D P Bonner

Amphotericin B lipid complex therapy of experimental fungal infections in mice.

The amphotericin B lipid complex (ABLC), which is composed of amphotericin B and the phospholipids dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol, was evaluated for its acute toxicity in mice and for its efficacy in mice infected with a variety of fungal pathogens. ABLC was markedly less toxic to mice when it was administered intravenously; it had a 50% lethal dose of greater than 40 mg/kg compared with a 50% lethal dose of 3 mg/kg for Fungizone, the desoxycholate form of amphotericin B. ABLC was efficacious against systemic infections in mice caused by Candida albicans, Candida species other than C. albicans, Cryptococcus neoformans, and Histoplasma capsulatum. ABLC was also efficacious in immunocompromised animals infected with C. albicans, Aspergillus fumigatus, and H. capsulatum. Against some infections, the efficacy of ABLC was comparable to that of Fungizone, while against other infections Fungizone was two- to fourfold more effective than ABLC. Against several infections. Fungizone could not be given at therapeutic levels because of intravenous toxicity. ABLC, with its reduced toxicity, could be administered at drug levels capable of giving a therapeutic response. ABLC should be of value in the treatment of severe fungal infections in humans.

Tissue Distribution of Amphotericin B Lipid Complex in Laboratory Animals

Abstract— Amphotericin B lipid complex (ABLC), under development for the treatment of serious fungal disease, is not a true liposome but a complex of amphotericin B, dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol with a particle size range of 1·6–6·0 μm. Tissue distribution of ABLC was determined in mice and rats after i.v. or i.p. administration. ABLC resembles typical liposomal preparations with amphotericin B concentrating in the reticuloendothelial system. After a single i.v. treatment with ABLC, amphotericin B was present in high concentrations in liver, lung and spleen of mice and rats while plasma levels were consistently low. Mouse liver contained 48% of the administered dose 1 h after treatment and always contained the largest amount of amphotericin B after ABLC treatment. In mice treated once daily for 7 consecutive days with 10 mg kg−1 ABLC, liver amphotericin B concentration reached 377 μg g−1. Tissue concentrations of amphotericin B were substantially lower when ABLC was given i.p. instead of i.v. with reticuloendothelial tissues containing 2‐ to 7‐fold more after i.v. treatment. Animals treated with 10 mg kg−1 ABLC for 14 consecutive days showed no overt signs of toxicity and had only transient changes in liver and kidney function after treatment.

Activity of quinolones in the Ames Salmonella TA102 mutagenicity test and other bacterial genotoxicity assays.

Eight quinolones were examined for their bacterial mutagenicity in the Ames Salmonella TA102 assay and for their effects in other bacterial genotoxicity assays. In the quantitative Ames plate incorporation assay, all eight quinolones induced His+ deletion reversion in Salmonella tester strain TA102, with maximum reversion observed at about two to eight times the MIC. The quinolones also induced the SOS response. At quinolone concentrations close to the MIC, SOS cell filamentation gene sulA was induced in sulA::lacZ fusion strain Escherichia coli PQ37. RecA-mediated cleavage of lambda repressor in lambda::lacZ fusion strain E. coli BR513 was measurable at about 10 times the MIC, though no induction occurred at 20 micrograms of nalidixic or oxolinic acid per ml. Genotoxicity of quinolones also was observed in the Bacillus subtilis DNA repair assay, in which the mutant strain M45 (recA) was more susceptible to quinolones than its parent strain, H17 (rec+). The results from these analyses indicate that quinolones induce SOS functions and are mutagenic in bacteria; these properties correspond to their antimicrobial activities. Images

Ciprofloxacin-induced, low-level resistance to structurally unrelated antibiotics in Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus.

The effects of ciprofloxacin on the rates of development of low-level resistance to other antibiotics were determined in vitro. Three methicillin-resistant Staphylococcus aureus and two Pseudomonas aeruginosa clinical strains were grown overnight in Mueller-Hinton broth with or without subinhibitory concentrations (1/2, 1/4, and 1/8 MICs) of ciprofloxacin or an aminoglycoside and then quantitatively plated onto medium containing 4 or 8 times the MICs of various antibiotics. The spontaneous mutational frequencies were determined and compared with those of cells not exposed to ciprofloxacin. Exposure of methicillin-resistant S. aureus strains to ciprofloxacin resulted in a > 100-fold increase in the isolation of variants with decreased susceptibilities to ciprofloxacin, tetracycline, imipenem, fusidic acid, and gentamicin, but not vancomycin. Likewise, a > 100-fold increase in the isolation of variants with decreased susceptibilities to ciprofloxacin and imipenem (35-fold) in P. aeruginosa A21213 was observed, and a > 100-fold increase in the isolation of variants with decreased susceptibilities to ciprofloxacin, amikacin, and cefepime in P. aeruginosa A22379 was observed. On the other hand, exposure of these strains to an aminoglycoside did not influence the development of resistance to nonaminoglycoside drugs. These results indicate that exposure to subinhibitory levels of ciprofloxacin can promote the development of low-level resistance to antibiotics with different modes of action.

In vitro antifungal and fungicidal spectra of a new pradimicin derivative, BMS-181184.

A new pradimicin derivative, BMS-181184, was compared with amphotericin B and fluconazole against 249 strains from 35 fungal species to determine its antifungal spectrum. Antifungal testing was performed by the broth macrodilution reference method recommended by the National Committee for Clinical Laboratory Standards (document M27-P, 1992). BMS-181184 MICs for 97% of the 167 strains of Candida spp., Cryptococcus neoformans, Torulopsis glabrata, and Rhodotorula spp. tested were < or = 8 micrograms/ml, with a majority of MICs being 2 to 8 micrograms/ml. Similarly, for Aspergillus fumigatus and 89% of the 26 dermatophytes tested BMS-181184 MICs were < or = 8 micrograms/ml. BMS-181184 was fungicidal for the yeasts, dermatophytes, and most strains of A. fumigatus, although the reduction in cell counts was less for A. fumigatus than for the yeasts. BMS-181184 was active against Sporothrix schenckii, dematiaceous fungi, and some members of the non-Aspergillus hyaline hyphomycetes. BMS-181184, however, was not fungicidal against members of the family Dematiaceae. BMS-181184 lacked activity or had poorer activity (MICs, > or = 16 micrograms/ml) against Aspergillus niger, Aspergillus flavus, Malassezia furfur, Fusarium spp., Pseudallescheria boydii, Alternaria spp., Curvularia spp., Exserohilum mcginnisii, and the zygomycetes than against yeasts. The activity of BMS-181184 was minimally (twofold or less) affected by changes in testing conditions (pH, inoculum size, temperature, the presence of serum), testing methods (agar versus broth macrodilution), or test media (RPMI 1640, yeast morphology agar, high resolution test medium). Overall, our results indicate that BMS-181184 has a broad antifungal spectrum and that it is fungicidal to yeasts and, to a lesser extent, to filamentous fungi.

Antibacterial activities of cefprozil compared with those of 13 oral cephems and 3 macrolides.

Thirteen oral cephems (cefprozil, loracarbef, cefaclor, cefuroxime axetil, cefpodoxime proxetil, cefetamet pivoxil, cefixime, cefdinir, cefadroxil, cephradine, cephalexin, cefatrizine, and cefroxadine), the cephalosporin class representative cephalothin, cefazolin, and the macrolides erythromycin, clarithromycin, and azithromycin were compared for their antibacterial activities against 790 recent clinical isolates. These oral agents differed in their spectra and antibacterial potencies against community-acquired pathogens.

Activity of gatifloxacin and ciprofloxacin in combination with other antimicrobial agents

The influence of non-quinolone antimicrobial agents on the antibacterial activities of gatifloxacin and ciprofloxacin was determined using chequerboard, fractional inhibitory concentration, (FIC) and time-kill analysis methods. In the chequerboard method, the quinolones were tested in combination with ten antimicrobial agents (macrolides, aminoglycosides, beta-lactams, vancomycin, rifampicin and chloramphenicol) against five bacterial strains (one strain each of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Streptococcus pneumoniae). In no incidence was antagonism (FIC > or = 4) or synergy (FIC < or = 0.5) observed; all dual drug combinations involving gatifloxacin or ciprofloxacin showed additivity/indifference (FIC > 0.5, < 4). By time-kill analysis, the strains were tested at a quinolone concentration equal to 8 x MIC in combination with a second antibiotic at 0.5xits MIC. These combinations killed non-enterococcal strains at rates similar to those with quinolones alone. However, rifampicin and chloramphenicol were often antagonistic (100-fold lesser killing) to the lethal action of gatifloxacin and ciprofloxacin against E. faecalis. These findings indicate that, with the exception of E. faecalis, the antibacterial activities of quinolones are generally additive/indifferent to those of other antimicrobial agents.

Susceptibility of bacterial isolates to gatifloxacin and ciprofloxacin from clinical trials 1997–1998

MICs of gatifloxacin and ciprofloxacin against 3482 pre-treatment, clinical trial isolates collected during 1997-1998 are reported. These data suggested that gatifloxacin was four- to eight-fold more active than ciprofloxacin against Gram-positive bacteria, with gatifloxacin MIC(90)s < or = 0.33 mg/l against Staphylococcus aureus and Streptococcus pneumoniae, and < or = 1.0 mg/l versus viridans streptococci and Enterococcus faecalis. Both quinolones had similar MIC(90)s versus Enterobacteriaceae (generally < or = 0.38 mg/l, except 0. 7-0.8 mg/l for Citrobacter freundii) and Pseudomonas aeruginosa ( approximately 8 mg/l). A total of 78% P. aeruginosa had gatifloxacin MICs < or = 2 mg/l. Gatifloxacin was more active than ciprofloxacin against Acinetobacter species and non-P. aeruginosa pseudomonads. Both had exceptional activity versus Haemophilus spp, Moraxella catarrhalis and Neisseria gonorrhoeae. In summary, compared to ciprofloxacin, gatifloxacin had improved activity against Gram-positive bacteria and comparable activity against Gram-negative bacteria.

Activity of gatifloxacin against strains resistant to ofloxacin and ciprofloxacin and its ability to select for less susceptible bacterial variants

Gatifloxacin is an 8-methoxy fluoroquinolone. On quinolones, this side chain imparts increased activity against Gram-positive bacteria and enhanced killing. Gatifloxacin was tested against ofloxacin non-susceptible (ofloxacin MIC>2 mg/l) strains of Streptococcus pneumoniae (gatifloxacin MIC(90), 1 mg/l) and methicillin-resistant Staphylococcus aureus (MRSA, gatifloxacin MIC(90), 4 mg/l), and to ciprofloxacin non-susceptible (ciprofloxacin MIC>1 mg/l) strains of Escherichia coli (gatifloxacin MIC(90),>16 mg/l) and ciprofloxacin non-susceptible (ciprofloxacin MIC>0.06 mg/l) Neisseria gonorrhoeae (gatifloxacin MIC(50), 0.12 mg/l and MIC(90), 0.5 mg/l). Though gatifloxacin showed some reduced susceptibility to these populations, the MIC(50) and MIC(90) values suggest that gatifloxacin may be useful against pneumococci and some gonococcal strains not susceptible to other fluoroquinolones. Gatifloxacin did not select for less susceptible variants of MRSA and pneumococci, in contrast to the 10- to 100-fold higher selection frequencies with ciprofloxacin and ofloxacin. The single-step E. coli mutants selected by gatifloxacin and the comparator quinolones had quinolone MICs within the susceptible range. These data suggest that gatifloxacin use may hinder the development of quinolone-resistance, particularly in Gram-positive bacteria.

Structure-activity relationships of carbapenems that determine their dependence on porin protein D2 for activity against Pseudomonas aeruginosa.

A number of carbapenem derivatives were examined to determine the structure-activity relationships required for dependence on porin protein D2 for activity against Pseudomonas aeruginosa. As suggested by J. Trias and H. Nikaido (Antimicrob. Agents Chemother. 34:52-57, 1990), carbapenem derivatives, such as imipenem and meropenem, containing a sole basic group at position 2 of the molecule utilize the D2 channel for permeation through the outer membrane of pseudomonads; they are more active against D2-sufficient strains of P. aeruginosa. Our results indicated that carbapenems with a basic group at position 1 or 6 of the molecule did not depend on the D2 channel for activity; i.e. they were equally active against D2-sufficient and D2-deficient pseudomonal strains. However, addition of a basic group at position 1 or 6 of a carbapenem derivative already containing a basic group at position 2 resulted in its lack of dependency on the D2 pathway. Comparison between meropenem and its 1-guanidinoethyl derivative, BMY 45047, indicated that they differed in their dependence on D2; while meropenem required the D2 channel for uptake, BMY 45047 activity was independent of D2. Meropenem and BMY 45047 had similar affinities for the penicillin-binding proteins of P. aeruginosa. However, BMY 45047 and meropenem differed in the morphological changes that they induced in pseudomonal cells. While meropenem induced filamentation, BMY 45047 induced filaments only in BMS-181139-resistant mutants and not in imipenem-resistant mutants or in carbapenem-susceptible P. aeruginosa strains. These results suggested that in Mueller-Hinton medium the uptake of BMY 45047 through the non-D2 pathway is more rapid than that of meropenem through the D2 porin. In summary, the presence of a basic group at position 2 of a carbapenem is important for its preferential uptake by the D2 channel. However the addition of a basic group at position 1 or 6 of a carbapenem already containing a basic group at position 2 dissociates its necessity for porin protein D2 for activity.