DESC:
FIELD OF THE INVENTION
The present invention relates to oral modified release pharmaceutical compositions of azathioprine comprising plurality of delayed release azathioprine particles, and at least one pharmaceutically acceptable excipient. Further, the modified release composition is in the form of a suspension or dry formulation for reconstitution. The present invention also relates to a process for the preparation of the oral modified release pharmaceutical compositions of azathioprine.

BACKGROUND OF THE INVENTION
Azathioprine is chemically 6-[(1-methyl-4-nitro-1H-imidazol-5-yl)thio]-1H-purine. The structural formula of azathioprine is:

It is an imidazolyl derivative of 6-mercaptopurine and many of its biological effects are similar to those of the parent compound.

Azathioprine is an immunosuppressive drug, which is approved in the USA with the brand name Imuran®. Tablets and injectable dosage forms are commercialized in the USA. Imuran® is indicated as an adjunct for the prevention of rejection in renal homotransplantation. It is also indicated for the management of active rheumatoid arthritis to reduce signs and symptoms. The approved label of Imuran® mentions that nausea and vomiting may occur within the first few months of therapy with Imuran®. In some patients, nausea and vomiting may be severe and may be accompanied by symptoms such as diarrhea, fever, malaise, and myalgias.

Alkhawajah et al, in Drugs & Aging (2015) 32:689–697, reported that azathioprine can be used for the treatment of chronic autoimmune conditions like myasthenia gravis (MG). Myasthenia gravis is diagnosed at a progressively later age and the incidence continuously increases in the aged with a clear male predominance. People above the age of 65 constitute more than 50 % of the newly diagnosed. Commonly, patients present with focal (ocular or bulbar) weakness. A high index of suspicion is needed to achieve early diagnosis and improve prognosis. Management options include acetylcholinesterase inhibitors, steroids, and immunosuppressants. Of the immunosuppressants, azathioprine is one of the most widely used due to its demonstrated effect and favourable side-effect profile.

M Llabre´s et al, in Journal of Neurology, Neurosurgery, and Psychiatry 2005;76:1297–1300, discloses that dysphagia is a frequent symptom in myasthenia gravis and it eventually occurs in 15–40% of patients with the generalised form.

US publication number 2014/0371242 discloses oral suspension of azathioprine (5-50 mg/ml) for use in auto-immune diseases (like myasthenia gravis, rheumatoid arthritis, pemphigus, Behcet's disease, autoimmune hepatitis, and inflammatory bowel disease, among others) to provide azathioprine at a dosage of about 0.5 mg/Kg/day to about 2.5 mg/Kg/day and/or dosage of about 25-100 mg/day. Disclosed azathioprine oral suspensions may be used to administer azathioprine to subjects such as children & geriatric patients that may have difficulty in swallowing solid dosage forms.

PCT publication number 2001/012264 discloses solution or suspension of azathioprine at a concentration of 0.5 to 50 mg/ml with dosage between 50 and 250 mg/day for treatment of oral tissue inflammation and ulceration caused by the onset of an oral autoimmune disease. It discloses that azathioprine is commonly prescribed for many autoimmune diseases, including severe rheumatoid arthritis, systemic lupus erythematosus, myasthenia gravis, autoimmune chronic active hepatitis, and pemphigus vulgaris.

US patent number 5,691,343 discloses a method for treatment of inflammatory bowel disease comprising topically administering to the colon of a patient by rectal enema or by means of an orally ingested unit dosage form comprising an effective amount of enterically coated azathioprine which is released from the dosage form in the terminal portion of the ileum and in the colon of said patient.

Azathioprine is usually administered orally, which results in a challenge when treating children or geriatric patients who exhibit difficulty in swallowing solid oral preparations, such as tablets and capsules. Moreover, azathioprine is known to cause gastrointestinal track related side effects. There is a need for a new administration form for azathioprine that may allow convenient administration of azathioprine to children and geriatric patients with reduced gastrointestinal side effects of the drug.

SUMMARY OF THE INVENTION
In one general aspect, the present invention provides an oral modified release pharmaceutical composition of azathioprine comprising plurality of delayed release azathioprine particles, and at least one pharmaceutically acceptable excipient, wherein the composition is in the form of a suspension or dry formulation for reconstitution.

In another aspect, the present invention provides a powder for suspension of azathioprine comprising azathioprine, sodium alginate, hydroxypropyl methylcellulose phthalate and methyl paraben.

In another aspect, the present invention provides an oral modified release pharmaceutical suspension of azathioprine comprising azathioprine, sodium alginate, carbopol, hydroxypropyl methylcellulose phthalate and methyl paraben.

Embodiments of the oral modified release pharmaceutical composition may include one or more of the following features. For example, the composition may further comprise at least one pharmaceutically acceptable excipient selected from the group consisting of diluent, binder, solubility modifier, disintegrant, antioxidant, suspending agent, dispersing agent, buffer, plasticizer, lubricant, sweetener, flavor, and combinations thereof.

In another general aspect, the present invention provides a method of preparing a raft suspension of azathioprine comprising the steps of:
i) Preparing a solution of an enteric polymer in a solvent;
ii) Adding at least one preservative in the solution prepared in step i);
iii) Dispersing azathioprine in the solution of step ii);
iv) Spray drying the material prepared in step iii);
v) Preparing dispersion/solution of sodium alginate and carbopol in water;
vi) Adding the material obtained in step iv) into the dispersion/solution of step v) with continuous stirring until uniform dispersion is formed; and
vii) Adding a sweetener and a flavor in sufficient quantity and making up of the volume with purified water.

In another general aspect, the present invention provides a method of preparing powder for suspension of azathioprine comprising the steps of:
i) Preparing a solution of an enteric polymer in a solvent;
ii) Adding at least one preservative in the solution prepared in step i);
iii) Dispersing azathioprine in the solution of step ii);
iv) Spray drying the material prepared in step iii);
v) Blending a mixture of sodium alginate, flavor and sweetener with the material obtained in step iv);
vi) Packing the powder in a suitable package.

In another general aspect, the present invention provides a method of reducing gastric irritation caused by azathioprine administration, wherein the method comprises use of the modified release composition of the invention.

In another general aspect, the present invention provides a method of treating myasthenia gravis comprising administering to the patient the modified release composition of the invention.

The details of one or more embodiments of the invention are set forth in the description below. Other features, objects and advantages of the invention will be apparent from the description.

DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have found that an oral modified release composition of azathioprine can be prepared in the form of a suspension or powder / granules for suspension, which may provide ease of administration to the patients including children and geriatric patients having dysphagia (difficulty in swallowing).

The suspension prepared by using delayed release azathioprine particles is useful to reduce level of gastrointestinal side effects of azathioprine.

The modified release pharmaceutical compositions offer many advantages over conventional immediate release formulations such as desired therapeutic effect for long period of time, attenuation of adverse effects, and improved patient convenience due to reduced frequency for administration etc.

The term “composition” or “formulation” or “dosage form” has been employed interchangeably for the purpose of the present invention and mean that it is a pharmaceutical formulation which is suitable for administration to a patient.

In one aspect, the invention provides an oral modified release pharmaceutical composition of azathioprine comprising plurality of delayed release azathioprine particles, and at least one pharmaceutically acceptable excipient, wherein the composition is in the form of a suspension or dry formulation for reconstitution.

In one embodiment, an oral modified release composition in the form of a suspension may comprise azathioprine in a concentration of from about 5 mg/mL to about 50 mg/mL. The azathioprine oral suspension may be administered at a dosage ranging from about 0.5 mg/kg/day to about 3.0 mg/kg/day. For example, the suspension is administered to provide azathioprine at a dosage of about 25-250 mg/day.

In one embodiment, the modified release pharmaceutical composition of the present invention is a suspension comprising plurality of delayed release azathioprine particles dispersed in a suspending agent. In another embodiment, the release profile of the modified release suspension of the present invention remains unchanged over the shelf life of the formulation. In one embodiment, modified release composition of the present invention in the form of suspension is prepared by dispersing the delayed release azathioprine particles in a suspension base made up of a suspending agent. In a further embodiment, the oral modified release pharmaceutical composition of the present invention in the form of a suspension comprises the delayed release azathioprine particles dispersed in sodium alginate.

In one general aspect, the modified release pharmaceutical composition of the present invention is in the form of a liquid or solid dosage form. In one embodiment, liquid dosage form may include, but not limited to, ready-to-use suspension for oral administration. Development of modified release liquid dosage form is particularly challenging, since the formulation should maintain its modified release characteristics over the shelf life in a liquid environment and yet provide the desired release profile upon administration. The leaching of the drug from the modified release suspended phase into the surrounding aqueous media during storage needs to be particularly controlled. One of the embodiments of the invention is related to modified release raft suspension of azathioprine. The raft suspension is an advanced revolution in liquid oral modified drug delivery system. This suspension is liquid at room temperature but undergo gelation when comes in contact with body fluids or change in pH. This suspension has a unique property of temperature dependent and cation induced gelation. The formed gel remains intact within the stomach contents for few hours thus the internal content of the suspension does not come in direct contact with stomach lining and so has an impact on reducing gastrointestinal side effects of azathioprine.

In another embodiment, solid dosage form may include, but not limited to, dry formulation for reconstitution, powder or granules for reconstitution and the like or any combinations thereof. Powder or granules for reconstitution may be filled into sachets or capsules. The solid dosage form, upon reconstitution, generates a suspension base saturated with azathioprine, wherein the delayed release azathioprine particles are dispersed.

In further embodiment, the modified release pharmaceutical composition of the present invention comprises plurality of delayed release azathioprine particles and at least one pharmaceutically acceptable excipient. The delayed release azathioprine particles may comprise azathioprine, at least one enteric polymer, at least one preservative and at least one solvent. The particles may further comprise at least one suspending agent. In a further embodiment, the delayed release azathioprine particles may range in size from about 1 micrometer to about 1000 micrometers. In another embodiment, the delayed release azathioprine particles may range in size from about 1 micrometer to about 750 micrometers. In still another embodiment, the delayed release azathioprine particles may range in size from about 5 micrometers to about 500 micrometers.

The delayed release property of the composition may be achieved by using an enteric polymer. Examples of suitable enteric polymers may include, but are not limited to, hydroxypropyl methylcellulose phthalate, cellulose acetate phthalate, cellulose acetate succinate, methylcellulose phthalate, hydroxypropylcellulose phthalate, ethylhydroxycellulose phthalate, polyvinylacetate phthalate, polyvinyl butyrate acetate, vinyl acetate-maleic anhydride copolymer, methyl methacrylate-methacrylic acid copolymer (Eudragit L-100 (methacrylic acid copolymer L) or Eudragit S-100 (methacrylic acid copolymer S)), methacrylic acid-ethyl acrylate copolymer (Eudragit L100-55 (dried methacrylic acid copolymer LD) or Eudragit L30D-55 (methacrylic acid copolymer LD)), methacrylic acid-methyl acrylate-methyl methacrylate copolymer (Eudragit FS30D), hydroxypropyl methylcellulose acetate succinate (HPMCAS), shellac or combinations thereof.

Preservatives are generally included in pharmaceutical compositions to prevent the growth of microorganisms during the product manufacturing and shelf life. Examples of suitable preservative may include, but are not limited to, chlorobutanol, benzalkonium chloride, methyl paraben, propyl paraben, benzyl alcohol, benzoic acid, sodium benzoate, sorbic acid, benzethonium chloride, cetyl pyridinium chloride, benzyl bromide, phenylmercury nitrate, phenylmercury acetate, thiomersal, merthiolate, chlorhexidine, phenylethyl alcohol, quaternary ammonium chloride, sodium benzoate, sodium propionate, or any combination thereof.

Solvents or cosolvents are water-miscible organic solvents used in drug formulations to increase the solubility of poorly water soluble substances and enhance the chemical stability of a drug. Examples of suitable solvents or cosolvents may include, but are not limited to, water, ethanol, isopropyl alcohol, butanol, dichloromethane, polyethylene glycols (PEG), sorbitol, glycerin, propylene glycol and benzyl alcohol.

The pharmaceutically acceptable excipients may include one or more of diluents, binders, solubility modifiers, disintegrants, antioxidants, suspending agents, dispersing agents, buffering agents, plasticizers, lubricants, sweeteners, flavors, and combinations thereof.

Examples of suitable diluents may include, but are not limited to, one or more of microcrystalline cellulose, starch, dibasic calcium phosphate, tribasic calcium phosphate, calcium carbonate, dextrose, kaolin, magnesium carbonate, magnesium oxide; sugars such as lactose or sucrose; sugar alcohols such as mannitol, sorbitol or erythritol; and mixtures thereof.

Examples of suitable binders may include, but are not limited to, one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, carbomers, dextrin, ethyl cellulose, methylcellulose, shellac, zein, gelatin, polymethacrylates, polyvinyl pyrrolidone, pregelatinized starch, sodium alginate, gums, synthetic resins, and the like.

Suitable solubility modifiers are added in the composition to increase solubility of an active agent in the media. These solubility modifiers may comprise of surfactants, solubilizes or wetting agents. Examples of suitable solubility modifiers may include, but are not limited to one or more of anionic, cationic, non-ionic or amphoteric surfactants or those known to the person skilled in the art. Non-limiting examples of surfactants include polyoxyethylene-polyoxypropylene co-polymers and block co-polymers, commercially available as Pluronic™ or Poloxamer™, ethoxylated cholesterins, commercially available as Solulan™ vitamin derivatives, e. g. vitamin E derivatives such as tocopherol polyethylene glycol succinate (TPGS), sodium dodecylsulfate or sodium lauryl sulfate; a bile acid or salt thereof, for example cholic acid, glycolic acid or a salt.

Examples of suitable disintegrants may include, but are not limited to, one or more of croscarmellose sodium, crospovidone, sodium starch glycolate, corn starch, potato starch, maize starch and modified starches, calcium silicates, and low substituted hydroxy- propylcellulose.

Examples of suitable antioxidants may include, but are not limited to, monothioglycerol, ascorbic acid, l-cysteine, sodium sulfite, sodium bisulfite, disodium edetate, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate, sodium ascorbate, erythorbic acid, potassium metabisulfite, propionic acid, sodium formaldehyde sulphoxylate, reduced glutathione, thiourea, n-acetylcysteine, methionine, propyl gallate, vitamin E, or other tocopherol analogs, including tocopherol acetate or TPGS, or any combination thereof.

Suspending agents used herein are the agents that are useful to form above mentioned raft suspension, which forms a gel when comes in contact with body fluids or change in pH. Examples of suitable suspending agent may include, but are not limited to, sodium alginate, pectin, gellan gum, xyloglucan, pectin, chitosan, poly(DL-lactic acid), poly (DL-lactide-co-glycolide), polycaprolactone, hyaluronic acid and combinations thereof.

Dispersing agents help active pharmaceutical ingredients stay suspended in the composition and prevent caking at the bottom of the container. Dispersing agents are substances added to a suspension to increase viscosity and retard sedimentation. A well-formulated suspension can be easily re-suspended by the use of moderate agitation or shaking. Examples of suitable dispersing agents may include, but are not limited to, cellulosic suspending agents, clays (including, bentonite and silicates), synthetic polymers (including carbomer, polyvinylpyrrolidone or PVP, and PVP copolymers such as PVP-vinyl acetate, sodium carboxymethyl cellulose), polysaccharide gums (including xanthan gum, acacia or gum arabic, and tragacanth), other polysaccharides (including agar and carrageenan), calcium phosphate, silicon dioxide, and gelatin.

Buffering agents generally provide stability and pH control to the pharmaceutical compositions. Examples of suitable buffering agents may include, but are not limited to, acetate buffer (e.g. sodium acetate and acetic acid etc.), phosphate buffer (e.g. monobasic sodium phosphate, dibasic sodium phosphate etc.), citrate buffer (e.g. anhydrous citric acid and trisodium citrate dihydrate etc.), lactate buffer, carbonate buffer, glycine buffer, borate buffer (boric acid/potassium chloride), tris buffer, tromethamine buffer, or any combination thereof.

Examples of suitable plasticizers may include, but are not limited to, one or more of glycerin fatty acid esters; triethyl citrate; propylene glycol; polyethylene glycol and the like.

Examples of suitable lubricants may include, but are not limited to, one or more of talc, metallic stearates such as magnesium stearate, calcium stearate, zinc stearate; colloidal silicon dioxide, finely divided silicon dioxide, stearic acid, hydrogenated vegetable oil, glyceryl palmitostearate, glyceryl monostearate, glyceryl behenate, polyethylene glycols, powdered cellulose, starch, sodium stearyl fumarate, sodium benzoate, mineral oil, magnesium trisilicate, kaolin; and mixtures thereof. It would be appreciated that a person skilled in the art is cognizant of the fact that lubricant, glidant or anti-tacking agent may be used interchangeably.

Sweeteners are generally added in the compositions that impart sweetness and improve patient compliance through taste masking. Examples of suitable sweeteners may include, but are not limited to, sucrose, dextrose, glucose, maltose, dextrins, D-tagatose, trehalose, dried invert sugar, fructose, galactose, polyhydric alcohols such as sorbitol, mannitol, xylitol, glycerol, hydrogenated starch hydrolysates, maltitol, isomaltitol, erythritol, lactitol, sodium saccharin; aspartame and the like, alone or in combination.

Flavors are generally added to increase patient acceptance of the drug by masking the specific taste sensations. Examples of suitable flavors may include, but are not limited to, cinnamon, wintergreen, eucalyptus, spearmint, peppermint, menthol, anise as well as fruit flavors such as apple, pear, peach, strawberry, cherry, apricot, orange, watermelon, banana and the like; bean-derived flavors, such as coffee, cocoa and the like or mixtures thereof.

In order to keep azathioprine particles in a uniformly suspended state upon shaking, it is necessary to identify a suitable dispersing agent and its optimum level. The pharmaceutical composition as per the invention has a viscosity in a range such that it can be ported for administration orally by spoon, cup, syringe, straw, pharmaceutical dropper, or the like and easily swallowed, including by individuals who have difficulty swallowing a pill or capsule, e.g., some pediatric, elderly, or disabled patients. Viscosity measurements can be performed, e.g., using a Brookfield viscometer at specific time point after each aqueous suspension is prepared. Viscosity values of the suspension of the composition as per the invention may be up to about 500 cps at proper storage conditions like at room temperature, for example, between 5 and 200 cps, between 25 and 150 cps, between 50 and 100 cps etc.

The specific gravity (relative density) of the suspension may be kept from 0.8 to 1.25 mg/mL at ambient conditions, e.g., from 0.95 to 1.15 mg/mL, from 1.00 to 1.10 mg/mL.

With respect to particle size, improved results may be obtained with particle sizes that include D90 = 200 µm, e.g. =100 µm, 70 to 90 µm; D50 =100 µm, e.g. = 25 µm, 10 to 20 µm; D10 =50 µm, e.g. = 10 µm, 1 to 8 µm.

In a further embodiment, the pH of the modified release pharmaceutical composition of the present invention may be acidic, in the pH range of 3.0 to 5.0 depending on the stability, solubility of azathioprine in the aqueous medium, the release profile and the site of its release. In one embodiment, pH of the composition after reconstitution may be maintained as acidic in the pH range of 3.0 to 5.0 depending on properties of azathioprine and its desired release profile. It may be possible that some pH adjusting agents are used to reach to the desired pH of the composition. In another embodiment, the modified release composition is a suspension, wherein the suspension exhibits a pH between 3.0 and 5.0.

In another embodiment, the modified release pharmaceutical composition of the present invention retains at least 90% of azathioprine concentration measured by its assay for at least 1 month, when stored at room temperature, for example, 2 months, 6 months, 12 months, 24 months, 36 months etc. The suspension as per the invention remains stable during shelf life of the product. In one embodiment, the modified release pharmaceutical composition may show azathioprine related compound A not more than 0.2%. In another embodiment, the modified release pharmaceutical composition may show impurity B (6-mercaptopurine) not more than 0.2%. In another embodiment, the modified release pharmaceutical composition may show azathioprine related compound G not more than 0.2%. In yet another embodiment, the modified release pharmaceutical composition may show any individual degradation product not more than 0.2%. In still another embodiment, the modified release pharmaceutical composition may show total degradation impurities not more than 1%.

Known impurities are mentioned below along with their IUPAC names and structures.

Azathioprine related compound A: 1-Methyl-4-nitro-1Himidazole-5-amine

Impurity B: 6-mercaptopurine / 9H-Purine-6-thiol

Azathioprine related compound G: 6-{(1-Methyl-4-nitro-1Himidazol-5-yl)thio}-9Hpurine-2-amine

Dissolution of azathioprine from the modified release composition of the present invention is determined as per below conditions:
Apparatus: USP II Apparatus (paddle)
Rotation Speed: 100 rpm
Test Temp: 37±0.5° C.
Dissolution Media: 750 mL of 0.1 N HCl for first two hours followed by 1000 mL of pH 6.8 buffer.

In one embodiment, the composition of present invention does not release more than 75% of azathioprine in first 2 hours in HCl medium. Further, the composition does not release less than 80% of azathioprine in 60 minutes in pH 6.8 buffer. In another embodiment, the composition releases less than 50% of azathioprine in a medium having an acidic pH over a period of 30 minutes.

In further specific embodiment, an oral modified release suspension of azathioprine comprises:
azathioprine in an amount of from 0.4 to 3% w/v,
hydroxypropyl methylcellulose phthalate in an amount of from 1 to 15% w/v,
methyl paraben in an amount of from 0.05 to 1% w/v,
propyl paraben in an amount of from 0.01 to 0.1% w/v,
sodium alginate in an amount of from 1 to 15% w/v,
carbopol in an amount of from 0.2 to 5% w/v,
triethyl citrate in an amount of from 0.1 to 5% w/v,
sweetener, and
flavor.

In further specific embodiment, a powder for suspension of azathioprine comprises:
azathioprine in an amount of from 1 to 12% w/w,
hydroxypropyl methylcellulose phthalate in an amount of from 10 to 65% w/w,
methyl paraben in an amount of from 0.01 to 2% w/w,
propyl paraben in an amount of from 0.01 to 0.2% w/w,
sodium alginate in an amount of from 1 to 60% w/w,
mannitol in an amount of from 5 to 60% w/w,
triethyl citrate in an amount of from 1 to 15% w/w,
sweetener, and
flavor.

In one embodiment, azathioprine may be present in an amount of from about 4 to about 40% w/w, based on weight of the delayed release particles. In another embodiment, azathioprine may be present in an amount of from about 1 to about 20% w/w, based on weight of the modified release composition.

In a specific embodiment, the invention provides a powder for suspension of azathioprine comprising azathioprine, gellan gum, hydroxypropyl methylcellulose acetate succinate and propyl paraben.

In another specific embodiment, the invention provides an oral modified release pharmaceutical suspension of azathioprine comprising azathioprine, pectin, carbopol, shellac and sodium benzoate.

In yet another specific embodiment, the invention provides an oral modified release pharmaceutical suspension of azathioprine comprising azathioprine, sodium alginate, carbopol, hydroxypropyl methylcellulose phthalate and methyl paraben. In further embodiment, the modified release pharmaceutical suspension comprises azathioprine and sodium alginate in a weight ratio of from 1:1 to 1:15, for example 1:5.5.

The modified release pharmaceutical composition of the present invention is in the form of a liquid or solid dosage form. Both type of dosage forms use plurality of delayed release particles of azathioprine. These delayed release particles comprising azathioprine, at least one enteric polymer, at least one preservative and at least one solvent, can be prepared according to methods such as, but not limited, wet granulation, dry granulation, roller compaction, extrusion-spheronization, melt granulation etc. In another embodiment, plurality of delayed release particles of azathioprine may be prepared by coating enteric polymer onto the core comprising azathioprine. The core of azathioprine may be a powder blend or granules of azathioprine along with other excipients; or azathioprine layering on the inert cores such as sugar spheres or microcrystalline cellulose spheres.

In one embodiment, a raft suspension of azathioprine may be prepared by following the steps of:
i) Preparing a solution of hydroxypropyl methylcellulose phthalate and triethyl citrate in a combination of isopropyl alcohol and dichloromethane;
ii) Adding methyl paraben and propyl paraben in the solution prepared in step i);
iii) Dispersing azathioprine in the solution of step ii);
iv) Spray drying the material prepared in step iii) to obtain plurality of delayed release particles of azathioprine;
v) Preparing dispersion of sodium alginate and carbopol in water;
vi) Adding the particles obtained in step iv) into the dispersion of step v) with continuous stirring until uniform dispersion is formed; and
vii) Adding sweetener and flavor in sufficient quantities and making up of the volume with purified water.

In one embodiment, powder for suspension of azathioprine may be prepared by following the steps of:
i) Preparing a solution of hydroxypropyl methylcellulose phthalate and triethyl citrate in a combination of isopropyl alcohol and dichloromethane;
ii) Adding methyl paraben and propyl paraben in the solution prepared in step i);
iii) Dispersing azathioprine in the solution of step ii);
iv) Spray drying the material prepared in step iii) to obtain plurality of delayed release particles of azathioprine;
v) Blending mixture of mannitol, sodium alginate, flavor and sweetener with the particles obtained in step iv);
vi) Packing the powder in a suitable package.

In one embodiment, the present invention provides a method of treating myasthenia gravis comprising administering to a human being in need thereof a modified release pharmaceutical composition comprising azathioprine.

In one embodiment, the present invention provides a method for prevention of rejection in renal homotransplantation comprising administering to a human being in need thereof a modified release pharmaceutical composition comprising azathioprine.

In one embodiment, the present invention provides a method of treating rheumatoid arthritis comprising administering to a human being in need thereof a modified release pharmaceutical composition comprising azathioprine.

In another embodiment, the present invention provides a method of reducing gastric irritation caused by azathioprine administration, wherein the method comprises administration of the modified release pharmaceutical composition comprising azathioprine. The formed gel remains intact within the stomach contents for few hours thus the internal content of the suspension does not come in direct contact with stomach lining and so has an impact on reducing gastrointestinal side effects of azathioprine. Moreover, plurality of delayed release azathioprine particles are further useful to decrease direct contact of azathioprine with stomach lining, and thus play a major role in reducing gastric irritation.

The term “Cmax” as used herein, unless and otherwise specifically mentioned, means maximum concentration of drug in plasma, achieved after administration of the composition (unit for example: ng/mL (nanogram/millilitre)). As per one embodiment, the pharmaceutical composition as per current invention may provide a mean blood plasma Cmax from about 10 to about 120 ng/mL for azathioprine and its metabolite, 6-mercaptopurine, when a dose of 10 mg to 200 mg the azathioprine is orally administered.

The term “AUC” as used herein, unless and otherwise specifically mentioned, means area under the curve for a plot of concentration of drug in plasma vs. time (unit for example: ng*hour/mL). As per one embodiment, the pharmaceutical composition as per current invention may provide a mean blood plasma AUC from about 10 to about 200 ng*hr/mL for azathioprine and its metabolite, 6-mercaptopurine, when a dose of 10 mg to 200 mg the azathioprine is orally administered.

The term “Tmax” used herein, unless and otherwise specifically mentioned, means time to achieve maximum concentration of the drug in plasma, achieved after administration of the composition (unit for example: minutes). As per one embodiment, the pharmaceutical composition as per current invention may provide a Tmax from about 0.1 to about 15 hours for azathioprine and its metabolite, 6-mercaptopurine, when a dose of 10 mg to 200 mg the azathioprine is orally administered.

The invention is further illustrated by the following examples which are provided to be exemplary of the invention and do not limit the scope of the invention. While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

Example 1: Liquid suspension of azathioprine

Sr. No. Ingredients Quantity
(% w/v)
1 Azathioprine 1.00
2 Hydroxypropyl methylcellulose phthalate 4.00
3 Methyl paraben 0.20
4 Propyl paraben 0.02
5 Triethyl citrate 0.90
6 Isopropyl alcohol q.s.
7 Dichloromethane q.s.
8 Sodium saccharin 0.2
9 Sodium alginate 5.0
10 Carbopol 0.8
11 Peppermint Flavor 0.02
12 Water q.s.
Total 100.00

Process for manufacturing:
(A) Hydroxypropyl methylcellulose phthalate and triethyl citrate were dissolved in isopropyl alcohol and dichloromethane to form a clear solution. Methyl paraben and propyl paraben were dissolved in the solution prepared above. Azathioprine was dispersed in above solution under stirring. The above dispersion was spray dried to obtain delayed release azathioprine particles.
(B) In a separate step, sodium saccharin was dissolved in required amount of water and sodium alginate was added and mixed thoroughly to get lump free dispersion. Carbopol was also added into this to get lump free dispersion.
(C) The delayed release azathioprine particles as prepared in step (A) were added into this dispersion of step (B) with continuous stirring until uniform dispersion was obtained. Peppermint flavor was added and final volume was made up with water.

Dissolution profile of the suspension of Example 1:
The above suspension was tested for in-vitro dissolution profile in 750 mL of 0.1 N HCl for first two hours followed by 1000 mL of pH 6.8 buffer at 100 RPM in USP II apparatus.

Sr. No. Time point % drug dissolved
0.1 N HCl
1 15 minutes 31
2 30 minutes 37
3 60 minutes 48
4 120 minutes 53
pH 6.8 buffer
5 10 minutes 100

Example 2: Powder for suspension of azathioprine

Sr. No. Ingredients Quantity
(% w/w)
1 Azathioprine 5.23
2 Hydroxypropyl methylcellulose phthalate 31.4
3 Methyl paraben 0.52
4 Propyl paraben 0.05
5 Triethyl citrate 4.71
6 Sodium saccharin 1.05
7 Sodium alginate 28.79
8 Mannitol 28.24
9 Peppermint flavor 0.04
Total 100.00

Process for manufacturing:
(A) Hydroxypropyl methylcellulose phthalate and triethyl citrate were dissolved in isopropyl alcohol and dichloromethane to form a clear solution. Methyl paraben and propyl paraben were dissolved in the solution prepared above. Azathioprine was dispersed in above solution under stirring. The above dispersion was spray dried to obtain delayed release azathioprine particles.
(B) In a separate step, sodium alginate and mannitol were co-sifted.
(C) The delayed release azathioprine particles as prepared in above step (A) were blended with sodium saccharin and peppermint flavor. The blend was packed in a sachet/bottle.

The content of the sachet/bottle was dispersed in purified water to obtain suspension, which was then tested for dissolution profile.

Dissolution profile of the suspension of Example 2:
The above suspension was tested for in-vitro dissolution profile in 750 mL of 0.1 N HCl for first two hours followed by 1000 mL of pH 6.8 buffer at 100 RPM in USP II apparatus.
Sr. No. Time point % drug dissolved
0.1 N HCl
1 15 minutes 22
2 30 minutes 30
3 60 minutes 41
4 120 minutes 52
pH 6.8 buffer
5 10 minutes 100

Example 3: Powder for suspension of azathioprine

Sr. No. Ingredients Quantity
(% w/w)
1 Azathioprine 5.26
2 Hydroxypropyl methylcellulose phthalate 31.58
3 Methyl paraben 0.53
4 Propyl paraben 0.05
5 Triethyl citrate 4.74
6 Sodium saccharin 0.53
7 Sodium alginate 28.95
8 Mannitol 26.32
9 Silicon dioxide 2.03
10 Peppermint flavor 0.02
Total 100.00

Process for manufacturing:
(A) Hydroxypropyl methylcellulose phthalate and triethyl citrate were dissolved in isopropyl alcohol and dichloromethane to form a clear solution. Methyl paraben and propyl paraben were dissolved in the solution prepared above. Azathioprine was dispersed in above solution under stirring. The above dispersion was spray dried to obtain delayed release azathioprine particles.
(B) In a separate step, flavor, silicon dioxide, sodium alginate and mannitol were co-sifted.
(C) The delayed release azathioprine particles as prepared in above step (A) were blended with step (B). The blend was packed in a sachet/bottle.

The content of the sachet/bottle was dispersed in purified water to obtain suspension, which was then tested for dissolution profile.

Dissolution profile of the suspension of Example 3:
The above suspension was tested for in-vitro dissolution profile in 750 mL of 0.1 N HCl for first two hours followed by 1000 mL of pH 6.8 buffer at 100 RPM in USP II apparatus.

Sr. No. Time point % drug dissolved
0.1 N HCl
1 15 minutes 37.1
2 30 minutes 50.1
3 60 minutes 62.8
4 120 minutes 73.2
pH 6.8 buffer
5 10 minutes 88.2

Results of fasting study when carried out in healthy human volunteers:

In-vivo Parameter for azathioprine Value
Mean Cmax (ng/mL) 18.7
Mean AUC (hr*ng/mL) 25.1
Median Tmax (hr) 0.5

,CLAIMS:We claim:
1. An oral modified release pharmaceutical composition of azathioprine comprising plurality of delayed release azathioprine particles, and at least one pharmaceutically acceptable excipient, wherein the composition is in the form of a suspension or dry formulation for reconstitution.
2. The modified release composition according to claim 1, wherein the azathioprine is present in an amount of from about 10 mg to about 200 mg, based on weight of the particles.
3. The modified release composition according to claim 1, wherein at least one pharmaceutically acceptable excipient is selected from the group consisting of diluent, binder, solubility modifier, disintegrant, antioxidant, suspending agent, dispersing agent, buffering agent, lubricant, sweetener, flavor, and combinations thereof.
4. The modified release composition according to claim 1, wherein the oral modified release composition in the form of a dry formulation for reconstitution, on reconstitution generates a suspension base saturated with azathioprine, wherein the delayed release azathioprine particles are dispersed.
5. The modified release composition according to claim 1, wherein the azathioprine is present in a concentration of from about 5 mg/mL to about 50 mg/mL.
6. The modified release composition according to claim 1, wherein the suspension is a raft suspension.
7. The modified release composition according to claim 1, wherein the suspension exhibits a pH between 3.0 and 5.0.
8. The modified release composition according to claim 1, wherein the suspension comprises azathioprine, sodium alginate, hydroxypropyl methylcellulose phthalate and methyl paraben.
9. The modified release composition according to claim 1, wherein the composition provides a mean blood plasma Cmax from about 10 to about 120 ng/mL, when a dose of 10 mg to 200 mg the azathioprine is orally administered.
10. The modified release composition according to claim 1, wherein the composition provides a mean blood plasma AUC from about 10 to about 200 ng*hr/mL, when a dose of 10 mg to 200 mg the azathioprine is orally administered.

Dated this 23rd day of July 2024.

(HARIHARAN SUBRAMANIAM)
IN/PA-93
Of SUBRAMANIAM & ASSOCIATES
ATTORNEYS FOR THE APPLICANTS