DESC:Field of the Invention:
The present invention relates to stable solid dispersion of anti-HCV compound Sofosbuvir, having the chemical name isopropyl (2S)-2-{[(S)-{[(2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydro-1(2H)-pyrimidinyl)-4-fluoro-3-hydroxy-4-methyltetrahydro-2-furanyl]methoxy}(phenoxy)phosphoryl]amino}propanoate, is known to be an effective anti-HCV agent, process for their preparation and pharmaceutical composition thereof.

Background of the Invention:
Hepatitis C is recognized as a chronic viral disease of the liver which is characterized by liver disease. Although drugs targeting the liver are in wide use and have shown effectiveness, toxicity and other side effects have limited their usefulness. Inhibitors of hepatitis C virus (HCV) are useful to limit the establishment and progression of infection by HCV as well as in diagnostic assays for HCV.

The hepatitis C virus (HCV) is an RNA virus belonging to the Hepacivirus genus in the Flaviviridae family. The enveloped HCV virion contains a positive stranded RNA genome encoding all known virus-specific proteins in a single, uninterrupted, open reading frame. The open reading frame comprises approximately 9500 nucleotides and encodes a single large polyprotein of about 3000 amino acids. The polyprotein comprises a core protein, envelope proteins El and E2, a membrane bound protein p7, and the non-structural proteins NS2, NS3, NS4A, NS4B, NS5A and NS5B.

HCV infection is associated with progressive liver pathology, including cirrhosis and hepatocellular carcinoma. Chronic hepatitis C may be treated with peginterferon-alpha in combination with ribavirin. Substantial limitations to efficacy and tolerability remain as many users suffer from side effects, and viral elimination from the body is often inadequate. Therefore, there is a need for new drugs to treat HCV infection.

Sofosbuvir is described in US 7964580 (‘580), and is the inhibitor of RNA-dependent RNA viral replication and is useful as inhibitor of HCV NS5B polymerase, as inhibitor of HCV replication and for treatment of hepatitis C infection in mammals. Sofosbuvir has the following chemical formula:

Extensive study is carried out in pharmaceutical industry for development of different polymorphs of various drug substances, to obtain suitable polymorphs that possess improved performance characteristics such as aqueous solubility, improved bioavailability, chemical stability, shelf life etc.

Literature survey reveals that Sofosbuvir can exist in different polymorphic forms, which differ from each other in terms of stability, physical properties and pharmacokinetics. The reported polymorphs of Sofosbuvir are incorporated here by way of reference.

US patent 8,618,076 B2 describes various polymorphs including amorphous form of Sofosbuvir.

PCT publication WO2013/101550 A1 discloses solid dispersion of various HCV inhibitors using hydrophilic polymer.

PCT publication WO 2015/150561 A2 discloses solid dispersion of sofosbuvir with syloid or other pharmaceutically acceptable polymer compound.

Polymorphs often improve physical and biological characteristics of mother compounds without modifying primary pharmacological activity, based on mechanism of action. Thus there is a continuing need to obtain new polymorphs of Sofosbuvir having improved physical and/or chemical properties.

The solid dispersion of Sofosbuvir shows benefits over other formulations of Sofosbuvir. For example, amorphous solid dispersion enhances flow property and solubility in water or aqueous media as an essential property of active pharmaceutical ingredients determining the performance of pharmaceutical formulation.

Description of drawings:
Figure 1: Illustrates X-ray powder diffraction (XRPD) pattern of solid dispersion of Sofosbuvir with Aerosil.

Summary of the Invention:
In one aspect, the present invention provides a stable solid dispersion of Sofosbuvir having enhanced stability, dissolution properties and purity.

In another aspect, the present invention provides a process for the preparation of a stable solid dispersion of Sofosbuvir.

In another aspect, the invention provides a pharmaceutical composition comprising said stable solid dispersion of Sofosbuvir and at least one pharmaceutically acceptable excipient or carrier.

Detail Description of the Invention:
The term “solid dispersion " is used herein to describe combinations of Sofosbuvir and at least one pharmaceutically acceptable excipient, wherein individual particles of the components cannot be distinguished using techniques such as optical microscopy. In embodiments, the drug is considered as being uniformly or non-uniformly distributed over surfaces of excipient particles. In other embodiments, the solid dispersion are considered to be in the nature of molecular dispersion, or solid solutions. Simple mixtures of powdered ingredients will not constitute solid dispersion.

The term "excipient" or “pharmaceutically acceptable excipient” means a component of a pharmaceutical product that is not an active ingredient, and includes but not limited to filler, diluent, disintegrants, glidants, stabilizers, surface active agents etc. The excipients that are useful in preparing a pharmaceutical composition are generally safe, non-toxic and neither biologically nor otherwise undesirable, and are acceptable for veterinary use as well as human pharmaceutical use. One excipient can perform more than one function.

The term "stable" herein means Sofosbuvir that substantially does not convert to any related substances or other solid form.

The known sofosbuvir solid dispersion are not stable above 30°C, also the formulation of these solid dispersion do not show desired stability. These solid dispersion show gradual increase in the content of total impurities and impurity defined by compound of formula 1.

Formula 1

Therefore, the problem underlying the present invention is the provision of a sofosbuvir solid dispersion and its compositions which are stable above 30°C and does not have presence of total impurities or impurity such as the impurity defined by compound of formula 1.

Surprisingly, it was found that this problem can be solved if a solid dispersion of sofosbuvir with Aerosil. Aerosil is available in various grades such as Aerosil R972; Aerosil R974; Aerosil R104; Aerosil R202, etc. Aerosil fumed silica have characteristic such as a low moisture adsorption, excellent dispersibility, and their ability to adjust rheological behavior, even that of polar systems.

In one embodiment of the invention, the present invention provides a stable Sofosbuvir solid dispersion with aerosil having enhanced flow property, stability, dissolution properties that can be easily formulated into pharmaceutical compositions.

In another embodiment, the present invention provides a stable Sofosbuvir solid dispersion with Aerosil, which is characterized by XRPD (X-ray powder diffractogram) as depicted in Figure 1.

In another embodiment, the invention provides a process for preparation of stable Sofosbuvir solid dispersion comprising the steps of:
(i) providing a solution of Sofosbuvir in a solvent;
(ii) adding aerosil in solution of step (i);
(iii) substantially removing the solvents from step (ii) and isolating stable Sofosbuvir solid dispersion from reaction mixture thereof.

The term "substantially removing" the solvent refers to at least 80%, specifically greater than about 85%, more specifically greater than about 90%, still more specifically greater than about 99%, and most specifically essentially complete (100%), removal of the solvent from the reaction mixture.

The sofosbuvir used in step (i) can be crystalline or amorphous form.

The solvent employed in step (i) is selected from halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane, chloroform and carbon tetrachloride; alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butyl alcohol; ketones such as acetone, ethyl methyl ketone, diethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate and t-butyl acetate; ethers such as diethyl ether, dimethyl ether, diisopropyl ether, methyl t-butyl ether and 1,4-dioxane; nitriles such as acetonitrile and propionitrile; water; and mixtures thereof;

The reaction of step (i) is carried out at a temperature of about 20 to about 100°C, preferably at about 50 to about 90°C and more preferably at a temperature of about 25 to about 50°C.

Removal of solvent in step (iii) is accomplished, for example, by filtration, substantially complete evaporation of the solvent, concentrating the solution or distillation of solvent, under inert atmosphere to obtain the stable Sofosbuvir solid dispersion.

In another embodiment, the solvent is removed by evaporation. Evaporation can be achieved at sub-zero temperatures by lyophilisation or freeze-drying techniques. The solution may also be completely evaporated in, for example, a Rota vapor, a Vacuum Paddle Dryer or in a conventional reactor under vacuum above about 720 mm Hg by flash evaporation techniques by using an agitated thin film dryer ("ATFD"), or evaporated by spray drying and isolating as a powder.

The distillation process can be performed at atmospheric pressure or reduced pressure. Specifically, the solvent is removed at a pressure of about 760 mm Hg or less, more specifically at about 400 mm Hg or less, still more specifically at about 80 mm Hg or less, and most specifically from about 30 to about 80 mm Hg.

Solvents can also be removed by spray-drying, in which a solution comprising of Sofosbuvir and a aerosil is sprayed into the spray drier at the flow rate ranging from about 10 to about 300 ml/hr, specifically about 40 to about 200ml/hr. The air inlet temperature to the spray drier used may range from about 30º C to about 150º C, specifically from about 65 º C to about 110 º C and the outlet air temperature used may range from about 30 º C to about 90 º C.

Another suitable method is vertical agitated thin-film drying (or evaporation). Agitated thin film evaporation technology involves separating the volatile component using indirect heat transfer coupled with mechanical agitation of the flowing film under controlled conditions. In vertical agitated thin-film drying (or evaporation) (ATFD-V), the starting solution is fed from the top into a cylindrical space between a centered rotary agitator and an outside heating jacket. The rotor rotation agitates the downside-flowing solution while the heating jacket heats it.

The Sofosbuvir solid dispersion with aerosil obtained by process disclosed herein may be further dried, preferably spin dried, in, for example, a Vacuum Tray Dryer, a Rotocon Vacuum Dryer, a Vacuum Paddle Dryer or a pilot plant Rota vapor, to further lower residual solvents. Drying can be carried out under reduced pressure until the residual solvent content reduces to the desired amount such as an amount that is within the limits given by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use ("ICH") guidelines.

In another embodiment, the present invention provides a pharmaceutical composition comprising Sofosbuvir solid dispersion with aerosil and at least one pharmaceutically acceptable excipient or carrier.

The Sofosbuvir solid dispersion can be formulated into various pharmaceutical compositions like powder, granules, capsules, tablets, pellets etc.

The pharmaceutical composition of the invention can be formed by various methods known in the art such as by dry granulation, wet granulation, melt granulation, direct compression, double compression, extrusion spheronization, layering and the like. The composition or formulation may be coated or uncoated. Coating of compositions such as tablets and caplets is well known in the art.

Although for many pharmaceutical compounds oral administration in the form of a tablet or capsule is preferred, some patients, for example elderly and pediatric patients, may have difficulties in swallowing such formulations. Therefore, liquid formulations such as oral solutions may offer a suitable alternative, avoiding the need of swallowing tablets or capsules. An oral solution further provides the possibility of a more flexible dosing regimen. In order to limit the volume of an oral solution it is necessary to have a high concentration of the active ingredient in the solution, which again requires a high solubility of the active ingredient. Hence the superior solubility of Sofosbuvir solid dispersion of the present invention makes this particular solid state form especially suitable for the preparation of liquid pharmaceutical formulations such as oral solutions

Pharmaceutically acceptable excipients may be utilized as required for conversion of the Sofosbuvir solid dispersion into the final pharmaceutical dosage forms and include, for example, any one or more of diluents, binders, stabilizers, lubricants, glidants, disintegrating agents, surfactants, and other additives that are commonly used in solid pharmaceutical dosage form preparations.

The present invention includes administration of an effective amount of Sofosbuvir solid dispersion (either alone or as the active component of a pharmaceutical composition), in particular for use in the treatment of hepatitis C virus.

In a further embodiment, the present invention relates to a method for the treatment hepatitis C virus, in a subject in need of such treatment, which method comprises administering to such subject a therapeutically effective amount of Sofosbuvir solid dispersion.

The present invention includes the use of Sofosbuvir solid dispersion in combination with other antiviral agents used in the treatment of Hepatitis C virus.

The diluents, binders, bulking agents, stabilizers, lubricants, glidants, disintegrating agents, surfactants, and other additives that are commonly used in solid pharmaceutical dosage form preparations includes

Diluents:
Various useful fillers or diluents include but are not limited to starches, lactose, mannitol (PearlitolTM SD200), cellulose derivatives, confectioner's sugar and the like. Different grades of lactose include but are not limited to lactose monohydrate, lactose DT (direct tableting), lactose anhydrous, FlowlacTM, PharmatoseTM and others. Different starches include but are not limited to maize starch, potato starch, rice starch, wheat starch, pregelatinized starch and starch 1500, starch 1500 LM grade (low moisture content grade) from Colorcon, fully pregelatinized starch and others. Different cellulose compounds that can be used include crystalline celluloses and powdered celluloses. Examples of crystalline cellulose products include but are not limited to CEOLUSTM KG801, AvicelTM PH101, PH102, PH301, PH302 and PH-F20, PH112 microcrystalline cellulose 114, and microcrystalline cellulose 112. Other useful diluents include but are not limited to carmellose, sugar alcohols such as mannitol (PearlitolTM SD200), sorbitol and xylitol, calcium carbonate, magnesium carbonate, dibasic calcium phosphate, and tribasic calcium phosphate.

Binders:
Various useful binders include but are not limited to hydroxypropylcelluloses, also called HPC (KlucelTM LF, Klucel EXF) and useful in various grades, hydroxypropyl methylcelluloses, also called hypromelloses or HPMC (MethocelTM) and useful in various grades, polyvinylpyrrolidones or povidones (such as grades PVP-K25, PVP-K29, PVP-K30, and PVP-K90), PlasdoneTM S-630 (copovidone), powdered acacia, gelatin, guar gum, carbomers (CarbopolTM), methylcelluloses, polymethacrylates, and starches.

Bulking agents:
Bulking agents are ingredients which may provide bulk to a pharmaceutical composition. Various useful binders include but are not limited to PEGs, mannitol, trehalose, lactose, sucrose, polyvinyl pyrrolidone, sucrose, glycine, cyclodextrins, dextran and derivatives and mixtures thereof.

Disintegrants:
Various useful disintegrants include but are not limited to carmellose calcium, carboxymethylstarch sodium, croscarmellose sodium, crospovidones, examples of commercially available crospovidone products including but not limited to crosslinked povidone, KollidonTM CL, PolyplasdoneTM XL, XI-10, and INF-10 and low-substituted hydroxypropylcelluloses. Examples of low-substituted hydroxypropylcelluloses include but are not limited to low-substituted hydroxypropylcellulose LH11, LH21, LH31, LH22, LH32, LH20, LH30, LH32 and LH33. Other useful disintegrants include sodium starch glycolate, colloidal silicon dioxide, and starches.

Stabilizers:
Various useful stabilizers include basic inorganic salts, such as but not limited to basic inorganic salts of sodium, potassium, magnesium and calcium. Examples of basic inorganic salts of sodium are sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, and the like. Examples of basic inorganic salts of potassium are potassium carbonate, potassium hydrogen carbonate, potassium hydroxide, and the like. Examples of basic inorganic salts of magnesium are heavy magnesium carbonate, magnesium carbonate, magnesium oxide, magnesium hydroxide, magnesium metasilicate aluminate, magnesium silicate, magnesium aluminate, synthetic hydrotalcite [Mg6Al2(OH)16.CO3.4H2O], aluminum hydroxide-magnesium [2.5MgO.Al2O3.xH2O], and the like. Examples of basic inorganic salts of calcium include precipitated calcium carbonate, calcium hydroxide, and the like.

Surface-Active Agents:
Useful surface-active agents include non-ionic, cationic and anionic surface-active agents. Useful non-ionic surface-active agents include ethylene glycol stearates, propylene glycol stearates, diethylene glycol stearates, glycerol stearates, sorbitan esters (SPANTM) and polyhydroxyethylenically treated sorbitan esters (TWEENTM), aliphatic alcohols and PEG ethers, phenol and PEG ethers. Useful cationic surface-active agents include quaternary ammonium salts (e.g. cetyltrimethylammonium bromide) and amine salts (e.g. octadecylamine hydrochloride). Useful anionic surface-active agents include sodium stearate, potassium stearate, ammonium stearate, and calcium stearate, triethenolamine stearate, sodium lauryl sulphate, sodium dioctylsulphosuccinate, and sodium dodecylbenzenesulphonate. Natural surface-active agents may also be used, such as for example phospholipids, e.g. diacylphosphatidyl glycerols, diaceylphosphatidyl cholines, and diaceylphosphatidic acids, the precursors and derivatives thereof, such as for example soybean lecithin and egg yolk.

Lubricants:
An effective amount of any pharmaceutically acceptable tableting lubricant can be added to assist with compressing tablets. Useful tablet lubricants include magnesium stearate, glyceryl monostearates, palmitic acid, talc, carnauba wax, calcium stearate sodium, sodium or magnesium lauryl sulfate, calcium soaps, zinc stearate, polyoxyethylene monostearates, calcium silicate, silicon dioxide, hydrogenated vegetable oils and fats, stearic acid and combinations thereof.

Glidants:
One or more glidant materials, which improve the flow of powder blends and minimize dosage form weight variations can be used. Useful glidants include but are not limited to silicone dioxide, talc and combinations thereof.

Coloring Agents:
Coloring agents can be used to color code the compositions, for example, to indicate the type and dosage of the therapeutic agent therein. Suitable coloring agents include, without limitation, natural and/or artificial compounds such as FD&C coloring agents, natural juice concentrates, pigments such as titanium oxide, silicon dioxide, iron oxides, zinc oxide, combinations thereof, and the like.

Useful additives for coatings include but are not limited to plasticizers, antiadherents, opacifiers, solvents, and optionally colorants, lubricants, pigments, antifoam agents, and polishing agents.

Plasticizers:
Various useful plasticizers include but are not limited to substances such as castor oil, diacetylated monoglycerides, dibutyl sebacate, diethyl phthalate, glycerin, polyethylene glycol, propylene glycol, triacetin, and triethyl citrate. Also, mixtures of plasticizers may be utilized. The type of plasticizer depends upon the type of coating agent. An opacifier like titianium dioxide may also be present, typically in an amount ranging from about 10% to about 20% based on the total weight of the coating.

Stability studies (Syloid solid dispersion v/s Aerosil solid dispersion):
Sofosbuvir solid dispersion with syloid and Aerosil were kept under standard stability conditions to monitor the generation of impurities by HPLC.

The sofosbuvir solid dispersion with syloid showed presence of total impurities or impurity such as compound of formula 1; whereas the sofosbuvir solid dispersion with Aerosil did not show presence of total impurity or impurity such as compound of formula 1 during/after stability. Table 1 describes the stability results.

Sofosbuvir solid dispersion stability study Sofosbuvir solid dispersion with Syloid Sofosbuvir solid dispersion with Aerosil
Batch No. Total Impurities or
Compound of formula 1 1 Month
(%) 2 Month
(%) 3 Month
(%) 1 Month
(%) 2 Month
(%) 3 Month
(%)
Batch A Compound of formula 1 0.06 0.05 0.05 BQL BQL BQL
Total Impurities 0.1 0.1 0.1 0.06 0.06 0.06
Batch B Compound of formula 1 0.05 0.05 0.07 BQL BQL BQL
Total Impurities 0.1 0.1 0.1 0.06 0.06 0.06
Batch C Compound of formula 1 0.06 0.11 0.13 BQL BQL BQL
Total Impurities 0.1 0.2 0.2 0.05 0.05 0.05
*BQL= below quantitation limit.

Instrument settings for XRPD
The X-ray powder diffraction spectrum (XRPD) was recorded at room temperature using PANalytical X’pert PRO diffractogram with Cu K radiation (?=1.54060 A°), running at 45 kv and 40ma.

Examples:
The sofosbuvir solid dispersion with syloid prepared according to the known methods in the art for example IN1856/MUM/2015.

Example: - 1 Preparation of Sofosbuvir solid dispersion (80%:20%) by using Aerosil R972 and methanol
Sofosbuvir (100gm),methanol (450ml) were charged to the flask at 25-30°C, stirred, filtered and washed with 50ml methanol. Filtrate was cooled to 2-8°C. Aerosil R972 (25gm) was added to reaction mass. Reaction mass was stirred till the reaction mass became homogenous and was taken for spray drying. Spray drying was done at inlet temperature of 70°C and outlet temperature of 42-52°C having low rate of 5-6ml/minute. Yield: - 105 gm; Purity: - > 99.5 %.

Example: - 2 Preparation of Sofosbuvir solid dispersion (50%:50%) by using Aerosil R972 and methanol
Sofosbuvir (100gm),methanol (750ml) were charged to the flask at 25-30°C, stirred, filtered and washed with 50ml methanol. Filtrate was cooled to 2-8°C. Aerosil R972 (100gm) was added to reaction mass. Reaction mass was stirred till the reaction mass became homogenous and was taken for spray drying. Spray drying was done at inlet temperature of 70°C and outlet temperature of 42-52°C having low rate of 5-6ml/minute.Yield: - 179 gm; Purity: - > 99.5 % .
,CLAIMS:1. A stable Sofosbuvir solid dispersion comprising sofosbuvir and Aerosil.

2. The stable sofosbuvir solid dispersion of claim 1 has XRPD as depicted in figure 1.

3. A process for preparing stable sofosbuvir solid dispersion comprising the steps of:
(i) providing a solution of Sofosbuvir in a solvent;
(ii) adding Aerosil in solution of step (i);
(iii) substantially removing the solvents from step (ii) and isolating stable Sofosbuvir solid dispersion from reaction mixture thereof.

4. The process of claim 3, wherein a solvent of step (i) is selected from dichloromethane, 1,2-dichloroethane, chloroform, carbon tetrachloride, methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butyl alcohol, acetone, ethyl methyl ketone, diethyl ketone, and methyl isobutyl ketone, ethyl acetate, n-propyl acetate, n-butyl acetate and t-butyl acetate, diethyl ether, dimethyl ether, diisopropyl ether, methyl t-butyl ether and 1,4-dioxane, acetonitrile, propionitrile, water and mixtures thereof.

5. The process of claim 3, wherein the removal of the solvent in step (iii) is accomplished by complete evaporation of the solvent, concentrating the solution or distillation, spray drying, vacuum drying, lyophilisation or freeze drying, agitated thin-film (ATFD) drying, or a combination thereof.

6. A pharmaceutical formulation comprising stable Sofosbuvir solid dispersion of claim 1 and at least one pharmaceutically acceptable excipient.

7. The pharmaceutical formulation of claim 6, is in the form of a tablet, capsule, powder, granules, pellets, pellets in capsule, powder in capsule and granules in capsule.

8. A method for treating Hepatitis C comprising administering a pharmaceutical composition that comprises a therapeutically effective amount of the stable Sofosbuvir solid dispersion of claim 1, along with additional pharmaceutically acceptable excipient and optionally combine with other anti-HCV agent.