WO2009095634A1

WO2009095634A1 - Amorphous forms of retapamulin

Info

Publication number: WO2009095634A1
Application number: PCT/GB2008/004305
Authority: WO
Inventors: Maja Devcic; Masa Rajic Linaric; Helena Ceric
Original assignee: Pliva Hrvatska D.O.O.; Bucks, Teresa, Anne
Priority date: 2008-02-01
Filing date: 2008-12-30
Publication date: 2009-08-06

Abstract

The present invention is directed to amorphous forms of retapamulin, methods of making the amorphous forms, pharmaceutical formulations containing the same, therapeutic uses thereof and methods of treatment employing the same.

Description

AMORPHOUS FORMS OF RETAPAMULIN

Field of Invention

[0001] The present invention is directed to amorphous forms of retapamulin, methods of making the amorphous forms, pharmaceutical formulations containing the same, therapeutic uses thereof and methods of treatment employing the same.

Background Art

[0002] Polymorphism, the occurrence of different crystal forms, is a property of some molecules and molecular complexes. A single molecule can give rise to a variety of crystalline forms as well as different amorphous forms, all having distinct structures and physical properties like melting point, X-ray powder diffraction pattern, infrared absorption fingerprint, and solid state NMR spectrum.

[0003] Polymorphic forms as referred to herein can include crystalline and amorphous forms as well as solvate and hydrate forms, which can be further characterized as follows: (i) crystalline forms have different arrangements and/or conformations of the molecules in the crystal lattice, (ii) amorphous forms consist of disordered arrangements of molecules that do not possess a distinguishable crystal lattice and (iii) solvates are crystal forms containing either stoichiometric or non-stoichiometric amounts of a solvent If the incorporated solvent is water, the solvate is commonly known as a hydrate. When a pharmaceutical substance exists in polymorphic forms, it is said to exhibit polymorphism.

[0004] These properties can have a direct effect on the ability to process and/or manufacture a pharmaceutical substance or product, as well as on the product's stability, dissolution, and bioavailability. When formulating solid dosage forms composed of drugs and excipients, the pharmaceutical scientist must deal with those factors that influence manufacturability, stability, bioavailability, and therapeutic performance. Although in the majority of cases drug entities enter the development stage in crystalline form, there are situations where they exist in a partially or fully amorphous form. In some cases it can simply be impossible to crystallize the material by available crystallization techniques. Processing {e.g., milling, lyophilization, granulating, drying) might introduce a certain level of amorphous structure to an otherwise highly crystalline material. The amorphous state can also be introduced deliberately to enhance the biopharmaceutical properties of the product.

[0005] Additionally many excipients can be in a fully or partially amorphous state (e.g., microcrystalline cellulose, starch, polyvinylpyrrolidone)), and other excipients can be purposefully rendered amorphous to enhance functionality (e.g., spray-dried lactose).

[0006] Since molecules in the amorphous state exist in a higher energy state than in the crystalline state, it is expected that properties requiring certain levels of molecular mobility (e.g., permeability) would be influenced by the presence of amorphous structure.

[0007] The three-dimensional long-range order that normally exists in a crystalline material does not exist in the amorphous state, and the position of molecules relative to one another is more random. Typically amorphous solids exhibit short-range order over a few molecular dimensions and have physical properties quite different from those of their corresponding crystalline states.

[0008] One polymorphic form can give rise to thermal behavior different from that of another form, thus polymorphism can affect the quality, safety, and efficacy of a pharmaceutical product. Thermal properties and behavior of polymorphs can be measured in the laboratory by thermal analytical methods such as capillary melting point, thermogravimetric analysis ("TGA") and differential scanning calorimetry ("DSC"), which can be used to distinguish polymorphic forms.

[0009] Thermal analytical methods have been widely used to characterize amorphous pharmaceutical systems, and several comprehensive reviews of their use have been published. Most often thermal analytical techniques are simply used to determine the glass transition temperature of an amorphous drug or of an excipient.

[0010] Thermal analytical methods can obviously be used to determine fundamental thermodynamic properties (e.g., heat capacity, enthalpy changes) of the amorphous state. The heat capacity of an amorphous material is always higher than that of its crystalline state and a change in the rate of heat capacity change with temperature defines its calorimetric glass transition temperature.

[0011] As there is no long-range three-dimensional molecular order associated with amorphous states, the diffraction of electromagnetic radiation (e.g., X-rays) is irregular compared to that of crystalline states. Diffraction techniques are perhaps the most definitive method of detecting and quantifying molecular order or absence of order (in case of an amorphous state) in any system. X-ray powder diffraction can also be used to investigate the existence of polymorphs. For amorphous forms, X-ray powder diffraction can normally only be used to identify their existence over the crystalline form but usually not for identification between several different amorphous forms.

[0012] Retapamulin is the international non-proprietary name (INN) given for the compound (3aS',4i?,55',65^r _:>8i?₅9i?_:,9ai?,10i-)-6-ethenyl-5-hydroxy-4_:>6,9₅10-tetramethyl-l- oxodecahydro-3a,9-propanocyclopenta[8]annulen-8-yl{[(li_-535'_J5<S)-8-methyl-8- azabicyclo[3.2.1]octan-3-yl]sulfanyl}acetate, WHO Drug Information, Vol. 19, No. 1, 2005. It has the following structure, of Formula I:

Formula I

[0013] It is approved at the EMEA as ALTARGO™ for use in short-term treatment of superficial skin infections, and is also approved by the FDA under the trade name ALTABAX. It can be used to treat impetigo (a skin infection causing crusting scabs), and small infected lacerations, abrasions and wounds that have been sutured.

[0014] It is sold as a 1% strength ointment made from white soft paraffin and presented in either in an aluminium tube or in an aluminium sachet. Upon analysis of the product ALTARGO we have found that the retapamulin is in the form of crystalline solid, suspended within the ointment vehicle, and is not dissolved within the ointment.

[0015] European patent no. EPOl 02896 IBl describes pleuromutilin derivatives of general formula (IA) or (IB):

processes for their preparation, pharmaceutical compositions containing them and to their use in medical therapy, particularly antibacterial therapy. One of preferred compounds disclosed in the application is mutilin 14-(exo-8-methyl-8-azabicyclo[3.2.1]oct-3- ylsulfanyl)-acetate of following formula (C):

[0016] Two examples of processes for the preparation of this compound are described in

Examples 41 and 46 of EP01028961B1. The title compound is isolated by evaporation after column chromatography and characterised by NMR and MS.

[0017] Published international patent application no. WO 2005/023257 provides an additional process for preparing pleuromutilin derivatives of formula (IA) or (IB) using a thiol in a phase transfer catalysis system. According to the application the phase transfer catalysis process provides a more efficient synthesis, with improved yield, and avoids a chromatography step to purify the reaction product. The disclosed process comprises reacting a compound of formula (IIA) or (IIB):

with a thiol compound of formula (111):

R2A.(CH₂)_m-SH

in a phase transfer catalysis system. The application also discloses crystalline retapamulin, characterized by FTIR, DSC (125-127 ⁰C) and XRPD, further hereinafter referred to as crystalline retapamulin form I.

[0018] The application further discloses pharmaceutically acceptable salts of mutilin 14-

(exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsuIfanyl)-acetate. Specifically described are crystalline hydrosuccinate, hydrofumarate, hydromaleate and tosylate salts of mutilin 14- (exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsulfanyl)-acetate.

[0019] Published international patent application no. WO 2006/092334 discloses another polymorphic form of mutilin 14-(exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsulfany)- acetate referred to as "the polymorph". The polymorph is characterized by FTIR, DSC (142-145 ⁰C)₅ TGA and XRPD.

[0020] Amorphous forms are characterized as having a higher energy state than their crystalline counterparts, and as being thermodynamically metastable. In addition they offer several physical properties that have possible advantages such as a higher degree of viscoelasticity (which can aid processability) and a larger degree of molecular mobility (which can translate through to a different behavior, such as increased dissolution and solubility). However, amorphous forms can spontaneously change to the crystalline state at any point during any process step that introduces energy into the amorphous solid, such as during formulation and storage, particularly at elevated temperatures. Therefore this must be taken into account during development, production and storage of products containing amorphous material.

[0021] In topical formulations the physical chemistry of the active ingredient is important as subtle changes will affect the way in which the active ingredient is absorbed into the skin and its clinical effectiveness. Physical properties such as solubility in the excipients, surface area and particle size will in particular affect the clinical effectiveness of the ointment.

[0022] The present invention is directed to an amorphous form of retapamulin. The amorphous form of retapamulin is advantageous due to better solubility than the crystalline form and for its favorable properties for manufacturing of desired pharmaceutical formulation. In particular, we have found that the amorphous form is soluble within paraffin, which is typically the main component of an ointment. This has particular advantages in improving the feel of the ointment when being applied by the user to the affected area of skin, by being less abrasive, and in addition possibly increasing the absorption across the dermis.

Brief Summary of the Invention

[0023] We have found a stable amorphous form of retapamulin. In addition we have found that the amorphous retapamulin can also exist as at least three different amorphous forms.

[0024] We have surprisingly found that retapamulin can form several different amorphous forms with different physical properties.

[0025] Therefore, we present as a feature of the invention:

[0026] Amorphous retapamulin as characterized by X-ray powder diffraction pattern substantially as shown in FIG. 1. [0027] Amorphous form I of retapamulin characterized as having no crystallization event, as measured by differential scanning calorimetry, at any point up to 240 "C.

[0028] Amorphous form I of retapamulin, characterized as having a glass transition event, as measured by differential scanning calorimetry, of 44 °C ± 2 °C.

[0029] Amorphous form I of retapamulin, characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 2.

[0030] Amorphous form II of retapamulin, characterized as having a glass transition event, as measured by differential scanning calorimetry, at 59 ⁰C ± 2 °C.

[0031] Amorphous form II of retapamulin, characterized as having a crystallization event, as measured by differential scanning calorimetry, at 94 °C ± 2 ⁰C.

[0032] Amorphous form II of retapamulin characterized as having a maximum peak of crystallization, as measured by differential scanning calorimetry, of 108 °C ± 2 ⁰C.

[0033] Amorphous form II of retapamulin characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 3.

[0034] Amorphous form III of retapamulin characterized as having a glass transition event, as measured by differential scanning calorimetry, at 55 ⁰C ± 2 °C.

[0035] Amorphous form III of retapamulin characterized as having a crystallization event, as measured by differential scanning calorimetry, at 81 ⁰C ± 2 °C.

[0036] Amorphous form III of retapamulin characterized as having a maximum peak of crystallization, as measured by differential scanning calorimetry, of 85 ⁰C ± 2 °C.

[0037] Amorphous form III of retapamulin characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 4. [0038] As defined herein the crystallization event is the temperature, as measured by

DSC, at which conversion of the amorphous form into a non-amorphous form occurs. The higher the temperature at which the crystallisation event occurs then the greater is the thermal stability of the amorphous form. The greater the thermal stability of the amorphous form then it can be predicted that the amorphous form is less likely to undergo a rearrangement into a crystalline form during a formulation process and during the storage conditions of the formulation. As defined herein a maximum peak of crystallization is the temperature reached within the crystallization event at which the highest heat flow rate is achieved, as measure by DSC.

[0039] As defined herein the glass transition event is the temperature as measured by

DSC, at which the physical properties of amorphous materials begin to change from the solid phase (glassy state) to a liquid like state. A material's glass transition temperature is the temperature below which molecules have low relative mobility. Glass transition temperature is usually applicable to wholly or partially amorphous phases such as glasses and plastics.

[0040] The present invention also provides a method of making amorphous form I of retapamulin the method comprising: (a) suspending retapamulin in water, (b) heating the suspension to 50 ⁰C (c) adding a 1 M aqueous solution of NaOH into the heated suspension of retapamulin and (d) filtering the precipitate yielding retapamulin in an amorphous form I with corresponding XRPD and DSC, as shown in FIGS. 1 and 2, respectively.

[0041] The present invention also provides a method of making amorphous form II of retapamulin the method comprising: (a) melting of retapamulin at around 130 °C and (b) quenching of melted retapamulin.

[0042] The present invention also provides a method of making amorphous form II of retapamulin the method comprising spray drying of an acetone or ethanol solution of retapamulin. [0043] The present invention also provides a method of making amorphous form III of retapamulin, the method comprising grinding of retapamulin in a mill for about 2 hours.

[0044] Retapamulin is a bacterial protein synthesis inhibitor and ribosome binding agent and is thus useful in the treatment of bacterial skin infections.

[0045] The present invention also provides a pharmaceutical formulation comprising: (a) a therapeutically effective amount of an amorphous retapamulin, according to the invention, and (b) a pharmaceutically acceptable excipient.

[0046] The pharmaceutical formulation, according to the invention, can be formulated for administration by any route, for example oral, topical or parenteral. The formulation can, for example, be made up in the form of tablets, capsules, powders, granules, lozenges, creams, ointments, gels, syrups, sprays or liquid preparations, for example solutions or suspensions, which can be formulated for oral use or in sterile form, for parenteral administration by injection or infusion. The preferred route for administration of the formulation, according to the invention, is topical.

[0047] The pharmaceutical formulation, according to the invention, intended for topical administration can for example, be in the form of gel, ointment, cream, lotion, eye ointment, eye drops, ear drops, nose drops, nasal spray, impregnated dressing, and aerosol. The pharmaceutical formulation, according to the invention is preferably in the form of an ointment. The formulation can contain pharmaceutically acceptable excipients such as additives (for example; preservatives, solvents to assist drug penetration, and emollients in ointments and creams) and carriers (for example; cream or ointment bases, ethanol or oleyl alcohol for lotions and aqueous bases for sprays).

[0048] The ointment base for use in the formulation can be any of the commonly known and commercially available ointments. It is known in the art that the specific ointment base to be used in pharmaceutical formulation is one that will provide for optimum drug delivery, and preferably, will provide for other desired characteristics as well, i.e., emolliency. As with other carriers or vehicles, an ointment base should be inert, stable, nonirritating and nonsensitizing. Generally, the ointment base can be grouped in four classes: oleaginous bases; emulsifiable bases; emulsion bases; and water-soluble bases. See, e.g., Remington: The Science and Practice of Pharmacy, 19th Ed. (Easton, Pa.: Mack Publishing Co., pp. 1301-1306 (1985). Oleaginous ointment bases include, for example, vegetable oils, fats obtained from animals, semisolid hydrocarbons obtained from petroleum and the like. Examples of oleaginous ointment bases include white ointment, yellow ointment, cetyl esters wax, paraffin, petrolatum, white petrolatum, white wax, yellow wax and the like and mixtures thereof.

[0049] Emulsifiable ointment bases, also known as absorbent ointment bases, contain little or no water and include, for example, hydroxystearin sulfate, anhydrous lanolin, hydrophilic petrolatum and the like and mixtures thereof. Emulsion ointment bases are either water-in-oil (W/O) emulsions, e.g. hydrophilic petrolatum, or oil-in-water (O/W) emulsions, and can include, for example, cetyl alcohol, lanolin, glyceryl monostearate, stearic acid and the like and mixtures thereof. Useful water-soluble ointment bases can be those prepared from glycol ethers such as, for example, polyethylene glycols of varying molecular weight, polysorbates and the like and mixtures thereof.

[0050] Quenching is an action of rapid cooling known in chemistry and metallurgy to be useful for preventing of low-temperature processes such as phase transformations from occurring during production process. It only provides a narrow window of time in which the reaction is both thermodynamically favourable and kinetically accessible. It can reduce crystallinity and thereby increase amorphousness in a system or increase toughness of both alloys and plastics. Extremely rapid cooling can prevent the formation of all crystal structure, resulting in amorphous material. As used herein, the above described meaning of "quenching" is intended to mean cooling by exposing melted material to room temperature and to a cooling rate achievable by said action without the need for employing any additional means of cooling such as (fan, liquid N₂). However, accelerated cooling by means such as by the use of accelerated cooling is within the meaning of quenching.

[0051] As used herein, a "pharmaceutical formulation" refers to a medium useful for administering retapamulin, to a subject in need thereof. In addition to retapamulin, such formulations of the present invention can contain one or more pharmaceutically acceptable excipients. "Pharmaceutically acceptable" refers to those compounds, materials, and/or compositions which are, within the scope of sound medical judgment, suitable for contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other possible complications commensurate with a reasonable benefit/risk ratio.

[0052] It is known in the art that a wide variety of pharmaceutically acceptable excipients can be used with the present invention including those listed in the Handbook of Pharmaceutical Excipients, Pharmaceutical Press 4th Ed. (2003), and Remington: The Science and Practice of Pharmacy, Lippincott Williams & Wilkins, 21st ed. (2005), which are incorporated herein by reference in their entirety.

[0053] As used herein, the term "therapeutically effective amount" means an amount of amorphous retapamulin, according to the present invention, which is capable of preventing, ameliorating or eliminating a disease state for which administration of retapamulin is indicated.

[0054] The present invention further provides use of amorphous retapamulin in therapy.

Amorphous retapamulin of the present invention, can be used in treatment of a disease state prevented, ameliorated or eliminated by the administration of bacterial protein synthesis inhibitor and ribosome binding agent. The present invention provides amorphous retapamulin, according to the present invention, for use in treating bacterial skin infections and more specifically, the present invention provides amorphous retapamulin, according to the present invention, for use in treating impetigo.

[0055] The present invention further provides use of amorphous retapamulin, for the manufacture of a medicament for the treatment of a disease state prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and ribosome binding agent. More specifically, the present invention provides amorphous retapamulin for use in the manufacture of a medicament for the treatment of bacterial skin infections.

[0056] The present invention also provides a method of treating a disease state prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent, in a patient in need of such treatment, wherein the method comprises, administering to the patient a therapeutically effective amount of amorphous retapamulin, according to the invention. More specifically, the present invention provides a method of treating bacterial skin infections in a patient in need of such treatment, wherein the method comprises administering to the patient a therapeutically effective amount of amorphous retapamulin, according to the invention.

Brief Description of the Drawings

[0057] FIG. 1. depicts an XRPD of amorphous retapamulin.

[0058] FIG. 2. depicts a DSC thermogram of amorphous form I of retapamulin.

[0059] FIG. 3. depicts a DSC thermogram of amorphous form II of retapamulin.

[0060] FIG. 4. depicts a DSC thermogram of amorphous form III of retapamulin.

Detailed Description of the Invention

[0061] The present invention is directed to amorphous retapamulin. The present invention is also directed to pharmaceutical formulations thereof; processes to prepare the stable form and the pharmaceutical formulations and methods of using the formulations.

[0062] Retapamulin, (3aS,4R,5S,6S,8R,9R,9aR, 10i?)~6-ethenyl-5-hydroxy-4,6,9, 10- tetramethyl-l-oxodecahydro-3a,9-propanocyclopenta[8]annulen-8-yl{[(li?,3i',55)-8- methyl-8-azabicyclo[3.2.1]octan-3-yl]sulfanyl}acetate, is a bacterial protein synthesis inhibitor and ribosome binding agent, useful in the treatment of bacterial skin infections.

[0063] In some embodiments of the present invention, amorphous forms of retapamulin can be characterized by their crystallization point measured by differential scanning calorimetry (DSC). As defined herein the crystallization point is the temperature, as measured by DSC, at which conversion of an amorphous form into a non amorphous form occurs. The higher the crystallisation point then the greater is the thermal stability of the amorphous form. The greater the thermal stability of the amorphous form the less likely it is to undergo a rearrangement into a crystalline form during a formulation process and during the storage conditions of the formulation.

[0064] In some embodiments of the present invention, amorphous forms of retapamulin can be characterized by their glass transition point measured by differential scanning calorimetry. As defined herein the glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids. A material's glass transition temperature is the temperature below which molecules have low relative mobility. Glass transition temperature is usually applicable to fully or partially amorphous phases such as glasses and plastics.

[0065] In some embodiments of the present invention amorphous retapamulin is characterized by X-ray powder diffraction pattern substantially as shown in FIG. 1.

[0066] In some embodiments amorphous form I of retapamulin is characterized as having a glass transition event as measured by differential scanning calorimetry, at 44 °C ± 2 ⁰C. In some embodiments amorphous form I of retapamulin is characterized as having no crystallization event, as measured by differential scanning calorimetry at any point up to 240°C. hi further embodiments amorphous form I of retapamulin is characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 2.

[0067] In some embodiments amorphous form II of retapamulin is characterized as having a glass transition event, as measured by differential scanning calorimetry, at 59 °C ± 2 °C. In some embodiments, amorphous form II of retapamulin is characterized as having a crystallization event, as measured by differential scanning calorimetry, at 94 °C ± 2 ⁰C. In some embodiments, amorphous form II of retapamulin is characterized as having a maximum peak of crystallization, as measured by differential scanning calorimetry, of 108 °C ± 2 ⁰C.

[0068] In further embodiment's amorphous form II of retapamulin is characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 3..

[0069] In some embodiments of the present invention, amorphous form III of retapamulin is characterized as having a glass transition event, as measured by differential scanning calorimetry, at 55 °C ± 2°C. In some embodiments amorphous form III of retapamulin is characterized as having a crystallization event, as measured by differential scanning calorimetry, at 81 ⁰C ± 2°C. Also in some embodiments of the present invention, amorphous form III of retapamulin can be characterized as having a maximum peak of crystallization, as measured by differential scanning calorimetry, of 85 ⁰C ± 2 ⁰C.

[0070] In further embodiment's amorphous form III of retapamulin characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 4.

[0071] In some embodiments the present invention also provides a method of making amorphous form I of retapamulin the method comprising: (a) suspending retapamulin in water, (b) heating the suspension to 50 °C (c) adding a 1 M aqueous solution of NaOH into the heated suspension of retapamulin and (d) filtering the precipitate.

[0072] In some embodiments the present invention also provides a method of making amorphous form II of retapamulin the method comprising: (a) melting of retapamulin at around 130 °C and (b) quenching of melted retapamulin.

[0073] In some embodiments the present invention also provides a method of making amorphous form II of retapamulin the method comprising spray drying of an acetone or ethanol solution of retapamulin.

[0074] In some embodiments the present invention also provides a method of making amorphous form III of retapamulin the method comprising grinding of retapamulin in a mill for about 2 hours.

[0075] In a further embodiment, the present invention is directed to a pharmaceutical formulation comprising: a therapeutically effective amount of an amorphous retapamulin; according to the invention, and one or more pharmaceutically acceptable excipients.

[0076] A further embodiment of the present invention is directed to a pharmaceutical formulation comprising amorphous retapamulin, wherein the amorphous retapamulin is substantially free of its acid addition salts and in some embodiments, wherein the therapeutically effective amount of amorphous retapamulin is selected from the group consisting of: amorphous retapamulin form I, amorphous retapamulin form II, amorphous retapamulin form III and combinations thereof.

[0077] In some embodiments, the formulation is in the form intended for topical administration such as gel, ointment or cream.

[0078] In some embodiments, the formulation is ointment.

[0079] In some embodiments the present invention is directed to use of amorphous retapamulin, in therapy of a disease prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent.

[0080] In some embodiments the present invention is directed to amorphous retapamulin, for use in therapy of a disease prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent.

[0081] In some embodiments the present invention is directed to use of amorphous retapamulin, according to the present invention, for the manufacture of a medicament for the treatment of a disease state prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent. [0082] In some embodiments the present invention is directed to a method of treating a disease prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and ribosome binding agent, in a subject in need thereof, the method comprising administering to the subject the pharmaceutical formulation of the present invention. In further embodiments the present invention is directed to a method of treating bacterial skin infections in a subject in need thereof, the method comprising administering to the subject the pharmaceutical formulation of the present invention. In a further embodiment, the present invention is directed to a method of treating a bacterial skin infection, wherein the bacterial skin infection is impetigo.

[0083] The X-ray powder diffraction analysis was performed by the experimental methods detailed in Table 1, where XRPD analysis was carried out on Philips X'Pert PRO diffractometer using CuKαl radiation and the amorphous forms of retapamulin were subjected to thermal analysis by the experimental procedure and condition listed in Table 2.

Table 1. X-ray powder diffraction (XRPD) experimental conditions

Experimental DSC:

Table 2. Experimental conditions for DSC analysis.

[0084] The following examples are for the purpose of illustration of the invention only and are not intended in any way to limit the scope of the present invention. It will thus be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be falling within the scope of the invention.

EXAMPLES

Example 1

[0085] Retapamulin fumarate (222 mg; 0.35 mmol) is suspended in water (18 mL) and heated at 50 °C. A solution of 1 M NaOH (0.8 mL; 0.80 mmol) in water (2.22 mL) is added into the suspension, the precipitate is filtered, yielding retapamulin in an amorphous form I with corresponding DSC, as shown in FIG 2.

Example 2 [0086] Amorphous form II of retapamulin is prepared by melting 300 mg of retapamulin crystalline form I at about 130 ⁰C and quenching it. The corresponding DSC is shown in FIG. 3.

Example 3

[0087] Amorphous form II of retapamulin can also be prepared by spray drying of retapamulin crystalline form I from ethanol, at an inlet temperature of about 100 ⁰C.

Example 4

Amorphous form II of retapamulin can also be prepared by spray drying of retapamulin crystalline form I from acetone, at an inlet temperature of about 80 °C.

Example 5

[0088] 300 mg of amorphous form III of retapamulin is prepared by grinding retapamulin crystalline form I in a ball mill FRITSCH Pulversette 7 at 800 rpm (volume of pan around 40 ml with 3 balls) for 2 hours. The corresponding DSC is shown in FIG. 4.

Claims

CLAIMS:

1. Amorphous retapamulin.

2. The amorphous retapamulin of claim 1, characterized as having an X-ray Powder Diffraction Pattern, substantially as shown in FIG. 1.

3. Amorphous form I of retapamulin characterized as having no crystallization event, as measured by differential scanning calorimetry, at any point up to 240 °C.

4. The amorphous form I of retapamulin of claim 3, characterized as having a glass transition event, as measured by differential scanning calorimetry, at 44°C ± 2 ⁰C.

5. The amorphous form I of retapamulin of claim 3, characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 2.

6. Amorphous form II of retapamulin characterized as having a glass transition event as measured by differential scanning calorimetry, at 59 °C ± 2 ⁰C.

7. The amorphous form II of retapamulin of claim 6, characterized as having a crystallization event, as measured by differential scanning calorimetry, at 94 °C ± 2°C.

8. The amorphous form II of retapamulin of claim 6, characterized as having a maximum peak of crystallization as measured by differential scanning calorimetry, of 108 °C ± 2 °C.

9. The amorphous form II of retapamulin of claim 6, characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 3.

10. Amorphous form III of retapamulin, characterized as having a glass transition event, as measured by differential scanning calorimetry, at 55 °C ± 2⁰C.

11. Amorphous form III of retapamulin of claim 10, characterized, as having a crystallization event as measured by differential scanning calorimetry, at 81 ⁰C ± 2°C.

12. The amorphous form III of retapamulin of claim 10, characterized as having a maximum peak of crystallization as measured by differential scanning calorimetry, of 85 °C ± 2 ⁰C.

13. The amorphous form III of retapamulin of claim 10, characterized as having a differential scanning calorimetry thermogram substantially as shown in FIG. 4.

14. A method of making amorphous form I of retapamulin comprising: (a) suspending retapamulin in water, (b) heating the suspension to 50 °C, (c) adding a 1 M aqueous solution of NaOH into the heated suspension of retapamulin and (d) filtering the precipitate.

15. A method of making amorphous form II of retapamulin the method comprising: (a) melting of retapamulin at around 130 ⁰C and (b) quenching of melted retapamulin.

16. A method of making amorphous form II of retapamulin by spray drying an acetone or ethanol solution of retapamulin.

17. A method of making amorphous form III of retapamulin the method comprising grinding of retapamulin in a ball mill for about 2 hours.

18. A pharmaceutical formulation comprising; (a) a therapeutically effective amount of an amorphous retapamulin and (b) one or more pharmaceutically acceptable excipients.

19. The pharmaceutical formulation of claim 18, wherein the amorphous retapamulin is substantially free of its acid addition salts.

20. The pharmaceutical formulation of claim 18, wherein the therapeutically effective amount of amorphous retapamulin is selected from the group consisting of: amorphous retapamulin form I, amorphous retapamulin form II, amorphous retapamulin form III and combinations thereof.

21. The pharmaceutical formulation of claim 18, wherein the formulation is topical.

22. The pharmaceutical formulation of claim 18, wherein the formulation is an ointment.

23. Use of amorphous retapamulin in therapy of a disease prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent.

24. Use of amorphous retapamulin in the manufacture of a medicament for the treatment of a disease state prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent.

25. A method of treating a disease prevented, ameliorated or eliminated by the administration of a bacterial protein synthesis inhibitor and a ribosome binding agent, in a subject in need thereof, the method comprising administering to the subject the pharmaceutical formulation of claim 18.

26. The method of claim 25 directed to treating bacterial skin infections in a subject in need thereof.

27. The method of claim 26, wherein the bacterial skin infection is impetigo.