Microcapsule

Abstract

An enterically active, controlled release microcapsule is disclosed which includes: (a) an internal phase or capsule core of a continuous matrix of water-soluble polymeric material having finely-divided particles of an active contained material and finely-divided particles of an enteric contained material mixed throughout; and (b) a seamless external coating of capsule wall of a water-insoluble polymeric material which prevents disintegration of the internal phase in aqueous liquids but which is permeable to aqueous solutions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an enterically active microcapsule which provides controlled release of a contained material in aqueous environments. It more particulary pertains to a microcapsule which exhibits rapid but controlled release of contained material in alkaline aqueous environments and which exhibits relatively slow release of contained material in acid aqueous environments. The slow release in acid environments is release as it would be expected from a microcapsule having a low internal phase content, but without enteric activity.

The microcapsule of this invention consists of an internal phase and a capsule wall encasing the internal phase;--the internal phase being a substantially homogeneous combination of water-soluble polymeric matrix material with finely-divided particles of an active material and of an enteric material mixed therethroughout. The enteric material is selected to be relatively insoluble in aqueous acid and relatively soluble in aqueous base. The capsule wall material is selected to be substantially insoluble in, but permeable to, all aqueous solutions thereby preventing disintegration of the internal phase in aqueous solutions. The matrix material, the enteric material and the capsule wall material operate in combination to produce the unexpected effect of providing rapid but sustained release of the active material in alkaline environments and of providing relatively slow release of the active material in acid environments. The microcapsule of this invention finds particular utility in the pharmaceutical and medical fields where it may be desired or required that an active, capsule-contained, medicament material pass through the acid-condition of the stomach with a relatively low, but definite, amount of solution to then be released, relatively rapidly, but in a sustained manner, in the relatively basic environment of the intestinal tract. The rate controlling factor for release of active material in acid environments is the barrier of enteric particles coupled with diffusion of dissolved material through the capsule walls and the rate controlling factor for release of active material in alkaline environments is diffusion through the capsule walls. The microcapsule of this invention finds utility in fields other than the pharmaceutical and medical fields and the term "enteric" is used simply as a matter of convenience. For purposes of this invention, the meaning of the word "enteric" is expanded to include progressively increased solubility with decreased acidity in aqueous environments, whether in a gastrointestinal tract or not. Also, for purposes of this invention, the "active" capsule-contained material is the material to be released from the capsule. The "active" material is the material of the internal phase excluding the matrix material and the enteric material.

2. Description of the Prior Art

In the past, several schemes have been developed for providing small particles of material with some degree of enteric activity or prolonged period of solution.

Examples representative of the prior art include: U.S. Pat. No. 2,553,544 issued May 22, 1951 on the application of Herman H. Bogin which discloses granular particles of a continuous, single-phase, matrix of gelatin, a plasticizer, and an enterically active material. The matrix is disclosed to contain, distributed therethroughout, droplets of a liquid vitamin compound. The granules disclosed by Bogin comprise a relatively homogeneous mixture of an enterically active, continuous, matrix with vitamins dispersed therein and with no covering film to form capsules. The granular particles disclosed by Bogin disintegrate and release their vitamin contents very rapidly in an aqueous system of alkaline pH. The particles disclosed by Bogin contain 30 to 40 percent, by weight, vitamin material;

U.S. Pat. No. 2,656,298 issued Oct. 20, 1953 on the application of Leo Loewe which discloses an enterically active medicament composition for oral administration which can include solid particles of a medicament dispersed in a continuous matrix of formalized protein. The continuous matrix is coated, externally, by enteric anion exchange resin. In all embodiments, the anion exchange resin is disclosed to be utilized as an enclosing material for the medicament to be protected;

U.S. Pat. No. 2,809,916 issued Oct. 15, 1957 on the application of Victor M. Hermelin which simply discloses a sustained release medicament composition comprising granules of intermixed binder and medicament. The binder can be enteric in nature and the process for producing the product is repeated granulation and;

U.S. Pat. No. 3,115,441 issued Dec. 24, 1963 on the application of Victor M. Hermelin discloses a tabletted composition comprising particles of medicament covered by several individual layers of enteric coating material and included in a matrix of medicament and filler. Enteric activity is provided only at the surface of individual particles.

The present invention represents a substantial improvement over the prior art and provides a microcapsule construction with a combination of material properties not before recognized or utilized. The active contained material is included in a continuous matrix of water-soluble polymeric material and the matrix is encapsulated by a water-insoluble polymeric film permeable to aqueous solution. The matrix also includes particles of an enteric material. Release of the active material is accomplished by solution and diffusion through the capsule wall and, very importantly, to the extent that the undissolved enteric material blocks solution or diffusion, release of the active material is slowed.

SUMMARY OF THE INVENTION

At times, a method is desired or required for releasing a material into a liquid system in a controlled manner wherein the liquid system has certain predetermined characteristics. As an example, in the administration of medicines, it is sometimes advantageous to provide a medicament in a special form such that the medicament will be passed through the patient's stomach with only a slight dosage there and then pass on into the intestine where the remainder is released in a relatively rapid but prolonged manner. This form of administration is especially advantageous when the medicament is in danger of being hydrolyzed or otherwise destroyed in an acid environment such as is usually found in a patient's stomach or, when release of a large amount of the medicament into a patient's stomach would cause unnecessary discomfort or irritation.

As further examples of the utility of selectively releasing active, capsule-contained materials, the rapid release of an encapsulated catalyst or reagent in a chemical reaction only during times when conditions in the system are correct for conducting the reaction may be mentioned, as can the release of an additive, such as a dye, to indicate change of conditions or presence of a new condition in a system.

It is an object of this invention to provide a microcapsule which is partially enterically active to exhibit slow release of contained material in acid aqueous conditions, as though the material to be released were in a non-enteric binder, and to exhibit relatively more rapid, controlled, released in alkaline aqueous conditions.

It is a further object of this invention to provide a microcapsule having a construction comprising a capsule internal phase of a water-soluble, polymeric, matrix binder containing a multitude of particles of enteric material and a multitude of particles of active material enclosed by a capsule wall of water-insoluble but permeable polymeric material.

It is a further object of this invention to provide the above microcapsule wherein the insoluble but permeable polymeric material prevents disintegration of the microcapsule in aqueous solution and wherein the finely-divided active material is included in a matrix of water-soluble polymeric material along with finely-divided enteric material, which enteric material serves, in aqueous acid environment, as a partial barrier to solution and consequent diffusion of the active material.

The inventors have not discovered and herein disclose and claim a microcapsule to accomplish the above objects and other objects as will be made apparent to those skilled in the art.

The novel microcapsule has a capsule wall and contains an internal phase. The internal phase includes finely-divided particles of active material, finely-divided particles of enteric material and a continuous matrix of water-soluble polymeric material which also serves as a binder for the particles. "Enteric material", as is referred to throughout this patent, means material which is relatively water insoluble in acidic conditions and is relatively water soluble in basic conditions. The capsule wall material is a water-insoluble polymer and provides a film barrier which prevents disintegration of the internal phase on immersion of the capsules in water. Additionally, the capsule wall material permits release of water-dissolved capsule contents by transfer through the capsule wall film. All release of active material from the capsule of this invention occurs by transfer of a solution of the material through the capsule wall. Each entity of capsule internal phase includes a multitude of finely-divided particles of active material and a multitude of finely-divided particles of enteric material; -- all of the particles being bound together by the matrix of water-soluble polymeric material. The rate of release of the active material is controlled by the rate at which the active material is made available at the capsule wall and by the rate of transfer therethrough. An important feature of the present invention and what is considered to be patentable herein, is the capsule as above-described having four essential elements and providing a release rate which is slow and controlled by a barrier of insoluble enteric particles at an acid pH and is more rapid and controlled by transfer rate through the capsule wall material at an alkaline pH. The four essential elements are particles of active material and particles of enteric material bound together as granules by water-soluble matrix material; -- the granules being encapsulated by a water-insoluble but permeable film of polymeric material. The novel capsule is individual and discrete alone or among others of its kind and is minute in size; --individual capsules having a size range of from 200 microns to 1000 microns or perhaps slightly larger.

Enteric materials eligible for use in this invention as a contained material include any material soluble at certain selected environmental conditions and insoluble at others. The microcapsules of this invention are normally used in aqueous systems and the enteric materials are selected to be soluble in water at alkaline pH and insoluble in water at acid pH. Examples of such materials include partial esters and half-esters of maleic anhydride copolymers such as poly(methylvinylether-co-maleic anhydride) and poly(ethylene-comaleic anhydride) and specifically include methyl, ethyl, n-butyl, isobutyl, and 2-ethylhexyl half and partial esters of maleic anhydride copolymers. Further examples of such materials include polycarboxylic acid partial esters of cellulose esters of lower aliphatic monocarboxylic acids including esters derived from combination of an aromatic polycarboxylic acid such as phthalic acid and an aliphatic acid such as acetic, propionic, butyric, and the like, acids. Preferred ones of those mentioned above are partial esters and half-esters of cellulose acetate phthalate, cellulose propionate phthalate, and cellulose butyrate phthalate. The above materials derive their enteric properties from being partial esters, that is, from having free carboxyl groups in some positions on the molecules. Although it is not required that each repeating unit of the enteric material molecule contain a free carboxyl group, the material as a whole should contain from about 5 to about 25 percent, by weight, free carboxyl groups. A free carboxyl group content from about 8 to about 15 percent, by weight, has been found to be most preferable for use in practicing this invention. It must be remembered, of course, that the enteric activity of the above materials is controlled by, among other things, the free carboxyl content; and that if desired or required for a particular use or effect, enteric materials can be used which have carboxyl contents outside the abovementioned ranges. Other materials eligible for use as the enteric material of this invention include: shellac, derivatives of shellac; certain fats, fatty acids, and waxes; esters of starch, methylcellulose, ethylcellulose, and ethyl(hydroxyethyl) cellulose; phthalates of sugars such as glucose, sucrose, sorbitol and dextrin; zein; and like materials.

Water-soluble polymeric matrix materials (also referred to, herein, as binder materials) eligible for use in this invention include: methyl cellulose; ethyl(hydroxyethyl) cellulose; poly(vinyl alcohol); gum arabic; gelatin, especially of low Bloom strength; poly(vinylpyrrolidone); completely hydrolyzed esters of maleic anhydride copolymers such as poly(methylvinylether-co-maleic anhydride) and poly(ethylene-co-maleic anhydride), and the like. Although not specifically polymeric, sugars and similar organic materials such as glucose, sucrose, sorbitol, and dextran are eligible for use. In short, any water-soluble polymeric, or equivalent, material is eligible for use as the matrix material of the present invention.

Polymeric materials eligible for use in this invention as capsule wall material include any material which is both substantially insoluble in the environmental conditions for use of the novel capsules and permeable to aqueous solutions of the materials to be contained within the capsule walls. The microcapsules of this invention are normally used in aqueous systems and the capsule wall material is, therefore, selected to be substantially insoluble in water. The selected capsule wall material, when used in a thin film such as found as capsule walls, must be permeable to aqueous solutions of the capsule-contained material. Examples of such eligible capsule wall materials include polymeric materials such as: poly(acrylics); --poly(methacrylates), poly(acrylates), and the like; celluloses; --cellulose acetate propionate, cellulose acetate butyrate, ethylcellulose, cellulose acetate, cellulose nitrate, and the like; poly(vinyls); --poly(vinyl acetate), poly(vinyl butyrate), poly(vinylidene chloride) and the like; poly(olefins); --polyethylene, polypropylene, and the like, including materials having the various forms of stero-regularity; poly(halocarbons); --poly(tetrafluoroethylene), poly(trifluorochloroethylene), fluorinated poly(ethylene), fluorinated poly(propylene), and the like; poly(styrenes) and copolymers of poly(styrenes) with other materials such as acrylonitrile or butadiene; poly(amides); poly(esters); poly(epoxides); and silicone resins. Preferred capsule wall materials are the cellulosic materials disclosed above and, in the present practice, most preferred of those is ethylcellulose.

Active material eligible to be contained by the microcapsule of this invention includes any material which can be included as a dispersion of fine particles in the matrix binder material without dissolving therein or reacting therewith. As has been previously disclosed, the capsule of this invention finds its normal utility in controlled release of the contained material in an aqueous environment. The preferred form of the invention is directed toward capsules containing water soluble materials which water soluble materials can be released by permeation of aqueous solution through the capsule wall material. A most preferred form of the invention is directed toward containing water soluble medicaments.

Any acid-sensitive medicament substance, as a class, is eligible for use, such as, for example: penicillin salts, aureomycin, chloromycetin, streptomycin, bacitracin, subtilin, polymyxin, dihydrostreptomycin; and other acid-sensitive materials such as acetylsalicyclic insulin, adrenalin, heparin and the like. Other eligible materials include acetylsalicyclic acid, digitoxin, pyralimine, caffeine, phenobarbital, stilbesterol, methyl testosterone, scopolamine methylbromide, pentaerythritol tetranitrate, hexamethonium chloride, N-acetyl-p-aminophenol, and veratrum viride, d-amphetamine sulfate, pentobarbituric acid, mephobarbital, mannitol hexanitrate, pyralimine maleate, and the like. Of course, other materials physiologically active or not, acid sensitive or not, may be employed in the present invention as desired or required to a particular use. Such a use may be in controlled provision of a catalyst or coreactant in certain pH environments or in controlled release of a dye or indicator material under certain conditions,

The method for manufacturing microcapsules of this invention is not important and forms no part of the invention. Particles of internal phase can be manufactured, for example, by granulating a paste of the matrix binder material mixed with finely-divided particles of the material to be contained and finely-divided particles of the enteric material. The paste if kneaded or otherwise mixed until homogeneous and then granules of the desired size are made and dried. Liquid to make the paste can be a solvent which dissolves the matrix material but does not dissolve the active material or the enteric material or it can be a solvent which dissolves the matrix material and the active material to the saturation of the active material.

The granules or particles, when manufactured, by whatever method, are coated by the polymeric film of capsule wall material. Any of several known methods can be used to apply the capsule wall material. Well-known examples of eligible capsule wall coating methods include: pan-coating, wherein a solution of the capsule wall material is sprayed onto internal phase particles which are tumbling in a rotating bowl; impingement coating, wherein the internal phase particles are impinged onto and cast through a liquid film of the capsule wall material and thereby become coated with the material; and encapsulation by liquid-liquid phase separation of the capsule wall material wherein the internal phase particles are distributed in a two-phase liquid capsule manufacturing system consisting of a phase of continuous suspending liquid and a phase of dispersed liquid droplets of the capsule wall material which droplets coat the internal phase particles to yield capsules. The phase separation method for coating the intended phase particles is preferred and will be used herein to teach practice of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a microcapsule of this invention in partial cross-section. The figure is a schematic representation and no attempt has been made to show relative dimensions or actual shapes of any components. A microcapsule of this invention may be more or less spherical than the representation of the figure.

FIG. 2 depicts a release comparison between active materials contained in capsules of this invention and active materials contained by prior art means.

Returning to FIG. 1, the novel capsule 10 comprises a homogeneous combination of active material 11 (hatching upward to the left), enteric material 14 (hatching upward to the right) and matrix binder material 13, all encased in a polymeric capsule wall 12. The particle sizes of the active material 11 and the enteric material 14 can be larger or smaller, in relation to the capsule size as a whole, than the particle size in the figure; and the concentration of active material 11 and enteric material 14 in the matrix binder material 13 can be greater or less. The ratio of active material 11 to enteric material 14 can be adjusted to any desired or required relation depending on the result to be achieved. Particle size for the active and enteric contained materials is usually less than 250 microns; a preferred size range being from a few microns to 150 microns. The contained materials are normally from about 85 to about 98 percent, by weight, of the internal phase; --about 90 to about 95 percent being preferred. The active material normally constitutes about 20 to 80 percent of the contained materials--about 50 percent being preferred. The polymeric capsule wall 12 is a seamless film substantially conforming to the shape of the internal phase particle. The thickness of the polymeric capsule wall 12 can be varied over a considerable range. The thickness may even change as the capsule is produced or used by virtue of the capsule wall material either absorbing or losing liquid. As used herein the words "internal phase" mean all material enclosed by a capsule wall and the words "contained material" mean the active and enteric material granulated into the matrix binder to yield internal phase.

The graph of FIG. 2 is a schematic representation of the release of contained material in an aqueous environment. The ordinate represents percent, by weight, (on a logarithmic scale) of contained material remaining in a composition being tested. The abscissa represents passage of time and a secondary ordinate, designated as i, represents a time when the pH of the aqueous environment is changed from 1.2 to 7.5 as is customary in some in vitro laboratory tests. Curves A and B depict the release expected for unencapsulated granules of active material in a non-enteric, insoluble, binder material and in an enteric, insoluble, binder material, respectively. It should be noted that curves A and B are located in the pH 1.2 region of the graph and that, in that region, the preferred enteric materials exhibit solubility characteristics substantially identical with non-enteric materials.

Curve B' depicts the release for granules with enteric binder in pH 7.5 aqueous medium. Time begins at the i axis for the curves A' and B'. What is intended to be represented by curve B' is the slightly greater rate of release for granules having enteric binder when placed in alkaline media as compared to release in acid media. Curve A' depicts a release relatively slower than that of curve B' and represents the release to be expected from granules having non-enteric binder material immersed in an alkaline medium. The release depicted by curve A and curve A' is substantially equal. Note that release from granules is quite rapid.

Curve C depicts the release expected for encapsulated granules of active material in a non-enteric, water insoluble, binder material with no enteric material added. It should be noted that the rate of release is substantially independent of pH and that the rate of release is substantialy slower than the unencapsulated granules of Curves A and B. The slope of curve C can vary considerably depending upon the type of non-enteric matrix, whether water soluble or not, the concentration of active contained material, and the like. Curve C evidences the fact that an insoluble capsule wall provided prolonged release of contained materials by virtue of the need for contained materials to be permeated through the capsule walls as liquid solution.

Curve D depicts the release expected for the capsule of this invention. It should be noted that a "knee" occurs in the release curve at the time of pH change;--the release rate in the alkaline medium being much greater than the release rate in the acid medium. Additionally, it is noted that release from the capsule of this invention is slower than release from the granules by reason of the rate controlling feature of transfer through the capsule wall material.

DESCRIPTION OF PREFERRED EMBODIMENT

An example of this invention, to be complete, will describe both, preparation of particles containing matrix, enteric material and active material and encapsulation of the particles in a water insoluble polymer wall. The processes utilized in this example are to be considered as representative and not as limiting the invention, which invention resides in the final product and can be manufactured by any of many processes including those disclosed hereinabove.

In this example, gum arabic is used for the water soluble matrix binder material; cellulose acetate hydrogen phthalate (CAP) is the enteric material; and N-acetyl-p-aminophenol (APAP) is the active material. Two hundred grams of dry CAP, powdered to an average particle size of less than about 50 microns, is combined with 200 grams of dry APAP having a similar average particle size. The powders are blended dry to achieve a substantially homogeneous mixture and then a 10 percent, by weight, aqueous solution of the binder is added in small incremental portions and under continued blending force. The binder solution is added until a pasty, granulable, mass is achieved; --about 400 grams usually sufficing. The mass is granulated by being force through a coarse (10 mesh) screen or by using a wet granulator which yields particles of about 1500 to 2500 microns in average diameter. The particles are dried, the dried particles are forced through a screen having openings of about 1200 microns, and the material retained on a screen having openings of about 500-600 microns is collected for use. The "fines" can be recycled through the granulating process to forestall waste of the materials. Internal phase particles could be used in the size range of from about 100 to more than about 1000 microns in average diameter.

The hydrophobic polymeric capsule wall material of this example is ethylcellulose. To accomplish encapsulation, 350 grams of cyclohexane, 105 grams of the granulated particles, 7 grams of ethylcellulose (as below specified) and 7 grams of polyethylene (as below specified) are added to a vessel equipped for heating and agitation. The ethylcellulose has an ethoxyl content of 48.0-49.5 percent and exhibits a viscosity of about 90-105 centipoises when tested at 20.degree. centigrade as a 5 percent, by weight, solution in a 4/1, toluene/ethanol solvent. (An example of such material is sold by The Dow Chemical Co., Midland, Michigan as a commercially available, standard material, carrying the designation Grade 100.) The polyethylene of this example serves as a phase-separation-inducing polymer, has a molecular weight of about 7000 and a ring and ball softening point of about 100.degree. centigrade determined according to Specification D-36-26 of the American Society for Testing Materials, (An example of such material is sold under the trademark, Epolene C-10, by Eastman Chemical Products, Inc., New York, N. Y.)

Agitation is commenced to disperse all of the solid materials. Agitation is continued while the system is heated to about 80.degree. centigrade and then slowly cooled to about 25.degree. centigrade. During the course of heating and cooling, capsules are formed wherein droplets of a liquid, separated phase, concentrated in ethylcellulose, wraps, as capsule wall material, about individual particles of the granulated material at the high temperature and wherein the liquid wall material solidifes as the temperature is lowered. The capsules are separated from the cyclohexane capsule manufacturing vehicle by filtration, are washed by two portions of cyclohexane, and the residual cyclohexane is removed by evaporation.

As a test of capsules made in the example above, release of active material was measured in aqueous media of acid, basic, and varied pH. In an aqueous solution, buffered at pH 1.2, release of the active material was as follows:

Time (hours) Cumulative Release (percent) ______________________________________ 0.5 24 1.0 45 2.0 70 3.5 88 ______________________________________

At the low pH, the enteric material is insoluble and acts as a barrier to the release of active material, Thus, at low pH, release of the active material is slowed by the combination of hydrophobic capsule wall material and by the interference caused by insoluble particles of the enteric material.

Release in aqueous solution buffered at pH 7.5 was as follows:

Time (hours) Cumulative Release (percent) ______________________________________ 0.5 52 1.0 83 2.0 99 ______________________________________

The release is rapid due to solubility of the enteric material; --the active material being slowed only by solution transfer through the capsule wall.

Release was as follows in an aqueous solution wherein the pH was increased as the test progressed:

Time (hours) pH Cumulative Release (percent) ______________________________________ 0.5 1.2 21.5 1.0 1.7 39.8 1.5 5.7 64.4 2.0 6.0 80.7 2.5 7.0 93.0 3.0 7.5 100.0 ______________________________________

The release is slow in the early portion of the test at low pH; --the enteric material serving to block release of the active material. As the pH is increased, the release is more rapid; --the active material being held only by the capsule wall.

These tests represent a significant exhibition of the invention described and claimed herein in that there is actual demonstration of the effect of the combination of hydrophobic capsule wall material and particulate enteric barrier material in release of active encapsulated material at a variety of pH levels.

The use of particulate enteric material in a water soluble binder is important to permit at least a partial release in acid aqueous environments. The hydrophobic polymeric capsule wall material is important to provide sustained release by diffusion and to prevent disintegration of the granules which would render release instantaneous.

Claims

What is claimed is:

1. A microcapsule consisting of an internal phase and a water soluble capsule wall permeable to aqueous solutions wherein the internal phase comprises an individual particle of a continuous matrix of water-soluble material and, distributed substantially evenly throughout the continuous matrix, a plurality of finely-divided particles of an active material and a plurality of finely-divided particles of enteric material and wherein the water insoluble capsule wall permeable to aqueous solutions comprises a thin coating of water-insoluble polymeric material substantially evenly covering the particle of continuous matrix material preventing disintegration of the internal phase.

2. A minute, enterically active, microcapsule having a capsule wall permeable to aqueous solutions and consisting essentially of hydrophobic polymeric film-forming material insoluble in aqueous systems and a solid core of finely-divided water-soluble active material and finely-divided enteric material intimately combined with a matrix of water-soluble binder material wherein the enteric material is relatively insoluble in acidic aqueous systems and is relatively more soluble in aqueous systems of decreased acidity and wherein the capsule wall prevents disintegration of the solid core.

3. The capsule of claim 2 wherein the hydrophobic polymeric film-forming capsule wall material is ethyl cellulose.

4. The capsule of claim 3 wherein the enteric material is cellulose acetate hydrogen phthalate.

5. A capsule consisting of:

a. a substantially water insoluble capsule wall permeable to aqueous solutions and

b. an internal phase comprising

i. a water-soluble, continuous, matrix binding

ii. a multitude of particles of finely-divided active material and

iii. a multitude of particles of finely-divided enteric material

wherein the enteric material and the active material are substantially homogeneously dispersed in and bound by the matrix and the capsule wall prevents disintegration of the internal phase.

6. The capsule of claim 5 wherein the capsule wall consists essentially of a film of water insoluble, hydrophobic, polymeric material permeable to aqueous solutions and encasing the internal phase in conformance with the internal phase shape and preventing disintegration of the internal phase.

7. The capsule of claim 6 wherein the particle of active material are water soluble and of a size substantially the same as the particles of enteric material.

8. The capsule of claim 6 wherein the internal phase is substantially spherical and of a size more than about 100 microns and less than about 1000 microns.

9. The capsule of claim 8 wherein the internal phase constitutes 85 to 98 percent, by weight, of the capsule;--the remainder being capsule wall material.