HK1018748B - Sustained release ionic conjugate - Google Patents

Description

Sustained release ionic conjugates

Technical Field

The present invention relates to sustained release drug delivery systems, and more particularly to microparticles for the preparation of sustained release ionic conjugates.

Background

Biodegradable polymeric drug delivery formulations have been developed and used to control the in vivo release of drugs, see U.S. Pat. Nos. 3,773,919 and 4,767,628. Such biodegradable polymeric formulations are designed to be included in a drug substance and slowly diffuse through the polymer matrix or coating as the biodegradable polymer depolymerizes.

International application WO 94/15587 describes sustained release ionic molecule conjugates of polyesters and drugs. Since polyester degradation is an important step in the release process, the surface area of the conjugate particles can control the release profile of the drug in the conjugate. It follows that in order to ensure minimal and reproducible surface area, conjugate particles should have small size and shape, such as microspheres.

DISCLOSURE OF THE INVENTION

In one aspect, the present invention relates to a method for preparing microparticles of sustained-release ion conjugates comprising a biodegradable polymer containing a free carboxyl group (a polyester made from monomers such as lactic acid, epsilon-caproic acid, glycolic acid, trimethylene carbonate or p-dioxanone, or copolymers thereof; the monomers may be optical isomers or racemates) and a drug containing a free amino group (e.g., a peptide drug such as somatostatin or LHRH), which are ionically bound to each other. The method comprises the following steps: (1) obtaining a first solution with the conjugate dissolved therein; (2) mixing the first solution (added as small droplets, such as through an atomizing nozzle, including an ultrasonic nozzle, a pneumatic nozzle, a rotary atomizer, or a pressure nozzle) with the first liquid to form a first dispersion, wherein the first liquid is miscible with the first solution and the combination is insoluble in the first liquid and precipitates from the first dispersion; and (3) separating the conjugate from the first dispersion.

In one embodiment, the drug is dissolved in a first liquid, which may be an alcohol (such as ethanol or isopropanol), hexane or water or mixtures thereof. When ethanol is used as the first liquid, the temperature at the time of use may be maintained at about 0 ℃ to-30 ℃. When isopropanol is used, the temperature may be maintained at about 0 ℃ to-70 ℃, for example by addition of dry ice for cooling.

The first solution, which may contain acetone, dichloromethane, acetonitrile, ethyl acetate, tetrahydrofuran or glyme or mixtures thereof, may be obtained by: (1) dissolving a biodegradable polymer in a second liquid (such as acetone, tetrahydrofuran, glycerol suppository, ethyl acetate, methyl acetate, acetonitrile, ethyl formate, or glyme, or mixtures thereof) to obtain a second solution; (2) dissolving the drug in a third liquid (e.g., water or acetone or a mixture thereof) to obtain a third solution, wherein the third liquid is miscible with the first liquid and the second liquid; and (3) mixing the second solution with the third solution to obtain a first solution, wherein the mixing allows the drug to ionically associate with the biodegradable polymer to obtain a conjugate in the first solution. The first solution may contain up to 40% by weight of the conjugate (e.g., 25 to 35% by weight of the conjugate). In one embodiment, a base, such as NaOH or KOH, may be added prior to mixing the second solution with the third solution. The carboxyl groups of the biodegradable polymer are neutralized with a base to form an ionic conjugate.

In addition, the first solution can also be obtained by: the biodegradable polymer and the drug are dissolved in a second liquid (e.g., acetone or a mixture of acetone and water) to provide a first solution, thereby providing the conjugate in the first solution. According to this method, the biodegradable polymer may be first dissolved in the second liquid, then the base is added to the second solution, and then the drug is dissolved in the second liquid. Furthermore, the first solution may be partially or completely evaporated from the first dispersion prior to isolation of the conjugate, if desired. The treated conjugate may conveniently be isolated by centrifugation or filtration of the first dispersion and the isolated conjugate may be mixed with an aqueous solution of mannitol prior to vacuum drying (e.g. freeze drying). The separated combination can be further formed into a film or a strip. The isolated conjugates can also be sphered into microspheres having an average diameter of 5 to 200 μm as described herein. "spheroidizing" refers to processing the microparticles to approximate a spherical shape.

In another aspect, the present invention relates to a method of sphering a sustained release ion conjugate as described above. The method comprises the following steps: (1) mixing the conjugate with a first liquid (e.g., an oil such as silicone oil, mineral oil, sesame oil, or vegetable oil) to obtain a first dispersion, wherein the conjugate has a particulate shape and is insoluble in the first liquid; (2) heating the first dispersion to a temperature greater than the Tg or Tm of the combination; (3) cooling the first dispersion to below the Tg or Tm temperature of the combination; (4) mixing the first dispersion with a second liquid (such as hexane, heptane, isopropyl cinnamate or an alcohol, such as ethanol or isopropanol) to obtain a second dispersion, wherein the second liquid is miscible with the first liquid and the conjugate is insoluble in the second liquid; and (5) separating the conjugate from the second dispersion. The combination may have a microcapsule shape with an average diameter of 5 μm to 200 μm before mixing with the first liquid, and the formed first dispersion is vigorously stirred while heating to assist the separation of particles. Once the conjugate has been isolated, it may be immersed in a second liquid and then vacuum dried. The conjugate may optionally be mixed with an aqueous mannitol solution prior to vacuum drying.

A third aspect of the present invention relates to a method of sphering the above sustained-release ion conjugate (e.g., a microcapsule having an average diameter of 5 μm to 200 μm). The method comprises the following steps: (1) mixing the conjugate in a first liquid (such as water) to obtain a first dispersion, wherein the conjugate is in the form of microparticles and the conjugate is insoluble in the first liquid; (2) stirring the first dispersion; (3) mixing the stirred dispersion with a second liquid (e.g., dichloromethane or chloroform) in an amount that is absorbed by the conjugate but does not dissolve the conjugate, wherein the second liquid is miscible with the first liquid; (4) evaporating the second liquid from the first dispersion; and (5) separating the precipitated conjugate from the first dispersion. If desired, the method may further comprise the steps of: to aid in the dissolution of the first dispersion, a surfactant (such as lecithin, tween 20, polysorbate, or lauryl sulfonate) may be added to the first dispersion, and the isolated conjugate may be immersed in the first liquid and dried under vacuum. Furthermore, the isolated conjugate may be mixed with an aqueous mannitol solution before vacuum drying.

In a further aspect of the invention, the present invention relates to a method of sphering the above sustained-release ion conjugate. The method comprises the following steps: (1) dissolving the conjugate in a first liquid (e.g., acetonitrile) to obtain a first solution; (2) stirring the first solution and a second liquid (e.g., an oil) to provide a first dispersion, wherein the second liquid is immiscible with the first solution; (3) evaporating the first liquid from the first dispersion to precipitate the conjugate from the first dispersion; and (4) separating the precipitated conjugate from the first dispersion. In the stirring step, the first solution may be added as small droplets to the second liquid.

The above method may further comprise the steps of: the isolated conjugate is impregnated with a third solution (e.g., hexane, heptane, or octane) that is miscible with the second liquid and is not the solvent for the conjugate. If desired, the isolated conjugate may be mixed with an aqueous mannitol solution prior to vacuum drying.

The biodegradable polymer in the conjugate contains at least one free carboxyl group (e.g., 2 to 10 free carboxyl groups per polymer chain). Examples of carboxylic acid-containing biodegradable polymers include polyesters in optically active form or racemates containing the following units: lactic acid, epsilon-hexanoic acid, p-dioxanone, epsilon-caproic acid, substituted and unsubstituted trimethylene carbonate, 1, 5-dioxahept-2-one, 1, 4-dioxahept-2-one, glycolic acid, alkylene oxide, cycloalkene oxide, alkylene succinate, or 3-hydroxybutyric acid; or a copolymer of any of the above units. Additional free carboxylic acid groups may also be incorporated into the biodegradable polyester by reaction with polycarboxylic acids such as malic acid, tartaric acid, palmitic acid, citric acid, succinic anhydride and glutaric anhydride, for example by ring-opening polymerisation or polycondensation. Thus, the biodegradable polymer may be a water-soluble polyester comprising lactic acid units with or without glycolic acid units. Other biodegradable polymers (e.g., polyorthoesters, polyorthocarbonates, and polyantals) may also be used. The biodegradable polymer has an average degree of polymerization (e.g., number average monomer per polymer chain) of 10 to 300.

The drug may have one or more (e.g., 1 to 10) free amine groups. In one embodiment, the drug is an acid stable peptide. Examples of suitable acid-stable peptides include Growth Hormone Releasing Peptide (GHRP), Luteinizing Hormone Releasing Hormone (LHRH), adrenomedullin, growth hormone, somatostatin, bombesin, Gastrin Releasing Peptide (GRP), calcitonin, bradykinin, galanin, Melanocyte Stimulating Hormone (MSH), growth hormone releasing factor (GRF), dextrin, tachykinin, incretins, parathyroid hormone (PTH), enkephalin, endothelin, Calcitonin Gene Releasing Peptide (CGRP), neuregulin, parathyroid hormone related protein (PTHrP), glucagon, neurotensin, Adrenocorticotropin (ACTH), peptide yy (pyy), glucagon releasing peptide (GLP), Vasoactive Intestinal Peptide (VIP), Pituitary Adenylate Cyclase Activating Peptide (PACAP), motilin, substance P, neuropeptide y (npy), TSH, and analogs and fragments thereof. The drug is soluble in the first liquid (e.g. greater than 0.1mg/ml, preferably greater than 1.0 mg/ml).

Other features and advantages of the invention will be apparent from the detailed description and from the claims.

Those skilled in the art can utilize the present invention to its fullest extent based on the description of the invention. The particular embodiments set forth below are therefore to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Furthermore, all publications, patent applications, patents, and other references mentioned above are incorporated herein by reference.

Best mode for carrying out the invention

Example 1

18g of poly-L-lactic-glycolic acid-D, L-malic acid polymer (L-lactic acid 66%, glycolic acid 32%, malic acid 2%; acid value 0.373 meq/g) 66/32/2 g/mol was dissolved in 180g of acetone (C: (A) (B))10% by weight of copolymer solution). Adding 14.4ml of 0.5N NaOH aqueous solution to form polymer sodium carboxylate, and adding 4.28g of peptide Lanreotide^TMAcetate (Kinerton, Dublin, Ireland; D-Nal-c [ Cys-Tyr-D-Trp-Val-Cys)]-Thr-NH₂(ii) a Acetate content 9.60% by weight) was dissolved in a mixture of 10g of acetone and 10g of deionized water. The amount of peptide dissolved corresponds to the stoichiometric ratio of polymer acid groups (e.g. 1) to peptide free amino groups (e.g. 2). The peptide solution was then dropped into the polymer solution, and the resulting solution was stirred for 2 hours, thereby causing salt exchange to give the polymer/peptide ion conjugate (PPIC) formed.

Example 2

In a temperature-controlled jacketed reactor (Schott Glass AGB, Dublin, Ireland), a 2 liter bath of deionized water was precooled to 0 ℃ and vigorously stirred. The PPIC solution of example 1 above was slowly added to the reactor by using a Masterflex pump (Bioblock Scientific, Illkvch, France) capable of generating a flow rate of 10-15ml/min through a silicone tube fitted with a 19-gauge probe at the top. Small solid particles were generated in a water bath by feeding the PPIC solution through a probe immobilized above the water surface at 0 ℃, then separating the solid particles from the supernatant by centrifugation (5000 rpm for 30 minutes at 0-5 ℃), soaking with fresh deionized water, resuspending in water, recentrifugation, and lyophilization. The separated conjugate was filtered through a 100 μm sieve to separate a large number of particles that could be injected through a 21 gauge probe. The size analysis of the resulting particles is described in table I.

Example 3

The PPIC solution of example 1 was precipitated according to the method described in example 2, except that an alcohol bath at a temperature of-20 ℃ was used instead of a water bath at 0 ℃. The size analysis of the resulting particles is described in table I.

Examples4

The PPIC solution of example 1 was dispersed in an ethanol bath at a controlled flow rate of 4ml/min in a temperature-controlled jacketed reactor at-10 ℃ through an atomizing nozzle (Bioblock; 50 Watts, 20kHz) containing a hollow head. In this atomization method, the polymer solution is released from the probe as very fine atomized droplets. The droplets fall into an ethanol bath, which causes deionized water and acetone to be extracted from the droplets, and eventually the polymer droplets harden into small solid particles. The particles were then recovered by centrifugation and lyophilized. The size analysis of the resulting particles is listed in table I. Diameter-10 (i.e., D0.1), diameter-50 (i.e., D0.5), or diameter-90 (i.e., D0.9) means the smallest diameter of greater than 10%, 50%, or 90%, respectively, of the total particles. The meaning of specific area refers to the average specific area of the resulting particles.

TABLE I

Examples diameter-10 diameter-50 diameter-90 specific area

(μm) (μm) (μm) (m²/g)

2 10 30 62 18.64

3 9 37 89 6.42

4 13 46 95 22.61

Example 5

5.0g of the PPIC described in example 4 were dissolved in 20g of acetone (PPIC concentration 20% by weight). This solution was atomized in a 500ml ethanol bath at-10 ℃ with a flow rate of 4.0ml/min according to the method described in example 4. After the PPIC particles were prepared in the bath, 500ml of deionized water was added to the bath, and the bath temperature was then raised to 0 deg.C, the bath was stirred for 30 minutes, the temperature was raised to 20 deg.C, and the stirring was continued for 30 minutes. The PPIC particles were then recovered by filtration and dried under vacuum at room temperature. The results of the analysis of the resulting particles are shown in table II.

TABLE II

Example D0.1D 0.5D 0.9 specific area

(μm) (μm) (μm) (m²/g)

#4 13 46 95 22.61

#5 50 99 180 0.11

As shown in table II, particles of different morphology were obtained. The particles of example 4 are larger and have a lower specific area. As shown by the scanning electron microscope, the particles obtained in example 4 were also more porous, probably due to the fact that the particles retained frozen water in them during precipitation, which was dissolved and flowed into the ethanol bath, leaving open channels in the particles. These particles are therefore more brittle and can produce small size chips.

Example 6

The PPIC solution described in example 5 above was atomized at 0 deg.C in 1.5 liters of deionized water at a rate of 2.5 ml/min. The results of the analysis of the resulting particles are shown in Table III.

Example 7

The PPIC solution described in example 5 above was atomized at-10 ℃ in 1.5 l of ethanol at a rate of 2.5 ml/min. The results of the analysis of the resulting particles are shown in Table III.

TABLE III

Example D0.1D 0.5D 0.9 specific area

(μm) (μm) (μm) (m²/g)

6 53.4 154.3 329.1 n/a

7 42.4 87.2 170.1 0.20

Example 8

Two PPIC solutions were prepared in acetone according to the procedure described in example 5. The PPIC concentration of the first solution was 15% and the PPIC concentration of the second solution was 20%. The solution was atomized at-10 ℃ at rates of 2.5, 3.5 and 5.0ml/min, respectively, according to the method described in example 5. The results of the analysis of the resulting particles are shown in Table IV.

TABLE IV

Concentration feed rate D0.1D 0.5D 0.9 specific area

(ml/min) (μm) (μm) (μm) (m²/g)

15％ 2.5 35.9 81.6 191.1 4.455

15％ 3.5 34.4 80.2 188.3 8.336

15％ 5.0 49.4 163.6 397.8 n/a

20％ 2.5 33.3 73.8 145.6 0.199

20％ 3.5 50.8 112.7 241.9 0.579

20％ 5.0 108.3 219.1 395.9 n/a

Particle analysis using scanning electron microscopy showed that both particle size and specific area increased with increasing feed rate.

Example 9

5.0g of the PPIC particles of example 4 were dissolved in 45ml of acetone (10% by weight concentration). The solution was added dropwise to 500ml of vigorously stirred n-hexane at room temperature. When PPIC precipitates, the n-hexane solution became turbid. The PPIC was isolated by filtration and dried under vacuum at room temperature.

Example 10

In a jacketed reactor, 3.0g of the PPIC microparticles described in example 2 were dissolved in 250ml of 12,500cs pharmaceutical grade silicone oil (Dow Corning, Midland, MI) (1% PPIC (by weight)) with vigorous stirring. Heating the mixture after stirring to 120 ℃ which is above the Tg 55 ℃ of PPIC; the mixture was maintained at this temperature for 30 minutes. During the heating process, the separated particles melt to form spherical droplets. The dispersion was then cooled to 20 ℃ and diluted with 1250ml of hexane. The hardened microspheres were then recovered by filtration, immersed in fresh hexane and finally dried under vacuum. The characteristics of the resulting microspheres are reported in table V. The diameter of the final particles was smaller than that of example 2 due to compression of the particles during the melting process.

TABLE V

Example D0.1D 0.5D 0.9 specific area

(μm) (μm) (μm) (m²/g)

#2 10 30 62 18.64

#7 2 10 47 ＜0.33

Example 11

0.2g of the PPIC particles described in example 2 were dispersed in 5ml of deionized water and vigorously stirred using a vortex shaker. Then 100ml of Dichloromethane (DCM) were added to the stirred dispersion. The surface of the PPIC particles was swollen by the addition of a small amount of DCM. Stirring was continued at room temperature for 4 hours and DCM was evaporated to harden the surface of the swollen particles. Scanning electron microscopy showed that the resulting particles were spherical with a smoother surface than the original material. The size distribution of both particles is narrow and the maximum particle size decreases with increasing density.

Example 12

1 liter of sesame oil (Vitamins, inc., Chicago, IL) was placed in a 2 liter three-neck flask immersed in a water bath. The sesame oil was stirred at 600rpm using a Teflon stirring rod connected to an overhead stirring motor. 500mg of a surfactant (soybean protein lecithin, Sigma Chemicals, St. Louis, Mo.) was added to the sesame oil, and the mixture was stirred for 10 minutes. Then 10g of the PPIC preparation was dissolved in 100ml of acetonitrile to give a clear solution. Using Lanreotide containing one of the following three polymers^TMPreparation of PPIC composition: 64/34/2 Poly-DL-lactic acid-glycolic acid-D, L-malic acid copolymer (weight average molecular weight 6,000) (composition 1); 74/24/2 poly-DL-lactic acid-glycolic acid-D, L-malic acid copolymer (weight average molecular weight 6,000) (composition 2) and 98/2 poly-DL-lactic acid-D, L-malic acid copolymer (composition 3).

The clear PPIC solution was added dropwise through a dropping funnel. When the addition was complete, the temperature of the internal water bath was raised to 40 ℃ and the oil was stirred for 20 hours. Then 1 liter of hexane was added, the sesame oil was diluted and the oil was filtered through a funnel of porous media. The microparticles collected in the filter funnel were washed several times with a total volume of 500ml of hexane. The particles were dried under vacuum at 36 ℃ for two days. The characteristics of the resulting microparticles are shown in table VI.

TABLE VI

Composition D0.1D 0.5D 0.9 specific area

(μm) (μm) (μm) (m²/g)

1 13 28 57 0.1426

2 13 25 59 0.1395

3 14 25 51 0.1480

Example 13

The reactor was charged with a solution of monomeric glycolide (Purac Biochem, Netherlands, 84.83g), lactide (Purac Biochem, Netherlands, 210.67g) and L (+) -tartaric acid (Ridel-deHaen, Seelze, Germany, cat # 33,801, 4.50g) and stannous 2-ethylhexanoate (Sigma, St. Louis, Missouri, USA, cat # S-3252) in toluene (Ridel-de Haen, Seelze, Germany) (0.1025M, 4.34 ml). L (+) -tartaric acid was previously dried in phosphorus pentoxide (Ridel-de Haen, Seelze, Germany) on an Abderhalden drying apparatus for 10 hours. The reactor (connected to a pump via a liquid nitrogen valve) was stirred under vacuum (0.04mbar) for 50 minutes to separate the toluene. The reactor was immersed in an oil bath (temperature 200 ℃) under an oxygen-free nitrogen atmosphere (BOC gas, Dublin, Ireland, moisture 8VPM) with the stirring speed increased to 125 rpm. Prior to impregnation, a heating tape (Thermolyne model 45500, input control 4) was placed on the reactor lid. The time taken to completely melt the reactor contents at 200 ℃ is typically 10 minutes for a charge of 300 g. Samples were taken at one hour intervals during the synthesis for GPC analysis to determine the percentage of residual monomer and thus numerical values for number average (Mn) and weight average (Mw) molecular weight. Typical reaction times are around 6 hours.

This gave an amorphous polymer containing 66.21% glycolide units, 33.11% lactide units and 0.68% tartaric acid units (66/33/1 PLGTA). The titration acid number was determined to be 0.303 milliequivalents/g (meq/g; NaOH equivalent concentration times the volume of NaOH solution required to neutralize 1g of polyester). The average value of the number average molecular weight of the copolymer was 10,250, the average value of the weight average molecular weight was 11,910, and the Mw/Mn value was 1.16.

41.32g of the above 10,000g/mol 66/32/2 poly-L-lactic-co-glycolic acid-L (+) -tartaric acid copolymer (acid number 0.303meq/g) were dissolved in 165.52g of acetone (Ridel-de Haen, Seelze, Germany) using a sonication method in a Branson sonication bath (Branson, Danbury, Connecticut, USA) to give a solution with a weight concentration of PLGTA of 19.98%.

To this solution was added 37.6ml of 0.2N sodium carbonate (Aldrich, Gillingham, Dorset, UK) giving a 1.2-fold excess of sodium in the carboxyl group of the polymer. The solution was then stirred for 30 minutes to drive the sodium salt to form. The solution was then fed into the atomizer nozzle at a rate of 8.0ml/min using a Masterflex pump (Cole Parmer, Barrington, Illinois, USA). The solution was atomized into a jacketed reactor containing 2 liters of deionized water cooled to 2.5 ℃ using a circulating bath (Huber, offsenburg, Germany). The water was stirred to 350rpm using a 4-blade stirrer connected to a stirring motor.

Once atomization was complete, the dispersion was placed in 6 centrifuge bottles and spun in a Sorvall centrifuge (DuPont Sorvall Products, Wilmington, Delaware, USA) at 5000rpm for 30 minutes. The obtained centrifugal cake is resuspended in deionized water and then centrifuged and rotated. The supernatant was removed and the cake was frozen in a refrigerator overnight and dried the next day in a mini-freezer (Edwards, Crawley, West Sussex, UK) to recover 33.16g of washed copolymer in 80.24% yield.

4.92g of the above-described 10,000g/mol 66/33/1 poly-L-lactic-glycolic acid-L (+) -tartaric acid copolymer (66% L-lactic acid, 32% glycolic acid, 1% tartaric acid) were dissolved in 11.58g acetonitrile (Ridel-de Haen, Seelze, Germany) using the sonication method in a Branson sonication bath (Branson, Danbury, CT, USA) to give a 29.82% by weight solution of PLGTA.

The copolymer/acetonitrile solution was fed from a glass reservoir through an atomizer nozzle at a rate of 2.0ml/min using an FMI rotary piston pump (FMI, Oyster Bay, NY, USA). The output energy of the atomizer is set at 50W, and the amplitude is 80%. The solution was atomized into a 6 liter jacketed reactor containing 1.5 liters of a common isopropanol reagent (Labscan, Dublin, Ireland) using CO₂The solid pellets (AIG, Dublin, Ireland) were cooled to-70 ℃ and stirred at 300rpm using a 4-blade stirrer connected to a stirring motor. The temperature of the isopropanol was maintained at-70 deg.c or close to-70 deg.c throughout the atomization time, which lasted approximately 8 minutes.

Once atomization was complete, the dispersion was allowed to warm to 10 ℃ automatically in 5.5 hours, then vacuum filtered on Whatman No.1 filter paper (9 cm diameter). The filter paper and filter cake were placed in a desiccator containing silica gel desiccant and the vacuum was withdrawn through an automatic freezer at-110 ℃. After 24 hours 4.24g of material were recovered. The results of the analysis of the resulting particles are shown in table VII.

TABLE VI

Example D0.1D 0.5D 0.9 specific area

(μm) (μm) (μm) (μ²/g)

13 31 68 139 0.16

It is to be understood that while the invention has been described in conjunction with the detailed description thereof, that this description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages and modifications of the invention are within the scope of the claims.

Claims (22)

1. A method for preparing microparticles of sustained-release ion conjugates comprising a biodegradable polymer having a free carboxyl group and a drug having a free amino group, which are ionically bound to each other, comprising the steps of:

obtaining a first solution having a conjugate dissolved therein, the first solution comprising acetone, acetonitrile, ethyl acetate, tetrahydrofuran, or glyme;

adding the first solution to a first liquid in the form of small droplets, and mixing the first solution and the first liquid to form a first dispersion, wherein the first liquid is miscible with the first solution and the combination is insoluble in the first liquid and precipitates from the first dispersion; and

separating the conjugate from the first dispersion.

2. The method according to claim 1, wherein the first solution is added to the first liquid through an atomizing nozzle.

3. The method according to any one of claims 1 to 2, wherein the drug is a peptide.

4. The method according to claim 1, wherein the biodegradable polymer is a polyester or a copolymer thereof, the polyester being made of lactic acid, epsilon-caproic acid, glycolic acid, trimethylene carbonate or p-dioxanone.

5. The method of claim 1 wherein said drug is dissolved in said first liquid.

6. The method according to claim 1, wherein the biodegradable polymer is a polyester containing lactic acid or glycolic acid or a copolymer thereof.

7. The method according to claim 6, wherein said polyester further comprises malic acid, tartaric acid, citric acid, succinic acid, or glutaric acid.

8. The method according to claim 7, wherein the polyester comprises lactic acid, glycolic acid, and tartaric acid.

9. A method according to claim 3, wherein the peptide is somatostatin or luteinizing hormone-releasing hormone.

10. The method according to claim 1, wherein the first liquid is alcohol or water or a mixture thereof.

11. The method according to claim 10, wherein the first liquid is ethanol maintained at 0 ℃ to-30 ℃ or isopropanol maintained at 0 ℃ to-70 ℃.

12. The method according to claim 1, wherein the first solution comprises acetone or acetonitrile.

13. The method according to claim 1, wherein the first solution is obtained by:

dissolving the biodegradable polymer in a second liquid to obtain a second solution;

dissolving the drug in a third liquid to provide a third solution, wherein the third liquid is miscible with the first liquid and the second liquid; and

mixing said second solution with said third solution to obtain said first solution, wherein said mixing ionically associates said drug with said biodegradable polymer to obtain said conjugate in said first solution.

14. The method of claim 13, wherein NaOH or KOH is added to the second solution prior to mixing the second solution and the third solution.

15. The method according to claim 13 or 14, wherein the second liquid is acetone; the third liquid is water or acetone or a mixture thereof.

16. The method according to claim 1, wherein the first solution is obtained by: dissolving the biodegradable polymer and the drug in a second liquid to provide the first solution, and forming the conjugate in the first solution.

17. The method according to claim 16, wherein the second liquid is acetone or a mixture of acetone and water.

18. The method according to claim 17, wherein the biodegradable polymer is first dissolved in the second liquid, then a base is added to the second solution, and then the drug is dissolved in the second liquid.

19. A method according to claim 1, wherein the conjugate is isolated by centrifugation or filtration of the first dispersion.

20. A method according to claim 19, wherein the first solution is partially or completely evaporated from the first dispersion prior to isolating the conjugate.

21. A method according to claim 20, wherein the isolated conjugate is mixed with an aqueous solution of mannitol prior to vacuum drying.

22. The method according to claim 21, wherein the polyester comprises lactic acid, glycolic acid, and tartaric acid.