FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
[Section 10, and Rule 13]
IMPROVED PROCESS FOR THE PREPARATION OF MICROPARTICLES
Applicant
Name; Torrent Pharmaceuticals Limited
Nationality: Indian
Address: Torrent House, Off Ashram Road, Near Dinesh
Hall, Ahmedabad 380 009, Gujarat, India
The following specification particularly describes the invention and the manner in which it is to performed

IMPROVED PROCESS FOR THE PREPARATION OF
MICROPARTICLES
FIELD OF THE INVENTION:
This invention relates to an improved process for the preparation of microparticles of nucleophilic compounds. The process is free from the use of benzyl alcohol as a solvent, which eliminates the need of intermediate drying and eventually reduce the residual solvent. The process also describes the use of aprotic solvent, which allows the molecular weight of polymer to remain significantly unchanged during the process, independent of hold time and hold temperature.
BACKGROUND:
Nucleophilic compound refers to a compound that promotes by nucleophilic catalysis the ester hydrolysis, such as the polymer scission, that occurs in the biodegradation of biodegradable polymers, such as polymers comprising varying lactide:glycolide ratios. A nucleophilic compound is a more effective nucleophile toward an ester group of the polymer than hydroxide ion or water.
Risperidone a nucleophilic compound (also known as 3-[2-[4-(6-fluoro-l,2-benzisoxazol-3-yl)-l-piperidinyl]ethyl]-6,7,8,9-tetrahydro-2-methyl-4H-pyrido[l,2-a]pyrimidin-4-one) is an atypical antipsychotic medication.
Risperidone microparticles are commercially available as RISPERDAL® CONSTA® and manufactured by Alkermes with Medisorb Technology and marketed by Janseen. It is an intramuscular microparticle formulation and is intended to deliver therapeutic levels of risperidone for two weeks. However due to inherent lag phase of most microparticle products, the patient is required to supplement the first 21 days of

RISPERDAL® CONSTA® treatment with daily doses of risperidone by oral therapy. Approximately three weeks after a single intramuscular injection of RISPERDAL® CONSTA® and concurrent daily doses of oral risperidone, the microparticles release sufficient risperidone in the systemic circulation so that the patient can discontinue supplementation with daily doses of oral therapy.
Alkermes and Janssen disclose risperidone and the process for making (via single emulsion) microparticles in US Patents 5688801, 5792477, 6194006, 6379704, 6824822. The inventor discloses that intermediate drying of microparticles during the process is necessary to achieve the selected release profile and to prevent burst release. The inventor also discloses that to get desired polymer molecular weight in the final microparticles, the hold period and hold temperature of first phase / organic phase is very critical for the degradation of molecular weight of polymer, which affects the release of nucleophilic agent. The inventor also discloses that non aqueous washing (alcohol or a blend of alcohol/alkane) of microparticles is necessary to lower down the residual solvent limit.
These patents also disclose that the factor that affects the performance of microparticle product is the molecular weight of the polymer or polymer matrix in final microparticle product. Molecular weight influence drug release characteristics and biodegradation rate of polymer. Nucleophilic compound catalyze the hydrolysis of PLGA polymer and resulting in loss of molecular weight.
To overcome this problem of loss of molecular weight, the inventors of US 6379704 disclose a process which allows microparticle products of varying polymer molecular weights to be produced using the same molecular weight starting material or vice versa. The process is to form an emulsion by combining the first organic phase and the second aqueous phase, maintaining the first phase at a hold temperature for hold period of sufficient duration to allow the starting molecular weight of the

polymer to reduce so that the selected microparticle polymer molecular weight is achieved.
The inventors succeed to control the release of active agent by controlling the molecular weight of polymer however the process depends on the holding of first phase / organic phase for a specified period and temperature. The process requires strict control and needs a lot of care to take during the hold period and temperature.
To achieve the selected release profile, the inventors of US6194006 disclose a process in which intermediate drying of microparticles during the process was performed.
To overcome the problem of residual solvent in the microparticle product, the inventors of US 6824822 disclose a process in which nonaqueous washing system is used for the washing of microparticles.
Thus, there is an unmet need of an easy, simple process, which can overcome or minimize the effects of process parameters such as hold time/temperature, intermediate drying, non aqueous washing system etc to achieve the desired results.
The inventors of the present invention have surprisingly found that loss of molecular weight of polymer, residual solvent limits and selected release profile can be controlled by selection of a proper solvent.
SUMMARY OF THE INVENTION:
The present invention relates to a method of preparing microparticles, which allows the molecular weight of polymer to remain significantly unchanged during the process.

The first embodiment of the present invention is to provide a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,
Wherein, the desired molecular weight of polymer does not change significantly.
Another embodiment of the present invention is to provide a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,
Wherein, the molecular weight of polymer does not change more than 15% from the desired molecular weight of polymer during hold period.
Another embodiment of the present invention is to provide a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,

Wherein, the molecular weight of polymer does not change more than 15% from the desired molecular weight of polymer at hold temperature.
Another embodiment of the present invention is to provide a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,
Wherein, the viscosity of first phase does not change significantly during hold period.
In another embodiment, the present invention provides a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) extracting solvent from the solution/suspension, thereby forming microparticles,
Wherein, the desired molecular weight of polymer does not change significantly.
In another embodiment, the present invention provides a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second solvent to carry out phase separation, forming microparticles,

Wherein, the desired molecular weight of polymer does not change significantly.
In another embodiment of the present invention is to provide a process of preparing microparticles, the process comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer and a solvent thereof;
(b) combining the first phase immediately with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles.
BRIEF DESCRIPTION OF THE FIGURES:
Figure 1: Change in viscosity v/s time for first phase (Risperidone in Dichloromethane)
DETAIL DESCRIPTION OF THE INVENTION:
In a general embodiment present invention provides a process of preparing microparticles wherein a first phase is prepared by combining nucleophilic compound and polymer of a desired molecular weight with aprotic solvent. The said first phase is optionally maintained at appropriate hold temperature for appropriate hold period, wherein the molecular weight of polymer does not change significantly. The said first phase is combined with second phase under the influence of mixing means to form emulsion which is followed by solvent extraction to form microparticles.
This invention is improved process for the preparation of microparticles. The process is free from the use of benzyl alcohol as a solvent, the process eliminates the need of intermediate drying, and provide microparticles with reduce residual solvent.

Due to very low solubility of benzyl alcohol in water it is difficult to remove from the microparticles with aqueous washing, so the benzyl alcohol is replaced with some other solvent which is miscible/soluble with water such as acetic acid, eliminates the need of non aqueous washing and intermediate drying of microparticles. It also gives an additional advantage of reducing the residual solvent in the final microparticles.
The process also uses aprotic solvent which allows the molecular weight of polymer to remain significantly unchanged during the process independent of hold time and hold temperature. The polymer degradation is high, when protic solvent is used in combination with nucleophilic compound, such as benzyl alcohol, acetic acid and degradation is nil or low in aprotic solvents, such as methylene chloride and chloroform. This process overcomes the disadvantage of strict control on molecular weight of polymer during the process as present in prior art. Another advantage is the minimum batch to batch variation in molecular weight of polymer, which eventually affects the release of nucleophilic compound.
The process also uses methyl ethyl ketone as a solvent to fasten the solidification of PLGA as the water solubility is very high.
Nucleophilic compound used in the process, can be subjected to size reduction by means of air jet milling, ball milling, sonication, high pressure homogenizer, controlled precipitation, wet milling to get controlled particle size distribution (PSD) which improves the entrapment efficiency, dissolution rate. PSD and shape of particles also contributes to the morphology.
Nucleophilic compound used in the process, may be kept in dispersed form to prevent or significantly reduce the degradation of PLGA and control the drug loading.
"Nucleophilic compound" as used herein are compound that promotes by nucleophilic catalysis the ester hydrolysis, such as the polymer scission, that occurs in

the biodegradation of biodegradable polymers, such as polymers comprising varying lactide:glycolide ratios. A nucleophilic compound is a more effective nucleophile toward an ester group of the polymer than hydroxide ion or water. Nucleophilic compounds that catalyze the polymer hydrolysis include, but are not limited to, amines and carboxylate anions, and can be "active agents" (defined below). Examples of nucleophilic compounds that are active agents include, but are not limited to, risperidone, 9-hydroxyrisperidone, and pharmaceutically acceptable salts of the foregoing, thioridazine, naltrexone, and oxybutynin, more preferably the nucleophilic compound is risperidone. It should be readily apparent to be one skilled in the art that the present invention is not limited to any particular nucleophilic compound, and that the present invention encompasses other nucleophilic active agents.
"Risperidone" as used herein can be present in the form of a free base, a metabolite, a prodrug or in the form of pharmaceutically acceptable salts. Further, risperidone, where applicable, may be present either in the form of substantially pure polymorph or as a mixture of polymorphs, any crystalline or amorphous form thereof.
"Microparticles" or "Microspheres" as used herein means particles that comprise a polymer that serves as a matrix or binder of the particle. The microparticles contain an active agent or other substance dispersed or dissolved within the polymeric matrix. The polymer is preferably biodegradable and biocompatible. By "biodegradable" is meant a material that should degrade by bodily processes to products readily disposable by the body and should not accumulate in the body. The products of the biodegradation should also be biocompatible with the body. By "biocompatible" is meant not toxic to the body, is pharmaceutically acceptable, is not carcinogenic, and does not significantly induce inflammation in body tissues. As used herein, "body" preferably refers to the human body, but it should be understood that body can also refer to a non-human animal body. Preferred examples of polymer include poly(glycolic acid), poly(d,l-lactic acid), poly(l-lactic acid), copolymers of the foregoing, and the like. Various commercially available poly

(lactide-co-glycolide) materials (PLGA) may be used in the method of the present invention. For example, 50:50 poly (d,l lactic co-glycolic acid) known as MEDISORB.RTM. 50:50 DL. This product has a mole percent composition of 50% lactide and 50% glycolide. Other suitable commercially available products are MEDISORB.RTM. 65:35 DL, 75:25 DL, 85:15 DL and poly(d,l-lactic acid) (d,l-PLA). Poly(lactide-co-glycolides) are also commercially available from Boehringer Ingelheim (Germany) under its Resomer mark, e.g., PLGA 50:50 (Resomer RG 502), PLGA 75:25 (Resomer RG 752) and d,l-PLA (Resomer RG 206), and from Birmingham Polymers (Birmingham, Ala.). Another examples are PUROSORB 7507 (PLGA 75:25), DURECET, WAKO. These copolymers are available in a wide range of molecular weights and ratios of lactic acid to glycolic acid.
The most preferred polymer for use in the practice of this invention is the copolymer, poly(d,l-lactide-co-glycolide). It is preferred that the molar ratio of lactide to glycolide in such a copolymer be in the range of from about 85:15 to about 50:50.
"Second phase" as used herein can be an aqueous solution or hydrophilic colloid or a surfactant. Second phase can be water also.
"Molecular weight of polymer does not change significantly" as used herein means the molecular weight of polymer in the final microparticles does not change more than 25%, preferably 15%), more preferably 10% of the polymer at the initial stage during the hold period of 2 to 8 hrs at a hold temperature of 15 to 35°C.
"Viscosity of first phase does not change significantly" as used herein means the viscosity of first phase does not change more than 25%, preferably 15%, more preferably 7% during the hold period of 1 to 4 hrs at a hold temperature of 15 to 35°C.

Solvent employed in the practice of the present invention include organic solvents, such as acetone; halogenated hydrocarbons, such as chloroform, methylene chloride, and the like; aromatic hydrocarbon compounds; halogenated aromatic hydrocarbon compounds; a linear or cyclic ethers; alcohols, such as, ethanol; ethyl acetate; a ketone such as ethyl methyl ketone and the like. Preferred solvents are dichloromethane, ethyl acetate and acetic acid, methyl ethyl ketone, methyl ethyl ketone and acetic acid, ethyl acetate or a mixture thereof. These solvents can also be used as second solvent in coacervation technique.
"Aprotic solvent" as used herein can be a single solvent or a combination of solvents, means the molecules of such solvent can not donate hydrogen (proton, H+). Without binding to any theory, the possible reason because of why the molecular weight of polymer is not affected during the process might be that protic solvents activate the ester carbonyl of polymer by protonation and makes it more electroplilic, which is otherwise a weak electrophile. The ester carbonyl after activation becomes more vulnerable to nucleophilic attack resulting in nucleophile induced hydrolysis. However, in case of aprotic solvents there is no activation of ester carbonyl and ester linkage remains unaffected by the presence of nucleophilic compound.
Preferred examples for aprotic solvents are Dichloromethane (DCM), Tetrahydrofurane (THF), Ethylacetate, Acetone, Dimethylformamide (DMF), Acetonitrile, Dimethylsulfoxamide (DMSO), Hexane, Benzene, Toluene, Dioxane, Chloroform, Diethylether and the mixture thereof.
"Extraction of solvent" can be done using suitable techniques such as solvent evaporation, quenching, or supercritical fluid technology. This is required to lower down the residual solvent in final microparticles.
"Solvent evaporation" as used herein means removal of solvent by means of stirring at a specified temperature for a specified time period.

"Quenching" as used herein means rapid removal of solvent in a short period of time with the addition of quenching media.
"Coacervation" as used herein means a reversible, emulsoid stage existing between the sol and gel formations, in which the addition of a third substance causes the separation of the sol into two immiscible liquid phases, which is called as phase separation. A common coacervating agent used for the process is silicon dioxide.
"Super critical fluid technology" as used herein means extraction of solvent with the help of super critical fluid e.g. carbon dioxide, di-nitogen oxide, carbon disulphide etc. Supercritical fluid is any substance at a temperature and pressure above its critical point. It can effuse through solids like a gas, and dissolve materials like a liquid. The advantages of supercritical fluid extraction (compared with liquid extraction) are that it is relatively rapid because of the low viscosities and high diffusivities associated with supercritical fluids. The extraction can be selective to some extent by controlling the density of the medium and the extracted material is easily recovered by simply depressurizing, allowing the supercritical fluid to return to gas phase and evaporate leaving no or little solvent residues. Carbon dioxide is the most common supercritical solvent.
"Size reduction" as used herein means to reduce the size of any material; size reduction can be done by air jet milling, ball milling, sonication, high pressure homogenizer, controlled precipitation, wet milling, and the like.
"Hold period" as used herein means to keep the first phase / organic phase for a specified period of time.
"Hold Temperature" as used herein means to keep the first phase / organic phase at a specified temperature.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.
Throughout this specification and the appended claims it is to be understood that the words "comprise" and "include" and variations such as "comprises", "comprising", "includes", "including" are to be interpreted inclusively, unless the context requires otherwise. That is, the use of these words may imply the inclusion of an element or elements not specifically recited.
The invention will be further illustrated by the following example, however, without restricting its scope to these embodiments.
EXAMPLE: Example 1:
A first phase/organic phase was prepared by dissolving 10.7 % of PLGA 75:25 (Purasorb 7507) and 7.1 % of Risperidone in dichloromethane. The organic phase was held at 25±5°C and solution viscosity was measured at regular interval (Table 1 and Figure 1). The change in viscosity of first phase/organic phase indicates change in polymer molecular weight as the viscosity depends on the molecular weight of polymer. No change in viscosity was observed even after 4 hours of hold period.
Microparticles were prepared by single emulsion (o/w), solvent evaporation method where dichloromethane was used as solvent for organic phase / first phase. Briefly, 1.2 g of PLGA 75:25 (Purosorb 7507) was dissolved in 15 ml of dichloromethane to form a polymeric solution using vortex mixer at room temperature. To polymer solution, 0.8 g of Risperidone was dissolved using vortex mixer at room temperature to get organic phase. The organic phase was added in to the aqueous phase (1% PVA

solution) under stirring (1000 rpm) at about 5±2°C to get o/w emulsion. The solvent was evaporated under stirring (800 rpm for 20 hrs) at room temperature (25±5°C) to get microparticles. The wet microparticles were collected on 25 μ sieve and rinsed with 100 ml of deionised water, washed with 500 ml of citrate buffer pH 5.0 and with stirring at 500 rpm for 45 min at 5±2°C. These washed microparticles were then collected on 25 μ sieve and rinsed with 50 ml deionised water and dried in vacuum desiccators at room temperature. Dried microparticles were analyzed for molecular weight using Gel Permeation Chromatography.

Table 1: Hold time study of example 1
Duration (Hrs) Viscosity (cps)
0 70.05
0.5 73.4
1 69.45
1.5 75.85
2 73.85
3 70.75
4 68.65
Molecular weight of starting polymer was found to be 86,435 Daltons and molecular weight of polymer in dried microparticles was found to be 85,071 Daltons. From the results, it is concluded that there was no significant change in molecular weight with time as compared to initial molecular weight.

We claim;
1. A process of preparing microparticles comprises:
(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,
Wherein, the desired molecular weight of polymer does not change significantly.
2. The process of preparing microparticles according to claim 1, wherein the molecular weight of polymer does not change more than 15% from the desired molecular weight.
3. A process of preparing microparticles comprises

(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) combining the first phase with a second phase under the influence of mixing means to form an emulsion;
(c) extracting solvent from the emulsion, thereby forming microparticles,
Wherein, the viscosity of first phase does not change significantly during hold period.
4. The process of preparing microparticles according to any of the preceding
claims, wherein aprotic solvent is selected from dichloromethane,
tetrahydrofurane, ethylacetate, acetone, dimethylformamide, acetonitrile,

dimethylsulfoxamide, hexane, benzene, toluene, dioxane, chloroform, diethylether or mixture thereof.
5. The process according to claim 5 wherein aprotic solvent is dichloromethane.
6. A process of preparing microparticles comprises

(a) preparing a first phase comprising a nucleophilic compound, polymer with a desired molecular weight and an aprotic solvent;
(b) extracting solvent from the solution/suspension, thereby forming microparticles,
Wherein, the desired molecular weight of polymer does not change significantly.
7. The process of preparing microparticles according to any of the preceding claims wherein polymer is selected from poly(glycolic acid), poly(d,l-lactic acid), poly(l-lactic acid) or copolymers thereof.
8. The process of preparing microparticles according to any of the preceding claims wherein nucleophilic compound is selected from risperidone, 9-hydroxyrisperidone, thioridazine, naltrexone, oxybutynin or pharmaceutically acceptable salt thereof.
9. A process of preparing microparticles as substantially described and exemplified herein.