Lyophilized formulations of rifabutin

Abstract

The invention provides solutions for lyophilization, a lyophilized formulation, and a reconstituted formulation containing rifabutin and methods of making the same.

Description

LYOPHILIZED FORMULATIONS OF RIFABUTINFIELD OF THE INVENTION

[0001] The invention generally relates to lyophilized formulations comprising rifabutin and methods of making the same.BACKGROUND OF THE INVENTION

[0002] Millions of people die each year from bacterial infections, and the numbers are increasing due to the spread of antibiotic-resistant bacterial strains. For example, according to official estimates, the annual number of deaths due to infections from antibiotic-resistant bacteria in the United States, European Union, and India alone is over 100,000, and some experts believe that official tallies are vast underestimates because the full impact of antibiotic resistance is still unknown. Unfortunately, the pipeline for development of new antibiotics in recent decades has slowed to a trickle, and many existing antibiotics are beset with problems that limit their effectiveness.

[0003] One existing antibiotic that has failed to reach its full therapeutic potential is rifabutin, sold as Mycobutin®. Although rifabutin is active against a broad spectrum of bacteria such as Acinetobacter baumannii and Staphylococcus aureus, its limited bioavailability after oral dosage makes the antibiotic difficult to deliver at doses effective for treating infections other than those reported in the Mycobutin® label.

[0004] WO 2016 / 178240 teaches freeze-dried pharmaceutical formulations of rifabutin comprising a surfactant or solubilizing agent such as Polysorbate 80, and a bulking agent such as mannitol for parenteral administration. However, the pre-lyophilized aqueous formulations taught in WO 2016 / 178240 only contained low (e.g., 6 mg / mL) concentrations of rifabutin and exhibited limited stability.

[0005] Pre-lyophilized aqueous formulations comprising an active ingredient at low concentration typically require longer lyophilization times and comparatively larger vials to contain a clinically relevant dose. This reduces the size of batches that can be prepared, becausefewer vials can be lyophilized at a time, and larger vials are less convenient to transport and store. Currently, there is no commercially-available lyophilized formulation of rifabutin.

[0006] US 2021 / 0077470 teaches liquid formulations of rifabutin comprising an acid, water, and a solvent such as dimethyl isosorbide (DMI).

[0007] Based on current studies on rifabutin and related antibiotics of the same class, it is believed that high levels of free rifabutin are necessary both for microbial killing and to prevent the development of resistance. So only with a parenteral formulation these limitations can be overcome. However, the poor solubility and wettability of rifabutin powder in aqueous media have made formulations that could be practically usable for parenteral administrations difficult. Furthermore, rifabutin in aqueous solutions has been shown to degrade easily, resulting in increased impurities due to degradation, oxidation and epimerization, which limit the shelf life of aqueous solutions. The poor solubility of rifabutin in aqueous media necessitates the use of solvents and various excipients, limits the concentration in mg / mL of rifabutin that can be achieved in the vial and, consequently, the useful amount of rifabutin that can be administered from a single vial, again making the process impractical and expensive.SUMMARY OF THE INVENTION

[0008] The invention provides methods and compositions for freeze-drying of rifabutin. The invention further provides compositions comprising rifabutin before freeze-drying and after freeze-drying.

[0009] As described herein, the present disclosure provides solutions for producing freeze-dried rifabutin. Surprisingly, the inventive solutions for producing freeze-dried rifabutin disclosed herein were able to dissolve high concentrations of rifabutin, especially in comparison to previous attempts to prepare freeze-dried formulations of rifabutin. The result is that a clinically relevant dose of rifabutin can be dissolved in less solvent than has previously been required by other attempts to prepare lyophilized formulations of rifabutin. The high concentration of rifabutin in the solutions enables the efficient preparation of lyophilized dosage forms. In preferred embodiments, a clinically relevant amount of rifabutin can be delivered to a single vialsuch as a 10-mL vial. For instance, to prepare a lyophilized dosage unit comprising 300 mg of rifabutin, only 3.0 mL of a 100 mg / mL solution of rifabutin as described herein is necessary.The 2.5 mL aliquot can be conveniently delivered to and lyophilized in a suitable 10R (i.e., 10 mL) vial.

[0010] Furthermore, lyophilized formulations prepared from the inventive solutions for producing freeze-dried rifabutin disclosed herein were found to be surprisingly stable for extended periods of time, even under accelerated storage conditions. As shown in the Examples below, the inventive lyophilized formulations maintained a purity of over 97%, even when kept at 40 °C for almost a full year (i.e., 50 weeks).

[0011] A composition of the invention comprises a solution for producing a freeze-dried rifabutin formulation. These freeze-dried formulations may be reconstituted to provide a reconstituted formulation as described in US2021 / 0077470, incorporated by reference herein.

[0012] The solution comprises a single solvent, a volatile acid, and rifabutin. The single solvent is the only solvent in the solution.

[0013] In one or more preferred embodiments, the single solvent is water. In one or more preferred embodiments, the volatile acid is acetic acid. Accordingly, in some embodiments, the solution consists essentially of water, acetic acid and rifabutin.

[0014] In embodiments of the invention containing a sufficiently high concentration of rifabutin, the solution does not include a bulking agent, or any other excipient such as for instance micelleforming agents or antioxidants or stabilizers or buffering agents or organic solvents.

[0015] Solutions of some embodiments advantageously contain high levels of rifabutin. Some embodiments of the disclosure contain greater than or equal to about 200 mg / mL.

[0016] According to some embodiments of the disclosure, a solution is prepared by dissolving rifabutin in diluted acetic acid under stirring at room temperature. The obtained solution is stable for at least 24 hours at 25°C prior to freeze drying.

[0017] According to some embodiments of the disclosure, the solutions disclosed herein are freeze-dried to provide a freeze-dried formulation. The freeze-dried formulations disclosed herein are sufficiently dried so as not to contain any solvent or solubilizing agent, which can affect the long-term stability (shelf-life) of the freeze-dried formulation. In some embodiments, the freeze-dried formulations do not contain a bulking agent or any other excipient such as for instance micelle-forming agents or antioxidants or stabilizers or buffering agents or residual organic solvents.

[0018] In fact, in some embodiments, the freeze-dried formulations consist of or consist essentially of rifabutin. Given the potential for adverse stability in the presence of oxygen, in some embodiments, the freeze-dried formulation is stored under nitrogen.

[0019] Freeze-dried formulations of this disclosure may be reconstituted to provide a reconstituted formulation. For instance, the reconstituted formulation comprises the freeze-dried formulation and an aqueous solution of 30-70 % (e.g., 50%) dimethyl isosorbide (DMI) and 1- 4% (e.g., 2%) acetic acid. As identified previously, the reconstituted solution is suitable as a concentrate for parenteral administration and / or further diluted with e.g., saline 0.9% or glucose 5% solution for intravenous administration.

[0020] Solutions disclosed herein can be freeze-dried through a primary drying cycle between - 40°C and +20°C performed in 24-48 hours. Subsequently, a secondary drying cycle is performed at 40-50°C for up to 72 hours. Preferably keeping drying times as short as possible. During these cycles, the solvent and the volatile acid are removed to acceptable residual levels to provide the stable freeze-dried formulation.

[0021] Some embodiments of the disclosure further comprise filtering and sterilizing the solution prior to the primary drying cycle. Some embodiments, further comprise portioning the sterile solution into small sterile vials before the primary drying cycle. In some embodiments, the freeze-dried formulation may be stored under nitrogen.

[0022] Additionally, some embodiments of the disclosure provide methods for reconstituting the formulation of freeze-dried rifabutin. The methods comprise adding an aqueous solution of dimethyl isosorbide and acetic acid to the freeze-dried rifabutin, using, for example, the ratios asdescribed in US2021 / 0077470, incorporated by reference herein. The reconstituted solutions have rifabutin concentrations greater than or equal to 200 mg / mL. Further, the reconstituted solutions can be diluted with e.g., saline 0.9% or glucose 5% solution for intravenous administration.

[0023] In one aspect, the present disclosure provides a solution for producing freeze-dried rifabutin, the solution comprising: a solvent, preferably a single solvent; a volatile acid; and rifabutin or a pharmaceutically acceptable salt thereof.

[0024] In some embodiments, the single solvent is water. In some embodiments, the volatile acid is acetic acid or formic acid. In some embodiments, the solution does not include a bulking agent. In some embodiments, the solution does not include a surfactant. In some embodiments, the solution is not buffered. In some embodiments, the solution consists essentially of water, acetic acid, and rifabutin.

[0025] In some embodiments, the solution comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 :1 to about 2: 1.

[0026] In one aspect, the present disclosure provides a freeze-dried formulation comprising rifabutin.

[0027] In some embodiments, the freeze-dried formulation does not include a solvent. In some embodiments, the freeze-dried formulation does not include a bulking agent. In some embodiments, the freeze-dried formulation does not include a surfactant. In some embodiments, the freeze-dried formulation consists of rifabutin. In some embodiments, the freeze-dried formulation is stored under nitrogen.

[0028] In one aspect, the present disclosure provides a reconstituted formulation comprising: the freeze-dried formulation as described herein; and an aqueous solution, preferably wherein said aqueous solution comprises dimethyl isosorbide and acetic acid.

[0029] In one aspect, the present disclosure provides a solution suitable for administration to a subject, the solution comprising the reconstituted formulation as described herein, wherein said reconstituted formulation is further diluted, preferably wherein said solution suitable for administration comprises rifabutin at a concentration of 0.6 mg / mL to about 1.2 mg / mL.

[0030] In one aspect, the present disclosure provides a method of freeze-drying rifabutin, the method comprising: dissolving rifabutin in a solvent, preferably a single solvent and a volatile acid to form a solution; performing a primary drying cycle, preferably between -40°C and +20°C for 24-48 hours; and optionally performing a secondary drying cycle, preferably at 40-50°C for up to 72 hours.

[0031] In some embodiments of the method, the solvent is water. In some embodiments of the method, the volatile acid is acetic acid. In some embodiments of the method, the acetic acid is diluted to 2% v / v. In some embodiments, the method further comprises filtering and sterilizing the solution prior to the primary drying cycle. In some embodiments, the method further comprises portioning the solution into vials. In some embodiments, the method further comprises storing the freeze-dried rifabutin under nitrogen within the vials.

[0032] In one aspect, the present disclosure provides a method of reconstituting a formulation of freeze-dried rifabutin, the method comprising adding an aqueous solution comprising a solvent and an acid to the formulation to form a reconstituted solution.

[0033] In one aspect, the present disclosure provides a method of reconstituting a formulation of freeze-dried rifabutin, the method comprising adding an aqueous solution of 50% dimethyl isosorbide and 2% acetic acid to the formulation to form a reconstituted solution.

[0034] In some embodiments, the reconstituted solution has a rifabutin concentration of greater than or equal to 200 mg / mL. In some embodiments, the reconstituted solution has a rifabutin concentration from about 50 mg / mL to about 100 mg / mL. In some embodiments, the reconstituted and diluted solution is suitable for intravenous administration.

[0035] In one aspect, the present disclosure provides a solution for administration comprising rifabutin for use as a medicament, preferably for use in a method of treating an infection caused by 4. baumannii.BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 illustrates an exemplary process of making and reconstituting a lyophilized formulation consisting of rifabutin.

[0037] FIG 2 is a plot showing the set vacuum, shelf temperature, measured vacuum, and product temperature used to lyophilize the rifabutin solutions described in Example 4. The term “Sampling” indicates the time points at which a part of the samples was removed from the freeze dryer.

[0038] FIG 3A is a plot of 18-acetyl-16-desacetyl rifabutin (identified as “14R epimer”) over time for the RBT low and RBT high formulations, prepared using each of the three secondary drying conditions described in Example 4.

[0039] FIG 3B is a plot of the rifabutin N-oxide (“N-oxide”) over time for the RBT low and RBT high formulations, prepared using each of the three secondary drying conditions described in Example 4.DETAILED DESCRIPTION OF THE INVENTION

[0040] Intravenous (IV) administration is a common, and sometimes necessary, method of administering medications. Unfortunately, some drugs are poorly soluble in water, making the IV administration of these drugs more difficult. These drugs are often solubilized for administration using different solvents, co-solvents, or specific conditions to promote solubility. Drugs may also be unstable in aqueous solution or exhibit increased sensitivity to temperature.

[0041] Freeze-drying, also referred to as lyophilization, is a technique that is widely used in the pharmaceutical industry. Under this process, a drug may be solubilized during manufacturing,and the solvent then removed. The dried product can be safely stored and shipped, and then reconstituted when needed for administration. The process improves the solubilization and reconstitution process by significantly increasing the surface area.

[0042] A typical freeze-drying process starts by dissolving an active pharmaceutical ingredient (API) in water. The solution is then sterilized by filtration and aseptically filled into vials which subsequently undergo the freeze-drying process. However, due to the poor water solubility of rifabutin, 0.19 mg / mL, a simple aqueous formulation is not possible.

[0043] Different excipients are routinely used to allow the freeze drying of drugs with poor water solubility (e.g. pH modifying agents or solubilizers such as polysorbate). However, currently there is no lyophilized product of rifabutin on the market.Definitions

[0044] The term "about" where used means especially ±10%, ±5% or ±3% (referring to the given numeric value, respectively), if not indicated otherwise. In each of the invention embodiments, "about" can be deleted.

[0045] As used herein, the term “rifabutin” is understood as an antibiotic having the structure below.(rifabutin).

[0046] Representative “pharmaceutically acceptable salts”, as used herein, include, e.g., water- soluble and water-insoluble salts, such as the acetate, amsonate (4,4-diaminostilbene-2,2- disulfonate), benzenesulfonate, benzonate, bicarbonate, bisulfate, bitartrate, borate, bromide, butyrate, calcium, calcium edetate, camsylate, carbonate, chloride, citrate, clavulariate, dihydrochloride, edetate, edisylate, estolate, esylate, fumarate, gluceptate, gluconate, glutamate, glycollylarsanilate, hexafluorophosphate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride, hydroxynaphthoate, hydroiodide, sethionate, lactate, lactobionate, laurate, magnesium, malate, maleate, mandelate, mesylate, methylbromide, methylnitrate, methyl sulfate, mucate, napsylate, nitrate, N-methylglucamine ammonium salt, 3-hydroxy-2-naphthoate, oleate, oxalate, palmitate, pamoate (l,l-methene-bis-2-hydroxy-3 -naphthoate, einbonate), pantothenate, phosphate / diphosphate, picrate, polygalacturonate, propionate, p-toluenesulfonate, salicylate, stearate, subacetate, succinate, sulfate, sulfosalicylate, suramate, tannate, tartrate, teoclate, tosylate, triethiodide, and valerate salts. In preferred embodiments, the rifabutin is present as a freebase.

[0047] A “patient” or “subject” is a mammal, e.g., a human, mouse, rat, guinea pig, dog, cat, horse, cow, pig, or non-human primate, such as a monkey, chimpanzee, baboon or rhesus.

[0048] As used herein, the term “freeze-drying” is interchangeable with the term “lyophilization”, and “freeze-dried” is interchangeable with “lyophilized”.

[0049] The term “clinically relevant dose” as used herein refers to a dose of rifabutin as described herein in an amount effective to treat a disease or disorder in a subject as described herein. The term “disorder” is used in this disclosure to mean, and is used interchangeably with, the terms disease, condition, or illness, unless otherwise indicated. In preferred embodiments, the disease or disorder is a bacterial infection, preferably a bacterial infection caused by antibiotic-resistant baumannii. The term “treating” with regard to a subject, refers to improving at least one symptom of the subject's disorder. Treating includes curing, improving, or at least partially ameliorating the disorder.

[0050] As used herein, the term “substantially pure” refers to a component, preferably a solvent (e.g., water) as described herein, wherein said solvent is at least 99.5% pure, preferably at least 99.9% pure.Solutions for Producing Freeze-Dried Rifabutin

[0051] In one aspect, the present disclosure relates to a solution for producing freeze-dried rifabutin, the solution comprising: a solvent, preferably a single solvent; a volatile acid; and rifabutin or a pharmaceutically acceptable salt thereof.

[0052] In some embodiments, the solvent is a protic solvent. As used herein, a protic solvent is a solvent comprising a labile proton (i.e., H+) and is thus capable of gaining or losing the proton to become a charged species (e.g. water can autoionize to OH' and HsO ). In preferred embodiments, the protic solvent comprises water or an alcohol (e.g., methanol, ethanol, propanol and the like). In some embodiments, the single solvent has a high freezing point (e.g., higher than -10 °C).

[0053] In some embodiments, the solvent comprises at least about 95% (v / v) water. In some embodiments, the solvent comprises at least about 96% (v / v) water. In some embodiments, the solvent comprises at least about 97% (v / v) water. In some embodiments, the solvent comprises at least about 98% (v / v) water. In some embodiments, the solvent comprises at least about 99% (v / v) water. In some embodiments, the solvent is a single solvent. As used herein, the term “single solvent” means that the single solvent is the only solvent in the solution, i.e., is not a mixed solvent or a mixture of solvents. In the most preferred embodiments, the single solvent is a substantially pure solvent, preferably substantially pure water.

[0054] Solutions of the invention preferably comprise a single solvent, a volatile acid, and rifabutin. Preferably, the single solvent is the only solvent in the solution. Stated differently, in preferred embodiments, the solutions of this disclosure do not utilize mixed solvents.

[0055] As used herein, a “volatile acid” is understood to refer to an acid with a measurable vapor pressure at about 20 °C. In preferred embodiments, a volatile acid is an acid that has a vaporpressure of at least about 0.1 kPa, preferably at least about 0.5 kPa at 20 °C and 1 atm of pressure. Preferably the volatile acid has a vapor pressure of at least about 1 kPa at 20 °C and 1 atm of pressure, more preferably of at least about 1.5 kPa at 20 °C and 1 atm of pressure. In some embodiments, the volatile acid is a weak acid (e.g., an acid with a pKafrom about 3 to about 6). In preferred embodiments, the volatile acid is a carboxylic acid.

[0056] In preferred embodiments, the volatile acid is acetic acid or formic acid. In some embodiments, the volatile acid is formic acid. In preferred embodiments, the volatile acid is acetic acid.

[0057] In preferred embodiments, the molar ratio of the volatile acid (preferably acetic acid) to rifabutin is at least about 1 : 1. In preferred embodiments, the molar ratio of the volatile acid (preferably acetic acid) to rifabutin is about 1 : 1 to about 2:1. In preferred embodiments, the molar ratio of the volatile acid (preferably acetic acid) to rifabutin is from about 1 : 1 to about 1.5: 1. In preferred embodiments, the molar ratio of the volatile acid (preferably acetic acid) to rifabutin is from about 1 : 1 to about 1.3: 1. In preferred embodiments, the molar ratio of the volatile acid (preferably acetic acid) to rifabutin is about 1 : 1.

[0058] In some embodiments the volatile acid is acetic or formic acid. In some embodiments, the solutions comprise water, acetic acid or formic acid, and rifabutin. In some embodiments, the solutions consist essentially of water, acetic acid or formic acid, and rifabutin.

[0059] In some embodiments, the solution comprises rifabutin at a concentration from about 25 mg / mL to about 500 mg / mL. In some embodiments, the solution comprises rifabutin at a concentration from about 30 mg / mL to about 300 mg / mL. In some embodiments, the solution comprises rifabutin at a concentration from about 30 mg / mL to about 200 mg / mL. In some embodiments, the solution comprises rifabutin at a concentration from about 80 mg / mL to about 160 mg / mL. In some embodiments, the solution comprises rifabutin at a concentration of about 80 mg / mL. In some embodiments, the solution comprises rifabutin at a concentration of about 160 mg / mL.

[0060] In preferred embodiments, the solution for producing freeze-dried rifabutin comprises rifabutin at a concentration from about 30 mg / mL to about 160 mg / mL.

[0061] In some embodiments, the solution for producing freeze-dried rifabutin comprises rifabutin at a concentration from about 20 mM to about 600 mM. In some embodiments, the solution comprises rifabutin at a concentration from about 29 mM to about 600 mM. In some embodiments, the solution comprises rifabutin at a concentration from about 300 mM to about 360 mM. In some embodiments, the solution comprises rifabutin at a concentration from about 35 mM to about 240 mM. In some embodiments, the solution comprises rifabutin at a concentration from about 90 mM to about 190 mM. In some embodiments, the solution comprises rifabutin at a concentration of about 90 mM. In some embodiments, the solution comprises rifabutin at a concentration of about 190 mM.

[0062] In some embodiments, the concentration of the API (i.e., rifabutin) in the solution is greater than or equal to about 200mg / mL. When freeze-dried and reconstituted, these formulations can provide dosage forms with similarly high concentrations of rifabutin.

[0063] Without being bound by theory, it is believed that the addition of the volatile acid to the solution increases the solubility of the rifabutin, but also decreases the stability of the rifabutin, e.g., over the long term. While this has been a drawback to other formulations of rifabutin, the solutions of this disclosure are expected to be quickly processed by freeze-drying, thereby eliminating the volatile acid and the solvent and eliminating the concerns regarding the stability of the rifabutin.

[0064] For the purposes of freeze-drying, the single solvent has a high freezing point. In some embodiments, the single solvent is ionizable (capable of having a pH). In a preferred embodiment, the single solvent is water.

[0065] Freeze-dried formulations can use bulking agents to supplement the active and form a suitable matrix for carrying the active. Exemplary bulking agents include mannitol, lactose, sucrose, dextran, trehalose, and glycine. Given the relatively high concentrations of rifabutin achievable with the disclosed solutions, some embodiments of the disclosure do not include a bulking agent.

[0066] In preferred embodiments, the solution does not include additional excipients such as, for instance, micelle-forming agents; antioxidants; stabilizers; buffering agents; or organic solvents.In preferred embodiments, the solution does not include a solubilizing agent or crystallization inhibitor, e.g., polyvinylpyrrolidone. In preferred embodiments, the solution does not include a surfactant, e.g., polyvinylpyrrolidone. In some embodiments, the volatile acid is a weak acid. In a preferred embodiment, the volatile acid is acetic acid. In some embodiments, the solution is not buffered to control pH. For example, a solution comprising acetic acid does not have any acetate salts added to buffer to stabilize the solution pH. It is understood that some quantity of acetate will be present as a result of the dissociation of the acid.

[0067] Accordingly, in some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) a volatile acid, preferably acetic acid.

[0068] In some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably wherein said single solvent is water; and (iii) a volatile acid, preferably acetic acid.

[0069] In some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0070] In some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably wherein said single solvent is water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0071] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) a volatile acid, preferably acetic acid. In some embodiments, the solution consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises atleast 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) a volatile acid, preferably acetic acid.

[0072] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably water; and (iii) a volatile acid, preferably acetic acid. In some embodiments, the solution consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably water; and (iii) a volatile acid, preferably acetic acid.

[0073] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) a volatile acid, preferably acetic acid; wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1. In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) a volatile acid, preferably acetic acid; wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0074] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably water; and (iii) a volatile acid, preferably acetic acid; wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1. In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a single solvent, preferably water; and (iii) a volatile acid, preferably acetic acid; wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0075] In some embodiments, the solution for producing freeze-dried rifabutin is prepared by dissolving rifabutin in water comprising the volatile acid under stirring at room temperature. Inpreferred embodiments, the solution thus obtained is stable for at least 24 hours at 25 °C prior to freeze-drying.

[0076] In some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 :1 to about 2: 1.

[0077] In some embodiments, the solution for producing freeze-dried rifabutin comprises (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0078] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 :1 to about 2: 1.

[0079] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0080] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molarratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2:1.

[0081] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0082] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0083] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0084] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 :1 to about 2: 1.

[0085] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 25 mg / mL to about 500 mg / mL; (ii) a single solvent, preferably water; and (iii) acetic acid; preferablywherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2:1.

[0086] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 :1 to about 2: 1.

[0087] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 30 mg / mL to about 200 mg / mL; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0088] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2:1.

[0089] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0090] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0091] In some embodiments, the solution for producing freeze-dried rifabutin comprises: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0092] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0093] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0094] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0095] In some embodiments, the solution for producing freeze-dried rifabutin consists essentially of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0096] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2:1.

[0097] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 29 mM to about 600 mM; (ii) a single solvent, preferably water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

[0098] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and: (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2:1.

[0099] In some embodiments, the solution for producing freeze-dried rifabutin consists of: (i) rifabutin or a pharmaceutically acceptable salt thereof at a concentration from about 35 mM to about 240 mM; (ii) a single solvent, preferably water; and: (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.Methods of Freeze-Drying Solutions For Producing Freeze-Dried Rifabutin

[0100] According to some embodiments of the disclosure, the solutions for producing freeze- dried rifabutin disclosed herein and above are freeze-dried to produce freeze-dried rifabutin.

[0101] Some methods of the disclosure are illustrated in FIG. 1. The methods begin with the solutions for producing freeze-dried rifabutin described above. As exemplified, rifabutin and dilute volatile acid (e.g., acetic acid; AcOH + water) are added to a vessel, and the rifabutin dissolved to form a solution. In some embodiments, the solution is then filtered and / or sterilized.In some embodiments, the solution is aliquoted into vials. Specifically, FIG l is a schematic of an exemplary process for preparing a lyophilized formulation comprising rifabutin as described herein and for reconstituting the lyophilized formulation to prepare a reconstituted formulation, which can optionally be diluted to prepare a solution suitable for administration to a subject. The processes are described in more detail herein. As shown in FIG 1, rifabutin powder is dissolved in a solvent comprising a volatile acid (e.g., a dilute solution of water and acetic acid) to prepare a solution for producing freeze-dried rifabutin. As shown in FIG 1, the solution can be sterilized, e.g., by sterile filtration, and aliquoted into suitable (preferably sterile) vials. The solution can then be lyophilized (preferably within the vials) to remove the solvent, (e.g., water) and the volatile acid (e.g., acetic acid) and to produce a lyophilized formulation comprising rifabutin. The lyophilized solution can then be reconstituted by addition of a suitable solution. The reconstituted solution can be used directly, or preferably can be further diluted to prepare a solution for administration, e.g., IV-administration to a subject

[0102] After being dissolved and / or filtered, sterilized, and aliquoted, the solution undergoes a lyophilization process. In some embodiments, the lyophilization process is performed in two stages. In some embodiments, during a primary drying cycle, the solution is maintained between -40°C and +20°C for 24-48 hours. Subsequently, during a secondary drying cycle, the solution is maintained at 40-50°C for up to 72 hours.

[0103] In one aspect, the present disclosure provides a method of freeze-drying a solution for producing freeze-dried rifabutin as described herein, the method comprising: (i) freezing the solution; (ii) performing a primary drying cycle; and (iii) optionally performing a secondary drying cycle. In one aspect, the present disclosure provides a method of freeze-drying a solution for producing freeze-dried rifabutin as described herein, the method comprising: (i) freezing the solution; (ii) performing a primary drying cycle from about -50 °C to about +20 °C for about 24 to about 48 hours; and (iii) optionally performing a secondary drying cycle from about +5 °C, preferably from about + 20 °C, to about +50 °C over about 1 hour to about 24 hours and preferably holding at a temperature of about +40 °C to about 50 °C for about 1 hour to about 72 hours.

[0104] In one aspect, the present disclosure provides a method of freeze-drying a solution comprising rifabutin or a pharmaceutically acceptable salt thereof as described herein, the method comprising: (i) dissolving the rifabutin or a pharmaceutically acceptable salt thereof in a solvent and a volatile acid to form a solution; (ii) freezing the solution; (iii) performing a primary drying cycle from about -50 °C to about +20 °C for about 24 to about 48 hours; and (iv) optionally performing a secondary drying cycle from about +5 °C, preferably from about + 20 °C, to about +50 °C over about 1 hour to about 24 hours and preferably holding at a temperature of about +40 °C to about 50 °C for about 1 hour to about 72 hours.

[0105] Preferably, the primary and / or secondary drying cycles are performed at a pressure below atmospheric pressure, e.g., preferably below about 100 Pa, more preferably below about 50 Pa, yet more preferably at about 10 Pa or below.

[0106] In preferred embodiments, the freeze-drying process includes the removal of most of the volatile acid, (e.g., acetic acid) used for solution preparation. Without wishing to be bound by theory, a low amount of residual volatile acid, e.g., acetic acid must be achieved in order for the freeze-dried formulation to exhibit a sufficient long-term stability (shelf-life) for storage prior to reconstitution and administration. In preferred embodiments, the freeze-drying process removes greater than or equal to about 50% of the volatile acid (e.g., acetic acid) present in the solutions described herein. In preferred embodiments, the freeze-drying process removes greater than or equal to about 60% of the volatile acid (e.g., acetic acid) present in the solutions described herein. In preferred embodiments, the freeze-drying process removes greater than or equal to about 70% of the volatile acid (e.g., acetic acid) present in the solutions described herein. In yet more preferred embodiments, the freeze-drying process removes greater than or equal to about 75% of the volatile acid (e.g., acetic acid) present in the solutions described herein. In more preferred embodiments, the freeze-drying process removes greater than or equal to about 85%, preferably greater than or equal to about 90% of the volatile acid (e.g., acetic acid) present in the solutions described herein.

[0107] In some embodiments, said freezing the solution comprises cooling the solution to a temperature from about -60 °C to about -40 °C, preferably from about -50 °C to about -40 °C, preferably for at least about 2 hours, preferably for between about 2 hours to about 6 hours.

[0108] In some embodiments, the freeze-drying process comprises a primary drying cycle, wherein the solution is maintained between about -50 °C and about +20 °C (preferably about -40 °C and about +5 °C). In some embodiments, the primary drying cycle is performed within about 24 to about 48 hours.

[0109] In some embodiments, the freeze-drying process comprises a secondary drying cycle, wherein the solution is maintained between about 40 °C to about 50°C for about 1 hour to about 72 hours. In some embodiments, said secondary drying cycle comprises increasing the temperature of the solution to about +40 °C over about 20 hours and holding the temperature at about +40 °C for about one hour. In some embodiments, said secondary drying cycle comprises increasing the temperature of the solution to about +50 °C over about 17 hours and holding the temperature at about 50 °C for about 72 hours.

[0110] In preferred embodiments, drying times are kept as short as possible.

[0111] Without wishing to be bound by theory, the solutions for producing a freeze-dried formulation of rifabutin are stable for an amount of time suitable for (e.g., sufficient for) filling the solution into vials and lyophilizing the solutions. In preferred embodiments, the solutions for producing a freeze-dried formulation of rifabutin are subjected to freeze-drying within 24 hours of preparation. Preferably, the solutions are subjected to freeze-drying within 6 hours, preferably within one hour of preparation.

[0112] In preferred embodiments, the solutions for producing a freeze-dried formulation of rifabutin are filtered and / or sterilized prior to lyophilization (e.g., prior to freezing the solutions). In preferred embodiments, the solutions (preferably sterile solutions) are portioned into sterile vials before lyophilization (e.g., prior to freezing the solutions). In preferred embodiments, the vials are 10-mL vials (e.g., 10R vials) or 6-mL vials (e.g., 6R vials).

[0113] Once freeze-dried, the rifabutin may be stored under nitrogen. If the solution was aliquoted into vials, the vials may be filled with nitrogen and then stoppered.Freeze-Dried Formulations Comprising Rifabutin

[0114] In one aspect, the present disclosure provides a freeze-dried formulation comprising rifabutin or a pharmaceutically acceptable salt thereof. In preferred embodiments, the freeze- dried formulation comprising rifabutin is prepared by freeze-drying a solution for producing freeze-dried rifabutin as described herein.

[0115] In one aspect, the present disclosure provides a freeze-dried formulation comprising rifabutin or a pharmaceutically acceptable salt thereof prepared from a solution for producing freeze-dried rifabutin as described herein.

[0116] In some embodiments of this disclosure, the freeze-dried formulations do not include any unevaporated solvents or solubilizing agents. Further, in some embodiments, the freeze-dried formulation does not use or require a bulking agent. In some embodiments, the freeze-dried formulation does not use or require a surfactant. In a preferred embodiment, the freeze-dried formulation consists of rifabutin. In another preferred embodiment, the freeze-dried formulation consists essentially of rifabutin.

[0117] In some embodiments, the freeze-dried formulations do not contain a bulking agent or any other excipient such as, for instance, micelle-forming agents or antioxidants or stabilizers or buffering agents or residual organic solvents. In some embodiments, the freeze-dried formulations do not comprise polyvinylpyrrolidone. In preferred embodiments, the solutions disclosed herein are sufficiently dried so as not to contain any solvent or solubilizing agent. In some embodiments, the freeze-dried formulations comprise less than about 1% water (w / w), preferably less than about 0.5% water (w / w), preferably less than about 0.1% water (w / w), more preferably less than 0.01% water (w / w).

[0118] In some embodiments, the freeze-dried formulations comprise less than about 2% (w / w) volatile acid (e.g., acetic acid), preferably less than about 1% (w / w) volatile acid (e.g., acetic acid), more preferably less than about 0.5% (w / w) volatile acid (e.g., acetic acid), yet more preferably less than about 0.1% (w / w) volatile acid (e.g., acetic acid), and yet more preferably less than about 0.01% (w / w) volatile acid (e.g., acetic acid).

[0119] In some embodiments, the freeze-dried formulations consist of or consist essentially of rifabutin or a pharmaceutically acceptable salt thereof.

[0120] After lyophilization the freeze-dried product is stable and can be stored, shipped, and reconstituted when needed for treatment. Specifically, as shown in the Examples below, the inventive lyophilized formulations maintained a purity of over 97%, even when kept at 40 °C for almost a full year (i.e., 50 weeks). Moreover, as shown in the Figures, the concentrations of the major degradation products of rifabutin, (e.g., rifabutin N-oxide and 18-acetyl-16-desacetyl rifabutin (“14R epimer”) remained below the threshold identified by the US Pharmacopeia (“USP”) monograph as acceptable for pharmaceutical compositions of rifabutin even when kept at 40 °C for 50 weeks.

[0121] As shown in the Examples below, stable and uniform lyophilized cakes were obtained from the solutions for producing a freeze-dried composition of rifabutin under a variety of lyophilization conditions. Specifically, stable and uniform lyophilized cakes could be obtained using various concentrations of rifabutin in the solutions for producing a freeze-dried formulation comprising rifabutin, using variously sized vials, and under various freeze-drying conditions (e.g., various conditions for secondary drying). Without wishing to be bound by theory, the Examples below suggest that the inventive solutions for producing a freeze-dried formulation comprising rifabutin can enable the preparation of stable lyophilized formulations in a wide range of doses (e.g., clinically relevant dosages) using industry- standard lyophilization equipment and conditions.Reconstituted Formulations Comprising Rifabutin

[0122] Freeze-dried formulations of this disclosure can be reconstituted to provide a reconstituted formulation, preferably suitable as a concentrate to prepare a solution for administration. Accordingly, in one aspect, the present disclosure provides a reconstituted formulation comprising a freeze-dried formulation as described herein; and an aqueous solution.

[0123] In one aspect the present disclosure provides a reconstituted formulation prepared from a freeze-dried formulation of rifabutin as described herein. In one aspect the present disclosureprovides a reconstituted formulation prepared by reconstituting a freeze-dried formulation of rifabutin as described herein.

[0124] In one aspect, the present disclosure provides a method of reconstituting a freeze-dried formulation comprising rifabutin or a pharmaceutically acceptable salt thereof as described herein, the method comprising: adding an aqueous solution to the formulation of freeze-dried rifabutin.

[0125] Some methods of the disclosure relate to the reconstitution of the freeze-dried formulations disclosed herein. Preferred methods comprise adding an aqueous solution containing a solvent and acid. In some embodiments the solvent is selected from the group consisting of PEG, propylene glycol, NMP, ethanol, DMA, transcutol HP, and dimethyl isosorbide (DMI); and the acid is selected from the group consisting of hydrochloric, methanesulfonic, phosphoric, L-tartaric, D-glucuronic, L-malic, D-gluconic, L-lactic, acetic and L-aspartic. In some embodiments the v / v water to solvent ratio is from about 1 : 1 to about 1 :2 and the molar ratio of acid to API (i.e., rifabutin) is about 1 : 1. In some embodiments the preferred solvent is selected from PEG, propylene glycol, and DMI. In some embodiments the preferred solvent is DMI. In some embodiments the preferred acid is acetic acid.

[0126] In preferred embodiments, the acid is a pharmaceutically acceptable acid. In some embodiments, the acid is a weak acid, i.e., the acid has a pKabetween about 3 and about 6. In some embodiments, the acid is selected from hydrochloric acid, methanesulfonic acid, phosphoric acid, L-tartaric acid, D-glucuronic acid, L-malic acid, D-gluconic acid, L-lactic acid, acetic acid and L-aspartic acid. In some embodiments, the acid is selected from hydrochloric acid, methanesulfonic acid, phosphoric acid, L-tartaric acid, L-lactic acid, acetic acid and L- aspartic acid. In some embodiments the preferred acid is acetic acid. In preferred embodiments, the molar ratio of the acid to rifabutin is about 1 : 1.

[0127] In preferred embodiments, the aqueous solution comprises the solvent at a concentration from about 30% (v / v) to about 70% (v / v), preferably from about 40% (v / v) to about 60% (v / v). In some embodiments, the aqueous solution comprises the solvent at a concentration of about 50% (v / v).

[0128] In some embodiments, the aqueous solution comprises the acid (preferably acetic acid) at a concentration from about 1% (v / v) to about 4% (v / v). In some embodiments, the aqueous solution comprises the acid at a concentration of about 2% (v / v).

[0129] In preferred embodiments, the reconstituted formulation comprises the freeze-dried formulation and an aqueous solution of dimethyl isosorbide at a concentration from about 30% (v / v) to about 70% (v / v), and acetic acid at a concentration from about 1% (v / v) to about 4% (v / v).

[0130] In preferred embodiments, the reconstituted formulation comprises the freeze-dried formulation and an aqueous solution of dimethyl isosorbide at a concentration of about 50% (v / v), and acetic acid at a concentration of about 2% (v / v).

[0131] In one aspect, the present disclosure provides a method of reconstituting a formulation of freeze-dried rifabutin or a pharmaceutically acceptable salt thereof as described herein, the method comprising: adding to the formulation of freeze-dried rifabutin an aqueous solution comprising dimethyl isosorbide at a concentration from about 30% to about 70% (v / v) and an acid at a concentration from about 1% to about 4% (v / v).

[0132] In some embodiments, the freeze-dried formulations described herein may be reconstituted to provide a reconstituted formulation as described in US2021 / 0077470, the disclosure of which is incorporated herein by reference.

[0133] In some embodiments, the freeze-dried rifabutin of this disclosure advantageously provides a reconstituted concentration of greater than or equal to 10 mg / mL, greater than or equal to 20 mg / mL, greater than or equal to 50 mg / mL, greater than or equal to 100 mg / mL, greater than or equal to 150 mg / mL, or greater than or equal to 200 mg / mL. In preferred embodiments, the reconstituted solutions comprise rifabutin at a concentration from about 50 mg / mL to about 100 mg / mL.Solutions for Administration Comprising Rifabutin

[0134] In some embodiments, the reconstituted solution is suitable as a concentrate to prepare a solution for administration, e.g., for parenteral administration, to a subject. In some embodiments, the reconstituted solution can be used directly for parenteral administration. In preferred embodiments, the reconstituted solution is further diluted prior to administration, e.g., prior to parenteral or intravenous administration. The solution for administration can be diluted to any desired concentration (e.g., using saline) prior to administering it to a patient.

[0135] The freeze-dried formulation readily dissolves in the DMI / AcOH aqueous solution. The reconstituted solution can be diluted in diluents suitable for pharmaceutical use, to any desired concentration. In some embodiments the reconstituted solution is diluted in sterile water, mannitol, such as 3-5% mannitol, 3% mannitol, 4% mannitol, 4.3% mannitol, and 5% mannitol, phosphate, acetate, additional tartrate, saline, such as physiological saline (0.9 %) , 1 / 2 physiological saline 0.45 %) , and 0.5 % saline, and the like. In some embodiments, the reconstituted and diluted solution is administered parenterally. In a preferred embodiment, the reconstituted and diluted solution is administered by inhalation. In another preferred embodiment, the reconstituted and diluted solution is administered intravenously.

[0136] In some embodiments, the solution for administration can comprise mannitol (e.g., 3% to 5% mannitol). In some embodiments, the solution for administration can comprise saline (e.g., about 0.4 to about 1% w / w / saline, e.g., about 0.9% w / w saline). In some embodiments, the solution for administration can comprise glucose (e.g., about 5% w / w glucose). In some embodiments, the solution for administration can comprise additional salts, e.g., phosphate, acetate, tartrate salts.

[0137] In some embodiments, the solution for administration comprises rifabutin at a concentration from about 0.1 mg / mL to about 2 mg / mL. In some embodiments, the solution for administration comprises rifabutin at a concentration from about 0.5 mg / mL to about 1.5 mg / mL. In some embodiments, the solution for administration comprises rifabutin at a concentration from about 0.6 mg / mL to about 1.2 mg / mL.

[0138] Without wishing to be bound by theory, rifabutin can be unstable after being reconstituted to form a reconstituted formulation and / or further diluted to prepare a solution for administration. Without wishing to be bound by theory, in preferred embodiments the reconstituted formulation or solution for administration (preferably the solution for administration) is administered shortly after preparation to ensure sterility of the reconstituted formulation or solution for administration (preferably the solution for administration). Accordingly, in some embodiments, the reconstituted formulation or solution for administration (preferably the solution for administration) is administered to a subject in need thereof within 24 hours, preferably within 12 hours, more preferably within six hours of preparation. In preferred embodiments, the reconstituted formulation or solution for administration (preferably the solution for administration) is administered within four hours of preparation, preferably within one hour of preparation.

[0139] In one aspect, the present disclosure provides a reconstituted formulation or solution for administration (preferably a solution for administration) as described herein for use as a medicament. In one aspect, the present disclosure provides a reconstituted formulation or solution for administration (preferably a solution for administration) as described herein for use in a method of treating a disease in a subject, e.g., a subject in need thereof. In one aspect, the present disclosure provides a method of treating a disease in a subject in need thereof, the method comprising administering to the subject an effective amount of a reconstituted formulation or solution for administration (preferably solution for administration) as described herein. In one aspect, the present disclosure provides the use of a reconstituted formulation or solution for administration (preferably a solution for administration) as described herein in the manufacture of a medicament for treating a disease in a subject. In one aspect, the present disclosure provides the use of a reconstituted formulation or solution for administration (preferably a solution for administration) as described herein for treating a disease in a subject.

[0140] In preferred embodiments, the disease is a bacterial infection, preferably a bacterial infection caused by A. baumannii. preferably wherein said A. baumannii is antibiotic-resistant baumannii.

[0141] In some embodiments, the reconstituted formulation or solution for administration (preferably the solution for administration) is suitable for parenteral administration. In another preferred embodiment, the reconstituted formulation or solution for administration (preferably the solution for administration) is suitable for intravenous administration. In some embodiments, the reconstituted formulation or solution for administration (preferably the solution for administration) is administered parenterally. In another preferred embodiment, the reconstituted formulation or solution for administration (preferably the solution for administration) is administered intravenously.Equivalents

[0142] While the present technology has been described in conjunction with the specific embodiments set forth above, many alternatives, modifications and other variations thereof will be apparent to those of ordinary skill in the art. All such alternatives, modifications and variations are intended to fall within the spirit and scope of the present invention.ExamplesExample 1 : Preparation of a Freeze-Dried Formulation Comprising Rifabutin From an 80 mg / mL Solution

[0143] 4g of rifabutin powder and approximately 30mL of an aqueous 2% (vol.) acetic acid solution were added to a beaker and the mixture stirred at room temperature until the rifabutin was completely dissolved. The solution was filled up to 50 mL with the same 2% acetic acid solution, reaching a final concentration of 80mg / mL, and sterile filtered through a 0.2pm polyethersulfone (PES) syringe filter. 2.5mL of the filtered solution were filled in 10R glass vials.

[0144] Freeze-drying of the vials was performed as describe in Table 1.Table 1 : Freeze-Drying Protocol for 80 mg / mL Solutions0145] Freeze drying resulted in a physically stable cake.Example 2: Preparation of a Freeze-Dried Formulation Comprising Rifabutin From an 160 mg / mL Solution

[0146] 8g of rifabutin powder and 16mL of an aqueous 4% (vol.) acetic solution were mixed in a beaker and stirred at room temperature until rifabutin was completely dissolved. The solution was diluted with water for infusion to a volume of 50mL, reaching a final concentration of 160mg / mL, and sterile filtered through a 0.2pm PES syringe filter. 1.25mL of the filtered solution were filled in 10R glass vials.

[0147] Freeze-drying of the vials was performed as described in Table 2.Table 2: Freeze-Drying Protocol for 160 mg / mL Solutions

[0148] Freeze drying resulted in a physically stable cake with overall good appearance. The vial containing 200mg of rifabutin could be easily reconstituted using 0.8mL of an aqueous reconstitution solution containing 50% DMI and 2% acetic acid, as described in patent US2021 / 0077470 Al. Dilution of the reconstituted solution in 0.9% saline resulted in a pH of 5.0, making it suitable for intravenous administration.

[0149] Stability of freeze-dried rifabutin was assessed after 1-month storage at 40 °C. Stability results are reported in Table 3.Table 3: Stability of Lyophilized Formulation after one month at 40 °CExample 3: Preparation of a Lyophilized Formulation Comprising Rifabutin

[0150] 3.2g of rifabutin powder and 6.4mL of an aqueous 4% (vol.) acetic acid solution were added to a beaker and the mixture stirred at room temperature until the rifabutin was completely dissolved. The solution was diluted to a total volume of 20 mL using water for infusion, reaching a final concentration of 160 mg / mL. The solution was sterile filtered through a 0.2pm polyethersulfone (PES) syringe filter. 1.25mL of the filtered solution was added to 10R glass vials.

[0151] Freeze drying of the vials was performed as described in Table 4.Table 4, Freeze-Drying Process for 160 mg / mL Rifabutin Solution*some vials were removed after 24 and 48 hours of drying

[0152] Freeze drying resulted in a physically stable cake.Example 4: Preparation and Stability of Freeze-Dried Formulations Comprising Rifabutin

[0153] In two separate beakers, 8g of rifabutin powder and 16mL of an aqueous 4% acetic solution were mixed and stirred at room temperature until the rifabutin was completely dissolved. The solutions thus obtained were diluted with water for infusion to a volume of 50mL or lOOmL respectively, to reach a final concentration of 160mg / mL rifabutin (“RBT high”) or of 80mg / mL rifabutin (“RBT low”). The solutions were sterile filtered through a 0.2 pm PES syringe filter and 1.25 mL or 2.5 mL of the filtered solution, respectively, were filled into 10R glass vials so that the total content of rifabutin in the vials was 200 mg. The solutions were then lyophilized according to the conditions given below in Table 5 and in FIG 2. Specifically, vials for both the RBT high and RBT low solutions were divided into three groups, and subjected to different secondary drying conditions. The first group was subjected to secondary drying for 24 hours, the second group was subjected to secondary drying for 48 hours, and the third group was subjected to secondary drying for 72 hours as shown below in Table 5.Table 5: Freeze-Drying Process for 80 mg / mL and 160 mg / mL Rifabutin Solutions

[0154] Stability of the freeze dried rifabutin was assessed after 50 weeks storage at 40°C.Stability results are reported in Table 6.Table 6: Stability of 80 and 160 mg / mL Lyophilized Formulations after 50 Weeks at 40 °C

[0155] FIG 3A is a plot of the 14R epimer of rifabutin over time for the RBT low and RBT high formulations, prepared using each of the three secondary drying conditions above. FIG 3B is aplot of the rifabutin N-oxide over time for the RBT low and RBT high formulations, prepared using each of the three secondary drying conditions above.INCORPORATION BY REFERENCE

[0156] References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes.EQUIVALENTS

[0157] Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification, and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof.

Claims

CLAIMSWhat is claimed is:

1. A solution for producing freeze-dried rifabutin, the solution comprising: a solvent, preferably a single solvent; a volatile acid; and rifabutin or a pharmaceutically acceptable salt thereof.

2. The solution of claim 1, wherein the single solvent is water.

3. The solution of claim 1 or claim 2, wherein the volatile acid is acetic acid or formic acid.

4. The solution of any of the preceding claims, wherein the solution does not include a bulking agent.

5. The solution of any of the preceding claims, wherein the solution does not include a surfactant.

6. The solution of any of the preceding claims, wherein the solution is not buffered.

7. The solution of any of the preceding claims, wherein the solution consists essentially of water, acetic acid, and rifabutin.

8. The solution of any of the preceding claims, wherein the solution comprises (i) rifabutin or a pharmaceutically acceptable salt thereof; (ii) a solvent, wherein said solvent comprises at least 95% (v / v) water, preferably at least 99% (v / v) water; and (iii) acetic acid; preferably wherein a molar ratio of acetic acid to rifabutin or a pharmaceutically acceptable salt thereof is from about 1 : 1 to about 2: 1.

9. A freeze-dried formulation comprising rifabutin.

10. The freeze-dried formulation of claim 9, wherein the formulation does not include a solvent.

11. The freeze-dried formulation of claim 9 or 10, wherein the formulation does not include a bulking agent.

12. The freeze-dried formulation of any of claims 9-11, wherein the formulation does not include a surfactant.

13. The freeze-dried formulation of any of claims 9-12, consisting of rifabutin.

14. The freeze-dried formulation of any of claims 9-13, wherein the formulation is stored under nitrogen.

15. A reconstituted formulation comprising: the freeze-dried formulation of any of claims 9- 14; and an aqueous solution, preferably wherein said aqueous solution comprises dimethyl isosorbide and acetic acid.

16. A solution suitable for administration to a subject, the solution comprising the reconstituted formulation of claim 15, wherein said reconstituted formulation is further diluted, preferably wherein said solution suitable for administration comprises rifabutin at a concentration of 0.6 mg / mL to about 1.2 mg / mL.

17. A method of freeze-drying rifabutin, the method comprising: dissolving rifabutin in a solvent, preferably a single solvent and a volatile acid to form a solution; performing a primary drying cycle, preferably between -40°C and +20°C for 24-48 hours; and optionally performing a secondary drying cycle, preferably at 40-50°C for up to 72 hours.

18. The method of claim 17, wherein the solvent is water.

19. The method of claim 17 or 18, wherein the volatile acid is acetic acid.

20. The method of any of claims 17 to 19, wherein the acetic acid is diluted to 2% v / v.

21. The method of any of claims 17 to 20, further comprising filtering and sterilizing the solution prior to the primary drying cycle.

22. The method of any of claims 17 to 21, further comprising portioning the solution into vials.

23. The method of claim 22, further comprising storing the freeze-dried rifabutin under nitrogen within the vials.

24. A method of reconstituting a formulation of freeze-dried rifabutin, the method comprising adding an aqueous solution comprising a solvent and an acid to the formulation to form a reconstituted solution.

25. A method of reconstituting a formulation of freeze-dried rifabutin, the method comprising adding an aqueous solution of 50% dimethyl isosorbide and 2% acetic acid to the formulation to form a reconstituted solution.

26. The method of claim 25, wherein the reconstituted solution has a rifabutin concentration of greater than or equal to 200 mg / mL.

27. The method of claim 25, wherein the reconstituted solution has a rifabutin concentration from about 50 mg / mL to about 100 mg / mL.

28. The method of claim 25, wherein the reconstituted and diluted solution is suitable for intravenous administration.

29. A solution for administration comprising rifabutin for use as a medicament, preferably for use in a method of treating an infection caused by A. baumannii.

Images