PROCESS FOR FORMING AMORPHOUS AZITHROMYCIN PARTICLES

FIELD OF THE INVENTION

The invention relates to processes for forming amorphous azithromycin particles using a rapid solvent-evaporation process.

BACKGROUND OF THE INVENTION

Azithromycin has the following structural formula:

Azithromycin is described in U.S. Pat. Nos. 4,517,359 and 4,474,768. It is also known as θ-deoxo-θa-aza-θa-methyl-θa-homoerythomycin A.

It has been found that the amorphous forms of a number of drugs exhibit different dissolution characteristics and in some cases different bioavailability patterns compared to the crystalline form (Konno T., Chem. Pharm. Bull., 1990;38:2003-2007). For some therapeutic indications one bioavailability pattern may be favored over another.

The preparation of amorphous azithromycin has been previously described. For example, U.S. Patent No. 6,245,903 describes an anhydrous form of azithromycin and a method to purify amorphous anhydrous azithromycin using a chromatographic procedure or by using a solvent evaporation method. U.S. Patent No. 6,451 ,990 B1 describes a procedure for the preparation of noncrystalline (i.e., amorphous) azithromycin by means of lyophilization of solutions of azithromycin in tert- butanol (2-methyl-2-propanol) or cyclic ethers, and by means of evaporation of solutions of azithromycin in aliphatic alcohols, such as ethanol or isopropanol.

WO 2004/009608A2 describes forming an orthorhombic isostructural pseudopolymorph of azithromycin, and then transforming this purified crystal form to the amorphous product by removal of solvent and excess water by lyophilization or by vacuum drying.

WO02/094843 A1 describes azithromycin in an amorphous state made by removal of water and/or solvents from the azithromycin crystal lattice. Amorphous azithromycin is formed by heating crystal form A of azithromycin under vacuum. Published U.S. Patent Application 2002/0111318 describes methods for preparation of non-hygroscopic azithromycin dihydrate.

There remains a continuing need for an efficient means for the preparation of small uniform particles of amorphous azithromycin.

SUMMARY OF THE INVENTION The invention relates a process for forming amorphous azithromycin comprising: (a) forming a solution comprising azithromycin and a solvent; (b) atomizing the solution into droplets; and (c) evaporating at least a portion of the solvent from the solution to form amorphous azithromycin. Preferably, the solvent is removed by spray drying or spray coating.

It has been discovered that amorphous azithromycin is formed when the azithromycin is dissolved in a solvent and the solvent is rapidly evaporated. Azithromycin has good solubility in a wide range of solvents and the process for forming amorphous azithromycin can be improved by reducing the amount of solvent needed. In addition, the small particle size achieved by these rapid formation processes alleviates the need for a milling step, thereby reducing the number of unit operations in production of material for commercial use. Rapid evaporation achieves yet another advantage, which is the formation of particles having relatively uniform particle size distribution and shape. Amorphous azithromycin formed by mechanically breaking apart a glassy foam, such as what is formed by lyophilization processes, tends to have a wide size distribution, and the individual particles tend to have rough or sharp edges. In contrast, particles formed by rapid evaporation tend to be rounder and have narrower size distributions. The particles formed by rapid evaporation have better flow characteristics and are less likely to become segregated during manufacturing, such as during handling to form tablets or other dosage forms. Thus, the present invention may reduce segregation during manufacturing of a dosage form by providing amorphous azithromycin that is easier to handle.

The small particle size achieved by rapid evaporation is also believed to yield particles that have more rapid dissolution characteristics. This may be due to the high surface area of the small particles.

The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a PXRD diffractogram of the azithromycin dihydrate used to form the spray solution for Example 1.

FIG. 2 shows a PXRD diffractogram of the amorphous azithromycin formed by the spray- drying process of Example 1. FlG. 3 shows a PXRD diffractogram of amorphous azithromycin after storage for 5 months at 40 ⁰ C and 75% relative humidity (RH).

FIG. 4 shows scanning electron microscopy (SEM) images of amorphous azithromycin formed via a spray drying process.

FIG. 5 shows scanning electron microscopy (SEM) images of jet-milled crystalline azithromycin dihydrate.

DETAILED DESCRIPTION OF THE INVENTION

The present process involves dissolving azithromycin in a solvent, atomizing the resulting solution, followed by evaporation of the solvent to form amorphous azithromycin. The term "amorphous," as used herein, means a particular solid form of azithromycin that does not have long- range three-dimensional translational order. The term "amorphous" is intended to include not only materia) which has essentially no order, but also material which may have some small degree of order, but the order is in less than three dimensions and/or is only over short distances. Partially crystalline materials and crystalline mesophases with, e.g. one-or two-dimensional translational order (liquid crystals), or orientational disorder (orientationally disordered crystals), or with conformational disorder

(conformationaily disordered crystals) are included as well. Amorphous material may be characterized by techniques known in the art such as powder x-ray diffraction (PXRD) crystallography, solid state NMR, or thermal techniques such as differential scanning calorimetry (DSC). The amount of crystalline azithromycin present in the resulting amorphous drug is small. Preferably at least 90 wt% of the azithromycin formed by the process of the present invention is amorphous. More preferably at least 95 wt%, and even more preferably at least 99 wt% of the azithromycin formed by the process of the present invention is amorphous.

As will be recognized by those skilled in the art, the azithromycin which is dissolved to form the solution may be in any morphological form such as, for example, crystalline or amorphous, as well as disordered crystals, liquid crystals, plastic crystals, mesophases, and the like, or any combination thereof. Azithromycin may readily be synthesized, for example, as described in United States Patent Numbers 4,517,359 and 4,474,768. The term "azithromycin" includes the free base form, salt forms, solvates, hydrates, polymorphs, pseudomorphs, and isomorphs.

The azithromycin used to form amorphous azithromycin by the process of the present invention may be any form of azithromycin, or be in a mixture of two or more forms of azithromycin. One of the advantages of the process of the present invention is that the azithromycin need not be purified into a single crystalline form prior to being used in the process of the present invention.

Amorphous azithromycin is formed by solvent processing using a solvent. Solvents suitable for solvent processing can be any solvent in which the azithromycin is soluble. Preferably, azithromycin has a solubility of at least 1 wt%, and more preferably at least 5 wt% in the solvent.

Preferably, the solvent is also volatile with a boiling point of 15O ⁰ C or less. In addition, the solvent should have relatively low toxicity and be removed from the amorphous azithromycin to a level that is acceptable according to The International Committee on Harmonization (ICH) guidelines. Removal of solvent to this level may require a subsequent processing step such as tray-drying. Preferred solvents include water; alcohols such as methanol, ethanol, n-propanol, isopropanol, and the various isomers of butanoi; ketones such as acetone, methyl ethyl ketone, methyl iso-butyl ketone, and cyclohexanone; esters, such as methyl acetate, ethyl acetate, and propyl acetate; ethers, such as dimethyl ether, tetrahydrofuran, methyl tetrahydrofuran, 1 ,3-dioxolane, and 1 ,4-dioxane; alkanes, such as butane and pentane; alkenes, such as pentene and cyclohexene; nitriles, such as acetonitrile; alkyl halides, such as methylene chloride, trichloroethane, chloroform, and trichloroethylene; aromatics, such as toluene; and mixtures thereof.

-A-

Lower volatility solvents such as dimethyl acetamide, dimethylformamide, or dimethylsulfoxide can also be used in small amounts in mixtures with a volatile solvent. Mixtures of solvents, such as 50% methanol and 50% acetone, can also be used, as can mixtures with water. Preferred solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, n-propanol, isopropanol, methyl acetate, ethyl acetate, toluene, methylene chloride, tetrahydrofuran, 1 ,4-dioxane, 1 ,3-dioxolane, and mixtures thereof. Most preferred solvents include acetone, methanol, ethanol, n-propanol, isopropanol, ethyl acetate, and mixtures thereof. Mixtures of the above with water may also be used.

Amorphous azithromycin is formed by (a) forming a solution comprising azithromycin dissolved in a solvent, (b) atomizing the solution, and (c) rapidly evaporating the solvent. The solution can be made by dissolving azithromycin in a solvent using techniques known in the art. This is generally accomplished by adding the solid azithromycin to the solvent and then mixing. Mixing may generally be done using mechanical means, such as overhead mixers, magnetically driven mixers and stir bars, planetary mixers, and homogenizers. The solution can be formed at ambient temperature, or the solvent can be heated to aid in dissolution of the azithromycin. Preferably, essentially all of the azithromycin in the solution is dissolved in the solvent.

The azithromycin may be dissolved in the spray solution up to the solubility limit; however, the amount dissolved is usually less than 80% of the solubility of azithromycin in the solution at the temperature of the solution prior to atomization. The concentration of azithromycin may range from 0.1 wt% to 30 wt% depending on the solubility of the drug and polymer in the solvent. The concentration of azithromycin in the solution is preferably at least about 0.1 wt%, more preferably at least about

0.5 wt%, even more preferably, at least about 1 wt%, and most preferably at least about 5 wt%. High concentrations of azithromycin in the solution are preferred since they reduce the volume of solvent that must be evaporated to form the amorphous azithromycin. However, the concentration of azithromycin should not be too high, or else the spray solution may be too viscous to atomize efficiently into small droplets. The spray solution viscosity may range from about 0.5 to about 50,000 cp, and more typically 10 to 2,000 cp.

In addition to the solvent, the spray solution may contain optional excipients so long as the azithromycin remains sufficiently soluble in the spray solution. The optional excipients may be dissolved in the spray solution, may be suspended in the spray solution, or any combination of these. In one embodiment, the solution contains an alkalizing agent. Addition of an alkalizing agent to the solution may promote chemical stability of the amorphous azithromycin during processing and/or in the final product. Alkalizing agents include, for example, antacids as well as other pharmaceutically acceptable (1 ) organic and inorganic bases, (2) salts of weak organic and inorganic acids, and (3) buffers. Examples of such alkalizing agents include, but are not limited to, aluminum salts such as magnesium aluminum silicate; magnesium salts such as magnesium carbonate, magnesium trisilicate, magnesium aluminum silicate, magnesium stearate; calcium salts such as calcium carbonate; bicarbonates such as calcium bicarbonate and sodium bicarbonate; phosphates such as monobasic calcium phosphate, dibasic calcium phosphate, dibasic sodium phosphate, tribasic sodium phosphate (TSP), dibasic potassium phosphate, tribasic potassium phosphate; metal hydroxides such as aluminum

hydroxide, sodium hydroxide, potassium hydroxide, and magnesium hydroxide; metal oxides such as magnesium oxide; N-methyl glucosamine; arginine and salts thereof; amines such as monoethanolamine, diethanolamine, triethanolamine, and tris(hydroxymethyl)aminomethane (TRIS); and combinations thereof. In another embodiment, the solution contains a matrix-forming material. The matrix- forming material may help stabilize the amorphous azithromycin, preventing or retarding formation of crystalline azithromycin, or may improve the properties of the amorphous azithromycin for processing into dosage forms. The matrix-forming material may be polymeric or non-polymeric, and may comprise a mixture of several components. Thus the matrix-forming material may comprise a mixture of polymeric components, a mixture of non-polymeric components, or a mixture of polymeric and non-polymeric components.

The term "polymeric" is used conventionally, meaning a compound that is made of monomers connected together to form a larger molecule. A polymeric component generally consists of at least about 20 monomers. Thus, the molecular weight of a polymeric component will generally be about 2000 daltons or more. The polymeric component may be neutral or ionizable, and may be cellulosic or non-cellulosic. In general, useful polymers have an aqueous-solubility of at least about 0.1 mg/mL Examples of neutral non-cellulosic polymers include vinyl polymers and copolymers, polyvinyl alcohols, polyvinyl alcohol/ polyvinyl acetate copolymers, polyethylene glycol/ polypropylene glycol copolymers, polyvinyl pyrrolidone, polyethylene/ polyvinyl alcohol copolymers, and polyoxyethylene/ polyoxypropylene block copolymers (also known as poloxamers). Examples of ionizable non-cellulosic polymers include carboxylic acid functionalized polymethacrylates and carboxylic acid functionalized polyacrylates, amine- functionalized polyacrylates and polymethacrylates, proteins such as gelatin and albumin, and carboxylic acid functionalized starches such as starch glycolate. Examples of neutral cellulosic polymers are hydroxypropyl methyl cellulose (HPMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methyl cellulose, hydroxyethyl methyl cellulose, and hydroxyethyl ethyl cellulose. Examples of ionizable cellulosic polymers are hydroxypropyl methyl cellulose acetate succinate (HPMCAS), hydroxypropyl methyl cellulose phthalate (HPMCP), carboxymethyl ethyl cellulose (CMEC), carboxyethyl cellulose, carboxymethyl cellulose, cellulose acetate phthalate (CAP), hydroxypropyl methyl cellulose acetate phthalate, and cellulose acetate trimellitate. By "non-polymeric" is meant that the component is not polymeric. Exemplary non- polymeric materials for use as a matrix-forming material include: organic acids and their salts, such as stearic acid, citric acid, fumaric acid, tartaric acid, malic acid, and pharmaceutically acceptable salts thereof; long-chain fatty acid esters, such as glyceryl monooleate, glyceryl monostearate, glyceryl palmitostearate, polyethoxylated castor oil derivatives, hydrogenated vegetable oils, glyceryl dibehenate, and mixtures of mono-, di-, and tri-alkyl glycerides; glycolized fatty acid esters, such as polyethylene glycol stearate and polyethylene glycol distearate; polysorbates; salts such as sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, sodium sulfate, potassium sulfate, sodium carbonate, and magnesium sulfate; amino acids such as alanine and glycine; sugars such as glucose, sucrose, xylitol, fructose, lactose, trehalose, mannitol, sorbitol, and maltitol; alkyl

sulfates such as sodium lauryl sulfate and magnesium lauryl sulfate; and phospholipids, such as lecithin; and mixtures thereof.

Once the solution comprising azithromycin and a solvent is formed, it is delivered to an atomizer that breaks the solution into small droplets. Generally, atomization occurs in one of several ways, including (1) by "pressure" or single-fluid nozzles; (2) by two-fluid nozzles; (3) by centrifugal or spinning-disk atomizers; (4) by ultrasonic nozzles; and (5) by mechanical vibrating nozzles. Detailed descriptions of atomization processes can be found in Lefebvre, Atomization and Sprays (1989) or in Perry's Chemical Engineers' Handbook (7th Ed. 1997). Generally, the droplets produced by the atomizer should be less than about 500 μm in diameter when they exit the atomizer. Examples of types of nozzles that may be used to form the droplets include the two-fluid nozzle, the fountain-type nozzle, the flat fan- type nozzle, the pressure nozzle and the rotary atomizer. In one embodiment, a pressure nozzle is used. Once atomized, at least a portion of the solvent is removed from the solution to produce a plurality of solid particles comprising amorphous azithromycin. As used herein, removing "at least a portion" of the solvent from the solution means that a sufficient amount of solvent is removed from the solution so as to form a solid material. The amount of solvent removed to form a solid material will depend on the solubility of azithromycin in the solvent and the concentration of azithromycin and any optional excipients in the solution. Generally, at least about 60 wt% of the solvent originally present in the solution is removed to form a solid material. The greater the amount of solvent removed from the solution, the less likely crystalline azithromycin is formed. Thus, the amount of solvent removed from the solution to form amorphous azithromycin may be at least 70 wt%, at least 80 wt%, or even at least 90 wt%.

It is also preferred that the solvent be rapidly removed from the solution to form amorphous azithromycin. The terms "rapidly removed" and "rapid removal" mean that the solvent is removed from the solution sufficiently fast so that at least 90 wt% of the solvent originally present in the solution is removed within 5 minutes or less. Rapid removal of the solvent is thought to result in a product that has a higher percentage of amorphous drug than processes that slowly remove the solvent. Thus, 90 wt% of the solvent may be removed within 5 minutes or less, within one minute or less, or even within 20 seconds or less.

A spray-drying process may be used to form amorphous azithromycin. The azithromycin is dissolved in a solvent and then sprayed into a spray-drying apparatus where the solvent is rapidly removed, forming solid particles of amorphous azithromycin. The term "spray-drying" is used conventionally and broadly refers to processes involving breaking up liquid mixtures into small droplets (atomization) and rapidly removing solvent from the mixture in a spray-drying apparatus where there is a strong driving force for evaporation of solvent from the droplets. Spray-drying processes and spray- drying equipment are described generally in Perry's Chemical Engineers' Handbook, pages 20-54 to 20-57 (Sixth Edition 1984). More details on spray-drying processes and equipment are reviewed by Marshall, "Atomization and Spray-Drying," 50 Chem. Eng. Prog. Monogr. Series 2 (1954), and Masters, Spray Drying Handbook (Fourth Edition 1985). The strong driving force for solvent removal is generally provided by maintaining the partial pressure of solvent in the spray-drying apparatus well below the vapor pressure of the solvent at the temperature of the drying droplets. This is accomplished by (1) maintaining

the pressure in the spray-drying apparatus at a partial vacuum (e.g., 0.01 to 0.50 atm); or (2) mixing the liquid droplets with a warm drying gas; or (3) both (1) and (2). In addition, at least a portion of the heat required for evaporation of solvent may be provided by heating the spray solution.

The solvent-bearing feed can be spray-dried under a wide variety of conditions and yet still yield amorphous azithromycin. For example, various types of nozzles can be used to atomize the spray solution, thereby introducing the spray solution into the spray-dry chamber as a collection of small droplets. Essentially any type of nozzle may be used to spray the solution as long as the droplets that are formed are sufficiently small that they dry sufficiently (due to evaporation of solvent) that they do not stick to or coat the spray-drying chamber wall. The solution can be delivered to the spray nozzle or nozzles at a wide range of temperatures and flow rates. Generally, the solution temperature can range anywhere from just above the solvent's freezing point to about 20 ⁰ C above its ambient pressure boiling point (by pressurizing the solution) and in some cases even higher. Solution flow rates to the spray nozzle can vary over a wide range depending on the type of nozzle, spray-dryer size and spray-dry conditions such as the inlet temperature and flow rate of the drying gas. Generally, the energy for evaporation of solvent from the solution in a spray-drying process comes primarily from the drying gas.

The drying gas can, in principle, be essentially any gas, but for safety reasons and to minimize undesirable oxidation of the azithromycin, an inert gas such as nitrogen, nitrogen-enriched air or argon is preferably utilized. The drying gas is typically introduced into the drying chamber at a temperature between about 60° and about 300 ⁰ C and preferably between about 80 ⁰ C and about 24O ⁰ C.

The large surface-to-volume ratio of the droplets and the large driving force for evaporation of solvent leads to rapid solidification times for the droplets. Solidification times should be less than about 20 seconds, preferably less than about 10 seconds, and more preferably less than 1 second. This rapid solidification is often critical to the particles maintaining a uniform, homogeneous amorphous material, in contrast to material comprising crystalline and amorphous azithromycin. In a preferred embodiment, the height and volume of the spray-dryer are adjusted to provide sufficient time for the droplets to dry prior to impinging on an internal surface of the spray-dryer, as described in detail in U.S. Patent No. 6,763,607.

Following solidification, the resulting solid powder of amorphous azithromycin typically stays in the spray-drying chamber for about 5 to 60 seconds, further evaporating solvent from the solid powder. The final residual solvent level of the amorphous azithromycin as it exits the dryer should be low. Generally, the solvent level of the amorphous azithromycin as it leaves the spray-drying chamber should be less than 10 wt% and preferably less than 2 wt%. Following formation, the amorphous azithromycin can be dried to remove residual solvent using a suitable drying process, such as tray drying, fluid bed drying, microwave drying, belt drying, rotary drying, vacuum drying, and other drying processes known in the art. The final residual solvent level after drying is preferably less than about 1 wt%, more preferably less than about 0.1 wt%.

The resulting spray dried amorphous azithromycin is usually in the form of small particles. The volume mean diameter of the particles may be less than about 500 μm in diameter, or less

than about 20(3 μm in diameter, or less than about 100 μm in diameter, or less than about 50 μm in diameter or less than about 25 μm in diameter.

Another useful parameter is "span," defined as

D ₅₀ where D ₅₀ is the diameter corresponding to the diameter of particles that make up 50% of the total volume of particles of equal or smaller diameter, D ₉₀ is the diameter corresponding to the diameter of particles that make up 90% of the total volume of particles of equal or smaller diameter, and D ₁₀ is the diameter corresponding to the diameter of particles that make up 10% of the total volume of particles of equal or smaller diameter. Span, sometimes referred to in the art as the Relative Span Factor or RSF, is a dimensionless parameter indicative of the uniformity of the particles size distribution. Generally, the lower the span, the more narrow the size distribution, resulting in improved flow characteristics. Preferably, the span of the particles produced by the process is less than about 3, more preferably less than about 2.5, and most preferably less than about 2.0. The size of the amorphous azithromycin particles can be determined using methods well known in the art, including processes such as by sieve analysis, microscopy, light scattering, and sedimentation. Examples of such equipment include the

Coulter Counter and the Malvern Particle Size Analyzer. See for example, Remington: The Science and Practice of Pharmacy, 20 ^th Edition (2000).

The amorphous azithromycin may also be made by spray coating. The term "spray coating" is used conventionally and refers to the coating or layering of the amorphous azithromycin onto a core. In this process, the azithromycin is dissolved in a solvent as described above. This solution is then atomized into droplets, which are sprayed onto a core. The solvent is removed from the droplets on the core, forming one or more solid layers of amorphous azithromycin on the core.

The core may be pharmaceutically inert. The core may be a solid particle or object, which does not disintegrate in the relevant body fluid. Alternatively, the core may comprise a disintegrating agent that will cause the layered particle to rapidly disintegrate in the relevant body fluid. The core is mainly intended for carrying the iayer(s) of amorphous azithromycin. Examples of core materials are non-pareil seeds, sugar beads, wax beads, glass beads, lactose, microcrystalline cellulose, polymer beads, starch, colloidal silica, etc. The core may be made by any known method, such as melt- or spray-congealing, extrusion/spheronization, granulation, spray-drying and the like. Alternatively, the core may be a dosage form such as a tablet, pill, multiparticulate or capsule. The dosage form may contain azithromycin or a different drug, and may provide either immediate or controlled release. Spray coating amorphous azithromycin onto the dosage form may be useful for a combination therapy of azithromycin and another drug.

The cores may have any shape, size, and size distribution suitable for the production of the desired layered particle. In one embodiment, the core is generally spherical with a smooth surface. In another embodiment, the cores range in size of from about 1 μm to about 3000 μm, preferably from about 10 μm to about 1000 μm, more preferably from about 50 μm to about 500 μm. To obtain a uniform final product it is generally desired to use cores with a narrow size distribution. The core may be an agglomerate, a granule, or a particle that has been layered with one or more layer(s) in accordance with

the invention. Agglomerates and granules can be made by any method conventionally used in the art, such as extrusion spheronization, rotary granulation, melt-congealing, spray-drying, vacuum drying, or spray granulation.

The core, which optionally can be layered one or more times with amorphous azithromycin, is sprayed with the atomized solution containing the azithromycin using coating equipment known in the pharmaceutical arts, such as pan coaters (e.g., Hi-Coater available from Freund Corp. of Tokyo, Japan, Accela-Cota available from Manesty of Liverpool, U.K.), fluidized bed coaters (e.g., Wϋrster coaters or top-sprayers available from Glatt Air Technologies of Ramsey, New Jersey and from Niro Pharma Systems of Bubendorf, Switzerland) and rotary granulators (e.g., CF-Granulator, available from Freund Corp). The spraying may be effected by a two fluid or three fluid nozzle while the cores are suspended in a gas. Alternatively, other nozzle types, such as a pressure nozzle, may be employed. The nozzle can be placed in the top, side walls or the bottom of the spraying chamber and the chamber can be provided with more than one nozzle.

The core particles may be suspended in the gas in any convenient manner. The core particle may be carried upwards from the bottom of the spraying chamber by a suitable stream of gas. The gas suspended core particles are then hit by one or more small droplets ejected from the nozzle. In one embodiment, the spray solution is directed in the same direction as the suspending gas.

After spraying, the solvent provided on the core particles is removed to obtain a deposit or layer of amorphous azithromycin on the core. It is preferred that the chamber the coating is effected in is also used for the removal of the solvent. In one embodiment, the cores may be moved through the spraying zone to an evaporation zone for drying the layered cores using the gas in which the cores are suspended.

The gas in which the cores are suspended may be the drying gas. During the movement upwards in the chamber and following spraying, the solvent is rapidly evaporated. Sufficient solvent is removed to prevent the particles from adhering to one another upon exiting the chamber.

Following sufficient evaporation of the solvent, the particles may be subject to a renewed treatment of spraying and evaporation, either immediately or after storage of the particles. The treatment of the layered particles continues until a predetermined particle size or weight is obtained. The determination of the desired particle size or weight can be conducted in accordance with known classification procedures. Alternately, a predetermined amount of the cores is sprayed with a predetermined amount of solution to produce the particles with the desired particle size or weight, or with the desired amount of azithromycin per mass of cores.

Preferably, the coated cores have a final size of less than about 3 mm, preferably less than about 2 mm, and more preferably less than about 1 mm. Preferably, the coated cores have a span of less than about 3, more preferably less than about 2.5, and most preferably less than about 2.0. Spray coated cores of amorphous azithromycin have the additional advantage of providing large, dense particles which are less likely to become segregated during manufacture than pure amorphous material. In addition, such coated cores also have round surfaces and narrow size distributions, which improves flow characteristics and facilitates handling.

Once the amorphous azithromycin has been formed, several processing operations can be used to facilitate incorporation of the amorphous azithromycin into a dosage form, such as tablets, capsules, suspensions, powders for suspension, creams, transdermal patches, depots, and the like. These processing operations include drying, granulation, and milling. The invention also relates to a method of treating a bacterial infection or a protozoal infection in a mammal, fish, or bird that comprises administering to said mammal, fish or bird a therapeutically effective amount of the amorphous azithromycin of the present invention.

The invention also relates to a pharmaceutical composition for the treatment of a bacterial infection or a protozoal infection in a mammal, fish, or bird that comprises a therapeutically effective amount of the amorphous azithromycin of the present invention and a pharmaceutically acceptable excipient.

The term "treatment", as used herein, unless otherwise indicated, means the treatment or prevention of a bacterial infection or protozoal infection as provided in the method of the present invention, including curing, reducing the symptoms of or slowing the progress of said infection. The terms "treat" and "treating" are defined in accord with the foregoing term "treatment".

As used herein, unless otherwise indicated, the term "bacterial infection(s)" or "protozoal infection" includes bacterial infections and protozoal infections that occur in mammals, fish, and birds as well as disorders related to bacterial infections and protozoal infections that may be treated or prevented by administering antibiotics such as the amorphous azithromycin of the present invention. Such bacterial infections and protozoal infections and disorders related to such infections include the following: pneumonia, otitis media, sinusitus, bronchitis, tonsillitis, and mastoiditis related to infection by Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, or Peptostreptococcus spp.; pharynigitis, rheumatic fever, and glomerulonephritis related to infection by Streptococcus pyogenes, Groups C and G streptococci, Clostridium diptheriae, or Actinohacillus haemolyticum; respiratory tract infections related to infection by Mycoplasma pneumoniae, Legionella pneumophila, Streptococcus pneumoniae, Haemophilus influenzae, or Chlamydia pneumoniae; uncomplicated skin and soft tissue infections, abscesses and osteomyelitis, and puerperal fever related to infection by Staphylococcus aureus, coagulase-positive staphylococci (i.e., S. epidermidis, S. hemolytlcus, etc.), Streptococcus pyogenes , Streptococcus agalactiae, Streptococcal groups C-F (minute-colony streptococci), viridans streptococci, Corynebacterium minutissimum, Clostridium spp., or Bartonella henselae; uncomplicated acute urinary tract infections related to infection by Staphylococcus saprophytics or Enterococcus spp.; urethritis and cervicitis; and sexually transmitted diseases related to infection by Chlamydia trachomatis, Haemophilus ducreyi, Treponema pallidum, Ureaplasma urealyticum, or Neiserria gonorrheae; toxin diseases related to infection by S. aureus (food poisoning and Toxic shock syndrome), or Groups A, B, and C streptococci; ulcers related to infection by Helicobacter pylori; systemic febrile syndromes related to infection by Borrelia recurrentis; Lyme disease related to infection by Borrelia burgdorferi; conjunctivitis, keratitis, and dacrocystitis related to infection by Chlamydia trachomatis, Neisseria gonorrhoeae, S. aureus, S. pneumoniae, S. pyogenes, H. influenzae, or Listeria spp.; disseminated Mycobacterium avium complex (MAC) disease related to infection by Mycobacterium avium, or Mycobacterium intracellular; gastroenteritis related to infection by

Campylobacter jejuni; intestinal protozoal related to infection by Cryptosporidium spp.; odontogenic infection related to infection by viridans streptococci; persistent cough related to infection by Bordetella pertussis; gas gangrene related to infection by Clostridium perfringens or Bacteroides spp.; and atherosclerosis related to infection by Helicobacter pylori or Chlamydia pneumoniae. Bacterial infections and protozoal infections and disorders related to such infections that may be treated or prevented in animals include the following: bovine respiratory disease related to infection by P. haem., P. multocida, Mycoplasma bovis, or Bordetella spp.; cow enteric disease related to infection by E. coli or protozoal (i.e., coccidia, Cryptosporidia, etc.); dairy cow mastitis related to infection by Staph, aureus, Strep, uberis, Strep, agalactiae, Strep, dysgalactiae, Klebsiella spp., Corynebacterium, or Enterococcus spp.; swine respiratory disease related to infection by A. pleuro., P. multocida, or Mycoplasma spp.; swine enteric disease related to infection by E. coli, Lawsonia intracellulars, Salmonella, or Serpulina hyodyisinteriae; cow footrot related to infection by Fusobacterium spp.; cow metritis related to infection by E. coli; cow hairy warts related to infection by Fusobacterium necrophorum or Bacteroides nodosus; cow pink-eye related to infection by Moraxella bovis; cow premature abortion related to infection by protozoal (i.e. neosporium); urinary tract infection in dogs and cats related to infection by £. coli; skin and soft tissue infections in dogs and cats related to infection by Staph, epidermidis, Staph, intermedius, coagulase neg. Staph, or P. multocida; and dental or mouth infections in dogs and cats related to infection by Alcaligenes spp., Bacteroides spp., Clostridium spp., Enterobacter spp., Eubacterium, Peptostreptococcus, Porphyromonas, or Prevotella. Other bacterial infections and protozoal infections and disorders related to such infections that may be treated or prevented in accord with the method of the present invention are referred to in J. P. Sanford et al., "The Sanford Guide To Antimicrobial Therapy," 26th Edition, (Antimicrobial Therapy, Inc., 1996).

Other features and embodiments of the invention will become apparent from the following examples that are given for illustration of the invention rather than for limiting its intended scope.

Example 1

Amorphous azithromycin was prepared using a solvent-based process using the following procedure. A spray solution was formed by dissolving 125 gm of azithromycin dihydrate in 1125 gm of acetone, forming a 10 wt% solution of azithromycin in acetone. The spray solution was pumped using a high-pressure pump (Bran Luebbe N-P31 ) to a spray drier (Niro type XP Portable Spray-Dryer with a Liquid-Feed Process Vessel [PSD-1]) equipped with a pressure atomizer (Spraying Systems Pressure Nozzle and Body (SK 80-16)). The PSD-1 was equipped with a 9-inch chamber extension. The spray drier was also equipped with a diffuser plate having a 1 % open area. The nozzle sat flush with the diffuser plate during operation. The spray solution was pumped to the spray drier at about 78 gm/min, with an atomization pressure of about 125 psig (9.5 atm). Drying gas (nitrogen) was delivered to the diffuser plate at an inlet temperature of about 100 ⁰ C. The evaporated solvent and wet drying gas exited the spray drier at a temperature of about 58°C. The resulting amorphous azithromycin was then stored in a vacuum desiccator at room temperature until used.

A sample of the azithromycin before (the crystalline dihydrate) and after spray drying (amorphous azithromycin) was analyzed by powder x-ray diffraction (PXRD) analysis on a Bruker

AXS D8 Advance diffractometer. A sample of the azithromycin (about 100 mg) before and after spray drying were packed in Lucite sample cups fitted with Si(511 ) plates as the bottom of the cup to give no background signal and the sample surface smoothed using a glass microscope slide to provide a consistently smooth sample surface that was level with the top of the sample cup. Samples were spun in the φ plane at a rate of 30 rpm to minimize crystal orientation effects. The X-ray source (KCu _α , λ=1.54 A) was operated at a voltage of 45 kV and a current of 40 mA. Data for each sample was collected over a period of from about 20 to about 60 minutes in continuous detector scan mode at a scan speed of about 1.2 to 1.8 seconds/step and a step size of 0.02° to 0.04° per step. Diffractograms were collected over the 2θ range of 4° to 40°. The results of this analysis before spray drying are shown in FIG. 1. This diffractogram shows the characteristic peaks for the crystalline dihydrate form of azithromycin.

FIG. 2 shows the diffractogram of the spray-dried azithromycin of Example 1. This figure shows an amorphous halo with no crystalline peaks detected within the accuracy of the analysis. These data show that the azithromycin formed by the spray drying process of Example 1 was almost completely amorphous.

Example 2

The chemical stability of the amorphous azithromycin of Example 1 was studied after storage in open dish containers for 1 and 3 weeks at different conditions as listed in Table 1. The stability samples were tested with powder X-ray diffraction and Reverse Phase High Performance Liquid

Chromatography (RP-HPLC). The RP-HPLC analysis was performed using an Agilent HP1100 system with an electrochemical detector and an ES Industries Alumina γRP-1 guard column and an ES Industries Alumina γRP-1 analytical column. The column temperature was ambient and the flow rate was 0.6 ml/min. An isocratic method was used with a mobile phase consisting of 77% 0.02 M KH ₂ PO ₄ /23% Acetonitrile (pH = 10.7).

To perform RP-HPLC testing, the powder samples were dissolved in 5 mL acetonitrile and 95 mL 77% 0.02 M KH ₂ PO ₄ /23% Acetonitrile (pH = 8.0), and the solution was injected into the HPLC column. The peaks were integrated to determine extent of degradation. Content of main degradation products is given in Table 1. Degradation products showed increased levels after three weeks at 70°C/30%RH and 70°C/75%RH whereas no increase was observed at other storage conditions. In addition, samples remained amorphous under all but 70°C/75%RH conditions. These data indicate that the spray-dried amorphous azithromycin is stable at temperatures below about 70 ⁰ C.

Table 1

Example 3

To further test the physical stability of amorphous azithromycin made using the process of Example 1 , samples were stored at 4O ⁰ C and 75% RH for five months and then removed and analyzed by PXRD as in Example 1. The results of this analysis, shown in FIG. 3, show that essentially all of the azithromycin was amorphous after storage for 5 months at these conditions.

Example 4 Samples of amorphous azithromycin formed by spray drying were analyzed by scanning electron microscopy (SEM). FIG. 4A shows an SEM image of the amorphous material at a magnification of 1000x, while FIG. 4B shows an SEM image of the amorphous material at a magnification of 650Ox. These images show that the spray dried amorphous particles produced by the spray drying process tend to be spherical, and generally in the form of collapsed spheres. As a result of this shape, amorphous azithromycin formed by spray drying has improved properties compared to crystalline azithromycin, with the amorphous particles exhibiting good flow properties and low brittleness.

As a comparison, FIG. 5 shows an SEM image of crystalline azithromycin dihydrate that had been jet milled at a magnification of 100Ox (FIG. 5A) and 650Ox (FIG. 5B). These images show the crystalline material to have an irregular shape, with many straight edges indicative of crystalline material.

Example 5

Amorphous azithromycin is prepared by the following procedure. A solution is formed consisting of about 2000 mg azithromycin and about 250 mg of the alkalizing agent trisodium phosphate (TSP) in a volatile solvent, such as acetone. The solution is then spray dried using the process described in Example 1 to form amorphous azithromycin.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.