Linezolid--a review of the first oxazolidinone

Successful Treatment of Cutibacterium acnes Prosthetic Joint Infection With Single-Stage Exchange and Oral Antibiotics

Interest has grown in less invasive surgical treatment and early use of oral antibiotics in the treatment of Cutibacterium acnes prosthetic joint infection. We report a series of patients who were successfully treated with single-stage exchange and an all-oral course of rifampin and linezolid.

Prevalence and risk factors for severe linezolid-associated thrombocytopenia in pediatric patients: An analysis of a public database

Linezolid is widely used in various clinical settings. Studies have revealed that it may cause thrombocytopenia in adults. However, the correlation between the use of linezolid and thrombocytopenia in pediatric patients is still unclear. This study aimed to identify the impact of Linezolid on the occurrence of thrombocytopenia in children. A retrospective observational study was conducted using data on patients treated with linezolid from the Pediatric Intensive Care clinical database. Univariate and multiple logistic regression analyses were performed to identify the risk factors of linezolid-related severe thrombocytopenia. A total of 134 patients were included. The prevalence of severe thrombocytopenia was 8.96% (12/134). Univariate analysis indicated that the severe thrombocytopenia group showed significantly higher proportion of concomitant carbapenem (75% vs 44.3%; P < .05) and piperacillin/tazobactam (25% vs 6.6%; P < .05) than that of the non-severe thrombocytopenia group. Multivariate analysis also revealed that the occurrence of severe thrombocytopenia was significantly associated with concurrent use of carbapenem (odd ratio = 4.058; 95% confidence interval: 1.012-16.274; P = .048) and piperacillin/tazobactam (odd ratio = 5.335; 95% confidence interval: 1.117-25.478; P = .036). 75% of patients (9/12) developed severe thrombocytopenia within the first 7 days of linezolid use. The concomitant use of carbapenem and piperacillin/tazobactam was associated with an increased probability of severe thrombocytopenia in pediatric patients undergoing linezolid treatment. Further prospective clinical studies are required, and more detailed mechanisms of blood toxicity in pediatric patients must be investigated.

Current Landscape and Future Perspective of Oxazolidinone Scaffolds Containing Antibacterial Drugs

The widespread use of antibiotics has made the problem of bacterial resistance increasingly serious, and the study of new drug-resistant bacteria has become the main direction of antibacterial drug research. Among antibiotics, the fully synthetic oxazolidinone antibacterial drugs linezolid and tedizolid have been successfully marketed and have achieved good clinical treatment effects. Oxazolidinone antibacterial drugs have good pharmacokinetic and pharmacodynamic characteristics and unique antibacterial mechanisms, and resistant bacteria are sensitive to them. This Perspective focuses on reviewing oxazolidinones based on the structural modification of linezolid and new potential oxazolidinone drugs in the past 10 years, mainly describing their structure, antibacterial activity, safety, druggability, and so on, and discusses their structure-activity relationships, providing insight into the reasonable design of safer and more potent oxazolidinone antibacterial drugs.

Staphylococcal meningitis therapy with linezolid in a young infant: efficacy, CSF levels and side effects

Background

Linezolid is a synthetic antibiotic which is active against most Gram-positive bacteria, especially on Staphylococcus aureus. Its administration can be required when the infection is due to staphylococcus strains, which are resistant to vancomycin. Although mostly well tolerated, some mild to moderate side effects have been reported.

Case presentation

This case report describes an infant with multiloculated hydrocephalus, staphylococcal meningitis and prolonged linezolid therapy, in which we observed the association between linezolid administration and a lengthened QTc interval at the electrocardiogram (ECG). To rule out toxic levels during the therapy, plasma and cerebro-spinal fluid concentrations of linezolid were measured and reported.

Conclusions

Although generally well tolerated in neonates and infants, linezolid prolonged administration seems be able to cause QTc interval prolongation. Therefore, its administration in such patients should be limited to cases of bacterial resistance to other antibiotics. In addition to well-known close monitoring of the platelet level, we suggest serial ECG controls before and during linezolid administration. In the case we report, linezolid plasma concentrations resulted within the therapeutic range during therapy, while cerebrospinal fluid (CSF) concentrations appeared lower than those considered effective.

Pharmacokinetic evaluation of linezolid administered intravenously in obese patients with pneumonia

OBJECTIVES

Altered linezolid pharmacokinetics (PK) in obese individuals has been hypothesized in previous studies. However, specific dosing recommendations for this population are still lacking. The main goal of this study was to evaluate PK/pharmacodynamic (PKPD) target attainment when using a 600 mg intravenous q12h linezolid dose against MRSA in obese patients with pneumonia.

METHODS

Fifteen obese pneumonia patients with a confirmed or suspected MRSA involvement treated with 600 mg of intravenous linezolid q12h were studied for 3 days. Population PK modelling was used to characterize the PK variability and to screen for influential patient characteristics. Monte Carlo simulations were carried out to investigate the PTA and time to target attainment for linezolid dosing against MRSA.

RESULTS

A two-compartment model with linear elimination adequately described the data. Body weight and age both have a significant effect on linezolid clearance. Simulations demonstrate that the probability of attaining PKPD targets is low. Moreover, the PTA decreases with weight, and increases with age. Standard linezolid dosing in obese pneumonia patients with MRSA (MICs of 1-4 mg/L) leads to unacceptably low (near zero to 60%) PTA for patients <65 years old.

CONCLUSIONS

Standard linezolid dosing is likely to provide insufficient target attainment against MRSA in obese patients. Body weight and especially age are important characteristics to be considered when administering linezolid to treat MRSA infections.

Solar-mediated degradation of linezolid and tedizolid under simulated environmental conditions: Kinetics, transformation and toxicity

Linezolid (LIN) and Tedizolid (TED) are representatives of oxazolidinone antibiotics of last resort with a strong efficacy against gram-positive bacteria. This study focused on their solar-mediated degradation to understand better their fate in aquatic environment, for the realistic concentrations in the range of 1 μg/L. Results showed that both antibiotics (ABs) are degradable by simulated sunlight (1 kW/m²), with half-lives of 32 and 93 h in ultrapure water, for LIN and TED, respectively. LIN showed similar photolytic behaviour in pure solution and in surface water, whereas sunlight enhanced the degradation of LIN in pure solutions, but not in surface water. Structure elucidation by liquid chromatography coupled to high resolution mass spectrometry provided information about seven transformation products for LIN and five for TED. The morpholinyl-ring was identified as the target site for most transformation reactions of LIN. TED was prone to oxidation and cleavage of the oxazolidinone ring. Results of a growth inhibition test on Bacillus subtilis exposed to UV light showed antibacterial efficacy of transformation products of LIN and no significant efficacy of degradation products of TED for the concentration range of 100 μg/L-10 mg/L of parent compounds. Photolytically treated solutions of the ABs maintained their inhibitory effect on the bioluminescence of Aliivibrio fischeri.

Improved synthesis of YG-056SP, a potent oxazolidinone antibacterial candidate against multi-drug resistant bacteria

An improved process for the synthesis of YG-056SP, a potent oxazolidinone candidate against multi-drug resistant bacteria, is developed. Compared with the original synthetic route, this new approach is two steps shorter, and all of the steps involve simple purifications without column chromatography. More importantly, it avoids the use of explosive azide compounds and expensive metal catalysts. The new reaction conditions are mild and safe, which is more suitable for the scalable synthesis of YG-056SP for preclinical studies.

Empiric Antibiotic Therapy of Nosocomial Bacterial Infections

Broad-spectrum antibiotics are commonly used by physicians to treat various infections. The source of infection and causative organisms are not always apparent during the initial evaluation of the patient, and antibiotics are often given empirically to patients with suspected sepsis. Fear of attempting cephalosporins and carbapenems in penicillin-allergic septic patients may result in significant decrease in the spectrum of antimicrobial coverage. Empiric antibiotic therapy should sufficiently cover all the suspected pathogens, guided by the bacteriologic susceptibilities of the medical center. It is important to understand the major pharmacokinetic properties of antibacterial agents for proper use and to minimize the development of resistance. In several septic patients, negative cultures do not exclude active infection and positive cultures may not represent the actual infection. This article will review the important differences in the spectrum of commonly used antibiotics for nosocomial bacterial infections with a particular emphasis on culture-negative sepsis and colonization.

Antibacterial, antifungal and antimycobacterial activities of some pyrazoline, hydrazone and chalcone derivatives

Twenty-seven previously reported chalcones and their pyrazoline and hydrazone derivatives as well as two further chalcones have been screened for their antimicrobial, antifungal and antimycobacterial activities against standard microbial strains and drug resistant isolates. The minimum inhibitory concentration (MIC) value of each compound was determined by a two-fold serial microdilution technique. The compounds were found to possess a broad spectrum of antimicrobial activities with MIC values of 8–128 μg/mL. One compound [(E)-1-(4-hydroxyphenyl)-3-p-tolylprop-2-en-1-one] had equal activity with gentamycin (8 μg/mL) against Enterococcus faecalis. Chalcones were found to be more active than their hydrazone and 2-pyrazoline derivatives against Staphylococcus aureus ATCC 29213 and E. faecalis ATCC 29212.

Synthesis and in vitro antibacterial activity of novel fluoroalkyl-substituted pyrazolyl oxazolidinones

A series of novel fluoroalkyl-substituted pyrazole bearing oxazolidinone derivatives were synthesized and evaluated for their antibacterial activity against six Gram-positive bacterial pathogens. Most have good antibacterial activity, three being comparable to linezolid.

An azido-oxazolidinone antibiotic for live bacterial cell imaging and generation of antibiotic variants

An azide-functionalised analogue of the oxazolidinone antibiotic linezolid was synthesised and shown to retain antimicrobial activity. Using facile 'click' chemistry, this versatile intermediate can be further functionalised to explore antimicrobial structure-activity relationships or conjugated to fluorophores to generate fluorescent probes. Such probes can report bacteria and their location in a sample in real time. Modelling of the structures bound to the cognate 50S ribosome target demonstrates binding to the same site as linezolid is possible. The fluorescent probes were successfully used to image Gram-positive bacteria using confocal microscopy.

Structure of the bacterial deacetylase LpxC bound to the nucleotide reaction product reveals mechanisms of oxyanion stabilization and proton transfer

The emergence of antibiotic-resistant strains of pathogenic bacteria is an increasing threat to global health that underscores an urgent need for an expanded antibacterial armamentarium. Gram-negative bacteria, such as Escherichia coli, have become increasingly important clinical pathogens with limited treatment options. This is due in part to their lipopolysaccharide (LPS) outer membrane components, which dually serve as endotoxins while also protecting Gram-negative bacteria from antibiotic entry. The LpxC enzyme catalyzes the committed step of LPS biosynthesis, making LpxC a promising target for new antibacterials. Here, we present the first structure of an LpxC enzyme in complex with the deacetylation reaction product, UDP-(3-O-(R-3-hydroxymyristoyl))-glucosamine. These studies provide valuable insight into recognition of substrates and products by LpxC and a platform for structure-guided drug discovery of broad spectrum Gram-negative antibiotics.

The safety and efficacy of linezolid and daptomycin as an additive in Optisol-GS against methicillin-resistant Staphylococcus aureus

PURPOSE

To evaluate the efficacy of adding either linezolid or daptomycin to Optisol-GS donor storage medium in reducing methicillin-resistant Staphylococcus aureus (MRSA) contamination of donor corneas.

METHODS

Optisol-GS was supplemented with either linezolid at 2×, 4×, or 10× minimum inhibitory concentration (MIC) or daptomycin and calcium at 5× or 50× MIC. Unsupplemented control groups were also used. Gentamicin-sensitive and gentamicin-resistant isolates of MRSA were added, and vials were refrigerated for 48 hours followed by sampling for viable colony counts immediately upon removal from refrigeration and after warming to room temperature for 3 hours. Safety studies of Optisol-GS supplemented with 50× MIC daptomycin and calcium were performed by evaluating the central corneal thickness and endothelial cell density of the donor cornea. Stability of daptomycin in Optisol-GS at storage was also tested.

RESULTS

No added benefit was observed with linezolid supplementation to Optisol-GS against gentamicin-sensitive MRSA, with reduction in viable colony counts by >90% in all groups. No benefit was observed with linezolid supplementation against gentamicin-resistant MRSA, with the majority of inocula remaining viable in all groups. Viable counts of gentamicin-sensitive MRSA and gentamicin-resistant MRSA were effectively reduced with both 5× MIC and 50× MIC daptomycin supplementation. 50× MIC daptomycin-supplemented Optisol-GS had no appreciable effect on the central corneal thickness or endothelial cell density of the donor cornea and was stable at storage for 14 days.

CONCLUSIONS

The addition of daptomycin to Optisol-GS significantly increases the anti-MRSA activity of the medium without any apparent negative effects on donor corneal tissue.

Combined retrospective analysis of seven phase II and III trials of the efficacy of linezolid in the treatment of pneumonia caused by multidrug-resistant Streptococcus pneumoniae

BACKGROUND

Antimicrobial resistance among Streptococcus pneumoniae is of concern. Up to 30% of pneumococcal isolates worldwide are multidrug resistant.

OBJECTIVE

The objective of this analysis was to assess the effectiveness of linezolid for the treatment of pneumonia caused by S pneumoniae, including multidrug-resistant S pneumoniae (MDRSP).

METHODS

Data from 7 Phase II and III clinical trials that assessed the efficacy of linezolid in community- or hospital-acquired pneumonia were pooled. Adults and children (aged ≤12 years) received linezolid 600 mg and 10 mg/kg, respectively, IV or PO q12h for 7 to 14 days, with the exception of patients with documented bacteremia who could be treated for up to 28 days. Patients with a confirmed baseline isolate of S pneumoniae, including MDRSP, were assessed for clinical and microbiological outcomes. MDRSP was defined as an isolated strain of S pneumoniae that was resistant to ≥3 classes of antibiotics. Clinical cure was defined as the resolution of clinical signs and symptoms of pneumonia compared with baseline, with either improvement or absence of progression of abnormalities on chest radiography. Microbiological eradication was defined as documented or presumed eradication at the test-of-cure (TOC) visit. Results from patients with indeterminate or missing outcomes at TOC were not included in the analyses.

RESULTS

Of the patients with no bacteremia and treated with linezolid, 19 adults had MDRSP and 165 had non-MDRSP, and 3 children had MDRSP and 7 had non-MDRSP. Clinical cure and microbiological eradication rates were not significantly different between those infected with an MDRSP or non-MDRSP pathogen, respectively, in adults (16/19 [84%] and 150/164 [91%]) and children (3/3 [100%] and 7/7 [100%]).

CONCLUSION

Linezolid was efficacious for the treatment of pneumonia caused by S pneumoniae, including multidrug-resistant strains.

Emerging drugs for complicated skin and skin-structure infections

IMPORTANCE OF THE FILED: With the worldwide surge of MRSA, skin and skin-structure infection (SSTI) treatment has become a challenge for physicians. Cultures and antibiotic susceptibility tests for SSTIs are the rule due to the implication in morbidity and mortality rates associated with MRSA infections. The need for new antibiotics is evident and the effort to decrease antibiotic resistance is a world priority.

AREAS COVERED IN THIS REVIEW

This manuscript accesses the actual treatments and the developing of antibiotics for MRSA SSTIs.

WHAT THE READER WILL GAIN

This is a review of the data on the available and emerging treatments for MRSA SSTIs.

TAKE HOME MESSAGE

There is an unmet medical need for new antibiotics in the new millennium. As physicians, we must assure all appropriate procedures are completed in order to reduce the bacterial resistance, especially for MRSA.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Antimicrobial resistance in Bacteroides spp.: occurrence and dissemination

Bacteroides spp. organisms, though important human commensals, are also opportunistic pathogens when they escape the colonic milieu. Resistance to multiple antibiotics has been increasing in Bacteroides spp. for decades, and is primarily due to horizontal gene transfer of a plethora of mobile elements. The mechanistic aspects of conjugation in Bacteroides spp. are only now being elucidated at a functional level. There appear to be key differences between Bacteroides spp. and non-Bacteroides spp. conjugation systems that may contribute to promiscuous gene transfer within and from this genus. This review summarizes the mechanisms of action and resistance of antibiotics used to treat Bacteroides spp. infections, and highlights current information on conjugation-based DNA exchange.

Synthesis and in vitro antibacterial activity of novel methylamino piperidinyl oxazolidinones

Design and synthesis of a few novel methylamino piperidinyl substituted oxazolidinones are reported. Their antibacterial activities have been evaluated in a MIC assay against broader panel of both susceptible and resistant Gram-positive strains. (S)-N-{3-[3-Fluoro-4-(methyl-{1-[3-(5-nitrofuran-2-yl)-acryloyl]-piperidin-4-yl}-amino)-phenyl]-2-oxo-oxazolidin-5-ylmethyl}-acetamide 4i has shown comparable antibacterial activity to linezolid and eperezolid in the MIC assay, additionally compound 4i showed good antibacterial activity with an in vitro MIC value of 2-4 microg/mL against linezolid resistant Staphylococcus aureus (linezolid 16 microg/mL).

Antibiotic resistance in Staphylococcus aureus and its relevance in therapy

Staphylococcus aureus is a major cause of infections. Only approximately 20% of the strains remain sensitive to penicillin. Beta-lactamase stable penicillins such as flucloxacillin form the mainstay of treatment of staphylococcal infection. Meticillin-resistant S. aureus (MRSA) are resistant to all beta-lactam antibiotics. Glycopeptide antibiotics are effective against most MRSA strains but, in the last few years, isolates of MRSA that have reduced susceptibility to glycopeptides (glycopeptide-intermediate S. aureus) have been isolated. Some strains exhibit frank resistance to glycopeptides (vancomycin-resistant S. aureus). Infections due to these strains are difficult to treat. This review summarises the therapeutic options for MRSA, glycopeptide-intermediate S. aureus and vancomycin-resistant S. aureus. Novel therapeutic strategies such as immunotherapy and vaccines are also discussed.

In vivo efficacy of a novel oxazolidinone compound in two mouse models of infection

A novel oxazolidinone, AM 7359, was evaluated in two mouse models of Staphylococcus aureus infection. AM 7359 and linezolid were equally efficacious in a methicillin-susceptible S. aureus organ burden model and a methicillin-resistant S. aureus localized infection model. However, AM 7359 was eightfold more efficacious than linezolid against a linezolid- and methicillin-resistant S. aureus strain in this localized (thigh) infection model.

The use of systemic antibiotics in the treatment of chronic wounds

The role of microorganisms in the etiology and persistence of chronic wounds remains poorly understood. The chronic wound bed houses a complex microenvironment that typically includes more than one bacterial species. Difficulty lies in determining when the presence of bacteria impedes wound healing, thereby warranting intervention. Indications for antibiotic therapy and optimal treatment regimens are ill defined. The goal of this article is to describe the appropriate role of systemic antibiotics in the management of chronic wounds. A common sense approach will be offered based on six clinically pertinent questions: Is infection present? Are systemic antibiotics necessary? Should treatment be enteral or parenteral? What antibiotic or combination of antibiotics should be used? What should be the duration of therapy? What special circumstances are present (i.e., concomitant illnesses, potential drug-drug interactions) that can impact therapy?

Structure-activity relationships of 3-aminoquinazolinediones, a new class of bacterial type-2 topoisomerase (DNA gyrase and topo IV) inhibitors

A series of 3-aminoquinazolinediones was synthesized and evaluated for its antibacterial and DNA gyrase activity. The SAR around the quinazolinedione core was explored and the optimal substitutions were combined to give two compounds, 2r and 2s, with exceptional enzyme potency (IC50 = 0.2 microM) and activity against gram-positive organisms (MIC's = 0.015-0.06 microg/mL).

Small molecules with antimicrobial activity against E. coli and P. aeruginosa identified by high-throughput screening

BACKGROUND AND PURPOSE

New antimicrobials are needed because of the emergence of organisms that are resistant to available antimicrobials. The purpose of this study was to evaluate a high-throughput screening approach to identify antibacterials against two common disease-causing bacteria, and to determine the frequency, novelty, and potency of compounds with antibacterial activity.

EXPERIMENTAL APPROACH

A high-throughput, turbidometric assay of bacterial growth in a 96-well plate format was used to screen a diverse collection of 150,000 small molecules for antibacterial activity against E. coli and P. aeruginosa. The statistical Z'-factor for the assay was > or = 0.7.

KEY RESULTS

Screening for inhibition of E. coli growth gave a 'hit' rate (> 60% inhibition at 12.5 microM) of 0.025%, which was more than 5-fold reduced for P. aeruginosa. The most potent antibacterials (EC50 < 0.5 microM) were of the nitrofuran class followed by naphthalimide, salicylanilide, bipyridinium and quinoazolinediamine chemical classes. Screening of > 250 analogs of the most potent antibacterial classes established structure-activity data sets.

CONCLUSIONS AND IMPLICATIONS

Our results validate and demonstrate the utility of a growth-based phenotype screen for rapid identification of small-molecule antibacterials. The favourable efficacy and structure-activity data for several of the antibacterial classes suggests their potential development for clinical use.

Efficacy and safety of linezolid in multidrug resistant tuberculosis (MDR-TB)—a report of ten cases

OBJECTIVES

Multidrug resistant tuberculosis (MDR-TB) is an increasing problem in many parts of the world and in Norway the increase has been substantial since 1998. New therapies for MDR-TB have not been introduced since the fluoroquinolones in the 1970s. The cure rate of this disease has been reported to be lower than for non-drug resistant TB, and the use of new experimental drugs in combination therapy is warranted.

METHODS

Ten consecutive patients with culture proven MDR-TB were treated with the novel antibiotic drug linezolid in combination regimens for 6-40 (median 17) weeks and followed up 11-50 (median 24) months after end of treatment. All strains were sensitive to linezolid with MIC<4 mg/l. Treatment was given as direct observed therapy (DOT) and sputum cultures, blood chemistry and neurologic examination were undertaken on a regular basis.

RESULTS

Nine patients were cured, one patient with poor adherence to treatment and advanced AIDS died. Seven of 10 patients experienced serious adverse events, which led to withdrawal of linezolid in all seven. Six patients developed peripheral neuropathy and five patients bone marrow depression, blood transfusions were given to three patients and in all five patients bone marrow function normalized after cessation of linezolid. Peripheral neuropathy was not fully reversed in all patients.

CONCLUSION

Linezolid seems highly active in combination treatment of MDR-TB. Cultures became negative 10-37 days after the introduction of the drug. However, peripheral neuropathy and bone marrow depression led to linezolid withdrawal in seven patients, and neuropathy may not be fully reversible in all patients.

Assessment of oral bioavailability and preclinical pharmacokinetics of DRF-6196, a novel oxazolidinone analogue, in comparison to linezolid

The aim of this study was to determine the bioavailability of a novel oxazolidinone, DRF-6196, in mice and rats following intravenous (i.v) and oral dosing and to compare the pharmacokinetics with those obtained following linezolid dosing. Blood samples were drawn at predetermined intervals up to 24 h post-dose after either DRF-6196 or linezolid administration. The concentrations of DRF-6196 and linezolid in various plasma samples were determined by a HPLC method. Following oral administration maximum concentrations of DRF-6196 were achieved within 0.5 h irrespective of the species. While the doses increased in the ratio of 1 : 3 : 10, mean Cmax and AUC(0-infinity) values in mice for DRF-6196 increased in the ratio of 1 : 3.87 : 8.53 and 1 : 2.51 : 9.24, respectively. Both the Cmax and AUC(0-infinity) values increased almost proportional to the dose administered in mice. Following i.v administration, the concentration of DRF-6196 declined in a bi-exponential fashion with terminal elimination half-life of 1.5 h irrespective of the species. The systemic clearance and volume of distribution of DRF-6196 in mice were 1.14 L/h/kg and 0.66 L/kg, respectively after i.v administration, while the respective values in rats were 0.61 L/h/kg and 0.41L/kg, respectively. Elimination half-life ranged between 0.8-1.5 h. Absolute oral bioavailability of DRF-6196 was found to be 80-96% across the test dose range. Although plasma levels of DRF-6196 were lesser compared to linezolid in the initial hours, it may not have any consequences on the clinical effectiveness of the molecule.

Update on linezolid: the first oxazolidinone antibiotic

Linezolid is the first of an entirely new class of antibiotics, the oxazolidinones, in decades. It has a spectrum of activity against virtually all important Gram-positive pathogens. The unique mechanism of action of linezolid makes cross-resistance with other antimicrobial agents unlikely. Linezolid has both intravenous and oral formulations and the latter is 100% bioavailable. Since its first approval and marketing in March 2000 in the US, linezolid has gained approval for use in many other countries for the treatment of community-acquired and nosocomial pneumonia, complicated and uncomplicated skin and soft-tissue infections, and infections caused by methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, including cases with concurrent bacteraemia. Several earlier comprehensive reviews summarised the chemistry, mechanism of action, pharmacokinetics, clinical efficacy and safety profile of linezolid. The present review provides an update on the latest data regarding the antimicrobial activity of linezolid versus other commonly used agents, the clinical and health-economic outcomes of linezolid versus vancomycin and teicoplanin, and safety issues.

Synthesis and Antimicrobial Activity of Some 5-[2-(Morpholin-4-yl)acetamido] and/or 5-[2-(4-Substituted piperazin-1-yl)acetamido]-2-(p-substituted phenyl)benzoxazoles

In this study, a series of twelve novel 5-[2-(morpholin-4-yl)acetamido] and/or 5-[2-(4-substituted pip-erazine-1-yl)acetamido]-2-(p-substituted phenyl]benzoxazole derivatives have been synthesized and their structures were confirmed by IR, (1)H NMR, and mass spectral data. These compounds were prepared by reacting 5-(2-chloroacetamido)-2-(4-p-substituted-phenyl)benzoxazoles, which were obtained by using 5-amino-2-[p-substituted-phenyl]benzoxazoles with chloroacetyl chloride, in the presence of morpholine or 1-substituted piperazines. All synthesized compounds 3-14 were tested by using the method of twofold serial dilution technique for in vitro activities against certain strains of Gram-positive, Gram-negative bacteria as well as the yeasts Candida albicans, Candida krusei, and Candida glabrata in comparison with standard drugs. Microbiological results showed that the newly synthesized compounds possessed a broad spectrum of activity, showing MIC values of 3.12-50 mug/mL against the Candida species.

Gemifloxacin: a new fluoroquinolone

Gemifloxacin is a dual targeted fluoroquinolone with potent in vitro activity against Gram-positive, -negative and atypical human pathogens--pathogens considered to be important causes of community-acquired respiratory tract infections. Gemifloxacin demonstrates impressive minimal inhibitory concentrations (MIC 90 ) values against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Chlamydia pneumoniae and Legionella spp., with MIC 90 values reported to be 0.016-0.06, < 0.0008-0.06, 0.008-0.3, 0.25, 0.125 and 0.016-0.07 microg/ml, respectively. Gemifloxacin is also active in vitro against a broad range of Gram-negative bacilli with MIC 90 values against the Enterobacteriaceae in the range of 0.016 to > 16 microg/ml ( Escherichia coli and Providencia stuartii, respectively), with the majority of the genus having MIC 90 drug concentrations < 0.5 microg/ml. The in vitro activity of gemifloxacin against anaerobic organisms is variable. The MIC values for gemifloxacin are not affected by beta-lactamase production nor by penicillin or macrolide resistance in S. pneumoniae. Gemifloxacin is approved by the FDA to be clinically efficacious against multi-drug resistant S. pneumoniae. The pharmacokinetics of gemifloxacin are such that the drug can be administered orally once-daily to yield or achieve sustainable drug concentrations exceeding the MIC values of clinically important organisms. Gemifloxacin has been shown to target both DNA gyrase (preferred target) and topoisomerase IV (secondary target) - enzymes critical for DNA replication and organism survival - against clinical isolates of S. pneumoniae. This dual targeting activity is thought to be important for reducing the likelihood for selecting for quinolone resistance. Gemifloxacin has been investigated and approved for therapy in patients with community-acquired pneumonia (CAP) and acute exacerbations of chronic bronchitis. In one study, more patients receiving gemifloxacin compared to clarithromycin remained free of exacerbations for longer periods of time (p < 0.016) and gemifloxacin had a shorter time to eradication of H. influenzae than did clarithromycin (p < 0.02). From efficacy studies, gemifloxacin was found to have an adverse profile that was comparable with other compounds. The most frequent side effects were diarrhoea, abdominal pain and headache. Gemifloxacin is a welcomed addition to currently available agents for the treatment of community-acquired lower respiratory tract infections. Other potential indications appear to be within the spectrum of this compound.

Synthesis and antibacterial activity of oxazolidinones containing pyridine substituted with heteroaromatic ring

A series of oxazolidinone derivatives, which morpholino group of linezolid was replaced with heteroaromatic ring substituted pyridine moiety, were newly synthesized, and their substituted effects on in vitro and in vivo antibacterial activities were evaluated against four problematic gram-positive strains including drug resistant strains and two gram-negative strains. Most compounds exhibited the enhanced in vitro activities with 4-16-fold and three compounds exerted more than 2-fold increased in vivo efficacies than linezolid.

Synthesis and in vitro antimycobacterial activity of novel 3-(1H-pyrrol-1-yl)-2-oxazolidinone analogues of PNU-100480

Pursuing our search program for new antitubercular drugs we decided to explore the potentiality of oxazolidinone moiety by synthesizing novel 3-(1H-pyrrol-1-yl)-2-oxazolidinone analogues of PNU-100480. The new derivatives were tested against atypical mycobacteria as well as against drug resistant Mycobacterium tuberculosis and some of them exhibited a fairly good activity against Mycobacterium avium complex (MAC).

Pharmacodynamics of telavancin (TD-6424), a novel bactericidal agent, against gram-positive bacteria

Telavancin (TD-6424) is a novel lipoglycopeptide that produces rapid and concentration-dependent killing of clinically relevant gram-positive organisms in vitro. The present studies evaluated the in vivo pharmacodynamics of telavancin in the mouse neutropenic thigh (MNT) and mouse subcutaneous infection (MSI) animal models. Pharmacokinetic-pharmacodynamic studies in the MNT model demonstrated that the 24-h area under the concentration-time curve (AUC)/MIC ratio was the best predictor of efficacy. Telavancin produced dose-dependent reduction of thigh titers of several organisms, including methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA), penicillin-susceptible and -resistant strains of Streptococcus pneumoniae, and vancomycin-resistant Enterococcus faecalis. The 50% effective dose (ED50) estimates for telavancin ranged from 0.5 to 6.6 mg/kg of body weight (administered intravenously), and titers were reduced by up to 3 log10 CFU/g from pretreatment values. Against MRSA ATCC 33591, telavancin was 4- and 30-fold more potent (on an ED50 basis) than vancomycin and linezolid, respectively. Against MSSA ATCC 13709, telavancin was 16- and 40-fold more potent than vancomycin and nafcillin, respectively. Telavancin, vancomycin, and linezolid were all efficacious and more potent against MRSA ATCC 33591 in the MSI model compared to the MNT model. This deviation in potency was, however, disproportionately greater for vancomycin and linezolid than for telavancin, suggesting that activity of telavancin is less affected by the immune status. The findings of these studies collectively suggest that once-daily dosing of telavancin may provide an effective approach for the treatment of clinically relevant infections with gram-positive organisms.

Comparative in vitro activity of antiribosomal agents on penicillin-susceptible and -resistant Streptococcus pneumoniae in relation to their resistance genotypes

A collection of 326 strains of Streptococcus pneumoniae isolated from blood, cerebrospinal fluid, bronchoalveolar lavage, transtracheal aspirate or sputum from January 1996-June 2002 were included in this study. The activity of clarithromycin, clindamycin, telithromycin, linezolid and quinupristin/dalfopristin against penicillin G and erythromycin A susceptible and resistant pneumococci were determined; the erythromycin A resistance phenotypes and genotypes were identified and susceptibilities of these agents were assessed according to the resistance genotypes. MICs were determined for all strains of pneumococci using an agar dilution method. MLS(B) resistance phenotypes were determined by the double disk (erythromycin A and clindamycin) diffusion method. Genetic determinants for macrolide resistance were identified by PCR using primers specific for erm(B) and mef(A). Erythromycin A resistance was detected in 13.8% of the strains. MLS(B) resistance phenotype was observed in 82% of these (60% being cMLS(B) and 40% being iMLS(B)), and M type resistance in about 18%. All the MLS(B) phenotype strains except four, revealed the presence of erm(B) gene and all except one M phenotype strains revealed the mef(A) gene. Of the erythromycin A resistant pneumococci about 49% were also resistant to clindamycin. No strains were resistant to telithromycin, quinupristin/dalfopristin and linezolid. Telithromycin had the lowest MIC values for both erythromycin A resistant and susceptible strains of all the antiribosomal agents tested. The most prevalent mechanism of macrolide resistance was mediated by the erm(B) gene leading to the expression of MLS(B) phenotype. Telithromycin was the most active antiribosomal agent, regardless of the macrolide resistance genotype of the pneumococci tested.

Linezolid penetration into bone and joint tissues infected with methicillin-resistant staphylococci

Penetration of linezolid into bone and joint tissues was studied by high-performance liquid chromatography in 13 patients suffering from implant-associated infections with methicillin-resistant staphylococci. Mean concentrations of linezolid in infected tissues were greater than 10 mg/liter in a sampling time range of 35 to 124 min after administration of the preoperative dose, except in bone specimens, where they reached 3.9 +/- 2.0 mg/liter.

Solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates

The first solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates is described. Synthesis of the title compounds was achieved by alkylation of resin-bound carbamates with glycidyl tosylate, followed by cycloaddition of the resulting epoxides with isocyanates at elevated temperature in high yields and purity. Because N-aryloxazolidinones have been known to possess various biological activities, this method is useful from the viewpoint of drug discovery.