FORM 2
THE PATENTS ACT 1970 (39 of 1970)
&
THE PATENTS RULE 2003
COMPLETE SPECIFICATION
(Section 10 and rule 13)
''STABLE PHARMACEUTICAL SUSPENSION"
Glenmark Generics Limited
an Indian Company, registered under the Indian company's Act 1957
having office at
Glenmark House,
HDO- Corporate Bldg,
Wing -A, B. D. Sawant Marg, Chakala,
Andheri (East), Mumbai - 400 099, INDIA
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF INVENTION
[0001] The present invention relates to stable pharmaceutical suspension comprising atovaquone wherein agglomerations of atovaquone particles have not been observed on shelf life.
BACKGROUND OF THE INVENTION
[0002] Atovaquone is an antipneumocystic drug disclosed in U.S. Pat. No. 5,053,432. Atovaquone is available in the market under trade name Mepron, Malarone Pediatric, and Malarone. Mepron is available in the form of oral suspension (750mg/5ml). Atovaquone is a highly lipophilic compound and has a low aqueous solubility. It is because of this the molecule has poor bioavailability after oral administration. It is reported that after a single oral dose, absorption of the drug is slow and erratic; it is increased about threefold by the presence of fatty food and is dose-limited above 750 mg.
[0003] The efficacy of atovaquone is limited by its bioavailability. US Patent 6,018,080 and 6,649,659 are related to the microfluidised atovaquone particle and the method of their preparation. The US Patent. '080 and '659 directed to improved bioavailability of atovaquone having particle size in the range of 0.1-3μm. US Patent 6,018,080 discloses the microfluidised particles of atovaquone and to a method for preparing them. But, the process of microfluidization is complicated, results in longer processing time and further the equipment and its maintenance costs are very high.
[0004] US20080241254 discloses atovaquone particles having d90 about 4-15μ and liquid composition comprising the same. But the patent is silent on stability data of such liquid composition. Atovaquone has a tendency to agglomerate over a period of time, which may directly affect its bioavailability.
[0005] Hence, there is a need for alternative composition and methods which will prevent the agglomeration of atovaquone over a period of time which in turn would lead to increased bioavailability.

SUMMARY OF INVENTION
[0006] One aspect of the present invention provides a stable pharmaceutical suspension comprising atovaquone and method of making such compositions that prevents agglomeration of atovaquone.
[0007] In one of the preferred embodiment, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein combination of solubilizers prevents agglomeration.
[0008] In one of the preferred embodiment, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein a process used for preparation is a conventional homogenizer method.
DETAILED DESCRIPTION OF INVENTION
[0009] The phrase "stable" as used herein, includes pharmaceutical suspension having no change in d90, d50 and diopaticle size of atovaquone on shelf life.
[0010] The term "about" as used herein includes within 15%, preferably within 10% and more preferably within 5% of a given value range.
[0011] The term "substantial change" as used herein includes within 5%, preferably within 3% and more preferably within 2% of a given value.
[0012] It has been observed that atovaquone has tendency to agglomerate over a period of time which increases its particle size and in turn affects its dissolution and bioavailability. But it has been surprisingly found that by using simple equipments such as conventional homogenizer and combination of commonly used pharmaceutical excipients, the agglomeration of atovaquone can be avoided over the shelf life.

[0013] Increasing the dissolution rate by reducing the particle size of poorly water-soluble drugs has been the most popular practice for many decades. Conventional methods of particle size reduction, such as comminution and spray drying, rely upon mechanical stress to disaggregate the active compound. Today, micronization of drugs is widely done by milling techniques using a jet mill, rotor stator, colloidal mill, and air attrition.
[0014] For the purpose of present invention as discussed above, finer particle size of atovaquone is required to improve its bioavailability. However, reducing the particle size of material usually creates increase particle surface energies. These static charge problems cause the small drug particles to agglomerate, thereby effectively decreasing its surface area, which may in turn decrease the dissolution rate and hence its bioavailability. Hence along with selection of proper method to decrease the particle size to the desired level, it is also very important to select appropriate pharmaceutical excipients which will help in preventing the agglomeration of micronized drug.
[0015] The inventors of the invention have discovered that the compositions of invention are bioequivalent to marketed formulation of atovaquone suspension i.e Mepron®.
[0016] In one of the preferred embodiment, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein atovaquone as such having d90 value of 10-11 u, d50 value of 4-5 μ and d10 value of 2-3 μ was used to make suspension of the present invention.
[0017] For the purpose of present invention, atovaquone having d90 value of 10-11 μ, d50 value of 4-5 μ and d10 value of 2-3 μ was used to make suspension along with other necessary components required for suspension formulation. Category of those components are but not limited to wetting agents/solubilizers, surface stabilizers, thickeners/suspending agents, preservative, coloring agents, flavoring agents, sweetners etc.

[0018] Wetting agents/Solubilizers are added to suspension to disperse solids in continuous liquid phase and stabilizing them. Examples of this category are surfactants, polymers, solvents etc. Surfactants decrease the interfacial tension between drug particles and liquid and thus liquid is penetrated in the pores of drug particle displacing air from them and thus ensures wetting. Surfactants in optimum concentration facilitate dispersion of particles. Both non inonic and ionic surfactants can be used for the purpose of the present invention. Disadvantages of surfactants are that they have foaming tendencies. Further they are bitter in taste. But both these disadvantages can be overcome by using antifoaming agents and sweetners in the formulation. Examples of surfactants includes but not limited to sodium lauryl sulfate, Sorbitan esters, quaternary ammonium and pyridinium cationic surfactants, polysorbates, poloxamers, ployethylen oxide, PEG-35 castor oil etc. Hydrophillic colloids or hydrophilic polymers can also be used as a stabilizer as they coat hydrophobic drug particles and thus help in their wetting. Example includes but not limited to methyl cellulose, alginates, acacia, guar gum, povidone etc. Solvents which generally used are alcohol,glycerin, polyethylene glycol and polypropylene glycol and they provide wetting is that they are miscible with water and reduce liquid air interfacial tension. Liquid penetrates in individual particle and facilitates wetting. These solubilizers can be used alone or in combination with other class of solubilizers.
[0019] Surface stabilizers are added to prevent crystal growth. By adding surface stabilizer one can stabilize the active agent against crystal growth which indirectly avoids agglomeration. For the purpose of present invention the commonly used, non-toxic pharmaceutical ingredients, such as glycerol, mannitol, povidone, sodium chloride and lactose, can function as crystal growth inhibitors. Surface stabilizer can be added before, during or after preparation of suspension. Many times, hydrophilic colloid used as solubilizer/ wetting agent may also act as surface stabilizer.
[0020] Thickeners/Suspending agents perform two functions i.e. besides acting as a suspending agent they also imparts viscosity to the solution. Suspending agents form film around

particle and helps in reducing the interaction between two particles which in turn prevents agglomeration of particles. Examples of thickeners/suspending agent includes but not not limited to xanthan gum, bentonite, carbomer, gelatin, carboxymethylcellulsoe, hydroxyethylcellulose, acacia, tragacanth, alginates etc,
[0021] Preservatives are added to prevent microbial growth in suspension. If naturally occurring suspending agents such as tragacanth, acacia, xanthan gum are used to prepare suspension, being natural in source these agents are more susceptible to microbial contamination. If suspension is not preserved properly then the increase in microbial activity may cause stability problem such as loss in suspending activity of suspending agents, loss of color, flavor and odor, change in elegance etc. commonly used preservatives are but not limited to propylene glycol, benzyl alcohol, benzoic acid, butylated hydroxyytoulene, butylated hydroxyanisole, methyl paraben, benzalkomum chloride, disodium edentate, sodium benzoate etc.
[0022] Flavoring agent and coloring agents are added to give aesthetic appeal to the finished dosage form. Coloring agents can be of natural or synthetic origin. Natural colors are obtained from mineral, plant and animal sources. Mineral colors (also called as pigments) are used to color lotions, cosmetics, and other external preparations. Plant colors are most widely used for oral suspension.
[0023] Sweeteners are used for taste masking of bitter drug particles. Sugars such as xylose,
ribose, glucose, mannose, galactose, fructose, dextrose, sucrose, and maltose, sugar alcohols such as sorbitol, xylitol, mannitol and glycerin or aspartame or sodium saccharin can be used as a sweetner.
[0024] For the purpose of the present invention, followings are the preferred choices of excipients:
Suspending agents 0.1% to 0.5%
Solubilizers 10 to 20%
Surface stabilizer 10 to 20%
Preservative 0.5 to 2%
Flavors 0.05 to 2%

Antifoaming agent 0.1 to 0.5%
Sweeteners 0.5 to 2%
Vehicle qs
[0025] Preferably, for the purpose of the present invention, followings are the preferred choices of
excipients:
Suspending agents 0.3%
Solubilizers 15%
Surface stabilizer 15%
Preservative 1%
Flavors 0.1%
Antifoaming agent 0.25%
Sweeteners 1.25%
Vehicle qs
[0026] Most Preferably, for the purpose of the present invention, followings are the preferred choices of excipients:
Xanthan gum 0.3%
Poloxamer 188 / Povidone / PEG 400/ 15%
Polysorbate 80/ Cremophor EL/HPMC
Lactose monohydrate/Mannitol 15%
Benzyl alcohol 1%
Lemon citrus flavor 0.1%
Simethicone 0.25%
Aspartame/Sodium Saccharine 1.25%
Purified water qs
[0027] For the purpose of the present invention, combination of two or more than two solubilizers are required to prevent agglomeration of atovaquone particles along with other components of suspensions. More preferably three and most preferably five different solubilizers are required for the purpose of the present invention.
[0028] In one of the preferred embodiment, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein no substantial change in particle size of atovaquone is observed after 3M stability. After

3M stability particle size of atovaquone was same as it was used initially during preparation of suspension i.e.d90 value of 10-11 u, d50 value of 4-5 μ and d10 value of 2-3 μ after 3M stability.
[0029] In another preferred embodiment, the present invention provides a process for the preparation of a stable pharmaceutical suspension comprising atovaquone wherein a process used for preparation is a conventional homogenizer method.
[0030] U.S. Patent '659 discloses that conventional methods of reducing the particle size of atovaquone were found to be unsuccessful in producing particles of the size required to improve bioavailability. Such conventional methods included dyno mill, ball mill etc. Patent also discloses that suspension having lμm of atovaquone is more bioavailable than suspension having atovaquone particle size of 3μm. To achieve such finer particle size micrfluidization is given as a method of choice. But it has surprisingly found in the present invention that a suspension of atovaquone prepared by conventional homgenizer method with relatively coarser particle size such as d90 value of 10-11 μ of atovaquone can also produce a desired bioavailability of atovaquone.
[0031] In one embodiment, for the preparation of a stable pharmaceutical suspension comprising atovaquone comprises
a) Soaking the suspending agent in small quantity of purified water for 12-18 hrs.
b) Mixing solubilizers, surface stabilizers, antifoaming agents in purified water under stirring.
c) Dispersing the active in step b under homogenization and homogenized for 22-24 hrs.
d) Mixing of step a and step c under continuous homogenization.
e) Addition of sweeteners and preservative.
f) Addition of flavoring agent.
g) Final make up of volume.

[0032] In one embodiment, the final finished suspension of the present invention was loaded on stability and was analyzed for particle size and dissolution for 3M. It has been observed that suspension obtained by the present invention remain stable over a period of 3M with respect to its particle size and dissolution as no agglomeration of atovaquone took place over a stability hence dissolution also remained same as intial. The stability of suspension of the present invention can be attributed to combination excipients and process used for making the suspension.
[0033] In another preferred embodiment of the invention, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein in vitro dissolution of atovaquone is such that about 90% of it dissolves within 10 minutes, as determined by the USP II method using 0.1N NaOH at 37°C as dissolution medium at 100 rpm.
[0C34] In another preferred embodiment of the invention, a stable pharmaceutical suspension comprising atovaquone and methods of making such compositions that prevent agglomeration wherein after exposure to 3M-40°C/75%RH condition, about 90% of atovaquone dissolves within 10 minutes, as determined by the USP II method using 0.1N NaOH at 37°C as dissolution medium at 100 rpm.
[0035] In the context of the present invention, "Bioequivalency" is determined by a 90% Confidence Interval (CI) of between 0.80 and 1.25 for both C[max] and AUC under USFDA regulatory guidelines.
[0036] The term "confidence interval, (CI)" as used herein refers, to the plain meaning known to one of ordinary skill in the art. The confidence interval refers to a statistical range with a specified probability that a given parameter lies within the range.

[0037] The term "covariance, (CV)" as used herein refers to the plain meaning known to one of ordinary skill in the art. It is a statistical measure of the variance of two random variables that are observed or measured in the same mean time period. This measure is equal to the product of the deviations of corresponding values of the two variables from their respective means.
[0038] The bioequivalence studies were carried out between Mepron® (reference) and compositions of the invention (test) in fasted state. The study was monitored in terms of C[max], AUC, T[max] achieved with the test products and the reference product.
[0039] The results of the relative bioavailability study of atovaquone suspension of the invention and atovaquone suspension under the trade name Mepron® with, is given in Examples section which concludes that the formulation explored in the present invention provides equivalent extent of absorption compared to marketed formulation of atovaquone suspension under the trade name Mepron®.
EXAMPLES
[0040] The following examples describe compositions of the present invention containing atovaquonr, but they are not to be interpreted as limiting the scope of the claims
EXAMPLE 1:
TABLE 1

Ingredient Mg/ml
Atovaquone 150
Lactose Monohydrate 75
Mannitol 75
Polaxamer 6.69
Povidone 27
PEG 400 96

Xanthan Gum 2
Polysorbate 80 10
Cremophor EL 40
Sodium saccharine 2.50
Benzyl alcohol 10
Aspartame 10
HPMC 3cps 10
Lemon citrus flavor 501050A 1
Simethicone 2.5
Purified water qs
The manufacturing process consists of following steps:
In one vessel, Xanthan gum was dissolved in 20% of total quantity of purified water and kept under stirring for 16 hours. In another vessel, 60% of total quantity of purified water was taken and in that water povidone, HPMC, poloxamer-188, polysorbate 80, cremophor El, mannitol, lactose monohydrate and simethicone were added and homgenised for 30 minutes. Atovaquone was added to second vessel under homogenization and was further homogenized for 22 hours. Slowly added xanthan gum solution to atovaquone suspension and further homogenized for 1 hour. Further added aspartame, sodium saccharine and benzyl alcohol to the resultant suspension and homogenized for 30 minutes. Finally flavor was added and volume was made up with purified water.
Stability data:
Suspension prepared by above process was packed in required packing configuration was loaded on stability. Samples were analysed for dissolution, pH and particle size. Media for dissolution: 900ml 0.1N NaOH, Appartus and rpm: USP II, 100 rpm

Time Initial lM/40°C/75% 2M/40°C/75% 3M/40°C/75% 3M/25°C/60%
points RH RH RH RH
(Mins)
% drug released

10 97 97 98 90 94
15 100 99 101 92 102
20 101 102 100 93 102
30 102 102 100 92 102
45 101 102 100 95 102
60 102 102 100 98 103
pH: (3.5 to 7)

Initial 1M/40°C/75%RH 2M/40°C/75%RH 3M/40°C/75% RH 3M/25°C/60% RH
4.43 4.20 4.25 3.99 4.07
Particle size:

By
Malvern Initial lM/40°C/75% RH 2M/40°C/75% RH 3M/40°C/75% RH 3M/25°C/60% RH
D10 2.3 2.3 2.2 2.3 2.3
D50 4.9 4.9 4.9 4.9 4.9
D90 10.2 10.3 10.3 10.4 10.3
In Vivo Study:
Bioavailability study (Fasting condition) of the Atovaquone suspension prepared according to example 1 was carried out on healthy volunteers taking Mepron® (750mg/5ml) as the reference, the results of which are given in below table

Parameter Unit Reference Test % T/R ratio
Cmax (ng/ml) 2491.92 2696.11 108.19
AUC (0-t) (ng.hr/ml) 183800.06 191075.33 103.96
AUC (o-oo) (ng.hr/ml) 238499.21 253689.22 106.37
AUC (0-96) (ng.hr/ml) 115912.70 123193.90 106.28
tl/2 (hr) 90.11 93.64 103.91
T max (hr) 3.42 3.38 98.69

Claims:
1. A stable pharmaceutical suspension of atovaquone wherein particle size of atovaquone remains same as initial on shelf life.
2. A stable pharmaceutical suspension of atovaquone of claim 1, wherein initial particle size of atovaquone is d90 10-11 μ, d50: 4-5 μ and d10: 2-3 μ
3. A stable pharmaceutical suspension of atovaquone of claim 1, wherein particle size of atovaquone on shelf life is d90: 10-11 μ, d50: 4-5 μ. and d10: 2-3 μ
4. A stable pharmaceutical suspension of atovaquone of claim 1 comprises suspending agent, solubilizers, surface stabilizers, preservatives, flavoring agent, sweetening agent, coloring agent and solvent.
5. A stable pharmaceutical suspension of atovaquone of claim 4 comprises combination of two or more than two solubilizers.
6. A stable pharmaceutical suspension of atovaquone of claim 4 comprises three solubilizers.
7. A stable pharmaceutical suspension of atovaquone of claim 4 comprises five solubilizers.
8. A stable pharmaceutical suspension of atovaquone of claim 4 wherein solubilizers can be selected from group of surfactants, solvents or polymers.
9. A stable pharmaceutical suspension of atovaquone of claim 4 comprising suspending agents 0.1% to 0.5%, solubilizers 10 to 20%, surface stabilizer 10 to 20%, preservative 0.5 to 2%, flavors 0.05 to 2%, antifoaming agent 0.1 to 0.5%, sweeteners 0.5 to 2%.
10. A method for preparing a stable pharmaceutical suspension of atovaquone wherein the method used is mixing of ingredients by conventional homogenizer.