Patent Description:
The targeting of drugs to the intestine is well known and has been known for over one hundred years. Commonly, the target of the drugs is the small intestine although the colon can be utilised as a means of achieving local therapy or systemic treatment. The requirements for the coatings on the drugs are different depending on the target site. In order to reach the colon, it is necessary for the drugs to pass through the small intestine, and therefore it is a requirement that a delayed release coating intended to release the drug in the colon does not release the drug in the small intestine.

Coated products for release in the small intestine commonly use polymer coatings which dissolve or disintegrate in a pH dependent manner. In the low pH environment of the stomach, the polymer coating is insoluble. However, on reaching the small intestine, the pH rises to <NUM> and above and the polymeric coating dissolves or disintegrates. A commonly used coating is one containing ionizable carboxylic groups. At higher pH levels, the carboxylic groups ionize, allowing the polymer coatings to disintegrate or dissolve. Common polymers of this type which are used include Eudragit® L and Eudragit® S. Various methods of improving the release in the small intestine by ensuring an earlier release of the drug are known. <CIT> is one of a number of references which discloses partially neutralizing the carboxylic groups in order to reduce the pH at which disintegration occurs. <CIT> discloses a tablet with an inner coat of partially neutralized material and an outer coat with less or no neutralization. This is said to result in disintegration at an earlier time point when transferred from the stomach.

Release of drugs in the colon typically requires an alternative approach. The colon is susceptible to a number of disease states, including inflammatory bowel disease, irritable bowel syndrome, constipation, diarrhoea, infection and carcinoma. In such conditions, drug targeting to the colon would maximise the therapeutic effectiveness of the treatment. The colon can also be utilised as a portal for the entry of drugs into the systemic circulation. Various formulations have been developed for colonic drug delivery, including pro-drugs as well as formulated dosage forms, with the latter being more popular since the concept once proved can be applied to other drugs.

The higher bacterial population in the colon has also been exploited in developing colonic drug delivery dosage forms through the use, as carrier materials, of naturally occurring polysaccharides that constitute substrates for the numerous enzymes of the resident colonic bacteria. These materials are able to pass through the upper gastrointestinal regions intact but are digested upon entry into the colon. Those studied so far include amorphous amylose, pectin, chitosan and galactomannan.

Amorphous amylose is resistant to digestion by the enzymes of the upper gastrointestinal tract. It is, however, fermented in the colon by α-amylase enzymes produced by over half of the <NUM> bacteria species resident in the colon.

One major attraction of using polysaccharides in this bacterial enzyme approach to colonic drug delivery is that materials used are of food grade and so would be safe for use in humans. They are usually applied as coatings or incorporated in the core material as a matrix carrier, and their digestion on entry into the colon by the colonic bacterial enzymes leads to the release of the drug load. An example of such a formulation, which employs an amylose coating, is disclosed in <CIT> (BTG International Limited).

A major limitation with these naturally occurring materials, however, is that they swell excessively in aqueous media leading to leaching of the drug load in the upper gastrointestinal regions. To circumvent this problem, the naturally occurring materials have been utilised in a mixture with various impermeable materials.

<CIT> (British Technology Group Ltd) teaches the use of an outer coating comprising a film forming cellulose or acrylate polymer material and amorphous amylose for a tablet comprising an active compound. The polymer material used is a pH independent release polymer material.

An article in <NPL>) reports the results of investigations concerning the incorporation of a range of insoluble polymers into an amylose coating in order to control amylose swelling. A range of cellulose and acrylate based co-polymers are assessed, and a commercially available ethyl cellulose (Ethocel®) is found to control the swelling most effectively. A pH dependent soluble coating of Eudragit® L100 is employed but only in a multi-layer system comprising a bioactive coated with an inner coating of amylose and then an outer coating of Eudragit® L100.

A further amylose-based coating composition is disclosed in <CIT> (BTG International Limited). The coating composition comprises a mixture of amylose and a water insoluble pH independent film-forming polymer which is formed from a water-insoluble cellulosic or acrylate polymer material.

<CIT>also discloses a delayed release coating comprising amylose and (preferably) ethyl cellulose or alternatively an acrylate polymer, the degradation of which is independent of pH. The coating composition also includes a plasticiser and the method finds particular application in the preparation of dosage forms comprising active materials that are unstable at temperatures in excess of <NUM>, as the composition is formed at lower temperatures than this.

<CIT> discloses a specific delayed release coating for the bioactive prednisolone sodium metasulphobenzoate comprising glassy amylose, ethyl cellulose and dibutyl sebacate.

The use of polysaccharides other than amorphous amylose in a delayed release coating is disclosed in <CIT>. Examples include guar gum, karaya gum, gum tragacanth and xanthan gum. Microparticles of these polysaccharides are dispersed in a water-insoluble film-form ing polymer matrix formed for example from a cellulose derivative, an acrylic polymer or a lignin.

<CIT> discloses a peroral pharmaceutical formulation containing a drug and a chitosan (a polysaccharide obtained from chitin) for controlling its release. The drug and the chitosan are mixed into a homogeneous mechanical powder mixture which is granulated and then optionally tabletised. The granulation may be performed with an enteric polymer (such as a copolymer of methacrylic acid) or the granules may be provided with a porous enteric coating.

<CIT> discloses a pH dependent drug release system which is a free-flowing powder of solid hydrophobic nano-spheres comprising a drug encapsulated in a pH-sensitive micro-sphere. The nano-spheres are formed from the drug in combination with a wax material, and the pH-sensitive micro-sphere formed from a pH-sensitive polymer (such as a Eudragit® polymer) in combination with a water-sensitive material such as a polysaccharide.

An article in the <NPL>) reports the results of investigations into the use of certain polymethacrylate polymers to, inter alia, control the swelling of inulin. The polymethacrylate polymers tested were Eudragit® RS; Eudragit® RL; <NUM>:<NUM> mixtures of Eudragit® RS and Eudragit® RL; Eudragit® FS; and <NUM>:<NUM> mixtures of Eudragit® RS and Eudragit® S.

<CIT> discloses an oral dosage form containing at least one active ingredient enclosed within a shell material which comprises a polysaccharide that decomposes in the colon. The shell material contains a film-forming polymer in admixture with the polysaccharide. The ratio by weight of polysaccharide to film forming polymer is from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. The reference exemplifies the use of a mixture of guar gum (or tragacanth with a film-forming enteric polymer selected from Eudragit RL <NUM> D, Eudragit® L <NUM> D or Eudragit® S <NUM> as a tablet coating.

<CIT> discloses an oral dosage form comprising a core containing bisacodyl, and an enteric polymer coating for the core, the coating comprising at least one inner coating layer and an outer coating layer. The or each inner coating layer is an enteric polymer that begins to dissolve in an aqueous medium at a pH from about <NUM> to about <NUM>, and the outer coating layer is an enteric polymer that begins to dissolve in an aqueous medium at a pH from about <NUM> to about <NUM>. The enteric polymer coating materials for the inner layer(s) are selected from the group consisting of cellulose acetate phthalate; cellulose acetate trimellitate; hydroxypropyl methylcellulose phthalate; hydroxypropyl methylcellulose acetate succinate; polyvinyl acetate phthalate; poly(methacrylic acid, methyl methacrylate) <NUM>:<NUM>; poly(methacrylic acid, ethyl acrylate) <NUM>:<NUM>; and compatible mixtures thereof.

<CIT> discloses a colonic drug delivery formulation in which a mixture of a pH dependent film forming polymeric material and a polysaccharide such as starch is used. Although it is known that this formulation shows delayed release followed by a relatively quick release of the drug, it would be preferred if the drug release was quicker in the colon.

<CIT> discloses an enteric coated oral dosage form. The enteric coating is a bilayer comprising an inner layer of neutral or near neutral pH <NUM> to <NUM>, and an outer layer of acidic pH <NUM> to <NUM>.

The paper entitled "<NPL>) discloses the results of studies into drug release from oral dosage forms comprising a core containing lactulose and a drug, an inner acid-soluble material layer, and an outer layer of enterosoluble material.

The paper entitled "<NPL>) describes oral dosage forms for colonic drug delivery having a coating comprising a blend of a digestible polysaccharide and a polymer that is insoluble in gastrointestinal fluids.

In accordance with a first aspect of the present invention, there is provided a delayed release drug formulation for oral administration to deliver a drug to the colon of a subject, said formulation comprising a core and a coating for the core, the core comprising a drug and the coating comprising an outer layer and an inner layer, wherein the outer layer comprises a mixture of a polysaccharide which is susceptible to attack by colonic bacteria and an enteric polymethacrylate polymer having a pH threshold from pH <NUM> to no more than <NUM> in a ratio in a range from <NUM>:<NUM> to <NUM>:<NUM>, and wherein the inner layer comprises a third polymeric material which is a non-ionic polymer that is soluble in intestinal fluid, and a buffer agent and a base.

The Inventors have discovered that a coating having an inner layer comprising a polymer that is soluble in intestinal fluid and an outer layer of a mixture of a first polymeric material being a polysaccharide susceptible to attack by colonic bacteria and a second polymeric material being an enteric polymethacrylate polymer having a pH threshold at from pH <NUM> to no more than <NUM> has superior colonic-release properties over comparative coatings designed for site-specific release in the colon. In this connection, drug release from formulations according to the present invention appears to be accelerated in the colon when compared to comparative colonic release formulations. Without wishing to be bound by any particular theory, the Inventors believe that, once intestinal fluid penetrates the outer layer, the inner layer begins to dissolve before the outer layer to form a fluid region between the core and the outer layer. The fluid region not only facilitates dissolution and/or disintegration of the outer layer from the inside, but also softens and begins to break up the core so that, when the outer layer degrades, the drug is released from the core more quickly.

It is preferred that the polysaccharide is selected from the group consisting of starch; amylose; amylopectin; chitosan; chondroitin sulfate; cyclodextrin; dextran; pullulan; carrageenan; scleroglucan; chitin; curdulan and levan. It is particularly preferred that the polysaccharide is starch.

The enteric polymethacrylate polymer is an anionic polymeric material, and is preferably an anionic copolymer of a (meth)acrylic acid and a (meth)acrylic acid alkyl ester.

The disadvantageous swelling of polysaccharides susceptible to attack by colonic bacteria, e.g. amylose, is controlled by the inclusion of a pH dependent material having a pH threshold of from pH <NUM>. to no more than <NUM>.

A further technical advantage of the present invention (compared, for example, to the formulation disclosed in <CIT>) is that substantially no drug is released for an extended period (that is, whilst the coating is intact and is being dissolved/disintegrated), following which the drug is released relatively quickly. This is in contrast to homogeneous tablets from which the drug release profile is gradual from the outset rather than delayed then pulsatile.

A yet further technical advantage of the present invention compared to <CIT> is accelerated release of the drug once the formulation is exposed to the conditions of the colonic environment.

The first polymeric material is a polysaccharide, preferably containing a plurality of glucose units, e.g. a polyglucoside. In a preferred embodiment, the polysaccharide is at least one polysaccharide selected from the group consisting of starch; amylose; amylopectin; chitosan; chondroitin sulfate; cyclodextrin; dextran; pullulan; carrageenan; scleroglucan; chitin; curdulan and levan. It is further preferred that the polysaccharide is starch, amylose or amylopectin, most preferably starch.

The person skilled in the art is capable of determining whether a polysaccharide is susceptible to attack by colonic bacteria using techniques comprising part of the common general knowledge. For example, a pre-determined amount of a given material could be exposed to an assay containing an enzyme from a bacterium found in the colon and the change in weight of the material over time may be measured.

The polysaccharide is preferably starch. Starches are usually extracted from natural sources such as cereals; pulses; and tubers. Suitable starches for use in the present invention are typically food grade starches and include rice starch; wheat starch; corn (or maize) starch; pea starch; potato starch; sweet potato starch; tapioca starch; sorghum starch; sago starch; and arrow root starch. The use of maize starch is exemplified below.

Starch is typically a mixture of two different polysaccharides, namely amylose and amylopectin. Different starches may have different proportions of these two polysaccharides. Most natural (unmodified) maize starches have from about <NUM> wt % to about <NUM> wt % amylose with the remainder being at least substantially made up of amylopectin. Starches suitable for use in the present invention typically have at least <NUM> wt %, e.g. at least <NUM>% or <NUM>%, preferably at least <NUM> wt %, amylose.

"High amylose" starches, i.e. starches having at least <NUM> wt % amylose, are suitable. Particularly suitable starches have from about <NUM> wt % to about <NUM> wt %, e.g. about <NUM> wt % or about <NUM> wt % amylose.

Starches suitable for use in the present invention may have up to <NUM> % amylopectin, more typically from about <NUM> wt % to about <NUM> wt % amylopectin. "Low amylose" starches, i.e. starches having no more than <NUM> wt % amylose and at least <NUM> wt % amylopectin, e.g. up to <NUM> wt % amylopectin and even as much as up to <NUM> wt % amylopectin, are still suitable. The starch may be, for example, unmodified waxy corn starch. This typically comprises about <NUM> % amylopectin.

Preferred starches have no more than <NUM> wt % amylopectin. As indicated above, particularly suitable starches are "high amylose" starches which have from about <NUM> wt % to about <NUM> wt % amylopectin, e.g. about <NUM> wt % or about <NUM> wt % amylopectin.

The person skilled in the art is capable of determining the relative proportions of amylose and amylopectin in any given starch. For example, near-infrared ("NIR") spectroscopy could be used to determine the amylose and amylopectin content of a starch using calibration curves obtained by NIR using laboratory-produced mixtures of known amounts of these two components. Further, starch could be hydrolysed to glucose using amyloglucosidase. A series of phosphorylation and oxidation reactions catalysed by enzymes result in the formation of reduced nicotinamide adenine dinucleotide phosphate ("NADPH"). The quantity of NADPH formed is stochiometric with the original glucose content. Suitable test kits for this procedure are available (e.g., R-Biopharm GmbH, Germany). Another method that could be used involves subjecting the coating to digestion by bacterial enzymes, e.g. α-amylase, to produce short chain fatty acids ("SCFA") which can be quantified by gas-liquid chromatography using a capillary column.

Preferred starches have amylose in its glassy form although amylose in its amorphous form may also be used in conjunction with the present invention.

Preferred starches are "off-the-shelf' starches, i.e. starches which require no processing prior to use in the context of the present invention. Examples of particularly suitable "high amylose" starches include Hylon™ VII (National Starch, Germany), Eurylon™ VI or Amylo N-<NUM> (Roquette, Lestrem, France), or Amylogel <NUM> (Cargill, Minneapolis, USA) all of which are examples of a maize starch having from about <NUM> to about <NUM> wt% amylose.

The present invention involves the use of a second polymeric material that dissolves in a pH dependent manner. The second material is a film forming polymethacrylate polymer that is pH sensitive, i.e. has a "pH threshold" which is the pH below which it is insoluble in aqueous media and at or above which it is soluble in aqueous media. Thus, the pH of the surrounding medium triggers dissolution of the second polymeric material and none (or essentially none) of the second polymeric material dissolves below the pH threshold. Once the pH of the surrounding medium reaches (or exceeds) the pH threshold, the second polymeric material becomes soluble.

Throughout the specification, the term "insoluble" is used to mean that <NUM> of a polymeric material requires more than <NUM>,<NUM> of solvent or "surrounding medium" to dissolve at a given pH. In addition, the term "soluble" is used to mean that <NUM> of a polymeric material requires less than <NUM>,<NUM>, preferably less than <NUM>,<NUM>, more preferably less than <NUM>, even more preferably less than <NUM> or <NUM> of solvent or surrounding medium to dissolve at a given pH.

By "surrounding medium", the Inventors mean to include the intestinal fluid. Alternatively, the surrounding medium may be a solution designed to recreate in vitro intestinal fluid.

The normal pH of gastric juice is usually in the range of pH <NUM> to <NUM>. The second polymeric material is insoluble below pH <NUM> and soluble at about pH <NUM> or above and, thus, is usually insoluble in gastric juice. Such a material may be referred to as a gastro-resistant material or an "enteric" material.

The second polymeric material has a pH threshold of pH <NUM> or above and preferably pH <NUM> or above. The second polymeric material has a pH threshold of no more than pH <NUM>. Preferably, the second polymeric material has a pH threshold within the range of pH found in intestinal fluid. The pH of intestinal fluid may vary from one person to the next, but in healthy humans is generally from about pH <NUM> to <NUM> in the duodenum, from about <NUM> to <NUM> in the jejunum, from about <NUM> to <NUM> in the ileum, and from about <NUM> to <NUM> in the colon. The second polymeric material preferably has a pH threshold of about <NUM>, i.e. is insoluble below pH <NUM> and soluble at about pH <NUM> or above, and more preferably has a pH threshold of about <NUM>, i.e. is insoluble below pH <NUM> and soluble at about pH <NUM> or above.

The pH threshold at which a material becomes soluble may be determined by a simple titration technique which would be part of the common general knowledge to the person skilled in the art.

The second polymeric material is a film-forming polymethacrylate polymer.

The second material is an "anionic" polymeric material, i.e. a polymeric material containing groups that are ionisable in aqueous media to form anions (see below), and more preferably a co-polymer of a (meth)acrylic acid and a (meth)acrylic acid C<NUM>-<NUM> alkyl ester, for example, a copolymer of methacrylic acid and methacrylic acid methyl ester. Such a polymer is known as a poly(methacrylic acid/methyl methacrylate) co-polymer. Suitable examples of such co-polymers are anionic and not sustained release polymethacrylates. The ratio of carboxylic acid groups to methyl ester groups (the "acid:ester ratio") in these co-polymers determines the pH at which the co-polymer is soluble. The acid:ester ratio may be from about <NUM>:<NUM> to about <NUM>:<NUM>, e.g. about <NUM>:<NUM> or, preferably, about <NUM>:<NUM>. The molecular weight ("MW") of preferred anionic co-polymers is usually from about <NUM>,<NUM> to <NUM>,<NUM>, preferably about <NUM>,<NUM>.

Preferred anionic poly(methacrylic acid/methyl methacrylate) co-polymers include Eudragit® L (acid:ester ratio about <NUM>:<NUM>; MW about <NUM>,<NUM>; pH threshold of about <NUM>); Eudragit® S (acid:ester ratio about <NUM>:<NUM>; MW about <NUM>,<NUM>; pH threshold of about <NUM>); and Eudragit® FS (a poly(methyl acrylate/methyl methacrylate/methacrylic acid); acid:ester ratio of about <NUM>:<NUM>; MW about <NUM>,<NUM>; pH threshold of about <NUM>).

The second material may be a copolymer of methacrylic acid and ethyl acrylate. Eudragit® L100-<NUM> poly(methacrylic acid/ethyl acrylate); acid:ester ratio of about <NUM>:<NUM>; MW about <NUM>,<NUM>; pH threshold of about <NUM> is suitable.

The Eudragit® co-polymers are manufactured and/or distributed by Evonik GmbH, Darmstadt, Germany.

Mixtures of film forming polymer materials may be used as appropriate. An example of a suitable mixture would include a mixture, e.g. a <NUM>:<NUM> mixture, of Eudragit® L and Eudragit® S. However, the use of a particular film forming polymer material, e.g. a poly(methacrylic acid/methyl methacrylate) co-polymer, alone is preferred. The use of Eudragit® S alone as the second polymeric material is particularly preferred.

The proportion of the first polymeric material to the second polymeric material is from <NUM>:<NUM> to <NUM>:<NUM> and preferably from <NUM>:<NUM> to <NUM>:<NUM>. In some particularly preferred embodiments, the proportion is from <NUM>:<NUM> to <NUM>:<NUM>, e.g. from <NUM>:<NUM> to <NUM>:<NUM> and preferably about <NUM>:<NUM>. In other particularly preferred embodiments, the proportion is from <NUM>:<NUM> to about <NUM>:<NUM>, e.g. about <NUM>:<NUM>.

The mixture of first and second polymeric materials is preferably substantially homogenous.

Optionally, conventional excipients such as those excipients selected from plasticisers for film formation (for example, triethyl citrate), anti-tack agents (such as glyceryl monostearate or GMS) and surfactants (such as polysorbate <NUM>), may be included in amounts up to <NUM> wt % of the final composition of the outer coating preparation.

The thickness of the outer coating of the core is typically from about <NUM> to about <NUM>. The thickness of a specific coating will, however, depend on the composition of the coating. For example, coating thickness is directly proportional to the amount of polysaccharide in the coating. Thus, in embodiments where the coating comprises high amylose starch and Eudragit™ S at a ratio of about <NUM>:<NUM>, the coating thickness may be from about <NUM> to about <NUM>, and preferably from about <NUM> to about <NUM>. The thickness (in µm) for a given coating composition is independent of core size.

The thickness of the outer coating is not related to the size of the core but is typically equivalent to about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, preferably from about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, and most preferably from about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, based on the dry weight of the second polymeric material, for cores having a diameter from about <NUM> × <NUM>-<NUM> m to about <NUM>.

The formulation according to the present invention additionally has an inner layer which is positioned between the core and the outer layer. The inner layer comprises a third polymeric material which is soluble in intestinal fluid.

By "intestinal fluid", the Inventors mean the fluid in the lumen of the intestine of a mammal, particularly a human. Intestinal fluid is a pale yellow aqueous fluid secreted from glands lining the walls of the intestine. Intestinal fluid includes fluid found in the small intestine, i.e. fluid found in the duodenum (or "duodenal fluid"), fluid found in the jejunum (or "jejunal fluid") and fluid found in the ileum (or "ileal fluid"), and fluid found in the large intestine, e.g. "colonic fluid".

The skilled person can readily determine whether a polymer is soluble in intestinal fluid. If a polymer is soluble in water (or aqueous solution, e.g. a buffer solution) at a pH from <NUM> to <NUM>, then that polymer would typically be soluble in intestinal fluid. Alternatively, the composition of intestinal fluid is known and may be replicated in vitro. If a polymer is soluble in artificial intestinal fluid in vitro, then it would be soluble in intestinal fluid in vivo.

Any pharmacologically acceptable water soluble film forming polymers are, in principle, suitable for use as the third polymeric material. The third polymeric material may be soluble in at least one fluid selected from duodenal fluid, jejunal fluid and ileal fluid. However, in preferred embodiments, the solubility of the third polymeric material in water is not dependent on pH; at least not within the range of pH found in the intestine. In preferred embodiments, the third polymeric material is soluble in fluid at any point in the intestine.

Polymers suitable for use as the third polymeric material are pharmacologically acceptable non-ionic polymers, i.e. pharmacologically acceptable polymers which do not ionise in aqueous media. In these embodiments, the inner layer additionally comprises a buffer agent and a base. Suitable examples of buffer agents and bases are discussed below.

Examples of suitable non-ionic polymers include methylcellulose (MC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), poly(ethyleneoxide)-graft-polyvinylalcohol, polyvinylpyrrolidinone (PVP), polyethylene glycol (PEG) and polyvinylalcohol (PVA).

Mixtures of film forming polymer materials may be used as appropriate. The polymer components in such mixtures may be non-ionic polymers, or a mixture of anionic and non-ionic polymers. Suitable anionic polymers include polycarboxylic acid polymers, i.e. polymers or co-polymers that contain a plurality of carboxylic acid functional groups that are ionisable in aqueous media such as intestinal fluid, to form carboxylate anions. Examples of suitable polycarboxylic acid polymers include cellulose acetate phthalate (CAP), polyvinyl acetate phthalate (PVAP), hydroxypropyl methylcellulose phthalate (HPMCP), hydroxypropyl methylcellulose acetate succinate (HPMC-AS), cellulose acetate trimellitate (CAT), xanthan gum, alginates and shellac.

An example of a suitable mixture would include a mixture, e.g. a <NUM>:<NUM> mixture, of Eudragit® S and HPMC. However, the use of a particular film forming polymeric material alone is preferred.

The inner layer comprises at least one base. The purpose of the base is to provide an alkaline environment on the underside of the outer layer once intestinal fluid begins to penetrate the outer layer. Without being bound by any particular theory, the Inventors believe that the alkaline environment facilitates disintegration of the outer layer since the pH of the alkaline environment is above the pH threshold of the second polymeric material, thereby accelerating release of the drug from the formulation once the outer coating is dissolved and/or disintegrates.

In principle, any pharmacologically acceptable base may be used. Suitable bases include inorganic bases such as sodium hydroxide, potassium hydroxide and ammonium hydroxide, and organic bases such as triethanolamine, sodium bicarbonate, potassium carbonate, trisodium phosphate, trisodium citrate or physiologically tolerated amines such as triethylamine. Hydroxide bases in general, and sodium hydroxide in particular, are preferred.

In embodiments in which the third polymeric material is a fully neutralised polycarboxylic acid polymer, the base entrapped within the inner layer is usually the base that was used to neutralise the polymer and to adjust the pH of the inner coating preparation to a pH from about pH <NUM> to about pH <NUM> (see below).

In embodiments in which the third polymeric material is a non-ionic polymer, the inner layer comprises a combination of a base and a buffer agent.

The amount of base present in the inner layer would depend at least in part on the final pH of the inner coating preparation prior to coating a given batch of cores; the number of cores to be coated in the batch; the amount of the inner coating preparation used in the coating process of the batch; and the efficiency of the coating process in terms of the amount of wasted coating preparation.

The inner coating comprises at least one buffer agent. The purpose of the buffer agent is to provide pH buffer capacity on the underside of the outer layer once intestinal fluid begins to penetrate the outer layer. Without wishing to be bound by any particular theory, the Inventors believe that the buffer agent increases the buffer capacity in the dissolving inner layer and assists the ionisation and dissolution of the polymer in the outer layer. It is believed that, for a given pH, the higher the buffer capacity, the faster the rate of polymer dissolution. In embodiments where there is a base in the inner layer, the buffer agent helps maintains the alkaline environment under the outer layer once intestinal fluid penetrates the outer layer.

The buffer agent may be an organic acid such as a pharmacologically acceptable carboxylic acid having from <NUM> to <NUM>, preferably <NUM> to <NUM>, carbon atoms. Suitable carboxylic acids are disclosed in <CIT>. Citric acid is an example of such a carboxylic acid. The carboxylic acids may be used in carboxylate salt form, and mixtures of carboxylic acids, carboxylate salts or both may also be used.

The buffer agent may also be an inorganic salt such as an alkali metal salt, an alkali earth metal salt, an ammonium salt, and a soluble metal salt. As metals for the soluble metal salts, manganese, iron, copper, zinc and molybdenum can be mentioned. Further preferred, the inorganic salt is selected from chloride, fluoride, bromide, iodide, phosphate, nitrate, nitrite, sulphate and borate. Phosphates such as potassium dihydrogen phosphate are preferred over other inorganic buffer salts and organic acid buffers due to their greater buffer capacity at the pH of the coating solution, for example pH <NUM>.

The buffer(s) is usually present in the inner layer in an amount from about <NUM> to about <NUM> wt %, e.g. from about <NUM> to about <NUM> wt %, preferably from about <NUM> to about <NUM> wt %, and more preferably about <NUM> wt %, based on the dry weight of the third polymeric material.

In addition to the buffer agent and the base, the inner layer may comprise conventional excipients for polymer films, including those excipients selected from plasticizers (such a triethyl citrate), anti-tack agents (such as GMS), and surfactants (such as polysorbate <NUM>).

The thickness of the inner coating of the core is typically from about <NUM> to about <NUM>. As with the outer layer, the thickness of the inner layer is not related to the size of the core but is typically equivalent to about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, preferably from about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, and most preferably from about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, based on the dry weight of the third polymeric material, for cores having a diameter from about <NUM> to about <NUM>.

The formulation of the present invention may have an additional (or isolation) layer either between the active core and the inner layer and/or a top coating layer coating the outer layer. The presence of an isolation layer between the active core and the inner layer is preferred. Any suitable isolation layer known to the skilled person can be used. In one preferred embodiment, the isolation layer comprises a non-ionic polymer such as HMPC or PVA. The isolation layer can additionally comprise polyethylene glycol.

The "core" is the solid body on which the inner layer is applied. The core may be any suitable dosage form, for example, a tablet, a pellet, a granule, a microparticle, a hard or soft capsule, or a microcapsule.

The core comprises the drug(s). The drug(s) may be contained within the body of the core, for example within the matrix of a tablet or pellet, or within the contents encapsulated within a capsule. Alternatively, the drug may be in a coating applied to the core, for example where the core is a bead of edible material such as sugar, e.g. where the core is in the form of a nonpareil bead or dragée.

The core may consist of the drug(s) alone, or more usually may consist of the drug(s) and at least one pharmacologically acceptable excipient. In this connection, the core is typically a tablet or pellet and consists of a mixture of the drug(s) with a filler or diluent material, e.g. lactose or cellulose material such as microcrystalline cellulose; a binder, e.g. polyvinylpyrrolidone ("PVP") or hydroxypropyl methylcellulose (HPMC); a disintegrant, e.g. croscarmellose sodium (e.g. Ac-Di-Sol™) and sodium starch glycolate (e.g. Explotab™); and/or a lubricant, e.g. magnesium stearate and talc. The core may be a compressed granulate comprising at least some of these materials.

The core may be uncoated or, as indicated above, the core may itself comprise a coating such as an isolation layer on to which the inner layer is applied.

The minimum diameter of each core is typically at least about <NUM>-<NUM>m, usually at least about <NUM> × <NUM>-<NUM>m and, preferably, at least about <NUM>-<NUM>m. The maximum diameter is usually no more than <NUM>, typically no more than <NUM> and, preferably, no more than <NUM>. In preferred embodiments, the core has a diameter from about <NUM> to about <NUM>, and preferably from about <NUM> to about <NUM> (e.g. for pellets or mini-tablets) or from about <NUM> to about <NUM> (e.g. for certain tablets or capsules). The term "diameter" refers to the largest linear dimension through the core.

The formulation may comprise a plurality of coated cores in order to provide a single dose of the drug(s), particularly in embodiments in which the core is "small", e.g. having a diameter of less than <NUM>. Multiunit dosage forms comprising coated cores having a diameter of less than <NUM> may be preferred.

The present invention has application in a multi-phasic drug release formulation comprising at least two pluralities of coated cores, e.g. coated pellets, in the same dosage form, e.g. a capsule, in which the coated cores of one plurality are differentiated from the coated cores of the or each other plurality by the coating. The coatings may differ from one plurality to the next in terms of coating thickness or composition, e.g. the ratio and/or identity of components. Multi-phasic drug release formulations would be particularly suitable for suffers of Crohn's disease affecting different regions along the intestine.

Release from formulations according to the present invention is typically delayed until at least the distal ileum and, preferably, the colon. Release from certain formulations may also be sustained. However, in preferred formulations, release is pulsatile.

The time between initial exposure to conditions suitable for drug release and the start of drug release is known as the "lag time". The lag time depends on a number of factors including coating thickness and composition and may vary from one patient to the next. Formulations according to the present invention usually display a lag time in colonic conditions of at least <NUM> minutes. In most embodiments, the lag time is from about <NUM> minutes to about <NUM> hours. For example, the lag time in faecal slurry at pH <NUM> may be from about <NUM> minutes to about <NUM> hours, e.g. from about <NUM> minutes to about <NUM> hours. Complete release of the drug may be achieved in no more than <NUM> hours, e.g. no more than <NUM> hours, after exposure to these conditions.

A formulation is usually defined as gastric resistant if there is less than <NUM> wt % drug release in acidic media after <NUM> hours. Formulations according to the present invention typically display far less than <NUM> wt % drug release in acidic media and may be considered to be gastric resistant. The formulations usually display less than <NUM> wt % drug release in acidic media and, typically, display substantially no drug release in acidic media. When starch is combined with an acrylate film forming material to form the outer layer of the coating for the core, typically less than <NUM>% drug release occurs over <NUM> hours in conditions simulating the stomach and small intestine.

In one embodiment, the core is a tablet having a diameter of <NUM>-<NUM>. The outer layer preferably comprises a <NUM>:<NUM> mixture of high amylose starch, e.g. Eurylon™ VII or VI, and a polymethacrylate polymer, e.g. Eudragit™ S, and the inner layer preferably comprises a fully neutralized polymethacrylate polymer, e.g. Eudragit™ S, applied from an inner coating preparation having a pH of about <NUM>. The core is preferably coated with the inner layer to a thickness from about <NUM> to about <NUM>/cm<NUM> (based on dry weight of the polymethacrylate polymer) to form an inner layer coated core, which is then coated with the outer layer to a thickness from about <NUM> to about <NUM>/cm<NUM> (based on dry weight of polymethacrylate polymer).

According to a second aspect of the present invention (not claimed), there is provided a formulation according to the first aspect for use in a method of medical treatment of the human or animal body by therapy.

The core comprises at least one drug. The formulation is usually used to administer a single drug as the sole therapeutically active component. However, more than one drug may be administered in a single formulation.

The formulation of the present invention is designed to administer a wide range of drugs. Suitable drugs include those drugs which are known for intestinal administration using known delayed release oral formulations. The present invention may be used to administer drugs having a local or a systemic effect.

The formulation of the present invention has particular application in the intestinal administration of a drug comprising at least one acidic group such as a carboxylic acid group. Such drugs may be acidic drugs or zwitterionic drugs. An example of such a drug is <NUM>-aminosalicylic acid (5ASA or mesalazine).

The identity of the drug(s) in the formulation obviously depends on the condition to be treated. In this connection, the formulation has particular application in the treatment of IBD (including Crohn's disease and ulcerative colitis); IBS; constipation; diarrhoea; infection; and carcinoma, particularly colon or colorectal cancer.

For the treatment or prevention of IBD, the formulation may comprise at least one drug selected from the group consisting of non-steroidal anti-inflammatory agents (e.g. 5ASA); steroids (e.g. prednisolone; budesonide or fluticasone); immunosuppressants (e.g. azathioprine; cyclosporin; and methotrexate); and antibiotics.

For the treatment or prevention of cancer, the formulation may comprise at least one antineoplastic agent. Suitable antineoplastic agents include fluorouracil; methotrexate; dactinomycin; bleomycin; etoposide; taxol; vincristine; doxorubicin; cisplatin; daunorubicin; VP-<NUM>; raltitrexed; oxaliplatin; and pharmacologically acceptable derivatives and salts thereof. For the prevention of colon cancer or colorectal cancer, primarily in patients suffering from colitis, the formulation may comprise the anti-inflammatory agent, 5ASA.

For the treatment or prevention of IBS, constipation, diarrhoea or infection, the formulation may comprise at least one active agent suitable for the treatment or prevention of these conditions.

Pharmacologically acceptable derivatives and/or salts of the drugs may also be used in the formulation. An example of a suitable salt of prednisolone is methyl prednisolone sodium succinate. A further example is fluticasone propionate.

The present invention has particular application in either the treatment of IBD (particularly, ulcerative colitis) or the prevention of colon cancer or colorectal cancer (primarily in colitis patients), both using 5ASA. It also has application as a portal of entry of drugs into the systemic circulation via the colon. This is particularly advantageous for peptide and protein drugs which are unstable in the upper gastrointestinal tract. The present invention may also be utilised for the purpose of chronotherapy.

In a third aspect of the invention (not claimed), there is provided a method of targeting a drug to the colon comprising administering to a patient a formulation as defined above.

In a fourth aspect of the invention (not claimed), there is provided the use of a formulation as defined above in the manufacture of a medicament for the treatment or prevention of IBD (particularly ulcerative colitis); IBS; constipation; diarrhoea; infection; and cancer.

There is also provided the use of at least one drug selected from anti-inflammatory agents and steroids in the manufacture of a medicament comprising a formulation as defined above for use in the treatment of IBD. In addition, there is also provided the use of at least one antineoplastic agent in the manufacture of a medicament comprising a formulation as defined above for use in the treatment of carcinoma. Further, there is also provided use of 5ASA in the manufacture of a medicament comprising a formulation as defined above for use in the prevention of colon cancer or colorectal cancer.

According to a fifth aspect of the present invention (not claimed), there is provided a method of medical treatment or prevention of IBD or carcinoma comprises administering to a patient a therapeutic amount of a formulation as defined above.

The formulation will typically comprise a therapeutically effective amount of the or each drug which may be from about <NUM> wt % to about <NUM> wt %, based on the total weight of the formulation. The actual dosage would be determined by the skilled person using his common general knowledge. However, by way of example, "low" dose formulations typically comprise no more than about <NUM> wt % of the drug, and preferably comprise from about <NUM> wt % to about <NUM> wt %, e.g. about <NUM> wt %, of the drug. "High" dose formulations typically comprise at least <NUM> wt % of the drug, and preferably from about <NUM> wt % to about <NUM> wt %, e.g. about <NUM> wt % or about <NUM> wt %.

According to a sixth aspect of the present invention, there is provided a method of producing a delayed release drug formulation for oral administration to deliver a drug to the colon according to the first aspect. The method comprises:.

The solvent system of the inner coating preparation is preferably aqueous.

The pH of the inner coating preparation is adjusted prior to coating to be at least <NUM> pH units higher than the pH threshold of the second polymeric material.

The pH of the inner coating preparation is preferably adjusted to be from pH <NUM> to pH <NUM>, e.g. from pH <NUM> to pH <NUM>, preferably from pH <NUM> to pH <NUM>, and more preferably pH <NUM>.

The outer coating may be applied using the method described in <CIT>.

Preferred embodiments of the present invention will now be described with reference to the drawings, in which:-.

<NUM>-aminosalicylic acid (mesalazine EP) was purchased from Cambrex Karlskoga AB, Karlskoga, Sweden. Lactose (Tablettose <NUM>) was purchased from Meggle, Hamburg, Germany. Sodium starch glycolate (Explotab™) was purchased from JRS Pharma, Rosenberg, Germany. Talc was purchased from Luzenac Deutschland GmbH, Düsseldorf, Germany. Polyvinylpyrolidon (PVP) was purchased from ISP Global Technologies, Köln, Germany. Magnesium stearate was purchased from Peter Greven GmbH, Bad Münstereifel, Germany. Eudragit® S <NUM> was purchased from Evonik, Darmstadt, Germany. Maize starch (N-<NUM>) was purchased from Roquette, Lestrem, France. Polysorbate <NUM>, butan-<NUM>-ol and sodium hydroxide were all purchased from Sigma-Aldrich, Buchs, Switzerland. Potassium dihydrogen phosphate, glyceryl monostearate (GMS) and triethyl citrate (TEC) were all purchased from VWR international LTD, Poole, UK.

Oblong shaped tablets with dimensions <NUM> x <NUM> were prepared by fluid bed granulation followed by blending and compression. Each tablet contains <NUM> wt % 5ASA (<NUM>; drug); <NUM> wt % lactose (filler); <NUM> wt % PVP (binder); <NUM> wt % sodium starch glycolate (disintegrant); and <NUM> wt % talc and <NUM> wt % magnesium stearate (lubricants).

The obtained tablet cores were coated as discussed below.

The inner coating layer was applied using an aqueous preparation of Eudragit® S <NUM>, where the pH is adjusted to pH <NUM>. The composition of the inner layer also includes <NUM>% of triethyl citrate (based on dry polymer weight), <NUM>% potassium dihydrogen phosphate (based on dry polymer weight), <NUM>% glyceryl monostearate (GMS; based on dry polymer weight) and <NUM>% polysorbate <NUM> (based on GMS weight). The pH was adjusted using <NUM> NaOH until the pH <NUM> was obtained. Potassium dihydrogen phosphate and triethyl citrate were dissolved in distilled water, followed by dispersion of the Eudragit® S <NUM> under mechanical agitation. The pH of the dispersion was then adjusted to pH <NUM> with <NUM> NaOH and left mixing for <NUM> hour.

A GMS dispersion was prepared at a concentration of <NUM>% w/w. Polysorbate <NUM> (<NUM>% based on GMS weight) was dissolved in distilled water followed by dispersion of the GMS. The dispersion was then heated to <NUM> for <NUM> minutes under strong magnetic stirring in order to form an emulsion. The emulsion was cooled at room temperature and under stirring.

The GMS dispersion was added to the neutralised Eudragit® S <NUM> solution and the final preparation was coated on to <NUM> 5ASA tablet cores, using a fluid bed spray coating machine until the coating amount reached <NUM> polymer/cm<NUM>. The total solids content of the coating solution is <NUM>%. The coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

The outer coating layer was applied from a mixture of an aqueous starch dispersion and an organic Eudragit® S <NUM> solution. The aqueous starch dispersion was prepared by dispersing maize starch into butan-<NUM>-ol, followed by water, under magnetic stirring. The ratio of maize starch : butan-<NUM>-ol : water was <NUM> : <NUM> : <NUM>. The resulting dispersion was heated to boiling and then cooled under stirring overnight. The % solids content of the cooled preparation was calculated based on the final weight of the dispersion (considering the evaporation during heating).

The organic Eudragit® S <NUM> solution was prepared by dissolving Eudragit® S <NUM> in <NUM>% ethanol under high speed stirring. The final solution contained about <NUM>% polymer solids. The starch dispersion was added dropwise to the Eudragit^ S <NUM> solution to obtain a ratio of starch : Eudragit® S of <NUM> : <NUM>. The mixture was mixed for <NUM> hours and <NUM>% triethyl citrate (based on total polymer weight) and <NUM>% glyceryl monostearate (GMS, based on total polymer weight) were added and mixed for further <NUM> hours.

The GMS was added in the form of a dispersion prepared at a concentration of <NUM>% w/w. Polysorbate <NUM> (<NUM>% based on GMS weight) was dissolved in distilled water followed by dispersion of the GMS. This dispersion was then heated to <NUM> for <NUM> minutes under strong magnetic stirring in order to form an emulsion. The emulsion was cooled at room temperature and under stirring.

The final preparation was coated on to 5ASA tablet cores, previously coated with the inner coating layer, using a fluid bed spray coating machine until a coating having <NUM> Eudragit® polymer/cm<NUM> was obtained. The spray coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

The coating layer containing Eudragit® S <NUM> was applied as an organic coating composition. The coating composition contained <NUM>% triethyl citrate (based on dry polymer weight), <NUM>% glyceryl monostearate (based on dry polymer weight) and <NUM>% polysorbate <NUM> (based on GMS weight). Briefly, triethyl citrate was dissolved in <NUM>% ethanol followed by Eudragit® S <NUM> under mechanical stirring and mixing continued for <NUM> hour.

The GMS was added in the form of a dispersion prepared at a concentration of <NUM>% w/w. Polysorbate <NUM> (<NUM>% based on GMS weight) was dissolved in distilled water followed by dispersion of GMS. This preparation was then heated to <NUM> for <NUM> minutes under strong magnetic stirring in order to form an emulsion. The emulsion was cooled at room temperature and under stirring.

The GMS dispersion was added to the organic Eudragit® S solution and the final coating solution was coated on to the 5ASA tablet cores, using a fluid bed spray coating machine to achieve a coating amount of <NUM> polymer/cm<NUM>. The coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

The coating layer composition contains a mixture of an aqueous starch dispersion and an organic Eudragit® S <NUM> solution. The aqueous starch dispersion was prepared by dispersing maize starch into butan-<NUM>-ol, followed by water, under magnetic stirring. The ratio of maize starch : butan-<NUM>-ol : water was <NUM> : <NUM> : <NUM>. The resulting dispersion was heated to boiling and then cooled under stirring overnight. The % solids content of the cooled preparation was calculated based on the final weight of the dispersion (considering the evaporation during heating).

The organic Eudragit® S solution was prepared by dissolution of Eudragit® S <NUM> in <NUM>% ethanol under high speed stirring. The final solution contained about <NUM>% polymer solids. The starch dispersion was added dropwise to the Eudragit^ S <NUM> solution to obtain a ratio of starch : Eudragit S of <NUM> : <NUM>. The mixture was mixed for <NUM> hours and <NUM>% triethyl citrate (based on total polymer weight) and <NUM>% glyceryl monostearate (based on total polymer weight) were added and the mixture was mixed for further <NUM> hours.

The final preparation was coated on to the 5ASA tablet cores in a fluid bed spray coating machine until a <NUM> Eudragit® S polymer/cm<NUM> was obtained. The spray coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

The inner coating layer is composed by an aqueous preparation of Eudragit® S <NUM>, where the pH is adjusted to pH <NUM>. The composition of the inner layer also includes <NUM>% of triethyl citrate (based on dry polymer weight), <NUM>% potassium dihydrogen phosphate (based on dry polymer weight), <NUM>% glyceryl monostearate (based on dry polymer weight) and <NUM>% polysorbate <NUM> (based on GMS weight). The pH was adjusted using <NUM> NaOH until the pH <NUM> is obtained. Potassium dihydrogen phosphate and triethyl citrate were dissolved in distilled water, followed by dispersion of the Eudragit^ S <NUM> under mechanical agitation. The pH was then adjusted to pH <NUM> with <NUM> NaOH and left mixing for <NUM> hour.

A GMS dispersion was prepared at a concentration of <NUM>% w/w. Polysorbate <NUM> (<NUM>% based on GMS weight) was dissolved in distilled water followed by dispersion of GMS. This preparation was then heated to <NUM> for <NUM> minutes under strong magnetic stirring in order to form an emulsion. The emulsion was cooled at room temperature and under stirring.

The GMS dispersion was added to the neutralised Eudragit® S solution and the final preparation was coated on to 5ASA tablet cores, using a fluid bed spray coating machine until the coating amount reached <NUM> polymer/cm<NUM>. The total solids content of the coating solution is <NUM>%. The coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

The outer coating layer is composed of Eudragit® S <NUM>, applied as an organic solution. The coating solution contains <NUM>% triethyl citrate (based on dry polymer weight), <NUM>% glyceryl monostearate (based on dry polymer weight) and <NUM>% polysorbate <NUM> (based on GMS weight). Briefly, triethyl citrate was dissolved in <NUM>% ethanol followed by Eudragit® S <NUM> under mechanical stirring and mixing continued for <NUM> hour.

A GMS dispersion was prepared at a concentration of <NUM>% w/w. Polysorbate <NUM> (<NUM>% based on GMS weight) was dissolved in distilled water followed by dispersion of the GMS. This dispersion was then heated to <NUM> for <NUM> minutes under strong magnetic stirring in order to form an emulsion. The emulsion was cooled at room temperature and under stirring.

The GMS preparation was added to the Eudragit® S <NUM> solution and the final coating solution was coated on to 5ASA tablet cores, previously coated with the inner coating layer, using a fluid bed spray coating machine to achieve a coating amount of <NUM> Eudragit® S polymer/cm<NUM>. The coating parameters were as follows: spraying rate <NUM>/min/kg tablets, atomizing pressure <NUM> bar and inlet air temperature <NUM>.

In vitro dissolution studies were performed on a USP type II apparatus using a paddle speed of <NUM> rpm and a media temperature of <NUM> ± <NUM>. Tablets were first tested in <NUM> HCl for <NUM> hours followed by <NUM> hours in Krebs buffer (pH <NUM>). The pH of the buffer was stabilised at <NUM> ± <NUM> by continuously sparging with <NUM>% CO<NUM> / <NUM>% O<NUM>. Absorbance measurements were taken at <NUM> minute intervals, with an absorbance wavelength of <NUM> in HCl and <NUM> in Krebs buffer. The composition per litre of Krebs buffer is <NUM> of KH<NUM>PO<NUM>, <NUM> of NaCl, <NUM> KCl, <NUM> MgSO<NUM>. <NUM><NUM>O, <NUM> CaCl<NUM>. <NUM><NUM>O and <NUM> NaHCOs. Only the measurements taken at <NUM> minute intervals are depicted in <FIG>.

The fermentation assays used to test the formulations were based on the method described by <NPL>).

The basal medium used to allow bacteria growth was prepared accordingly to the supracited publication and the composition per litre is as follows: <NUM> peptone water; <NUM> yeast extract; <NUM> NaCl; <NUM> K<NUM>HPO<NUM>; <NUM> MgSO<NUM>. <NUM><NUM>O; <NUM> CaCl<NUM>. <NUM><NUM>O; <NUM> NaHCO<NUM>; <NUM> haemin; <NUM> L-cysteine HCl; <NUM> bile salts; <NUM> Tween <NUM>; <NUM> vitamin K; and <NUM> of <NUM>% (w/v) resazurin solution. This composition was mixed in a ratio of <NUM>:<NUM> with a faecal slurry, which was prepared by homogenizing fresh human faeces (<NUM> different donors) in phosphate buffered saline pH <NUM> at a concentration of <NUM>% w/w. The final concentration of the prepared faecal slurry (diluted with basal medium) is <NUM>% w/w. The donors had not received antibiotic treatment for at least <NUM> months before the study.

Each experiment was repeated <NUM> times, i.e. tablets from each test batch were tested in <NUM> different containers with faecal slurry (one tablet per container).

The pH of the slurry was adjusted to <NUM> by adding <NUM> NaOH dropwise, dispersing the NaOH with a sterile spoon and remeasuring the pH. The pH meter was allowed to equilibrate inside the anaerobic working station (at <NUM> and <NUM>% RH) for approximately <NUM> minutes before calibration. The pH electrode was calibrated using a two point method with pH <NUM> and <NUM> buffer solutions.

Each tablet being tested was placed in an individual plastic transparent container containing <NUM> of slurry.

The containers were placed on an IKA® VXR basic Vibrax® bench top shaker at a speed of <NUM> shakes per minute. This agitation speed did not cause mechanical damage to the tablet coatings.

<NUM> samples were removed at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> hours into <NUM> labelled eppendorf tubes. After time <NUM>, before a sample was withdrawn, the slurry was stirred manually to ensure the active drug was homogeneously dissolved in the slurry. Samples were withdrawn from <NUM> different sites.

The pH was found to drop below pH <NUM> during the first four hours. Thus, during this period, the pH was measured every <NUM> minutes and adjusted to pH <NUM> using <NUM> NaOH. After <NUM> hours, the pH was checked every hour and adjusted using NaOH or HCl when necessary.

All of the eppendorf tubes were centrifuged at <NUM>,<NUM> rpm from <NUM> minutes using an eppendorf International Centrifuge <NUM>. The supernatant was collected from the eppendorf tubes using a <NUM> syringe and filtered through a <NUM> Millex GP syringe driven filter unit into plastic wells.

100µl of the filtered supernatant was measured using a micropipette into labelled <NUM> amber glass HPLC vials and diluted with 900µl of mobile phase (<NUM>% water, <NUM>% methanol and <NUM>% trifluoracetic acid (TFA)).

The samples were analysed for 5ASA content using an Agilent Technologies <NUM> Series HPLC using the following conditions:.

As for Drug Release Test #<NUM> but the pH of the faecal slurry was maintained at pH <NUM>.

In vitro dissolution studies were performed on a USP type II apparatus using a paddle speed of <NUM> rpm and a media temperature of <NUM> ± <NUM>. Tablets were first tested in <NUM> HCl for <NUM> hours followed by <NUM> hours in Hanks buffer (pH <NUM>). The pH of the buffer was stabilised at <NUM> ± <NUM> by continuously sparging with <NUM>% CO<NUM> / <NUM>% O<NUM>. Absorbance measurements were taken at <NUM> minute intervals, with an absorbance wavelength of <NUM> in HCl and <NUM> in Hanks buffer pH <NUM>. The composition per litre of Hanks buffer is <NUM> of KH<NUM>PO<NUM>, <NUM> Na<NUM>HPO<NUM>. <NUM><NUM>O, <NUM> NaCl, <NUM> KCl, <NUM> MgSO<NUM>. <NUM><NUM>O, <NUM> CaCl<NUM>. <NUM><NUM>O and <NUM> NaHCO<NUM>.

The results presented in <FIG> indicate that the coated tablets according to the present invention are significantly superior to the tablets of the comparative examples. In this connection, an acceleration of drug release would be observed for the tablets according to the present invention, both at a pH higher (pH <NUM>) than the pH threshold (pH <NUM>) of the second polymeric material and at a lower pH (pH <NUM> or pH <NUM>) than the pH threshold, relative to the comparator tablets.

In aqueous solution at pH <NUM> (drug release test #<NUM>; <FIG>), there was no release of 5ASA from any of the tablets tested in the <NUM> hours that the tablets were exposed to simulated gastric conditions. However, it should be noted that, once the tablets were exposed to pH <NUM>, initial release of 5ASA from Reference Example <NUM> tablets occurred significantly earlier than from Comparative Example <NUM>( which is a conventional site-specific colonic release formulation) and from Comparative Example <NUM> (which is a site-specific colonic release formulation described in <CIT>). The profile of release of 5ASA from Reference Example <NUM> closely followed that for Comparative Example <NUM>. The similar release profiles may be explained by the similarities in the formulations themselves (Reference Example <NUM> differing only in the presence of starch in the outer coating) and the absence of any colonic enzymes in the surrounding medium to digest the starch.

In faecal slurry at pH <NUM> (drug release test #<NUM>; <FIG>), initial release of 5ASA from the tablets of Reference Example <NUM> occurred after about <NUM> hour, and complete release occurred in about <NUM> hours after initial release. In contrast, initial release from the tablets of both Comparative Examples <NUM> and <NUM> occurred after about <NUM> hours, with significant release from the tablets of Comparative Example <NUM> occurring only after <NUM> hours. In addition, while the tablets of Comparative Example <NUM> provided complete release after about <NUM> hours, the tablets of Comparative Example <NUM> provided less than <NUM> % release over <NUM> hours. The results indicate that the presence of the inner soluble layer accelerates drug release under colonic conditions from tablets having an outer layer comprising a mixture of starch and Eudragit S. The results also indicate that, without the polysaccharide in the outer layer (Comparative Example <NUM>), release under colonic conditions is not complete.

In faecal slurry at pH <NUM> (drug release test #<NUM>; <FIG>), initial release of 5ASA from the tablets of Reference Example <NUM> occurred after about <NUM> hours, whereas initial release from the comparator tablets occurred only after about <NUM> hours. In addition, even though the pH of the surrounding medium was significantly below the pH threshold of Eudragit S, tablets according to Reference Example <NUM> had release about <NUM>% of the 5ASA after about <NUM> hours. In contrast, the tablets of Comparative Example <NUM> had released less than <NUM>% of the 5ASA after <NUM> hours. These results indicate that the presence of starch in the outer layer enables release of a significant amount of the active when exposed to colonic enzymes even though the pH of the surrounding medium is well below the pH threshold of the second polymeric material.

The Inventors have also observed that less than <NUM>% of 5ASA is released from tablets of Reference Example <NUM> when exposed to aqueous solution at pH <NUM> for <NUM> hours (see drug release test #<NUM>; <FIG>). This result demonstrates the requirement for the presence of colonic enzymes in the surrounding medium to achieve significant release of the active from tablets according to the present invention.

It can be seen therefore that the delayed release formulation according to the present invention is significantly superior to comparative formulations.

Claim 1:
A delayed release drug formulation for oral administration to deliver a drug to the colon of a subject, said formulation comprising a core and a coating for the core, the core comprising a drug and the coating comprising an outer layer and an inner layer, wherein the outer layer comprises a mixture of a polysaccharide which is susceptible to attack by colonic bacteria and an enteric polymethacrylate polymer having a pH threshold from pH <NUM> to no more than <NUM> in a ratio in a range from <NUM>:<NUM> to <NUM>:<NUM>, and wherein the inner layer comprises a third polymeric material which is a non-ionic polymer that is soluble in intestinal fluid, a buffer agent, and a base.