In vitro activities of a dual-action antibacterial agent, Ro 23-9424, and comparative agents

The Odd Couple(s): An Overview of Beta-Lactam Antibiotics Bearing More Than One Pharmacophoric Group

β-lactam antibiotics are among the most important and widely used antimicrobials worldwide and are comprised of a large family of compounds, obtained by chemical modifications of the common scaffolds. Usually these modifications include the addition of active groups, but less frequently, molecules were synthesized in which either two β-lactam rings were joined to create a single bifunctional compound, or the azetidinone ring was joined to another antibiotic scaffold or another molecule with a different activity, in order to create a molecule bearing two different pharmacophoric functions. In this review, we report some examples of these derivatives, highlighting their biological properties and discussing how this strategy can lead to the development of innovative antibiotics that can represent either novel weapons against the rampant increase of antimicrobial resistance, or molecules with a broader spectrum of action.

Dual beta-lactam-fluoroquinolone compounds: a novel approach to antibacterial treatment

Codrugs comprise a beta-lactam-fluoroquinolone antibacterial hybrid. These new agents have been developed with the aim of enhancing the antibacterial spectrum of current therapies, overcoming intrinsic and acquired resistance, and diminishing severe side-effects. A few compounds, including Ro 23-9424, have entered Phase I clinical trials. Furthermore, a series of oral codrugs have been synthesised, although clear oral bioavailability has not yet been demonstrated. New drugs are urgently needed to treat Gram-positive resistant bacteria.

Synthesis and activity of cephalosporins containing an oxyiminomethylene functionality in the ortho-position of a phenyl- or phenoxyacetic acid C-7 side chain substituent

A new series of cephalosporins having in the C-7 side chain a phenyl- or a phenoxyacetamido group bearing an oxyiminomethyl function in the ortho-position of the aromatic ring was prepared. Their in vitro activity was tested against both Gram+ and Gram- strains.

CQ-397 and CQ-414: antimicrobial activity and spectrum of two fluoroquinolone---cephalosporin, dual-action compounds with carboxamido bonds

OBJECTIVE: To evaluate the potential spectrum of activity of two novel dual-action compounds with carboxamido bonds (CQ-397 and CQ-414; Laboratorios Aranda, San Rafael, Mexico) against human pathogens. METHODS: Approximately 800 Gram-positive and Gram-negative aerobic clinical bacteria were tested in vitro using the Mueller-Hinton broth microdilution method of the National Committee of Clinical Laboratory Standards. RESULTS: CQ-397 (cefamandole+enrofloxacin) and CQ-414 (cefamandole+norfloxacin) were equally potent against Enterobacteriaceae (MIC90 range, 0.06--0.5 microg/mL and 0.06--1 microg/mL, respectively). Citrobacter freundii (MIC90, 4 microg/mL) and Providencia spp. (MIC90, >32 microg/mL) exhibited elevated study drug MICs. Enterobacteriaceae resistant to fluoroquinolones generally remained resistant. CQ-397 and CQ-414 were active against Stenotrophomonas maltophilia (MIC90, 4 microg/mL) and oxacillin-susceptible staphylococci (MIC90, 0.25 microg/mL), but not oxacillin-resistant Staphylococcus aureus (MIC90, >32 microg/mL), Staphylococcus epidermidis (MIC90, 8 microg/mL), and enterococci (MIC90s, 8 to >32 microg/mL). There was no difference in the dual-action drug activity (MIC90, 2 microg/mL) between penicillin-susceptible and -resistant pneumococci. Haemophilus influenzae and Moraxella catarrhalis were very susceptible (MIC range, less-than-or-equal0.015--0.06 microg/mL) to both compounds. CONCLUSIONS: The activity of these novel dual-action compounds, formed from the bonding of older antimicrobials, warrants further investigation for potential human and/or animal health use, including toxicology and pharmacokinetics.

The use of capillary electrophoresis to monitor the stability of a dual-action cephalosporin in solution

Ro 23-9424 is a broad-spectrum antibacterial agent consisting of a cephalosporin and a quinolone moiety which are held together by an ester linkage. This compound has limited solubility in water but is more soluble at alkaline pH. Such high pH values, however, lead to stability problems due to the lability of the ester linkage, and result in the formation of the free quinolone and cephalosporin moieties. The balance between solubility and stability presents a challenge in formulation development for this compound. Thus, it is important to effectively monitor the stability of Ro 23-9424 after it has been reconstituted in different solvent systems. In this manner, a diluent which does not lead to degradation of the drug can be identified. A capillary electrophoresis method was developed and validated to monitor the stability of Ro 23-9424. The method was found to meet acceptable criteria for method precision, system precision, linearity and limits of detection and quantitation. The method was used to monitor the stability and measure the half-life of Ro 23-9424 in water and in an L-arginine-sodium benzoate-saline diluent designed to mimic the drug delivery system. This work shows that capillary electrophoresis can be used to compare the stability of a drug in different solutions as an aid in formulation development.

The role of cefotaxime in the treatment of surgical infections

This study examines the role of cefotaxime in the treatment of both Gram-negative and Gram-positive surgical infections. A dose of 2 g of cefotaxime will sustain peripheral compartment concentrations of 2.6, 3.9, 1.6, and 0.7 micrograms/ml for 6, 8, 10 and 12 h, respectively. Therefore, the proportion of pathogens with a minimal inhibitory concentration (MIC) below the peripheral compartment cefotaxime concentrations was assessed as a measure of therapeutic potential. It was observed that bacterial elimination in infections correlates well with such pharmacodynamic predictions. Therefore, treatment recommendations for surgical infections are based on the following pharmacodynamics. The times above the MIC in the tissue compartment for various pathogens (1988-1994) known to cause surgical infections were: Escherichia coli, 12 h; all pyogenic streptococci, 12 h; pneumococci, 12 h; Haemophilus spp., 12 h; Proteus mirabilis, 12 h; Klebsiella spp., 10.9 h; viridans streptococci, 10.6 h; oxacillin-susceptible, coagulase-negative staphylococci, 9.7 h; Providencia spp., 9.2 h; Clostridium perfringens, 8.6 h; Peptostreptococcus spp., 8 h; oxacillin-susceptible Staphylococcus aureus, 7.3 h; and all S. aureus, 6.8 h. From the examination of pharmacodynamic parameters, cefotaxime appears to be a viable choice for the therapy of surgical infections other than the Gram-negative anaerobes. For those infections, metronidazole with cefotaxime would be preferred.

Low-level resistance to the cephalosporin 3'-quinolone ester Ro 23-9424 in Escherichia coli

Four spontaneous, single-step mutants of Escherichia coli K-12 resistant to low levels of the cephalosporin 3'-quinolone ester Ro 23-9424 were isolated at a frequency of 10(-10) to 10(-11) mutants per CFU plated. The mutants were cross-resistant to both cephalosporin (cefotaxime) and quinolone (fleroxacin) components. Accordingly, they had altered porins and replicative DNA biosynthesis resistant to fleroxacin. There was no increase in beta-lactamase activity when tested with nitrocephin, and the penicillin-binding protein profiles were normal.

Quinolone activity against anaerobes: microbiological aspects

Currently available quinolones are either inactive or marginally active against anaerobic bacteria. This review summarises the in vitro activity of currently available as well as experimental quinolones against clinically significant anaerobic bacteria. Quinolones with low activity against anaerobes include ciprofloxacin, ofloxacin, levofloxacin, fleroxacin, pefloxacin, enoxacin, lomefloxacin and probably E 4868 and NM 441. Compounds with intermediate anaerobe activity include sparfloxacin, grepafloxacin, PD 131628 and AM 1155. Quinolones that are very active against anaerobes include clinafloxacin and DU 6859a. CP 99,219, a naphthyridone, is also very active against anaerobes. Toxicity problems have necessitated the withdrawal of some quinolones shown to have intermediate activity (temafloxacin and tosufloxacin) and the discontinuation of the development of some investigational agents (Win 57273 and BAY Y 3118) with high activity. Conclusions regarding the therapeutic value of quinolones against human anaerobic infections await further clinical toxicological and pharmacokinetic studies.

Antimicrobial activity of a new antipseudomonal dual-action drug, Ro 25-0534

Ro 25-0534, a tertiary amine-linked dual action combination (DAC) of a catechol cephalosporin and ciprofloxacin, was compared with a previously described DAC (Ro 23-9424), ciprofloxacin and cefotaxime. A total of 688 recent clinical isolates were tested and an additional collection of 110 Gram-negative bacilli possessing documented resistance to broad-spectrum antimicrobials were used. Ro 25-0534 was active against all tested species of Enterobacteriaceae (MIC90 range, 0.06-2 micrograms/ml), oxacillin-susceptible staphylococci, beta-hemolytic streptococci, and penicillin-susceptible pneumococci (MIC90 range, 1-2 micrograms/ml). Haemophilus influenzae (MIC90 range, 0.25-0.5 micrograms/ml), Moraxella catarrhalis (MIC90, 0.5 microgram/ml), and most nonenteric Gram-negative bacilli (MIC90 range, 2-4 micrograms/ml) such as Pseudomonas aeruginosa, Acinetobacter spp., and Xanthomonas maltophilia. Enterococci and Bacteroides fragilis isolates were resistant to Ro 25-0534. The Ro 25-0354 potency against most susceptible strains was generally severalfold less than that of Ro 23-9424 (except for Pseudomonas-Xanthomonas) or ciprofloxacin alone.

Determination of a new antibacterial agent (Ro 23-9424) by multidimensional high-performance liquid chromatography with ultraviolet detection and direct plasma injection

Analysis of a new antibacterial agent, Ro 23-9424 (I), in plasma has been complicated by the fact that its metabolite, fleroxacin (II), is formed not only in vivo, but also nonenzymatically by the hydrolysis of the ester bond of I. In order to minimize sample preparation time and possible hydrolysis during sample preparation, a high-performance liquid chromatographic procedure was developed which features direct injection of plasma and multidimensional chromatography. The first dimension size-exclusion separation allows plasma proteins to elute with the column void volume. The second dimension reversed-phase column provides a high-resolution separation dependent upon the hydrophobicity of the sample species. With a 5-microliters injection, the limit of quantitation of the method is 0.35 microgram/ml for I and 0.27 microgram/ml for II. The method was used to determine steady state plasma vs. time profiles for I and II from 750 mg i.v. doses of I administered twice daily.

In vitro activity of Ro 23-9424, a dual-acting cephalosporin-quinolone antimicrobial agent

In vitro activity of new dual-acting antibacterial Ro 23-9429 was tested against 1294 bacterial isolates from patients in a major tertiary care referral hospital in Saudi Arabia. Its activity was compared with that of ciprofloxacin, fleroxacin, ampicillin, cephalothin, cefoxitin, cefotaxime, ceftazidime, piperacillin, oxacillin, gentamicin, amikacin, imipenem, and vancomycin. Of the 621 members of Enterobacteriaceae tested, every single isolate was inhibited by Ro 23-9429 at minimum inhibitory concentration ranging between < .03 and 8 micrograms/mL. No other antimicrobial tested was as active as this dual-acting cephalosporin-fluoroquinolone. Similarly, all of the 255 isolates of Acinetobacter, Aeromonas hydrophila, Pseudomonas aeruginosa, and Xanthomonas maltophilia were susceptible to Ro 23-9429. It inhibited all the 120 isolates of methicillin-resistant Staphylococcus aureus. Its in vitro activity against coagulase-negative staphylococci and enterococci was superior or comparable to that of other drugs that are commonly used in clinical practice.

In vitro activity of Ro 23-9424 against clinical isolates of Legionella species

Agar and broth microdilution MICs of Ro 23-9424 that inhibited 90% of 22 Legionella clinical isolates tested were 0.64 and 0.08 micrograms/ml, respectively; respective erythromycin values were 1.0 and 0.12 micrograms/ml. Ro 23-9424 (1 microgram/ml) was slightly more active than the same erythromycin concentration in a macrophage system, for both Legionella pneumophila strains studied.

In vitro activity of Ro 23-9424, a dual-action antibacterial agent, against bacterial isolates from cancer patients compared with those of other agents

The in vitro activity of Ro 23-9424 against bacterial isolates from patients with cancer was compared with those of fleroxacin, ciprofloxacin, cefoperazone, and ceftazidime. Ro 23-9424 inhibited the majority of the members of the family Enterobacteriaceae and all Aeromonas isolates at a concentration of less than or equal to 1.0 micrograms/ml. It was also active against Acinetobacter spp. and Haemophilus influenzae, including beta-lactamase-producing strains. The MIC for 90% of isolates (MIC90) of Pseudomonas aeruginosa was 16.0 micrograms/ml. All group A and B streptococci were inhibited by less than or equal to 0.25 micrograms/ml, and 90% of group G streptococci and Streptococcus pneumoniae were inhibited by 1.0 micrograms/ml. All methicillin-susceptible strains of Staphylococcus aureus and 60% of methicillin-resistant strains were susceptible to 2.0 micrograms of Ro 23-9424 per ml, whereas the MIC90 for Staphylococcus epidermidis and Staphylococcus hominis isolates was 4.0 micrograms/ml. Staphylococcus haemolyticus and Enterococcus spp. were less susceptible; MIC90s for them were 16.0 and 32.0 micrograms/ml. Ro 23-9424 has a broad antibacterial spectrum and potential utility for therapy of infections in cancer patients.

Escherichia coli resistant to cephalosporins and quinolones is still susceptible to the cephalosporin-quinolone ester Ro 23-9424

Ro 23-9424 is a broad-spectrum antibacterial agent consisting of a cephalosporin (desacetylcefotaxime) linked through an ester bond to a fluoroquinolone (fleroxacin). Its activity against mutants of Escherichia coli TE18 resistant to both antibacterial components was examined. E. coli TE18 overproduces the AmpC beta-lactamase and is resistant to several cephalosporins, including desacetylcefotaxime (MIC, 50 micrograms/ml), although it is still susceptible to Ro 23-9424 (MIC, 0.2 microgram/ml). Thirty-five spontaneous, two-step mutants of E. coli TE18 which were resistant to fleroxacin (MIC, 50 micrograms/ml) were isolated. In the mutants, replicative DNA biosynthesis (permeabilized cells) was resistant to fleroxacin, and some mutants had porin abnormalities. However, all remained susceptible to Ro 23-9424 (MIC, 0.5 microgram/ml). Examination of beta-lactamase activity in the parent strain revealed that it hydrolyzes desacetylcefotaxime more rapidly than it does Ro 23-9424. Thus, Ro 23-9424 may be less susceptible to the gram-negative, chromosomal beta-lactamases that hydrolyze several broad-spectrum cephalosporins and may be effective in cases in which neither of its two components is active.

In vitro activity of Ro 24-6392, a novel ester-linked co-drug combining ciprofloxacin and desacetylcefotaxime

In preliminary in vitro susceptibility tests Ro 24-6392 (desacetylcefotaxime with a 3'-ciprofloxacin substitution) demonstrated activity against a wide spectrum of aerobic bacteria, 98.6% of strains being inhibited by less than or equal to 8 mg/l. Of the commonly isolated species tested, only enterococcal strains were resistant (MICs greater than or equal to 32 mg/l). The potency of Ro 24-6392 was generally between that observed for the two hydrolysis components, except in the case of Providencia stuartii and penicillin-resistant pneumococci isolates which were more susceptible to Ro 24-6392. This new dual-action compound appears to be slightly more active than the previously studied peer drug Ro 23-9424, principally because of the superior activity of the fluoroquinolone component, ciprofloxacin.

Antimicrobial activity of Ro 24-6778, a covalent bonding of desmethylfleroxacin and desacetylcefotaxime

A new "dual action" cephalosporin (Ro 24-6778), representing an ester-linked desacetylcefotaxime and desmethylfleroxacin was tested against 287 aerobic bacteria. Ro 24-6778 was found to be very active (minimal inhibitory concentrations [MIC90], less than or equal to 0.5 micrograms/ml) against Enterobacteriaceae, Streptococcus spp., and Aeromonas hydrophila. Moderate Ro 24-6778 activity (MIC90, 1-8 micrograms/ml) was demonstrated against Bacillus spp., Staphylococcus spp. (including oxacillin-resistant strains), Flavobacterium spp., Enterococcus durans, and Acinetobacter anitratus. More Ro 24-6778-resistant strains (MIC90, 16- greater than 32 micrograms/ml) were usually found among the enterococci, Xanthomonas hydrophila, Pseudomonas spp., and Achromobacter xyloxidans isolates. These preliminary Ro 24-6778 MIC test results show a spectrum superior (93.4% of strains susceptible at less than or equal to 8 micrograms/ml) to the comparison drugs (cefotaxime or fleroxacin) and possible clinical utility for therapy of many fluoroquinolone- or cephalosporin-resistant strains.

In vitro activity of Ro 23-9424, a dual-action cephalosporin, compared with activities of other antibiotics

The in vitro activity of Ro 23-9424, which is desacetyl-cefotaxime linked to fleroxacin, was compared with the activities of cefotaxime, desacetyl-cefotaxime, fleroxacin, ofloxacin, and ciprofloxacin. It inhibited the majority of members of the family Enterobacteriaceae, except for some Serratia marcescens, Citrobacter freundii, and Enterobacter cloacae strains, at less than or equal to 0.25 microgram/ml and had an MIC for 90% of strains tested (MIC90) of 8 micrograms/ml against Pseudomonas aeruginosa. Most group A, B, C, and G streptococci and Streptococcus pneumoniae were inhibited at less than or equal to 0.25 microgram/ml. Ninety percent of the staphylococci were inhibited at less than or equal to 4 micrograms/ml, except for some methicillin-resistant Staphylococcus aureus isolates. The MIC90S of Ro 23-9424 for Enterococcus faecalis and Listeria monocytogenes were greater than or equal to 16 micrograms/ml. Ninety percent of Clostridium perfringens isolates were inhibited by less than or equal to 2 micrograms/ml, whereas Bacteroides fragilis had an MIC90 of 32 micrograms/ml. There was a minimal inoculum size effect. The MICs and MBCs were either identical or within a twofold dilution. The MICs of Ro 23-9424 for Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Enterobacter cloacae, Citrobacter freundii, Pseudomonas aeruginosa, and Staphylococcus aureus increased 16- to 128-fold after 2 weeks of transfer in the presence of Ro 23-9424, showing that the presence of two agents does not prevent resistance.

Structure-activity relationships in DNA gyrase inhibitors

The review brings the status of research into DNA gyrase inhibitors up to date. Structure-activity relationships in both coumarin antibiotics, like novobiocin or coumermycins, and quinolones are discussed. In the section dealing with the quinolones, promising drugs under further evaluation are pointed out. Recently discovered new types of DNA gyrase inhibitors, i.e. tetramic acid derivatives and biphenyl dicarboxylic acid monoamides, are also briefly mentioned.