Linezolid: a new antibiotic

Linezolid Pharmacokinetics in Critically Ill Patients: Continuous Versus Intermittent Infusion

BACKGROUND

Linezolid has been found to have considerable interindividual variability, especially in critically ill patients, which can lead to suboptimal plasma concentration. To overcome this shortcoming, several solutions have been proposed. These include using loading dose, higher maintenance doses, and dose stratification according to the patient's particularities, therapeutic drug monitoring, and drug administration via continuous infusion (CI) instead of intermittent infusion (II). In the present study, we aim to compare the pharmacokinetic (PK) parameters of linezolid after administration as II versus CI to critically ill patients.

METHODS

In a prospective study conducted in an intensive care unit, we compared the same two daily doses of linezolid administered via II versus CI. The serum concentration was measured, and pharmacokinetic parameters were calculated. The pharmacokinetic/pharmacodynamic (PK/PD) indices for efficacy chosen were area under the concentration-time curve at steady state divided by the minimum inhibitory concentration over 80 (AUC24-48/MIC > 80).

RESULTS

Greater serum concentration variability was observed in the II group than in the CI group. The %T > MIC > 80% was achieved for MICs of 1 and 2 µg/mL 100% of the time, whereas for the II group, this was 93% and 73%, respectively. AUC24-48/MIC > 80 was reached in 100% of cases in the CI group compared with 87% in the II group for a MIC of 1 µg/mL.

CONCLUSIONS

The two infusion methods may be used comparably, but utilizing CI as an alternative to II may have potential benefits, including avoiding periods of suboptimal concentrations, which may enhance safety profiles and clinical outcomes. Considering the relatively few studies performed on linezolid to date, which are increasing in number, the results of the present study may be of interest.

The burden of antibiotic resistance of the main microorganisms causing infections in humans - review of the literature

One of the biggest threats to human well-being and public health is antibiotic resistance. If allowed to spread unchecked, it might become a major health risk and trigger another pandemic. This proves the need to develop antibiotic resistance-related global health solutions that take into consideration microdata from various global locations. Establishing positive social norms, guiding individual and group behavioral habits that support global human health, and ultimately raising public awareness of the need for such action could all have a positive impact. Antibiotic resistance is not just a growing clinical concern but also complicates therapy, making adherence to current guidelines for managing antibiotic resistance extremely difficult. Numerous genetic components have been connected to the development of resistance; some of these components have intricate paths of transfer between microorganisms. Beyond this, the subject of antibiotic resistance is becoming increasingly significant in medical microbiology as new mechanisms underpinning its development are identified. In addition to genetic factors, behaviors such as misdiagnosis, exposure to broad-spectrum antibiotics, and delayed diagnosis contribute to the development of resistance. However, advancements in bioinformatics and DNA sequencing technology have completely transformed the diagnostic sector, enabling real-time identification of the components and causes of antibiotic resistance. This information is crucial for developing effective control and prevention strategies to counter the threat.

Bioisosteric modification of Linezolid identified the potential M. tuberculosis protein synthesis inhibitors to overcome the myelosuppression and serotonergic toxicity associated with Linezolid in the treatment of the multi-drug resistance tuberculosis (MDR-TB)

Linezolid is the first and only oxazolidinone antibacterial drug was approved in the last 35 years. It exhibits bacteriostatic efficacy against M. tuberculosis and is a crucial constituent of the BPaL regimen (Bedaquiline, Pretomanid, and Linezolid), which was authorized by the FDA in 2019 for the treatment of XDR-TB or MDR-TB. Despite its unique mechanism of action, Linezolid carries a considerable risk of toxicity, including myelosuppression and serotonin syndrome (SS), which is caused by inhibition of mitochondrial protein synthesis (MPS) and monoamine oxidase (MAO), respectively. Based on the structure toxicity relationship (STR) of Linezolid, in this work, we used a bioisosteric replacement approach to optimize the structure of Linezolid at the C-ring and/or C-5 position for myelosuppression and serotogenic toxicity. Extensive hierarchical multistep docking, drug likeness prediction, molecular binding interactions analyses, and toxicity assessment identified three promising compounds (3071, 7549 and 9660) as less toxic potential modulators of Mtb EthR protein. Compounds 3071, 7549 and 9660 were having the significant docking score of -12.696 Kcal/mol, -12.681 Kcal/mol and -15.293 Kcal/mol towards the Mtb EthR protein with less MAO-A and B affinity [compound 3071: MAO A (-4.799 Kcal/mol) and MAO B (-6.552 Kcal/mol); compound 7549: MAO A (> -2.00 Kcal/mol) and MAO B (> -2.00 Kcal/mol) and compound 9660: MAO A (> -5.678 Kcal/mol) and MAO B (> -6.537Kcal/mol) and none of them shown the Leukopenia as a side effect due to the Myelosuppression. The MD simulation results and binding free energy estimations correspond well with docking analyses, indicating that the proposed compounds bind and inhibit the EthR protein more effectively than Linezolid. The quantum mechanical and electrical characteristics were evaluated using density functional theory (DFT), which also demonstrated that the proposed compounds are more reactive than Linezolid.Communicated by Ramaswamy H. Sarma.

Emergence of linezolid-resistant Enterococcus faecium in a tertiary hospital in Copenhagen

Linezolid is used as first-line treatment of infections caused by vancomycin-resistant Enterococcus faecium. However, resistance to linezolid is increasingly detected. The aim of the present study was to elucidate the causes and mechanisms for the increase in linezolid-resistant E. faecium at Copenhagen University Hospital - Rigshospitalet. We therefore combined patient information on linezolid treatment with whole-genome sequencing data for vancomycin- or linezolid-resistant E. faecium isolates that had been systematically collected since 2014 (n=458). Whole-genome sequencing was performed for multilocus sequence typing (MLST), identification of linezolid resistance-conferring genes/mutations and determination of phylogenetically closely related strains. The collection of E. faecium isolates belonged to prevalent vancomycin-resistant MLST types. Among these, we identified clusters of closely related linezolid-resistant strains compatible with nosocomial transmission. We also identified linezolid-resistant enterococcus isolates not genetically closely related to other isolates compatible with de novo generation of linezolid resistance. Patients with the latter isolates were significantly more frequently exposed to linezolid treatment than patients with related linezolid-resistant enterococcus isolates. We also identified six patients who initially carried a vancomycin-resistant, linezolid-sensitive enterococcus, but from whom vancomycin-resistant, linezolid-resistant enterococci (LVRE) closely related to their initial isolate were recovered after linezolid treatment. Our data illustrate that linezolid resistance may develop in the individual patient subsequent to linezolid exposure and can be transmitted between patients in a hospital setting.

Synthesis, antimicrobial activity and toxicity to nematodes of cyclam derivatives

The antimicrobial activity and toxicity to nematodes of the cyclam salt [H₂{H₂(^4-CF₃PhCH₂)₂Cyclam}](CH₃COO)₂⋅(CH₃COOH)₂ were evaluated. Estimated minimum inhibitory concentrations (MICs) of 9, 261 and 15 µg/mL were obtained for Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, respectively. For selected Candida spp., the estimated MICs obtained ranged from 32 µg/mL to 63 µg/mL. Bactericidal activity was demonstrated but the compound was not reliably fungicidal. Concentrations of the cyclam salt up to 32 µg/mL did not significantly affect survival of the nematode Caenorhabditis elegans; however, concentrations equal or above this value significantly affected nematode survival in a dose-dependent manner.

Bacteriostatic antimicrobial combination: antagonistic interaction between epsilon-viniferin and vancomycin against methicillin-resistant Staphylococcus aureus

Stilbenoids have been considered as an alternative phytotherapeutic treatment against methicillin-resistant Staphylococcus aureus (MRSA) infection. The combined effect of ε-viniferin and johorenol A with the standard antibiotics, vancomycin and linezolid, was assessed against MRSA ATCC 33591 and HUKM clinical isolate. The minimum inhibitory concentration (MIC) value of the individual tested compounds and the fractional inhibitory concentration index (FICI) value of the combined agents were, respectively, determined using microbroth dilution test and microdilution checkerboard (MDC) method. Only synergistic outcome from checkerboard test will be substantiated for its rate of bacterial killing using time-kill assay. The MIC value of ε-viniferin against ATCC 33591 and johorenol A against both strains was 0.05 mg/mL whereas HUKM strain was susceptible to 0.1 mg/mL of ε-viniferin. MDC study showed that only combination between ε-viniferin and vancomycin was synergistic against ATCC 33591 (FICI 0.25) and HUKM (FICI 0.19). All the other combinations (ε-viniferin-linezolid, johorenol A-vancomycin, and johorenol A-linezolid) were either indifferent or additive against both strains. However, despite the FICI value showing synergistic effect for ε-viniferin-vancomycin, TKA analysis displayed antagonistic interaction with bacteriostatic action against both strains. As conclusion, ε-viniferin can be considered as a bacteriostatic stilbenoid as it antagonized the bactericidal activity of vancomycin. These findings therefore disputed previous report that ε-viniferin acted in synergism with vancomycin but revealed that it targets similar site in close proximity to vancomycin's action, possibly at the bacterial membrane protein. Hence, this combination has a huge potential to be further studied and developed as an alternative treatment in combating MRSA in future.

Antibacterial discovery and development--the failure of success?

A combination of approaches and compounds-many of which failed to yield immediate results in the past-will ultimately prove invaluable to the drug industry in the ongoing battle against infectious disease.

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.

Novel 4-N-substituted aryl pent-2-ene-1,4-dione derivatives of piperazinyloxazolidinones as antibacterials

A few substituted piperazinylphenyloxazolidinone compounds 6-13 having substitution on the distant nitrogen atom of piperazine ring scaffold have been synthesized and evaluated for their antibacterial activity in Gram-positive bacteria. A few compounds showed superior in vitro antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Streptococcus pyogenes than linezolid and eperezolid.

Novel Mannich ketones of oxazolidinones as antibacterial agents

A few Mannich ketones of piperazinyl oxazolidinone derivatives have been synthesized and their antibacterial activity in various Gram-positive organisms such as Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis were evaluated by MIC determination. Compound 12 showed comparable activity (MIC) to linezolid and superior to eperezolid.

Oxazolidinone: search for highly potent antibacterial

A number of substituted piperazinyl oxazolidinone derivatives have been synthesized and their antibacterial activities were evaluated by MIC determination. A systematic SAR was carried out to get highly potent oxazolidinone derivatives.

Novel tetrahydro-thieno pyridyl oxazolidinone: an antibacterial agent

Synthesis of a number of 4,5,6,7-tetrahydro-thieno[3,2-c]pyridine substituted oxazolidinones have been reported. They have been screened against a panel of Gram-positive pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. A SAR has been developed. Compound 15 showed comparable activity (MIC) to linezolid and superior to eperezolid.

Synthesis and evaluation of novel bacterial rRNA-binding benzimidazoles by mass spectrometry

A series of novel benzimidazoles were efficiently synthesized using both solution- and solid-phase chemistry. These compounds were found to bind to the bacterial 16S ribosomal RNA A-site with micromolar affinities using unique mass spectrometry-based assays.

Antibacterials: are the new entries enough to deal with the emerging resistance problems?

Fifty years of making analogs based on less than ten antibacterial scaffolds has resulted in the development and marketing of over 100 antibacterial agents but, with the exception of the oxazolidinone core, no new scaffolds have emerged in the past 30 years to address emerging resistance problems. As the support for antibacterial research shifts away from large pharmaceutical companies, a wave of biotechnology companies have pursued a diverse choice of targets resulting in several novel classes of agent in late-stage development. Although critical for certain resistance niche needs, these agents are unlikely to provide the solution to the requirement for a major novel scaffold class of antibacterials.

[Role of linezolid in antimicrobial therapy]

The progressive emergence of multi-resistant gram-positive strains has prompted the search for new molecules (quinolones, streptogramins, oxazolidinones, ketolides, glycopeptides, daptomycin) to add to the current therapeutic arsenal. Linezolid, the first commercially available member of the oxazolidinone family, has evidenced activity against multi-resistant gram-positive strains (methicillin-resistant Staphylococcus aureus, S. aureus with decreased glycopeptide sensitivity, vancomycin-resistant Enterococcus spp., Streptococcus pneumoniae with decreased sensitivity to penicillin and cephalosporins), thereby providing a new option for treating infections by these microorganisms. This work reviews the microbiologic and pharmacologic aspects of this agent in order to establish its position among the available options for antimicrobial chemotherapy.

Isolation and characterization of process-related impurities in linezolid

Two unknown impurities in linezolid bulk drug at levels below 0.1% (ranging from 0.05 to 0.1%) were detected by a simple isocratic reverse phase high performance liquid chromatography (HPLC). These impurities were isolated from crude sample of linezolid using reverse phase preparative HPLC. Based on the spectroscopic data (IR, NMR and MS) the structures of the impurities were characterized as (S)-N-[[-(3-(3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl] acetate(I) and (S)-N-[[-(3-(3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl] chloride(II). The synthesis from an unambiguous route and the formation of impurities was discussed.