Antibiotic combination therapy

Abstract

The present invention provides antibiotic combination therapies for treating Acinetobacter baumannii infection in a subject. These combination therapies comprise rifudine and a second antibiotic such as colistin and cefdinir.

Description

[0001] Related applications

[0002] This case is a divisional application of the invention patent application filed on August 3, 2020, with application number 202080077930.0 and invention title "Antibiotic Combination Therapy". Technical Field

[0003] This invention generally relates to rifabutin combination therapy for the treatment of Acinetobacter baumannii infection. Background Technology

[0004] The emergence of multidrug-resistant (MDR) or extensively drug-resistant (XDR) bacterial strains over the past few decades has made bacterial infections a growing public health problem. One such bacterium posing a significant threat to health is *Acinetobacter baumannii*, which can cause pneumonia, meningitis, and infections of the blood, urinary tract, and skin. Because *Acinetobacter baumannii* cells can survive for extended periods on artificial surfaces, the bacterium easily spreads in hospital settings, and most *Acinetobacter baumannii* infections are hospital-acquired. For example, many soldiers in the Middle East contract *Acinetobacter baumannii* while receiving treatment for injuries sustained during combat, and multidrug-resistant strains of this bacterium represent a serious complication in the recovery process of wounded soldiers.

[0005] Treating Acinetobacter baumannii infections is challenging. Through the use of transposon elements, Acinetobacter baumannii strains have developed resistance to several different classes of antibiotics, including aminoglycosides, aminocyclic alcohols, tetracyclines, chloramphenicol, and carbapenems. Polymyxins, such as colistin, are often used as a last resort due to their severe side effects, but some Acinetobacter baumannii strains are also resistant to colistin (Zubair et al., 2015). Therefore, existing tools for treating and preventing diseases caused by this bacterium are insufficient for many patients. Significant efforts have been made to find solutions for treating these hospital-acquired pathogens, one of which is combination therapy (Levin et al., 1999; Wood et al., 2003). Combinations of two antibiotics have shown different effects on each other, and in many cases, the effect is synergistic or enhancing, but in some cases, antagonistic effects have been observed (Montero et al., 2004; Tripodi et al., 2007). Rifampicin (an antibiotic belonging to the rifamycin class, like rifabutin) targets the bacterial DNA-dependent RNA polymerase B subunit (rpoB) and is frequently used in combination with other antibiotics. Rifampicin has been shown to have synergistic effects with colistin against Acinetobacter baumannii; however, the outcome of this combination depends on the MIC of rifampicin (Giannouli et al., 2012). Specifically, no synergistic effect of rifampicin with colistin has been observed in Acinetobacter baumannii isolates, where the elevated rifampicin MIC is due to mutations in the rpoB target gene. Summary of the Invention

[0006] This invention provides combination therapies for treating Acinetobacter baumannii infections, comprising rifabutin and a second antibiotic, such as a polymyxin (e.g., colistin, polymyxin B, polymyxin B nonapeptide; polymyxin analogs exemplified by MRX-8), other cationic antimicrobial peptides (e.g., SPR741; chimeric peptide mimic antibiotics exemplified by POL7306; octapeptin cyclic peptide), or cefdil. This invention is based on the discovery that rifabutin works synergistically with certain other antibiotics to inhibit Acinetobacter baumannii cell growth. The combination of antibiotics has shown a synergistic effect on a wide range of Acinetobacter baumannii strains. This synergistic effect significantly increases the susceptibility of Acinetobacter baumannii cells to rifabutin and colistin, with some strains showing a more than 500-fold increase in sensitivity to the antibiotic when used in combination with other antibiotics compared to when the antibiotic is used alone. Furthermore, and unexpectedly, the combination of rifabutin and colistin works synergistically to inhibit the growth of strains resistant to both antibiotics when administered alone, thus making these strains susceptible to combination therapy, even though the elevated MIC of rifabutin and rifampin is due to mutations in the rpoB gene. This observation contrasts sharply with results observed in the case of the rifampin and colistin combination, where mutated strains remain resistant to the combination. Therefore, this invention unlocks the therapeutic potential of antibiotics in their previously ineffective context and provides an effective therapy for treating severe Acinetobacter baumannii infections.

[0007] On one hand, the present invention provides a method for treating Acinetobacter baumannii infection in a subject by administering rifabutin and a second antibiotic to the subject infected with Acinetobacter baumannii.

[0008] The second antibiotic can be a polymyxin (e.g., colistin, polymyxin B, polymyxin B nonapeptide) or cefdil.

[0009] The subject may have been infected with a strain of Acinetobacter baumannii resistant to one or more antibiotics. This strain may be resistant to one or more of the following: aminocyclohexol, aminoglycosides, β-lactams, β-lactamase inhibitors, carbapenems, cephalosporins, polymyxins, quinolones, rifamycin, sulfonamides, minocycline, eravacycline, sulbactam, and tetracyclines. This strain may be resistant to one or more of the following: amikacin, trimethoprim-sulfamethoxazole, cefepime, cefdil, ceftazidime, chloramphenicol, ciprofloxacin, colistin, polymyxin B, doripenem, gentamicin, imipenem, levofloxacin, meropenem, penicillin, piperacillin, rifabutin, rifampin, tazobactam, and tigecycline.

[0010] Each antibiotic can be administered via a separate route of administration. Two or more of these antibiotics can be administered via the same route of administration. Each antibiotic can be administered independently via intravenous, oral, parenteral, subcutaneous, inhalation, injection, and / or infusion.

[0011] Each antibiotic may be administered as a single compound. Two or more of these antibiotics may be administered as a single compound. These antibiotics may be administered according to the same dosing regimen, or two or more antibiotics may be administered according to different dosing regimens. The dosing regimen may include one or more of the following: dose, frequency of dosing, or intervals between doses.

[0012] The subject can be a person. The subject can be a child, newborn, infant, toddler, child, adolescent, young adult, adult, or elderly subject. The subject can be in emergency care, intensive care, neonatal intensive care, pediatric intensive care, coronary care, cardiothoracic care, surgical intensive care, medical intensive care, long-term intensive care, operating room, ambulance, field hospital, or off-site environment.

[0013] This method may include providing one or more antibiotics in addition to the first two antibiotics (e.g., rifabutin and colistin or cefdil). The one or more additional antibiotics may be aminocyclohexol, aminoglycoside, β-lactam, β-lactamase inhibitor, carbapenem, cephalosporin, polymyxin, quinolone, rifamycin, sulfonamides, minocycline, ilavacycline, sulbactam, and tetracycline. The one or more additional antibiotics may be amikacin, trimethoprim-sulfamethoxazole, cefepime, cefdil, ceftazidime, chloramphenicol, ciprofloxacin, colistin, doripenem, gentamicin, imipenem, levofloxacin, meropenem, penicillin, piperacillin, polymyxin B, rifabutin, rifampin, tazobactam, and tigecycline.

[0014] In another aspect, the present invention provides a combination therapy comprising a therapeutically effective amount of rifabutin and a second antibiotic to treat a subject with Acinetobacter baumannii infection. The second antibiotic may be a polymyxin (e.g., colistin, polymyxin B, polymyxin B nonapeptide) or cefdil.

[0015] The subject may be infected with Acinetobacter baumannii strains that are resistant to one or more antibiotics, such as any of the antibiotics mentioned above.

[0016] Each antibiotic can be administered via a separate route of administration. Two or more of these antibiotics can be administered via the same route of administration. Each antibiotic can be administered independently via intravenous, oral, parenteral, subcutaneous, inhalation, injection, and / or infusion.

[0017] Each antibiotic may be administered as a single compound. Two or more of these antibiotics may be administered as a single compound. These antibiotics may be administered according to the same dosing regimen, or two or more antibiotics may be administered according to different dosing regimens. The dosing regimen may include one or more of the following: dose, frequency of dosing, or intervals between doses.

[0018] The subject can be a person or a group of people, such as any of those mentioned above.

[0019] This combination therapy may include one or more additional antibiotics, such as any of the antibiotics described above, that provide a therapeutically effective amount.

[0020] In another aspect, the present invention provides the use of a combination comprising rifabutin and a second antibiotic for the preparation of one or more medicaments for treating Acinetobacter baumannii infection in a subject. The second antibiotic may be colistin or cefdil.

[0021] In embodiments of this use, the subject may be infected with Acinetobacter baumannii strains resistant to one or more antibiotics, such as any of the antibiotics described above.

[0022] In embodiments of this use, each antibiotic is administered via a separate route of administration. In embodiments of this use, two or more of these antibiotics are administered via the same route of administration. In embodiments of this use, each antibiotic is administered independently via intravenous, oral, parenteral, subcutaneous, inhalation, injection, and / or infusion.

[0023] In embodiments of this use, each antibiotic is administered as a separate formulation. In embodiments of this use, two or more of these antibiotics are administered as a single formulation. In embodiments of this use, these antibiotics are administered according to the same dosing schedule. In embodiments of this use, two or more of these antibiotics are administered according to different dosing schedules. The dosing schedule may include one or more of the following: dose, frequency of dose, or intervals between doses.

[0024] In embodiments of this use, the subject may be a person or a member of a class of people, such as any of those described above.

[0025] In embodiments of this use, the combination comprises any one of the antibiotics described above, or one or more other antibiotics. Attached Figure Description

[0026] Figure 1 This is an image of a 96-well plate chessboard containing Acinetobacter baumannii cells cultured with various concentrations of rifabutin and colistin.

[0027] Figure 2 This is an image of a 96-well plate chessboard containing Acinetobacter baumannii cells cultured with various concentrations of rifabutin and cefdil. Detailed Implementation

[0028] This invention provides combination therapies for treating Acinetobacter baumannii infections in subjects. These combination therapies are based on the discovery that rifabutin works synergistically with antibiotics such as colistin and cefdil to inhibit Acinetobacter baumannii cell growth. Therefore, in the treatment of Acinetobacter baumannii infections, rifabutin in combination with colistin or cefdil is more effective than either of these antibiotics alone. Furthermore, and unexpectedly, the combination of rifabutin and colistin is effective even against Acinetobacter baumannii strains that have become susceptible to treatment when administered in combination, even against strains resistant to either antibiotic when administered alone.

[0029] Combination therapy

[0030] The combination therapy of the present invention comprises two antibiotics that work synergistically to inhibit the growth of Acinetobacter baumannii cells. The synergistic effect between antibiotics such as rifabutin and colistin can be determined by any suitable method. One method comprises determining the minimum inhibitory concentration (MIC) of each antibiotic, both alone and in combination, and calculating the fractional inhibitory concentration index (FICI) as follows:

[0031]

[0032] The pair of antibiotics is characterized by whether they act synergistically, based on the following criteria: synergistic effect (FICI ≤ 0.5); unrelated effect (FICI > 0.50 and ≤ 4); antagonistic effect (FICI > 4). The determination of synergistic effects of antibiotics based on FICI is described, for example, in: Jenkins, SG and Schuetz, AN, Current Concepts in Laboratory Testing to Guide Antimicrobial Therapy. Mayo Clin. Proc. 87, 290-308 (2012), the contents of which are incorporated herein by reference.

[0033] The combination therapies of the present invention include rifabutin as one of the antibiotics. These combination therapies contain a second antibiotic that acts synergistically with rifabutin. This second antibiotic may be a polymyxin such as colistin or a cephalosporin such as cefdil. Colistin may be provided in the form of colistimethate sodium or colistin sulfate. These combination therapies may contain additional antibiotics; for example, they may contain 3, 4, 5, or more different antibiotics. Each antibiotic may independently be an aminocyclol, aminoglycoside, β-lactam, β-lactamase inhibitor, carbapenem, cephalosporin, polymyxin, quinolone, rifamycin, sulfonamide, minocycline, iravacycline, sulbactam, or tetracycline. Each antibiotic can be, independently, amikacin, trimethoprim-sulfamethoxazole, cefepime, cefdil, ceftazidime, chloramphenicol, ciprofloxacin, colistin, doripenem, gentamicin, imipenem, levofloxacin, meropenem, penicillin, piperacillin, polymyxin B, rifabutin, rifampin, tazobactam, or tigecycline.

[0034] Rifabutin is a deep reddish-purple powder with the molecular formula C. 46 H 62 NO 11 It has a molecular weight of 847.02 and the following structure:

[0035]

[0036] Rifabutin possesses broad-spectrum antimicrobial activity. Compared to rifampin, rifabutin exhibits significantly higher activity against MAC, Mycobacterium tuberculosis, and Mycobacterium leprae. Rifabutin is also active against most atypical mycobacteria, including Mycobacterium kansasii; however, it is relatively resistant to Mycobacterium chelonae. Rifabutin is also active against Staphylococcus aureus, Group A Streptococcus, Neisseria gonorrhoeae, Neisseria meningitidis, Haemophilus influenzae, Haemophilus ducreyi, Campylobacter jejuni, Helicobacter pylori, Chlamydia trachomatis, Toxoplasma gondii, and Acinetobacter baumannii.

[0037] Each antibiotic may be administered via any suitable route of administration. For example, and without limitation, each antibiotic may be administered independently via intravenous, oral, parenteral, subcutaneous, inhalation, injection, and / or infusion.

[0038] One or more antibiotics in these combination therapies may be administered relative to the same dosing regimen. One or more antibiotics may be administered according to different dosing regimens. Dosing regimens may include dose, schedule, or administration, or both. A dose may be described as an absolute amount of the drug (e.g., mg) or as a relative amount of the drug to the subject (e.g., mg / kg). A schedule of administration may be described as the intervals between doses. For example, and not limited to, the intervals between doses may be approximately one hour, approximately two hours, approximately three hours, approximately four hours, approximately six hours, approximately eight hours, approximately twelve hours, approximately twenty-four hours, approximately thirty-six hours, approximately forty-eight hours, approximately three days, approximately four days, approximately five days, approximately six days, approximately seven days, or longer.

[0039] Mixtures

[0040] One or more of these antibiotics may be provided as a single formulation. Each formulation may be prepared for delivery via a specific route of administration, such as intravenous, oral, parenteral, subcutaneous, by inhalation, by injection, and / or by infusion.

[0041] These antibiotics may be provided in the form of pharmaceutically acceptable salts, such as non-toxic acid addition salts, which are salts of amino groups formed using inorganic acids such as, but not limited to, hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid, and perchloric acid, or using organic acids such as, but not limited to, acetic acid, maleic acid, tartaric acid, citric acid, succinic acid, methanesulfonic acid, glucuronic acid, malic acid, gluconic acid, lactic acid, aspartic acid, or malonic acid.

[0042] This formulation can be administered by injection, infusion, implantation (intravenous, intramuscular, subcutaneous, etc.), or by inhalation in a dosage form, formulation, or via a suitable delivery device or implant containing conventional, non-toxic, pharmaceutically acceptable carriers, solvents, diluents, and adjuvants. Formulations and formulations of such compositions are well known to those skilled in the art of pharmaceutical formulations.

[0043] Preparations intended for parenteral use may be provided in unit dosage forms (e.g., in single-dose ampoules and vials), in vials containing several doses and in which suitable preservatives may be added (see below), in pre-filled syringes, or in pre-filled IV bags.

[0044] The pharmaceutical compositions described herein may be in a form suitable for aseptic injection.

[0045] The formulation may contain a solution containing rifabutin. A rifabutin solution and a method for preparing a rifabutin solution are described in co-owned, co-pending U.S. Application No. 62 / 902,019, the contents of which are incorporated herein by reference.

[0046] Depending on the patient's needs and clinical symptoms, intravenous administration of the composition may be preferred over oral administration because it allows for rapid introduction of the antibiotic into the systemic circulation, provides full bioavailability, allows for better control of pharmacokinetic parameters that drive pharmacological efficacy, and avoids issues of stability and absorption in the gastrointestinal tract.

[0047] The typical dose of rifabutin is able to achieve rifabutin C max A dose >2 mg / L but <50 mg / L and with an AUC of 10 mg / h / L or <200 mg / h / L at the plasma or local level.

[0048] The formulation can be prepared for parenteral administration, such as by injection or infusion. This injection or infusion can be subcutaneous or intravenous.

[0049] Treatment of Acinetobacter baumannii infection

[0050] The combination therapy of this invention can be used to treat Acinetobacter baumannii infection in a subject. The subject can be a human being. The subject can be a child, newborn, infant, toddler, child, adolescent, young adult, youth, adult, or elderly subject. The subject can be in emergency care, intensive care, neonatal intensive care, pediatric intensive care, coronary artery disease monitoring, cardiothoracic monitoring, surgical intensive care, medical intensive care, long-term intensive care, operating room, ambulance, field hospital, or off-site environment.

[0051] The subject may have an antibiotic-resistant Acinetobacter baumannii infection. For example, and not limited to, Acinetobacter baumannii infection can be resistant to one or more of the following: aminocyclohexol, aminoglycoside, β-lactam, β-lactamase inhibitors, carbapenems, cephalosporins, polymyxins, quinolones, rifamycin, sulfonamides, tetracyclines, amikacin, trimethoprim-sulfamethoxazole, cefepime, cefdil, ceftazidime, chloramphenicol, ciprofloxacin, colistin, domperidone, gentamicin, imipenem, levofloxacin, meropenem, penicillin, piperacillin, rifabutin, rifampin, tazobactam, and tigecycline. Acinetobacter baumannii infection can be resistant to rifabutin, colistin, or both. Acinetobacter baumannii infection can be resistant to rifabutin, cefdil, or both.

[0052] The antibiotics in this combination therapy can be administered simultaneously or sequentially. Sequential or alternating administration can involve exclusively providing each antibiotic for a specific duration. Sequential administration can include overlapping time periods during which the subject is provided with both an IV formulation containing rifabutin and a formulation containing another therapeutic agent. The exclusive time periods and overlapping time periods can be independently 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 1 week, or 2 weeks.

[0053] Example

[0054] Overview

[0055] The goal of this study was to identify standard of care (SoC) antibiotics that synergize with rifabutin against Acinetobacter baumannii. Synergistic effects were assessed using checkerboard minimum inhibitor concentrations (MICs) against multiple Acinetobacter baumannii clinical isolates. First, the LAC-4 strain was tested to identify synergistic effects of rifabutin with colistin and cefdil. When tested against a cohort of strains, rifabutin / cefdil synergy was observed in 100% of the strains, with a ≥4-fold reduction in the MIC of cefdil. A robust synergistic effect of rifabutin / colistin was observed in 100% of the strains, independent of the initial resistance level to either rifabutin or colistin. When combined with colistin, rifabutin showed higher activity than rifampin because, as described in the literature, synergistic effects with rifampin depend on the initial resistance level to rifampin and the presence of the rpoB mutation. Surprisingly, the rifabutin / colistin combination was active against strains resistant to rifabutin (including isolates with the rpoB mutation) and / or strains resistant to colistin, indicating that the combination overcomes both resistances.

[0056] In summary, rifabutin has the ability to enhance the antibacterial activity of cefdil and colistin against Acinetobacter baumannii strains.

[0057] Antibacterial agents

[0058] BV-015-3219-001-02 (Rifabutin (batch number 17008MR89D)) was manufactured by Olon SpA, and a 10 g / L stock solution was prepared in DMSO. Stock solutions of rifampin (Sigma R3501) and cefidil (Synnovator SYNNAAX397783) were prepared in DMSO at a concentration of 10 mg / mL. Stock solutions of colistin sulfate (Sigma C4461), meropenem (Sigma M2578), cefotaxime (Acros 45495), tobramycin (Sigma T1783), ilacycline (MedChemExpress HY-16980A), minocycline (Sigma M9511), and SPR741 (Spero Therapeutics, FullReg P0271508-1) were prepared in water at a concentration of 10 mg / mL. Finally, a stock solution of ciprofloxacin (Sigma 17850) was prepared in 0.1N NaOH at a concentration of 10 mg / mL. The stock solutions were stored at -20°C until use.

[0059] bacterial strains

[0060] The Acinetobacter baumannii clinical isolates used in this study were obtained from the BioVersys strain collection. These strains were stored at -80°C in 20% (v / v) glycerol stock cultures.

[0061] Antimicrobial susceptibility and synergistic effect test

[0062] The synergistic effect of rifabutin with SoC antibiotics was tested using a broth microdilution checkerboard method. The checkerboard method was performed according to CLSI parameters for the MIC5 of microdilution in broth. RPMI was prepared according to CLSI guidelines using CA-MHB, iron-depleted CA-MHB (ID-CA-MHB), or RPMI supplemented with 10% FCS medium. Rifabutin was serially diluted along the x-axis and the combined antibiotics along the y-axis. This setup allowed for the combination of rifabutin and another antibiotic at increasing concentrations to provide a final classification of the combination based on the fractional inhibitory concentration (FICI) index as follows: synergistic (FICI ≤ 0.5); unrelated (FICI > 0.50 and ≤ 4); antagonistic (FICI > 4). FICI was calculated as follows:

[0063]

[0064] Therefore, synergy is defined when the MIC of the antibiotics tested in the combination is reduced by at least 4 times compared to the MIC of the antibiotics tested alone.

[0065] Example 1

[0066] Rifabutin, in synergistic effect with colistin and cefdil, targets Acinetobacter baumannii strain LAC-4. A checkerboard assay was used to test the synergistic effect of rifabutin with SoC antibiotics against Acinetobacter baumannii strain LAC-4. A checkerboard assay was performed against cefdil in CA-MHB or ID-CA-MHB. Results are shown in Table 1.

[0067] Table 1.

[0068]

[0069]

[0070] * Testing cefoperazone in ID-CA-MHB

[0071] Of the eight SoC antibiotics tested, only colistin and cefidil showed synergistic effects with rifabutin, while the other six did not.

[0072] Figure 1This is an image of a 96-well plate checkerboard containing Acinetobacter baumannii cells cultured with various concentrations of rifabutin and colistin. Wells used to determine the MIC of individual antibiotics are circled in green, wells with combined MICs are circled in blue, and wells used to calculate FICI are circled in red.

[0073] Figure 2 This is an image of a 96-well plate checkerboard containing Acinetobacter baumannii cells cultured with various concentrations of rifabutin and cefidil. Wells used to determine the MIC of individual antibiotics are circled in green, wells with combined MICs are circled in blue, and wells used to calculate FICI are circled in red.

[0074] Example 2

[0075] Rifabutin reduced the MIC of cefdil against the tested Acinetobacter baumannii strain by ≥4-fold.

[0076] To further investigate the synergistic effect of rifabutin and cefdil against Acinetobacter baumannii, a checkerboard assay was performed on 16 MDR clinical isolates of Acinetobacter baumannii, including 5 isolates with mutations in the rpoB gene that exhibited elevated MICs (≥32 mg / L) against rifabutin (and rifampin). To describe the level of synergistic effect in more detail, Table 2 presents the MICs of rifabutin and cefdil alone and in combination, as well as the fold changes associated with these MICs, for each strain. As expected, cefdil in combination with rifabutin had little or no effect on the activity of rifabutin against isolates with mutations in the rpoB gene. Unexpectedly, rifabutin reduced the MIC of cefdil against all tested Acinetobacter baumannii strains by at least 4-fold.

[0077] Table 2.

[0078]

[0079]

[0080] **Identify synergies in ID-CA-MHB.

[0081] In summary, this data demonstrates that combining rifabutin with cefdil can improve treatment outcomes for Acinetobacter baumannii infection.

[0082] Example 3

[0083] Rifabutin showed a strong synergistic effect with colistin on 100% of the tested Acinetobacter baumannii strains.

[0084] The same procedure was performed for the synergistic effect of rifabutin and colistin against Acinetobacter baumannii. A checkerboard assay was performed on a panel of 16 MDR clinical isolates of Acinetobacter baumannii, including 5 isolates with mutations in the rpoB gene exhibiting elevated MICs (>32 mg / L) against rifabutin (and rifampin) and 5 colistin-resistant strains (MIC>4 mg / L). The synergistic effect was tested in CA-MHB medium, an approved medium for testing colistin MICs. The results are shown in Table 3. Unexpectedly, colistin in combination with rifabutin significantly enhanced the activity of rifabutin against isolates with mutations in the rpoB gene. In these cases, the rifabutin MIC changed >32-fold in combination with colistin.

[0085] Table 3.

[0086]

[0087]

[0088] A synergistic effect of rifabutin and colistin was observed in 100% of the strains tested in CA-MHB. Significantly, as illustrated in CA-MHB, the synergistic effect was independent of the original resistance level of either rifabutin or colistin, where the colistin MIC was reduced by at least 16-fold in colistin-resistant strains, making all but one colistin-sensitive. These results suggest that combining rifabutin with colistin has the potential to overcome rifabutin and colistin resistance in clinical isolates of Acinetobacter baumannii.

[0089] These observations suggest that colistin acts as a cell permeability activator, synergistically with rifabutin. To assess whether colistin acts solely as a permeability activator, the synergistic effect of rifabutin combined with the colistin derivative SPR741, which retains permeability activity but loses antibacterial activity, was tested. The results are shown in Table 4.

[0090] Table 4.

[0091]

[0092] A synergistic effect between rifabutin and SPR741 was observed in 88% of the strains. However, for most strains, this synergistic effect was less pronounced compared to the synergistic effect observed with the colistin and rifabutin combination, where the MIC remained in the range of 0.125–2 mg / L. Furthermore, the SPR741 concentration required to achieve a synergistic effect with rifabutin was at least 8 times higher than that of colistin. These results suggest that the intrinsic antibacterial activity of colistin is essential for a strong synergistic effect with rifabutin.

[0093] Example 4

[0094] A comparison of the synergistic effects of rifampin and colistin combination against Acinetobacter baumannii isolates.

[0095] As a comparative example, the synergistic effect of rifampin and colistin was determined for a group of Acinetobacter baumannii strains. The results are shown in Table 5.

[0096] Table 5.

[0097]

[0098] Synergistic effects were observed on 88% of the strains. Regarding rifabutin, as demonstrated by its synergistic effect against most colistin-resistant strains, the synergistic effect was independent of colistin resistance levels. However, unlike rifabutin, and as expected from the literature, the synergistic effect of rifampin / colistin on isolates with mutations in the rpoB gene was weak. For these isolates, the MIC of the rifampin combination remained high (≥32 mg / L).

[0099] Overall, it was demonstrated that colistin can enhance the activity of rifabutin against Acinetobacter baumannii strains with elevated MICs to rifabutin, colistin, or both, and vice versa. However, unexpectedly, unlike rifampin, rifabutin in combination with colistin showed activity against isolates with mutations in the rpoB gene that were originally resistant to these antibiotics.

[0100] By incorporating via reference

[0101] Throughout this disclosure, references and citations have been made to other sources, such as patents, patent applications, patent publications, magazines, books, papers, and web content. All such sources are hereby incorporated herein by reference in their entirety for all purposes.

[0102] equivalent

[0103] Based on the entire contents of this document, including references to scientific and patent literature cited herein, various modifications to the invention and many other embodiments thereof will become apparent to those skilled in the art, in addition to those shown and described herein. The subject matter of this document contains important information, examples, and guidance that may be adapted to practice the invention in its various embodiments and equivalents.

Claims

1. A method for treating a subject with Acinetobacter baumannii infection, the method comprising administering to the subject infected with Acinetobacter baumannii rifabutin and a second antibiotic selected from the group consisting of colistin and cefiderocol.

2. The method of claim 1, wherein the subject is infected with a strain of Acinetobacter baumannii that is resistant to rifabutin.

3. The method of claim 1, wherein the subject is infected with an Acinetobacter baumannii strain resistant to the second antibiotic.

4. The method according to claim 1, wherein the second antibiotic is colistin.

5. The method according to claim 1, wherein the second antibiotic is cefdil.

6. The method of claim 1, wherein the rifabutin is administered intravenously.

7. The method of claim 1, wherein the rifabutin is administered by inhalation.

8. The method of claim 1, wherein the rifabutin and the second antibiotic are provided as a single compound.

9. The method of claim 1, wherein the rifabutin and the second antibiotic are provided separately.

10. The method of claim 1, wherein the Acinetobacter baumannii comprises the rpoB mutation.

11. A combination therapy comprising rifabutin and a second antibiotic selected from the group consisting of colistin and cefdil, wherein the combination therapy comprises a therapeutically effective amount of rifabutin and the second antibiotic to treat a subject with Acinetobacter baumannii infection.

12. The combination therapy of claim 11, wherein the subject is infected with a strain of Acinetobacter baumannii that is resistant to rifabutin.

13. The combination therapy of claim 11, wherein the subject is infected with a strain of Acinetobacter baumannii that is resistant to the second antibiotic.

14. The combination therapy of claim 11, wherein the second antibiotic is colistin.

15. The combination therapy of claim 11, wherein the second antibiotic is cefdil.

16. The combination therapy of claim 11, wherein the rifabutin is administered intravenously.

17. The combination therapy of claim 11, wherein the rifabutin is administered by inhalation.

18. The combination therapy of claim 11, wherein the rifabutin and the second antibiotic are provided as a single compound.

19. The combination therapy of claim 11, wherein the rifabutin and the second antibiotic are provided separately.

20. The combination therapy of claim 11, wherein the Acinetobacter baumannii comprises the rpoB mutation.

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