylcellulose in which the sodium carbonate has been dissolved . let the mixture dry partly at 80 ° c . for 30 minutes , sieve it , complete drying and sieve it again . let the remaining quantity of kollidon ® cl absorb a quantity equal to its own weight of a 1 % aqueous solution of methocel ® k4m hydroxypropyl methylcellulose in which the tartaric acid has been dissolved . let the mixture dry partly at 80 ° c . for 30 minutes , sieve it , complete drying and sieve it again . to the two mixtures , add the methocel ® k4m hydroxypropyl methylcellulose , the talc and the mg stearate and mix for 20 minutes in a turbula ® mixer . compress the mixture with a tablet press equipped with punches with a concave and a convex face with diameter 7 . 4 mm . granulate the aluminium hydroxide with the active principle and with a 1 % aqueous solution of polyvinylpyrrolidone . dry , calibrate on sieve 25 # and compress the mixture with a tablet press equipped with flat punches with diameter 7 . 4 mm . for the preparation of the finished system , rigid gelatine capsules are used , of the type snap fit ™ 00 , with internal diameter 8 mm and a total closed capsule height of 23 . 4 mm . the floating modules and the release elements are stuck together by means of a 12 . 5 % solution of cellulose acetate phthalate in acetone , before being inserted in the capsule in the following sequence : a thin film of adhesive solution is applied on the base of a release element ; the concave base of the floating element is stuck onto this . the gluing operation is repeated , sticking a second floating module onto the second base of the release element . accordingly , while only a few embodiments of the present invention have been shown and described , it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention .
an innovative pharmaceutical form for controlled drug release relates to systems obtained by the assembly of individual release modules , of which the capacity to release the drug in time and in space depends on the way in which the modules have been assembled . the modular structure offers high reproducibility of manufacture and flexibility of release .