Comparative in vitro activities of ciprofloxacin, gemifloxacin, grepafloxacin, moxifloxacin, ofloxacin, sparfloxacin, trovafloxacin, and other antimicrobial agents against bloodstream isolates of gram-positive cocci

Potential new fluoroquinolone treatments for suspected bacterial keratitis

Topical fluoroquinolones (FQs) are an established treatment for suspected microbial keratitis. An increased FQ resistance in some classes of bacterial pathogens is a concern. Some recently developed FQs have an extended spectrum of activity, making them a suitable alternative for topical ophthalmic use. For example, the new generation FQs, avarofloxacin, delafloxacin, finafloxacin, lascufloxacin, nadifloxacin, levonadifloxacin, nemonoxacin and zabofloxacin have good activity against the common ophthalmic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae and several of the Enterobacteriaceae. However, because there are no published ophthalmic break-point concentrations, the susceptibility of an isolated micro-organism to a topical FQ is extrapolated from systemic break-point data and wild type susceptibility. The purpose of this review is to compare the pharmacokinetics and pharmacodynamics of the FQs licensed for topical ophthalmic use with the same parameters for new generation FQs. We performed a literature review of the FQs approved for topical treatment and the new generation FQs licensed to treat systemic infections. We then compared the minimum inhibitory concentrations (MIC) of bacterial isolates and the published concentrations that FQs achieved in the cornea and aqueous. We also considered the potential suitability of new generation FQs for topical use based on their medicinal properties. Notably, we found significant variation in the reported corneal and aqueous FQ concentrations so that reliance on the reported mean concentration may not be appropriate, and the first quartile concentration may be more clinically relevant. The provision of the MIC for the microorganism together with the achieved lower (first) quartile concentration of a FQ in the cornea could inform management decisions such as whether to continue with the prescribed antimicrobial, increase the frequency of application, use a combination of antimicrobials or change treatment.

A Combination of Pharmacophore-Based Virtual Screening, Structure-Based Lead Optimization, and DFT Study for the Identification of S. epidermidis TcaR Inhibitors

The transcriptional regulator (TcaR) enzyme plays an important role in biofilm formation. Prevention of TcaR-DNA complex formation leads to inhibit the biofilm formation is likely to reveal therapeutic ways for the treatment of bacterial infections. To identify the novel ligands for TcaR and to provide a new idea for drug design, two efficient drug design methods, such as pharmacophore modeling and structure-based drug design, were used for virtual screening of database and lead optimization, respectively. Gemifloxacin (FDA-approved drug) was considered to generate the pharmacophore model for virtual screening of the ZINC database, and five hits, namely ZINC77906236, ZINC09550296, ZINC77906466, ZINC09751390, and ZINC01269201, were identified as novel inhibitors of TcaR with better binding energies. Using structure-based drug design, a set of 7a–7p inhibitors of S. epidermidis were considered, and Mol34 was identified with good binding energy and high fitness score with improved pharmacological properties. The active site residues ARG110, ASN20, HIS42, ASN45, ALA38, VAL63, VAL68, ALA24, VAL43, ILE57, and ARG71 are playing a promising role in inhibition process. In addition, we performed DFT simulations of final hits to understand the electronic properties and their significant role in driving the inhibitor to adopt apposite bioactive conformations in the active site. Conclusively, the newly identified and designed hits from both the methods are promising inhibitors of TcaR, which can hinder biofilm formation.

A Review of New Fluoroquinolones : Focus on their Use in Respiratory Tract Infections

The new respiratory fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and on the horizon, garenoxacin) offer many improved qualities over older agents such as ciprofloxacin. These include retaining excellent activity against Gram-negative bacilli, with improved Gram-positive activity (including Streptococcus pneumoniae and Staphylococcus aureus). In addition, gatifloxacin, moxifloxacin and garenoxacin all demonstrate increased anaerobic activity (including activity against Bacteroides fragilis). The new fluoroquinolones possess greater bioavailability and longer serum half-lives compared with ciprofloxacin. The new fluoroquinolones allow for once-daily administration, which may improve patient adherence. The high bioavailability allows for rapid step down from intravenous administration to oral therapy, minimizing unnecessary hospitalization, which may decrease costs and improve quality of life of patients. Clinical trials involving the treatment of community-acquired respiratory infections (acute exacerbations of chronic bronchitis, acute sinusitis, and community-acquired pneumonia) demonstrate high bacterial eradication rates and clinical cure rates. In the treatment of community-acquired respiratory tract infections, the various new fluoroquinolones appear to be comparable to each other, but may be more effective than macrolide or cephalosporin-based regimens. However, additional data are required before it can be emphatically stated that the new fluoroquinolones as a class are responsible for better outcomes than comparators in community-acquired respiratory infections. Gemifloxacin (except for higher rates of hypersensitivity), levofloxacin, and moxifloxacin have relatively mild adverse effects that are more or less comparable to ciprofloxacin. In our opinion, gatifloxacin should not be used, due to glucose alterations which may be serious. Although all new fluoroquinolones react with metal ion-containing drugs (antacids), other drug interactions are relatively mild compared with ciprofloxacin. The new fluoroquinolones gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin have much to offer in terms of bacterial eradication, including activity against resistant respiratory pathogens such as penicillin-resistant, macrolide-resistant, and multidrug-resistant S. pneumoniae. However, ciprofloxacin-resistant organisms, including ciprofloxacin-resistant S. pneumoniae, are becoming more prevalent, thus prudent use must be exercised when prescribing these valuable agents.

Alternative strategies for proof-of-principle studies of antibacterial agents

The proof that a new antibacterial agent is not only active in vitro but also effective in vivo under clinically relevant conditions is currently provided (i) by using appropriate nonclinical models of infection and pharmacokinetic-pharmacodynamic (PK-PD) analysis providing evidence of the likelihood of clinical efficacy and (ii) by examining the study drug in exploratory clinical trials, as well as dose and schedule finding during phase II of clinical development. This approach is both time-consuming and costly. Furthermore, PK-PD targets for any novel antibacterial agent cannot be derived from studies with experimental animals. Therefore, alternative strategies have to be identified to prove the principle that a novel antibacterial agent is active under clinically relevant conditions. This review summarizes evidence that the quantitative analysis of shifts in the viable counts of pathogens in infected patients or the evaluation of the PD effect of an investigational agent on indicator organisms of the human resident microflora or colonizers of healthy volunteers, if paralleled with PK monitoring of serum and the target site, provides an alternative to a classical proof-of-principle study in the course of a phase II study program.

Changes in bacterial population of gastrointestinal tract of weaned pigs fed with different additives

This study aimed to provide novel insights into the gastrointestinal microbial diversity from different gastrointestinal locations in weaning piglets using PCR-restriction fragment length polymorphism (PCR-RFLP). Additionally, the effect of different feed additives was analyzed. Thirty-two piglets were fed with four different diets: a control group and three enriched diets, with avilamycin, sodium butyrate, and a plant extract mixture. Digesta samples were collected from eight different gastrointestinal segments of each animal and the bacterial population was analysed by a PCR-RFLP technique that uses 16S rDNA gene sequences. Bacterial diversity was assessed by calculating the number of bands and the Shannon-Weaver index. Dendrograms were constructed to estimate the similarity of bacterial populations. A higher bacterial diversity was detected in large intestine compared to small intestine. Among diets, the most relevant microbial diversity differences were found between sodium butyrate and plant extract mixture. Proximal jejunum, ileum, and proximal colon were identified as those segments that could be representative of microbial diversity in pig gut. Results indicate that PCR-RFLP technique allowed detecting modifications on the gastrointestinal microbial ecology in pigs fed with different additives, such as increased biodiversity by sodium butyrate in feed.

Antibacterial activity of moxifloxacin on bacteria associated with periodontitis within a biofilm

The activity of moxifloxacin was compared with ofloxacin and doxycycline against bacteria associated with periodontitis within a biofilm (single strain and mixed population) in vitro. MICs and minimal bactericidal concentrations (MBCs) of moxifloxacin, ofloxacin and doxycyline were determined against single strains and mixed populations in a planktonic state. Single-species biofilms of two Porphyromonas gingivalis and two Aggregatibacter actinomycetemcomitans strains and a multispecies biofilm consisting of 12 species were formed for 3 days. The minimal biofilm eradication concentrations (MBECs) were determined after exposing the biofilms to the antibacterials (0.002-512 µg ml(-1)) for 18 h, addition of nutrient broth for 3 days and subsequent subcultivation. Photographs were taken using confocal laser-scanning microscopy and scanning electron microscopy. The MICs and MBCs did not differ between ofloxacin and moxifloxacin against A. actinomycetemcomitans, whilst moxifloxacin was more active than the other tested antibacterials against anaerobes and the mixed population. The single-species biofilms were eradicated by moderate concentrations of the antibacterials, and the lowest MBECs were always found for moxifloxacin (2-8 µg ml(-1)). MBECs against the multispecies biofilms were 128, >512 and >512 µg ml(-1) for moxifloxacin, ofloxacin and doxycycline, respectively. In summary, moxifloxacin in a topical formulation may have potential as an adjunct to mechanical removal of the biofilms.

Efficacy and safety of moxifloxacin as antibacterial prophylaxis for patients receiving autologous haematopoietic stem cell transplantation: a randomised trial

Patients receiving high-dose chemotherapy with autologous peripheral blood stem cell transplantation (PBSCT) are at high risk of infections, especially bacteraemia. A prospective, double-blind, randomised, placebo-controlled, single-centre, pilot study was performed on oral moxifloxacin 400mg versus placebo for preventing bacteraemia in PBSCT recipients. Patients received moxifloxacin or placebo for the duration of neutropenia or until emergence of fever or other infections necessitating intravenous antibiotic treatment. Of 68 patients included in the trial, 2 were excluded from the trial before taking their first dose. The remaining 66 patients were eligible for evaluation in the intention-to-treat analysis set. Neutropenia with an absolute neutrophil count of <500cells/μL developed in 30 moxifloxacin-treated patients (88.2%) and 21 patients in the placebo group (65.6%) (P<0.03). Nine patients (26.5%) and eight patients (25.0%), respectively, were prematurely discontinued from study treatment. Breakthrough bacteraemia occurred in 3 moxifloxacin-treated patients (8.8%) and 9 patients in the placebo group (28.1%) (P=0.042). The time period until fever was 9.5 days [95% confidence interval (CI) 8.06-10.94 days) and 7.69 days (95% CI 6.51-8.85 days), respectively (P=0.0499). There was no difference in adverse events or toxicities between the groups. Moxifloxacin prevented bacteraemia and shortened febrile episodes in patients receiving autologous PBSCT. No significant increase of adverse events in the moxifloxacin arm was observed, possibly due to the rather small sample size.

Validated Method for the Simultaneous Determination of Gemifloxacin and H2‐receptor Antagonists in Bulk, Pharmaceutical Formulations and Human Serum by RP‐HPLC; In‐vitro Applications

Simple, isocratic and rapid RP‐HPLC method has been developed for the simultaneous analysis of gemifloxacin and H2‐receptor antagonists i.e. Cimetidine, Famotidine and Ranitidine, in bulk, pharmaceutical formulation and human serum. Separation was achieved on the RP‐Mediterranea column [C18 (250 × 4.6 mm, 5 μ)] at ambient temperature using mobile phase consisting of acetonitrile: methanol: water (20:28:52 v/v/v pH 2.8 adjusted by phosphoric acid). Flow rate was 1.0 mL/min with an average operating pressure of 180 kg/cm2. Gatifloxacin (GATI) was used as an internal standard (IS). Quantitation was achieved with UV detection at 221, 256 and 267 nm, respectively. Linear calibration curves, at concentration ranges of 0.05‐37.5 μgmL‐L with a correlation coefficient of ±0.9994. The detection and quantification limits were in the ranges of 0.023‐0.250 μgmL‐L and 0.071‐0.756 μgmL‐L, respectively. Friedman's and Student's t‐test were applied to correlate these results. Method was validated in terms of selectivity, linearity, precision, robustness, recovery, limits of detection and quantitation and is applicable to the routine analysis of GFX and H2‐receptor antagonists, alone or in combination.

Moxifloxacin in the treatment of skin and skin structure infections

Moxifloxacin is a recent addition to the fluoroquinolone class, differing from ciprofloxacin and other older agents in having much better in vitro activity against Gram-positive aerobes while retaining potent activity against Gram-negative aerobes. It is also active against the pathogens of human and animal bite wounds and those species of atypical mycobacteria associated with dermatologic infections. Its activity against anaerobes is quite variable. Moxifloxacin penetrates well into inflammatory blister fluid and muscle and subcutaneous adipose tissues. Moxifloxacin should thus be a reasonable option for the treatment of skin and skin structure infections (SSSIs). In 3 randomized controlled trials (RCTs), oral moxifloxacin was as effective as cephalexin in the treatment of uncomplicated SSSIs in adults while in 2 RCTs, intravenous/oral moxifloxacin was as effective as intravenous/oral β-lactam/β-lactamase inhibitor therapy in the treatment of complicated SSSIs in adults. Moxifloxacin does not inhibit cytochrome P450 enzymes and thus interact with warfarin or methylxanthines. However, multivalent cations can reduce its oral bioavailability substantially. Dosage adjustment is not required in the presence of renal or hepatic impairment. The clinical relevance of its electrophysiologic effects (QT_c prolongation) remains unresolved.

Successful treatment with moxifloxacin of experimental aortic valve endocarditis due to methicillin-resistant Staphylococcus aureus (MRSA)

Moxifloxacin (MXF) is an 8-methoxyquinolone with high activity against Gram-positive bacteria. In an experimental model of aortic valve endocarditis (EAVE), the efficacy of MXF was evaluated against a strain of methicillin-resistant Staphylococcus aureus (MRSA). Rabbits with catheter-induced aortic valve vegetations were randomly assigned to a control group or to groups receiving MXF 20 mg/kg intravenous (i.v.) twice a day (bid) or vancomycin (VAN) 30 mg/kg i.v. bid for a total of eight doses (4 days). Rabbits were sacrificed 15 h after the last dose of antibiotics. In another group, treatment with MXF was extended to 5 days and rabbits were sacrificed 5 days after the last dose (10th dose) of MXF in order to detect possible relapses of endocarditis after the end of treatment (test-of-cure (TOC) study). Both MXF and VAN significantly reduced the bacterial load in vegetations (P < 0.001 vs. controls). All animals in the MXF-TOC group had sterile vegetations. MXF given at a dose of 20 mg/kg i.v. bid for 4 days was equally effective as VAN in the treatment of EAVE due to MRSA. When treatment with MXF was extended to 5 days, the cure rate reached 100% and no relapses of endocarditis were observed.

Synergy between gemifloxacin and trimethoprim/sulfamethoxazole against community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

The rapid emergence of methicillin-resistant Staphylococcus aureus from the community (CA-MRSA) presents difficulties in making treatment choices. We evaluated whether combining another orally available agent commonly used to treat CA-MRSA with gemifloxacin would enhance gemifloxacin activity against CA-MRSA.

METHODS

Fifty strains of SCCmec IV, agr group 1, Panton-Valentine leucocidin-positive CA-MRSA were evaluated for susceptibilities to gemifloxacin, trimethoprim/sulfamethoxazole, doxycycline, levofloxacin, rifampicin, clindamycin and erythromycin. Twenty of these strains were evaluated for the potential for synergy between gemifloxacin and trimethoprim/sulfamethoxazole, clindamycin and rifampicin by time-kill analysis. Two strains were further evaluated in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model.

RESULTS

In time-kill analyses, gemifloxacin combined with trimethoprim/sulfamethoxazole produced additivity (6/20) or synergy (11/20) in 85% of the isolates tested. The addition of clindamycin to gemifloxacin showed additivity (3/20) or synergy (2/20) in 25% of the isolates. All isolates displayed indifference to the combination of gemifloxacin and rifampicin. In the PK/PD model, combining gemifloxacin and trimethoprim/sulfamethoxazole provided potent and sustained bactericidal activity to detection limits of 2 log(10) cfu/mL by 48 h; gemifloxacin combined with clindamycin or with rifampicin killed to detection limits by 56 h or later. One isolate developed efflux-mediated resistance to gemifloxacin at 96 h with gemifloxacin monotherapy. All combinations prevented the emergence of this resistance.

CONCLUSIONS

Synergy or additivity was demonstrated by time-kill analysis between gemifloxacin and trimethoprim/sulfamethoxazole in most isolates tested. In the PK/PD model, the addition of trimethoprim/sulfamethoxazole, clindamycin and rifampicin enhanced the activity of gemifloxacin against CA-MRSA and suppressed the emergence of resistance to gemifloxacin.

The response of gastrointestinal microbiota to avilamycin, butyrate, and plant extracts in early-weaned pigs

An experiment was designed to evaluate the effects of 3 different additives on the gastrointestinal microbiota of early-weaned pigs. Early-weaned (18 to 22 d; n = 32) pigs (6.0 +/- 0.10 kg of BW) from 8 litters were randomly distributed into 8 pens. Each pen was assigned 1 of 4 dietary treatments: a prestarter or control diet, the control diet with 0.04% avilamycin (AB), with 0.3% sodium butyrate, or with 0.03% plant extract mixture (XT; standardized mixture with 5% (wt/wt) carvacrol extracted from Origanum spp., 3% cinnamaldehyde extracted from Cinnamonum spp., and 2% capsicum oleoresin from Capsicum annum). At the end of the experimental period, 8 pigs per treatment were killed, and samples of their intestinal content were taken. The total bacterial load along the gastrointestinal tract (GIT; stomach, jejunum, cecum, and distal colon) and the lactobacilli and enterobacteria in the jejunum and cecum were measured by quantitative PCR. The total microbial counts along the GIT did not differ among the diets, but there was an increase in the lactobacilli:enterobacteria ratio in the cecum of the piglets on the XT diet (P = 0.003). Restriction fragment length polymorphism of the PCR-amplified V3, V4, and V5 regions of the 16S rDNA gene showed changes in the structure of the microbial community in the jejunum. Dendrograms grouped animals by diets; control with 0.3% sodium butyrate was the treatment that promoted the biggest changes in the microbial ecosystem, followed by AB and then XT. Biodiversity increased when using additives compared with the control diet (P = 0.002). Microbial metabolic activity along the hindgut was studied using the concentration of purine bases and carbohydrase activities. Different patterns for purine bases were observed between diets (diet x intestinal section, P = 0.01). The control diet reached a maximum purine base concentration at the end of the colon, whereas that of the AB diet was reached at the cecum. We could not detect any cellulase or xylanase activities in animals of this age. Appreciable amylase and amylopectinase activities were found, but they did not differ between diets. The results suggest that the effects of avilamycin, butyrate, or the plant extract would not be related to a reduction in the number of total bacteria inhabiting different sections of the GIT but rather to changes in the ecological structure and metabolic activity of the microbial community.

History and evolution of antibiotic resistance in coagulase-negative staphylococci: Susceptibility profiles of new anti-staphylococcal agents

Coagulase-negative staphylococci (CNS) are a heterogenous group of Gram-positive cocci that are widespread commensals among mammalia. Unlike their coagulase-positive counterpart, Staphylococcus aureus, CNS produce few virulence patterns and normally refrain from invading tissue. Yet, not only can CNS cause infections in normal host tissue, but modern medicine has also seen their rise as opportunists that display adherence to medical device materials to produce a protective biofilm. CNS have historically been more resistant to antimicrobials, including the beta-lactam antibiotics, than S. aureus and some hospitals reveal rates of oxacillin resistance in CNS approaching 90%. Cross resistance to non-beta-lactam agents has been a recurrent theme over the past 40 years in the CNS. Thus, there has been a pressing need for newer antimicrobial agents with good antistaphylococcal activity. Those new agents tend to have excellent antistaphylococcal activity include daptomycin, linezolid, oritavancin, telavancin, tigecycline, dalbavancin, new quinolones, and ceftibiprole, several of which have unique mechanisms of action. The MIC₉₀ for these new compounds typically ranges from 0.5-4 mug/mL. Staphylococcal biofilm formation is quite common in CNS infections and markedly increases the MIC for most older antimicrobials. Several of the newer agents offer some promise of penetration of biofilm to inhibit or kill adherent staphylococci. CNS will likely remain a major cause of infections in the modern age, evolve further antimicrobial resistance mechanisms, and require development of newer antimicrobials for curative therapy.

Interaction between quinolones antibiotics and bacterial outer membrane porin OmpF

In these work, we try to establish a relation between the hydrophobicity of some quinolones and their interaction with OmpF. In order to do that, the values of the binding constant of some quinolones of different "generations" with OmpF were determined by UV-visible spectrophotometry and by fluorimetry. Our results show that there is a strong interaction between all the drugs and the protein and that it becomes larger for the last "generation" fluoroquinolones. These results were compared with previous ones obtained for the interaction of these drugs with simpler biomembrane models (liposomes) and it is possible to conclude that some of the quinolones associate preferably with the protein than with these models. This suggests that an interaction drug/porin is, probably, the preferentially used for the latest fluoroquinolones what makes reasonable to believe that a strong affinity for OmpF means a better capacity to transpose the barrier formed by the outer membrane.

Oxazolidinones: new players in the battle against multi-resistant Gram-positive bacteria

For many years the pharmaceutical industry did not pursue the development of antimicrobial agents that specifically targeted Gram-positive bacteria. Semi-synthetic penicillins and vancomycin were the mainstays of therapy for methicillin-susceptible and -resistant strains of staphylococci, respectively, as was penicillin for Streptococcus pneumoniae and beta-lactam-aminoglycoside combinations for serious enterococcal infections. In the 1980s enterococci resistant to glycopeptides emerged, followed shortly thereafter by a dissemination of penicillin-insensitive S. pneumoniae and, more recently, the occurrence of vancomycin-intermediately susceptible Staphylococcus aureus. The emergence of fully glycopeptide-resistant S. aureus is clearly on the horizon. Multi-resistant Gram-positive bacteria now pose an important therapeutic challenge for clinicians. New drugs with activity against some of these dangerous pathogens have recently been pursued, and linezolid, the first member of the oxazolidinone class, has now been licensed for clinical use in many countries. This drug has excellent in vitro and in vivo activity against all clinically relevant multi-resistant Gram-positive cocci and fills an important void in infectious disease chemotherapy.

Moxifloxacin: a review of its use in the management of bacterial infections

Moxifloxacin (Avelox) is a fluoroquinolone antibacterial with a methoxy group in the C-8 position and a bulky C-7 side chain. Moxifloxacin is approved for use in the treatment of acute exacerbations of chronic bronchitis (AECB), community-acquired pneumonia (CAP), acute bacterial sinusitis and uncomplicated skin and skin structure infections (approved indications may differ between countries). Moxifloxacin has a broad spectrum of antibacterial activity, including activity against penicillin-resistant Streptococcus pneumoniae. It achieves good tissue penetration and has a convenient once-daily administration schedule, as well as being available in both intravenous and oral formulations in some markets. Moxifloxacin has good efficacy in the treatment of patients with AECB, CAP, acute bacterial sinusitis and uncomplicated skin and skin structure infections, and is generally well tolerated. Thus, moxifloxacin is an important option in the treatment of bacterial infections.

In vitro activity of gemifloxacin and contemporary oral antimicrobial agents against 27,247 Gram-positive and Gram-negative aerobic isolates: a global surveillance study

This study was a multi-centre, multi-country surveillance of 27247 Gram-positive and Gram-negative isolates collected from 131 study centres in 44 countries from 1997 to 2000. MICs of gemifloxacin were compared with penicillin, amoxicillin-clavulanic acid, cefuroxime, azithromycin, clarithromycin, trimethoprim-sulphamethoxazole, ciprofloxacin, grepafloxacin and levofloxacin by broth microdilution. Penicillin resistance in Streptococcus pneumoniae was extremely high in the Middle East (65.6%), Africa (64.0%) and Asia (60.4%) and lower in North America (40.3%), Europe (36.9%) and the South Pacific (31.8%). Macrolide resistance in S. pneumoniae was highest in Asia (51.7%) but varied widely between laboratories in Europe (26.0%), North America (21.6%), the Middle East (13.7%), the South Pacific (10.6%) and Africa (10.0%). All the study quinolones were highly active against penicillin-resistant and macrolide-resistant S. pneumoniae. Overall, gemifloxacin had the lowest MIC(90) at 0.06 mg/l with MICs 4-64-fold lower than ciprofloxacin, levofloxacin and grepafloxacin against S. pneumoniae. Gemifloxacin MICs were more potent than grepafloxacin > levoflaxacin > ciproflaxin against the Gram-positive aerobes and shared comparable Gram-negative activity with ciprofloxacin and levofloxacin.

In vitro antimicrobial activity of moxifloxacin compared to other quinolones against recent clinical bacterial isolates from hospitalized and community-based cancer patients

The in vitro spectrum of moxifloxacin (a C-8-methoxyquinolone) was compared to that of ciprofloxacin and levofloxacin against 924 recent clinical isolates from cancer patients. Moxifloxacin was more active than the comparator agents against Gram-positive pathogens, with potent activity against Aerococcus spp., Listeria monocytogenes, Micrococcus spp., Rhodococcus equi, and Stomatococcus mucilaginous, methicillin-susceptible Staphylococcus spp., all beta hemolytic streptococci, viridans streptococci and Streptococcus pneumoniae. It also had good to moderate activity against Bacillus spp., Corynebacterium spp., Enterococcus faecalis, and methicillin-resistant staphylococci. Although ciprofloxacin was the most active agent tested against the Enterobacteriaceae, moxifloxacin inhibited the majority of these isolates at < or =2.0 microg/ml. Moxifloxacin was the least active of the three agents tested against Pseudomonas aeruginosa, but had significant activity against other non-fermentative Gram-negative bacilli including Acinetobacter spp., Flavobacterium spp., Pseudomonas spp. other than P. aeruginosa, and Stenotrophomonas maltophilia. The overall broad spectrum of moxifloxacin, and its availability for both oral and parenteral administration, warrants its evaluation for the prevention and treatment of infections in cancer patients.

The penetration of moxifloxacin into the pancreas of male rats in experimental acute necrotizing pancreatitis

Infectious complications of acute necrotizing pancreatitis (ANP) determine the extent of multiorgan failure and account for 80% of deaths. Prophylactic use of antibiotics can reduce the incidence of these complications. However, the actual indication as well as choice of drug remains a controversial matter. We examined the penetration of moxifloxacin, a new broad-spectrum fluoroquinolone, in healthy and inflamed pancreatic tissue in rats after inducing ANP. The concentration of moxifloxacin in pancreatic tissue and serum was determined 10, 30, 60 and 240 min after the administration of moxifloxacin (5 mg/kg, i.v.). Mean serum concentrations 10 min after administration in rats with ANP were 1,886 ng/ml versus 1,805 ng/ml in healthy controls, and these values decreased to 350 versus 222 ng/ml, respectively, after 240 min. Corresponding concentrations in pancreatic tissue were in the mean 2-3 times higher.

Novel antibacterial agents for the treatment of serious Gram-positive infections

With the continuing development of clinical drug resistance among bacteria and the advent of resistance to the recently released agents quinupristin-dalfopristin and linezolid, the need for new, effective agents to treat multi-drug-resistant Gram-positive infections remains important. This review focuses on agents presently in clinical development for the treatment of serious multidrug-resistant staphylococcal, enterococcal and pneumococcal infections, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and penicillin-resistant Streptococcus pneumoniae. Agents to be discussed that affect the prokaryotic cell wall include the antimethicillin-resistant S. aureus cephalosporins BAL9141 and RWJ-54428, the glycopeptides oritavancin and dalbavancin and the lipopeptide daptomycin. Topoisomerase inhibitors include the fluoroquinolones gemifloxacin, sitafloxacin and garenoxacin. Protein synthesis inhibitors are represented by the ketolides telithromycin and cethromycin, the oxazolidinones and the glycylcycline tigecycline. Although each of these compounds has demonstrated antibacterial activity against antibiotic-resistant pathogens, their final regulatory approval will depend on an acceptable clinical safety profile.

Topoisomerase targeting with and resistance to gemifloxacin in Staphylococcus aureus

Gemifloxacin, a novel quinolone with potent activity against Staphylococcus aureus, was 8- to 16-fold more active against wild-type S. aureus than ciprofloxacin. The two- to fourfold increase in the MIC of gemifloxacin in genetically defined grlBA mutants and the twofold increase in a single gyrA mutant, supported by the low frequency of selection of resistant mutants at twice the MIC (7.4 x 10(-11) to 1.1 x 10(-10)), suggested similar targeting of the two enzymes by gemifloxacin. Dual mutations in both gyrase and topoisomerase IV caused a 64- to 128-fold increase in the MIC of gemifloxacin, similar to that seen with ciprofloxacin. Gemifloxacin also had similar activity in vitro against topoisomerase IV and gyrase purified from S. aureus (50% inhibitory concentrations of 0.25 and 0.31 micro g/ml, respectively). This activity was 10- to 20-fold higher than that of ciprofloxacin for topoisomerase IV and 33-fold higher than that for gyrase. In contrast to the in vitro findings, only topoisomerase IV mutants were selected in first-step mutants. Overexpression of the NorA efflux pump had a minimal effect on resistance to gemifloxacin, and a mutation in the promoter region of the gene for NorA was selected only in the sixth step of serial selection of mutants. Our data show that although gemifloxacin targets purified topoisomerase IV and gyrase similarly in vitro, topoisomerase IV is the preferred target in the bacteria. Selection of novel resistance mutations in grlA requires further expansion of quinolone-resistance-determining regions, and their study may provide increased insight into enzyme-quinolone interactions.

In vitro activity of linezolid, synercid and telithromycin against genetically defined high level fluoroquinolone-resistant methicillin-resistant Staphylococcus aureus

The in vitro activity of levofloxacin, moxifloxacin, gatifloxacin, erythromycin, telithromycin, linezolid, synercid and vancomycin was measured against 36 genetically defined, gyrA/grlA double mutant MRSA clinical strains with an MIC to ciprofloxacin > or = 8 mg/l. The three newer fluoroquinolones tested were more active than ciprofloxacin. Resistance rates for levofloxacin and gatifloxacin were high (44.5 and 36.1%, respectively). All the strains were moxifloxacin-susceptible, though most of them had MICs close to the break point. All the strains were intermediate or resistant to erythromycin and most were also resistant to telithromycin. No strains were resistant to linezolid, synercid or vancomycin (MIC(90): 2, 1 and 2 mg/l, respectively).

Coagulase-negative staphylococci as a cause of infections related to intravascular prosthetic devices: limitations of present therapy

Coagulase-negative staphylococci (CNS) are an important cause of catheter-related bloodstream infections. This review will shed light on the pathogenesis related to biofilm formation, and will discuss antimicrobial susceptibility of CNS to older and newer antibiotics, as well as therapeutic options.

A critical review of the fluoroquinolones: focus on respiratory infections

The new fluoroquinolones (clinafloxacin, gatifloxacin, gemifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin) offer excellent activity against Gram-negative bacilli and improved Gram-positive activity (e.g. against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Ciprofloxacin still maintains the best in vitro activity against Pseudomonas aeruginosa. Clinafloxacin, gatifloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (e.g. Bacteroides fragilis) versus ciprofloxacin. All of the new fluoroquinolones display excellent bioavailability and have longer serum half-lives than ciprofloxacin allowing for once daily dose administration. Clinical trials comparing the new fluoroquinolones to each other or to standard therapy have demonstrated good efficacy in a variety of community-acquired respiratory infections (e.g. pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis). Limited data suggest that the new fluoroquinolones as a class may lead to better outcomes in community-acquired pneumonia and acute exacerbations of chronic bronchitis versus comparators. Several of these agents have either been withdrawn from the market, had their use severely restricted because of adverse effects (clinafloxacin because of phototoxicity and hypoglycaemia; grepafloxacin because of prolongation of the QTc and resultant torsades de pointes; sparfloxacin because of phototoxicity; and trovafloxacin because of hepatotoxicity), or were discontinued during developmental phases. The remaining fluoroquinolones such as gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin have adverse effect profiles similar to ciprofloxacin. Extensive post-marketing safety surveillance data (as are available with ciprofloxacin and levofloxacin) are required for all new fluoroquinolones before safety can be definitively established. Drug interactions are limited; however, all fluoroquinolones interact with metal ion containing drugs (eg. antacids). The new fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin) offer several advantages over ciprofloxacin and are emerging as important therapeutic agents in the treatment of community-acquired respiratory infections. Their broad spectrum of activity which includes respiratory pathogens such as penicillin and macrolide resistant S. pneumoniae, favourable pharmacokinetic parameters, good bacteriological and clinical efficacy will lead to growing use of these agents in the treatment of community-acquired pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis. These agents may result in cost savings especially in situations where, because of their potent broad-spectrum activity and excellent bioavailability, they may be used orally in place of intravenous antibacterials. Prudent use of the new fluoroquinolones will be required to minimise the development of resistance to these agents.

Comparative in vitro activity of gemifloxacin against gram-positive and gram-negative clinical isolates in Argentina

The in vitro activity of gemifloxacin against 1,000 clinical isolates of 147 Streptococcus pneumoniae (115, penicilin susceptible; 26, intermediate penicillin-resistant and 6, penicillin-resistant), 127 Hemophilus influenzae (109, beta lactamasa non-producer; 18, beta lactamase producers), 95 Streptococcus pyogenes (6, azytromycin-resistant), 84 Moraxella catarrhalis (79, beta lactamase producers), 110 Staphilococcus aureus (89, methicillin-susceptible; 21, methicilin-resistant), 98 Eenterococcus faecalis and 339 Enterobacteriacea, (recovered from patients with respiratory tract infection; skin and soft tissue infection and urinary tract infection), was compared with the activities of four fluorquinolones and five other antimicrobial agents. Of the quinolones tested, gemifloxacin was the most potent against Streptococcus pneumoniae, including penicillin intermediate and resistant strains. Mic(90) values obtained for gemifloxacin, ciprofloxacin, ofloxacin, levofloxacin and trvafloxacin were 0.03, 2, 2, 1 and 0.25 mg/L respectively. Gemifloxacin was 16 fold more potent than ciprofloxacin against methicillin-susceptible Staphylococcus aureus and 32 fold more potent than ciprofloxacin against Streptococcus pyogenes. When tested against Hemophilus influenzae, Moraxella catarrhalis and Enterobacteriaceae, all the quinolones showed similar activity. Our results demonstrate that gemifloxacin has similar activity than the other quinolones tested against Gram-negative organisms and is considerably more potent against Gram-positive organisms.

Comparative in vitro activity of the new quinolone gemifloxacin (SB-265805) with other fluoroquinolones against respiratory tract pathogens

The in vitro activity of gemifloxacin (SB-265805) was compared with that of other fluoroquinolones against 302 clinical isolates of Streptococcus pneumoniae, 300 clinical isolates of Haemophilus influenzae and 28 clinical isolates of Moraxella catarrhalis, including multiply resistant strains. Gemifloxacin at 0.12 mg/L inhibited all microorganisms tested. MIC(90) values of gemifloxacin, trovafloxacin, grepafloxacin and levofloxacin against all (630) isolates tested were 0.03, 0.12, 0.12 and 1 mg/L, respectively. MIC(90) values of the same fluoroquinolones against S. pneumoniae were 0.06, 0.25, 0.12 and 1 mg/L, respectively.

Comparative in vitro activity of gemifloxacin, ciprofloxacin, levofloxacin and ofloxacin in a North American surveillance study

The in vitro activity of gemifloxacin, a new fluoroquinolone, was compared to three marketed fluoroquinolones; ciprofloxacin, levofloxacin and ofloxacin against over 4,000 recent clinical isolates covering 29 species isolated in the United States and Canada between 1997-1999. Based on MIC(90)s, gemifloxacin was the most potent fluoroquinolone tested against a majority of Gram-positive isolates: Streptococcus pneumoniae, penicillin resistant S. pneumoniae, macrolide resistant S. pneumoniae, ciprofloxacin non-susceptible (MIC > or = 4 microg/mL) S. pneumoniae, S. pyogenes, S. agalactiae, viridans streptococci, Enterococcus faecalis, methicillin susceptible Staphylococcus aureus, methicillin resistant S. aureus, S. epidermidis, S. hemolyticus, and S. saprophyticus. Against Enterobacteriaceae and aerobic non-Enterobacteriaceae Gram-negatives, gemifloxacin was usually comparable to ciprofloxacin and levofloxacin and more potent than ofloxacin for the following species: Citrobacter freundii, Enterobacter aerogenes, E. cloacae, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Morganella morganii, Proteus mirabilis, P. vulgaris, Providencia stuartii, Serratia marcescens, Acinetobacter lwoffii, A. baumannii, Burkholderia cepacia, Haemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia. Gemifloxacin was generally 16-64 fold more potent than the other fluoroquinolones tested against Gram-positive organisms and retains excellent activity comparable with ciprofloxacin and levofloxacin against a majority of Gram-negative pathogens.

In vitro activity of gemifloxacin against Streptococcus pneumoniae isolates in Germany

The MICs (minimal inhibitory concentrations) of gemifloxacin, moxifloxacin, ofloxacin, ciprofloxacin, levofloxacin, sparfloxacin, penicillin G, tetracycline and erythromycin were determined for 200 clinical pneumococcal isolates using the microbroth dilution method. MIC(50) and MIC(90) values were as follows (mg/l): 0.016 and 0.016 (gemifloxacin, penicillin-intermediate strains), 0.03 and 0.06 (gemifloxacin, penicillin-susceptible strains); 0.125-0.5 and 0.25 (moxifloxcacin); 1-2 and 4 (ciprofloxacin and ofloxacin); 1 and 2 (levofloxacin), and 0.25-0.5 and 0.5 (sparfloxacin). MIC(50) and MIC(90) values for the fluoroquinolones were nearly identical for individual antimicrobial agents in the penicillin-susceptible and penicillin-intermediate groups of strains. Erythromycin and tetracycline were less active against penicillin-intermediate pneumococci isolates (erythromycin: MIC(90) 8 mg/l; MIC range 0.06-> or =64 mg/l; tetracycline: MIC(90) > or =64 mg/l, MIC range 0.25- > or =64 mg/l) as compared to penicillin-susceptible isolates (erythromycin: MIC(90) 0.5 mg/l, MIC range 0.06-> or =64 mg/l; tetracycline: MIC(90) 8 mg/l, MIC range 0.06-> or =64 mg/l).

In vitro activity of gemifloxacin against contemporary clinical bacterial isolates from eleven North American medical centers, and assessment of disk diffusion test interpretive criteria

A total of 5499 contemporary clinical bacterial isolates were tested for susceptibility to gemifloxacin and four comparison agents by the broth microdilution method. Gemifloxacin activity against Enterobacteriaceae was generally comparable to that of ciprofloxacin and trovafloxacin, but because the gemifloxacin susceptible MIC breakpoint is lower, the percent susceptible to gemifloxacin was less than that to the other quinolones for some species. All agents were less active against Pseudomonas spp. Gemifloxacin was the most active agent tested against Gram-positive species, though Corynebacterium jeikeium and vancomycin-resistant enterococci were uniformly resistant to all agents tested. With staphylococci, a bimodal distribution of gemifloxacin MICs corresponded with susceptibility or resistance to ciprofloxacin. The significance of ciprofloxacin-resistant staphylococci that have susceptible gemifloxacin MICs is not known at this time. Disk diffusion tests were performed simultaneously with gemifloxacin and trovafloxacin as a control drug. Gemifloxacin MIC-zone diameter scattergrams indicated that interpretive discrepancy rates based on previously proposed criteria when using < or = 0.5 microg/ml as the susceptible MIC breakpoint was within acceptable limits. However, with the currently proposed MIC breakpoint of < or = 0.25 microg/ml, tentative zone diameter breakpoints of > or = 22 mm for susceptible, 19-21 mm for intermediate and < or = 18 mm for resistant are proposed.

New agents for Gram-positive bacteria

Infections caused by multiple-resistant Gram-positive organisms continue to occur at an alarming rate worldwide. Two new and unique antimicrobial agents targeted specifically against such organisms, quinupristin/dalfopristin and linezolid, have been approved for use in the USA in the past year and will play an important role in the treatment of life-threatening infections. In addition, several new fluoroquinolones have been approved recently or will be available in the near future to aid in the treatment of infections caused by resistant strains of Streptococcus pneumoniae.

Gemifloxacin

Gemifloxacin is a fluoroquinolone antibacterial agent which has an enhanced affinity for topoisomerase i.v.. It has potent activity against most Gram-positive bacteria, particularly Streptococcus pneumoniae. Gemifloxacin is over 30-fold more active than ciprofloxacin and 4- to 8-fold more active than moxifloxacin against this pathogen. Gemifloxacin has excellent activity against Haemophilus influenzae and Moraxella catarrhalis, and is unaffected by beta-lactamase production. It is generally 2-fold less active than ciprofloxacin against most Enterobacteriaceae. Atypical respiratory pathogens (Legionella, Mycoplasma and Chlamydia spp.) are highly susceptible to gemifloxacin. Preliminary results from phase II trials show that oral gemifloxacin 320 mg/day produced bacteriological responses of 94.7% in patients with acute exacerbations of chronic bronchitis and 95% of patients with uncomplicated urinary tract infections. Adverse events included nausea, abdominal pain, headache and mild rash in patients and healthy volunteers treated with gemifloxacin 320 mg/day. Gemifloxacin has a low potential for mild phototoxicity (comparable to that of ciprofloxacin).