Abstract:
A salt sensitive capsule has been developed which dissolves in the mouth and releases the encapsulated internal ingredient(s). The outer salt sensitive shell maintains its integrity when kept at a preselected aqueous salt concentration. When introduced into the mouth, the degree of salinity is lower and causes the shell to disassociate and release the internal component. The capsules may be associated with an adhesive system so that the capsules are topically applied to mouth tissue. The adhesive system is compatible with maintenance of the salt sensitive shell.

Description:
This Ser. No. 333,189, filed Apr. 4, 1989, now U.S. Pat. No. 5,064,650, which is a division of application is a continuation-in-part of U.S. Ser. No. 183,591 with a filing date of Apr. 19, 1988, and entitled &#34;Controlled-Release Capsules By The Use Of A Salt Sensitive Shell Material&#34;, Chel W. Lew, inventor. 
    
    
     BACKGROUND OF THE INVENTION 
     Encapsulation processes have been developed to make very small capsules containing a selected compound or mixture coated with a layer of another composition. The capsules can be in the size range of about 1 micron to several millimeters. The smallest capsules can be used in emulsion formulas. The smaller capsules are sometimes referred to as microcapsules. 
     Some microcapsules are designed to break under pressure so that the internal compound is released when rubbed over a surface. Microcapsules have been used containing therapeutic agents to be ingested coated with films broken down due to pH increases in the gastric system. Other films or shells on capsules are soluble in particular solvents. Release of the internal component is governed generally by solubility characteristics and the thickness of the shell. 
     The microcapsules are made by methods well known in the art and have been used in various industrial and commercial applications. Typical processes are centrifugal extrusion, pan coating and air suspension methods. U.S. Pat. Nos. 3,692,690; 3,015,128 and 3,310,612 are exemplary of encapsulation techniques known and practiced in the art. In addition to those illustrated by the patents, other techniques are available. The present invention can utilize any of the available methods for preparing capsules or microcapsules. 
     SUMMARY OF THE INVENTION 
     The invention is a capsule for oral use containing an internal active ingredient which is coated with a shell of a non-toxic salt sensitive material. The salt sensitive capsules may be associated with an adhesion system. In this invention salt sensitivity relates to the integrity of the shell of the capsule or microcapsule in varying concentrations of salt in solution. The salt sensitive compositions are a rigid gel and insoluble when the salt level in an aqueous solution is maintained at a preselected level. Decreasing the level of salt by diluting the solution containing the capsules causes the salt sensitive shell to lose its structure, break down and dissolve. There are a number of polymers which are insoluble at certain preselected salt levels, depending on the polymer and salt used, and soluble at a lower salt levels. 
     The adhesive system associated with the salt sensitive encapsulated active ingredient does not affect the integrity of the capsule shell. The adhesive may be associated with the outer shell. The adhesive system may also be an adhesive in an aqueous gel with a salt concentration of the gel adjusted to the preselected level to maintain the integrity of the capsule shell. 
     The capsules are designed so that when they are placed in the human mouth with the normal salt (electrolytes) concentration, the capsules dissolve. The shell&#39;s composition can be formulated to provide slow or fast rate of dissolution. The capsules used with the adhesive system provide a mixture which can be placed inside the mouth on selected tissue. The capsules dissolve over a sustained period of time while the adhesion system holds them in place. The active ingredient is released over time in a specific region of the oral cavity. 
     The characteristics of the active ingredient to be enclosed must be considered in designing the capsule of this invention. A water soluble active ingredient is not to be encapsulated with a water soluble salt sensitive shell. If the active ingredient is water soluble, a water insoluble film layer must enclose the active ingredient which in turn is coated with the salt sensitive shell. There would be a two layer process for encapsulation so that the internal soluble ingredient will be protected from the salt sensitive shell with the water insoluble layer. The water insoluble layer is water dispersible so that the active ingredient is released once the capsule is placed in sufficiently diluted concentrations of salt to dissolve the salt sensitive layer exposing the water insoluble layer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description of the invention is for particular embodiments of capsules including microcapsules that can be used for oral medication. The invention is for a non-toxic, salt sensitive shell for release of an active ingredient such as medication or a breath freshener in the mouth. The active ingredient is contained inside the shell and is not released until the shell dissolves in the mouth. The alternative embodiment is the mixture of the capsules in a non-toxic adhesive system in which the bioadhesive is part of the outer shell of the capsules or the bioadhesive is a gel containing the capsules. The adhesive system is compatible with the salt sensitive shell such that the integrity of the shell is not affected by the adhesive. 
     A salt sensitive shell can be used in a single layer capsule to encapsulate a water insoluble ingredient. A water soluble active ingredient cannot be effectively encapsulated with a salt sensitive layer which reacts to water soluble compounds. Also, certain other active ingredients may be reactive with the compound or compounds selected for the salt sensitive shell. In instances where the internal component of the capsule cannot be in contact with the salt sensitive compound a non-toxic water insoluble and/or nonreactive layer of film encapsulates the internal component which in turn is coated with an outer shell of salt sensitive compound. The capsule has a two layer coating. The water insoluble compound should be water dispersible so that the active internal ingredient will be released in solution. The internal component of the capsule will be released upon the dissolution of the salt sensitive outer layer in a diluted salt concentration level and the following dispersal of the insoluble layer. 
     The capsules can be made as microcapsules using known encapsulation techniques such as centrifugal extrusion, pan coating and air suspension. The capsules of this invention include microcapsules and the broad categories of known capsules and encapsulation techniques. The following Table 1 are examples of non-toxic salt sensitive materials. The materials are salted out of solution at a certain level of salt concentration and are insoluble. Table 1 has the maximum salt concentration for solubility. The mouth environment does not contain a high enough salt concentration to maintain the integrity of the capsules which would dissolve in the oral cavity. 
     
                       TABLE 1______________________________________       Max. Salt Conc. for Solubility       wt. % in sol&#39;n of saltSalt Sensitive Material         NaCl    Na.sub.2 SO.sub.4                          Na.sub.2 CO.sub.3                                 Na.sub.2 PO.sub.4______________________________________Polyvinyl alcohol          14%     4%       4%     9%(PVA)Methyl Cellulose (MC)         11      6        4        2.9Hydroxypropyl Methyl -         17      6        5        3.9(HPMC) CelluloseEthylhydroxyethyl -          8        2.5    3      3(EHEC) Cellulose______________________________________ *Information from Handbook of Water Soluble Gums and Resins by Robert L. Davidson (1980). 
    
     Other salt sensitive materials include polyethylene oxide and Carrageenan. 
     An example of non-toxic film for use with a water soluble internal component is oil base Span®. The Span® materials are partial esters of fatty acids and hexitiol anhydrides and the food grade acceptable Spans® would be suitable. Also edible fats such as triglycerides would be suitable. 
     An example of a water insoluble compound used in this invention as the internal active ingredient is ethyl aminobenzoate. This compound, also known as benzocaine, is used as a local or topical anesthetic in the mouth. Benzocaine is relatively insoluble in water as one gram dissolves in about 2500 ml. Benzocaine is used at about 5% to 20% strength in a suitable carrier for anesthetics. For the purpose of this specification and claims, the water insoluble active ingredients can have some slight solubility in water such as benzocaine. Capsules of benzocaine are prepared using a salt sensitive shell. The shell is formulated to dissolve in the electrolyte concentration of the mouth releasing the benzocaine. 
     Other active ingredients to be encapsulated can be antibiotics capable of oral delivery such as bankcomycin, gentamicin, imipenem and ceptazidime. The antibiotics of this invention may be water soluble or water insoluble and are defined us oral antibiotics for the terminology of this invention. 
     The capsules may be included in an aqueous gel adhesive system which has a salt concentration of a preselected level high enough to maintain the integrity of the outer shell of the capsule surrounding the active ingredient. More than one active ingredient may be included inside the shell as long as the active ingredient does not adversely affect the shell by chemically reactivity or otherwise. For instance, a water insoluble flavoring oil may be mixed with the benzocaine for an oral anesthetic. The encapsulated component may be a mixture of ingredients. The active component can be any ingredient desired to be released in the mouth. 
     Examples of bioadhesives which can be used as a capsule coating or in a gel adhesive system are calcium polycarbophil, polyacrylic acid, gelatin, CMC, natural gums such as karaya and tragacanth, algin, chitosan, HPMC, starches, pectins and mixtures thereof. Compounds such as CMC or HPMC may have adhesive qualities as well as salt sensitivity. The adhesives are coated on the capsule shell or made part of the capsule shell provided there is compatibility with the shell composition to maintain integrity. 
     The adhesives may be mixed with a hydrocarbon gel base, composed of polyethylene and mineral oil, with a preselected salt level to maintain the capsule integrity. 
     The adhesive gel is adjusted to a preselected salt concentration with a non-toxic salt. The capsules are dispersed in the gel. The gel containing the capsules is applied to the tissue in the oral cavity where the delivery of the active ingredient is desired. 
     A typical bioadhesive aqueous gel system with benzocaine is comprised of CMC 1-30%, Pectin 1-5%, gelatin 0.1-10.0% and polyethylene (5% in mineral oil) 10-35%, and the remainder is water. 
     The adhesives of this invention allow the capsules to be placed in the mouth and adhere to the tissue in the oral cavity for a sustained period of time for delivery of the antibiotic, local anesthetic, breath freshener or other active ingredient.