The oxazolidinones as a new family of antimicrobial agent

High accumulation of linezolid and its major metabolite in the serum of patients with hepatic and renal dysfunction is significantly associated with thrombocytopenia and anemia

This study aims to examine the serum levels of linezolid and its metabolites (PNU-142300 and PNU-142586) in patients with varying hepatic and renal function. It seeks to understand how these levels relate to thrombocytopenia and anemia and to identify concentration thresholds that could cause these adverse effects, thereby aiding in personalized drug dosing. This prospective study was conducted from January to December 2023. According to the established inclusion and exclusion criteria, 77 patients with infections treated with linezolid were selected as the research subjects. Venous blood samples were collected every 48 h starting from the first use of linezolid, specifically 30 min before the next dose. Laboratory data were obtained through biochemical analysis and blood routine tests, and blood drug concentration monitoring was carried out based on the pre-established high-performance liquid chromatography (HPLC) method. The exposure levels of linezolid and its metabolites in the serum of patients under different liver and kidney function states were compared, and the relationships between these drug exposure levels and platelet count and hemoglobin concentration were analyzed. Additionally, the receiver operating characteristic (ROC) curve was used to determine the blood drug concentration thresholds of linezolid and its metabolites that led to thrombocytopenia or anemia. Finally, survival analysis was used to evaluate the time differences in the occurrence of adverse reactions, such as thrombocytopenia and anemia, between the liver and kidney function impairment group and the normal group after the use of linezolid. Exposure to linezolid and its metabolites increased with the severity of hepatic and renal impairment. Patients with severe and moderate hepatic and renal impairment had a substantially higher median Cmin of linezolid and its metabolites 2 and 3 than those with mild hepatic and renal impairment. The platelet count and hemoglobin concentration were significantly associated with linezolid and its metabolite overexposure. The concentration threshold for linezolid and its metabolites 2 and 3 to cause thrombocytopenia and anemia were 7.0, 3.6, and 4.3 mg/L. Patients with hepatic and renal impairment exhibit higher levels of linezolid and its metabolites, potentially leading to adverse effects like thrombocytopenia and anemia. It is recommended to monitor drug levels and develop individualized dosage regimens.

IMPORTANCE

The accumulation of plasma linezolid and its metabolites increased with the degree of liver and kidney injury. High plasma linezolid and its metabolite accumulation is significantly associated with thrombocytopenia and anemia. Linezolid and its metabolite concentration threshold can warn the clinical prevention of hematological adverse reactions. Individual therapy guided by therapeutic drug monitoring (TDM) can improve the efficacy of linezolid and reduce toxic reactions. Patients with severe hepatic and renal dysfunction should actively monitor the blood routine and linezolid concentration and adjust the dosage in time.

A Novel LC-APCI-MS/MS Approach for the Trace Analysis of 3,4-Difluoronitrobenzene in Linezolid

Background/Objectives: Oxazolidinones are novel antimicrobial agents used to combat bacterial infections, particularly multidrug-resistant strains. However, the synthesis of oxazolidinone derivatives, such as linezolid, often involves the use of 3,4-difluoronitrobenzene (DFNB) as an initiator. Despite its effectiveness, residual DFNB in drug products raises significant health concerns due to its structural similarity to toxic and carcinogenic nitrobenzenes. This contamination is particularly concerning in pharmaceutical formulations, where it poses potential patient safety hazards. Therefore, strict concentration limits for this impurity are necessary. Methods: To ensure tight control of DFNB concentrations, this study established an 8.3 µg/g target limit. An advanced high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to overcome current limitations in detecting trace DFNB. Under negative atmospheric pressure chemical ionization (APCI) conditions, DFNB exhibited characteristic ion formations, including [M]•- through electron capture and [M - F + O]- via substitution reactions. The quantitative method utilizes MS/MS ion transitions of the substitution product while optimizing chromatographic and spectrometric parameters to enhance both sensitivity and specificity. Conclusions: Validation tests confirm the efficiency, precision, and accuracy of this method, with a low limit of quantification (LOQ) of 5 ng/mL (0.83 µg/g). This technique enables accurate detection and quantification of DFNB in linezolid active pharmaceutical ingredient (API) and various formulations, providing a reliable tool for quality control. This method ensures the safe use of linezolid by effectively monitoring and minimizing the risks associated with DFNB contamination.

Comparative analysis of linezolid, vancomycin, and hyperbaric oxygen therapies in a rat model of ventriculoperitoneal shunt infection

PURPOSE

Staphylococcus epidermidis is the most common causative microorganism of ventriculoperitoneal shunt infections. This study aimed to compare linezolid and vancomycin treatments and to examine the effect of these antibiotics alone and combined with hyperbaric oxygen therapy on the amount of bacterial colonies in the experimental S. epidermidis shunt infection model.

METHODS

A shunt catheter was placed in the cisterna magna of 49 adult male Wistar albino rats. The rats were randomly divided into seven groups, as follows: sterile control, infected control, vancomycin, linezolid, hyperbaric oxygen, vancomycin + hyperbaric oxygen, linezolid + hyperbaric oxygen. In all groups except the sterile control group, 0.2 ml 107 CFU/mL S. epidermidis was inoculated to the cisterna magna. Parenteral vancomycin was administered 40 mg/kg/day to the vancomycin groups, and 50 mg/kg/day of enteral linezolid to the linezolid groups. Hyperbaric oxygen groups were given 100% oxygen at a pressure of 2.4 ATA for 50 min a day. One day after the last treatment, colony quantities in the shunt catheters and CSF were analyzed.

RESULTS

The number of CSF colonies in the linezolid group was significantly lower than in the vancomycin group (p < 0.05). The number of CSF colonies in the linezolid + HBO group was significantly lower than in the vancomycin + HBO group (p < 0.05).

CONCLUSIONS

Linezolid treatment was found to be more effective than vancomycin in ventriculoperitoneal shunt infection caused by S. epidermidis. There was no statistical difference among other treatment groups. Hyperbaric oxygen therapy is shown to contribute to the sterilization of cultures.

Chemical Classes Presenting Novel Antituberculosis Agents Currently in Different Phases of Drug Development: A 2010-2020 Review

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a curable airborne disease currently treated using a drug regimen consisting of four drugs. Global TB control has been a persistent challenge for many decades due to the emergence of drug-resistant Mtb strains. The duration and complexity of TB treatment are the main issues leading to treatment failures. Other challenges faced by currently deployed TB regimens include drug-drug interactions, miss-matched pharmacokinetics parameters of drugs in a regimen, and lack of activity against slow replicating sub-population. These challenges underpin the continuous search for novel TB drugs and treatment regimens. This review summarizes new TB drugs/drug candidates under development with emphasis on their chemical classes, biological targets, mode of resistance generation, and pharmacokinetic properties. As effective TB treatment requires a combination of drugs, the issue of drug-drug interaction is, therefore, of great concern; herein, we have compiled drug-drug interaction reports, as well as efficacy reports for drug combinations studies involving antitubercular agents in clinical development.

Stereoselective Synthesis of Oxazolidin-2-Ones via an Asymmetric Aldol/Curtius Reaction: Concise Total Synthesis of (-)-Cytoxazone

Herein, we are reporting an efficient approach toward the synthesis of 4,5-disubstituted oxazolidin-2-one scaffolds. The developed approach is based on a combination of an asymmetric aldol and a modified Curtius protocol, which uses an effective intramolecular ring closure to rapidly access a range of oxazolidin-2-one building blocks. This strategy also permits a straightforward and concise asymmetric total synthesis of (−)-cytoxazone. Consisting of three steps, this is one of the shortest syntheses reported to date. Ultimately, this convenient platform would provide a promising method for the early phases of drug discovery.

Development of Delpazolid for the Treatment of Tuberculosis

A novel oxazolidinone with cyclic amidrazone, delpazolid (LCB01-0371), was synthesized by LegoChem BioSciences, Inc. (Daejeon, Korea). Delpazolid can improve the minimum bactericidal concentration of Mycobacterium tuberculosis H37Rv and significantly reduce resistance rates, especially of multi-drug-resistant tuberculosis (MDR-TB) isolates, compared with linezolid. Therefore, delpazolid can be used to treat MDR-TB. The safety, tolerability, and pharmacokinetics of delpazolid have been evaluated in a phase 1 clinical trial, which revealed that it does not cause adverse events such as myelosuppression even after three weeks of repeated dosing. Interim efficacy and safety results, particularly those from a clinical phase 2a early bactericidal activity trial including patients with drug-susceptible tuberculosis, were reported and the findings will be further analyzed to guide phase 2a studies.

Ultrahigh-throughput absolute quantitative analysis of linezolid in human plasma by direct analysis in real time mass spectrometry without chromatographic separation and its application to a pharmacokinetic study

Therapeutic drug monitoring (TDM) is necessary in the clinical management of linezolid to improve its efficacy and reduce the risk of time- and dose-dependent toxicity. A novel and ultrahigh-throughput analytical method for the determination of linezolid in human plasma was developed based on direct analysis in real-time tandem mass spectrometry (DART-MS/MS) without chromatographic separation. After solid-phase extraction with Waters Oasis HLB, the linezolid and internal standard linezolid-d₃ were detected by positive ion electrospray ionization followed by multiple reaction monitoring (MRM) of the transition at m/z 338.1 → 296.2 and 341.2 → 297.3, respectively. The use of DART-MS obviates the need for chromatographic separation and allowed determination of linezolid in a total run time of only 24 s per sample. The method was linear in the concentration range 0.20-25 μg mL^-1 with intraday and interday precision <14.5% and accuracy ranging from -3.85% to 12.7%. The method was successfully applied to a pharmacokinetic study of linezolid in healthy male volunteers after oral administration of a 600 mg tablet. DART-MS/MS provides a rapid and sensitive method for the determination of linezolid that does not require chromatographic separation. It is eminently suitable to meet the high-throughput challenge of clinical TDM. Graphical abstract.

Mechanisms of antimicrobial resistance among hospital-associated pathogens

INTRODUCTION

The introduction of antibiotics revolutionized medicine in the 20th-century permitting the treatment of once incurable infections. Widespread use of antibiotics, however, has led to the development of resistant organisms, particularly in the healthcare setting. Today, the clinician is often faced with pathogens carrying a cadre of resistance determinants that severely limit therapeutic options. The genetic plasticity of microbes allows them to adapt to stressors via genetic mutations, acquisition or sharing of genetic material and modulation of genetic expression leading to resistance to virtually any antimicrobial used in clinical practice. Areas covered: This is a comprehensive review that outlines major mechanisms of resistance in the most common hospital-associated pathogens including bacteria and fungi. Expert commentary: Understanding the genetic and biochemical mechanisms of such antimicrobial adaptation is crucial to tackling the rapid spread of resistance, can expose unconventional therapeutic targets to combat multidrug resistant pathogens and lead to more accurate prediction of antimicrobial susceptibility using rapid molecular diagnostics. Clinicians making treatment decisions based on the molecular basis of resistance may design therapeutic strategies that include de-escalation of broad spectrum antimicrobial usage, more focused therapies or combination therapies. These strategies are likely to improve patient outcomes and decrease the risk of resistance in hospital settings.

Elimination of Linezolid by an in vitro Extracorporeal Circuit Model

Linezolid is an oxazolidinone antibiotic with activity against important grampositive aerobic bacteria, including nosocomial pathogens. It is not known whether dosage adjustments are necessary in patients treated with continuous renal replacement therapies. This in vitro study was conducted to investigate the elimination of linezolid in an in vitro continuous hemo(dia)filtration model using different filter materials (polysulfone, polyacrylonitrile, polyamide), surface areas, and different modes of renal replacement therapies. Linezolid was measured using HPLC with UV-detection. No adsorption of linezolid to any of the tested membranes was detected. Recovery of linezolid in the ultrafiltrate was 98.2 ± 10.5% in the filtration mode. During dialysis, recovery was significantly less (87.6 ± 16.1%; p = 0.02). Linezolid elimination was not altered by filter size, when polysulfone filters with surface areas of 0.7 m2 and 1.3 m2 were tested. In conclusion, the dosage recommendations for linezolid are independent of the filter materials. However, the elimination is significantly higher during hemofiltration compared to dialysis.

Synthesis Approaches to (-)-Cytoxazone, a Novel Cytokine Modulator, and Related Structures

(−)-Cytoxazone, originally isolated from cultures of a Streptomyces species has an oxazolidin-2-one 4,5-disubstituted ring. It is known that this natural product presents a cytokine modulator effect through the signaling pathway of Th2 cells (type 2 cytokines), which are involved in the process of growth and differentiation of cells. From this, the interest in the development of research aimed at the total synthesis of this molecule and its analogs has remained high, which can be confirmed by the large number of publications on the topic, more than 30 to date. This review focuses on the various creative methods for the synthesis of (−)-cytoxazone and its congeners. The assessment of the preparation of this oxazolidinone and related structures serves as a treatise on the efforts made in the synthesis of this important class of compound from its first total synthesis in 1999.

Antibiotics and sweeteners in the aquatic environment: biodegradability, formation of phototransformation products, and in vitro toxicity

In the present study, in vitro toxicity as well as biopersistence and photopersistence of four artificial sweeteners (acesulfame, cyclamate, saccharine, and sucralose) and five antibiotics (levofloxacin, lincomycin, linezolid, marbofloxacin, and sarafloxacin) and of their phototransformation products (PTPs) were investigated. Furthermore, antibiotic activity was evaluated after UV irradiation and after exposure to inocula of a sewage treatment plant. The study reveals that most of the tested compounds and their PTPs were neither readily nor inherently biodegradable in the Organisation for Economic Co-operation and Development (OECD)-biodegradability tests. The study further demonstrates that PTPs are formed upon irradiation with an Hg lamp (UV light) and, to a lesser extent, upon irradiation with a Xe lamp (mimics sunlight). Comparing the nonirradiated with the corresponding irradiated solutions, a higher chronic toxicity against bacteria was found for the irradiated solutions of linezolid. Neither cytotoxicity nor genotoxicity was found in human cervical (HeLa) and liver (Hep-G2) cells for any of the investigated compounds or their PTPs. Antimicrobial activity of the tested fluoroquinolones was reduced after UV treatment, but it was not reduced after a 28-day exposure to inocula of a sewage treatment plant. This comparative study shows that PTPs can be formed as a result of UV treatment. The study further demonstrated that UV irradiation can be effective in reducing the antimicrobial activity of antibiotics, and consequently may help to reduce antimicrobial resistance in wastewaters. Nevertheless, the study also highlights that some PTPs may exhibit a higher ecotoxicity than the respective parent compounds. Consequently, UV treatment does not transform all micropollutants into harmless compounds and may not be a large-scale effluent treatment option.

In vitro characterization of the anti-bacterial activity of SQ109 against Helicobacter pylori

The most evident challenge to treatment of Helicobacter pylori, a bacterium responsible for gastritis, peptic ulcers and gastric cancer, is the increasing rate of resistance to all currently used therapeutic antibiotics. Thus, the development of novel therapies is urgently required. N-geranyl-N'-(2-adamantyl) ethane-1, 2-diamine (SQ109) is an ethylene diamine-based antitubercular drug that is currently in clinical trials for the treatment of tuberculosis (TB). Previous pharmacokinetic studies of SQ109 revealed that persistently high concentrations of SQ109 remain in the stomach 4 hours post oral administration in rats. This finding, combined with the need for new anti-Helicobacter therapies, prompted us to define the in vitro efficacy of SQ109 against H. pylori. Liquid broth micro-dilution was used for susceptibility studies to determine the antimicrobial activity of SQ109 against a total of 6 laboratory strains and 20 clinical isolates of H. pylori; the clinical isolates included a multi-drug resistant strain. All strains tested were susceptible to SQ109 with MIC and MBC ranges of 6-10 µM and 50-60 µM, respectively. SQ109 killing kinetics were concentration- and time-dependent. SQ109 killed H. pylori in 8-10 h at 140 µM (2MBCs) or 4-6 h at 200 µM (~3MBCs). Importantly, though the kinetics of killing were altered, SQ109 retained potent bactericidal activity against H. pylori at low pH. Additionally, SQ109 demonstrated robust thermal stability and was effective at killing slow growing or static bacteria. In fact, pretreatment of cultures with a bacteriostatic concentration of chloramphenicol (Cm) synergized the effects of typically bacteriostatic concentrations of SQ109 to the level of five-logs of bacterial killing. A molar-to-molar comparison of the efficacy of SQ109 as compared to metronidazole (MTZ), amoxicillin (AMX), rifampicin (RIF) and clarithromycin (CLR), revealed that SQ109 was superior to MTZ, AMX and RIF but not to CLR. Finally, the frequency of resistance to SQ109 was low and electron microscopy studies revealed that SQ109 interacted with bacterial inner membrane and cytoplasmic content(s). Collectively, our in vitro data demonstrate that SQ109 is an effective monotherapy against susceptible and multi-drug resistant strains of H. pylori and may be useful alone or in combination with other antibiotics for development as a new class of anti-Helicobacter drugs.

The oligo-acyl lysyl antimicrobial peptide C₁₂K-2β₁₂ exhibits a dual mechanism of action and demonstrates strong in vivo efficacy against Helicobacter pylori

Helicobacter pylori has developed antimicrobial resistance to virtually all current antibiotics. Thus, there is a pressing need to develop new anti-H. pylori therapies. We recently described a novel oligo-acyl-lysyl (OAK) antimicrobial peptidomimetic, C(12)K-2β(12), that shows potent in vitro bactericidal activity against H. pylori. Herein, we define the mechanism of action and evaluate the in vivo efficacy of C(12)K-2β(12) against H. pylori after experimental infection of Mongolian gerbils. We demonstrate using a 1-N-phenylnaphthylamine (fluorescent probe) uptake assay and electron microscopy that C(12)K-2β(12) rapidly permeabilizes the bacterial membrane and creates pores that cause bacterial cell lysis. Furthermore, using nucleic acid binding assays, Western blots, and confocal microscopy, we show that C(12)K-2β(12) can cross the bacterial membranes into the cytoplasm and tightly bind to bacterial DNA, RNA, and proteins, a property that may result in inhibition of enzymatic activities and macromolecule synthesis. To define the in vivo efficacy of C(12)K-2β(12), H. pylori-infected gerbils were orogastrically treated with increasing doses and concentrations of C(12)K-2β(12) 1 day or 1 week postinfection. The efficacy of C(12)K-2β(12) was strongest in animals that received the largest number of doses at the highest concentration, indicating dose-dependent activity of the peptide (P < 0.001 by analysis of variance [ANOVA]) regardless of the timing of the treatment with C(12)K-2β(12). Overall, our results demonstrate a dual mode of action of C(12)K-2β(12) against the H. pylori membrane and cytoplasmic components. Moreover, and consistent with the previously reported in vitro efficacy, C(12)K-2β(12) shows significant in vivo efficacy against H. pylori when used as monotherapy. Therefore, OAK peptides may be a valuable resource for therapeutic treatment of H. pylori infection.

Clinical outcome with oral linezolid and rifampin following recurrent methicillin-resistant Staphylococcus aureus bacteremia despite prolonged vancomycin treatment

Drug-resistant Gram-positive bacteria, especially Staphylococcus aureus, are emerging as the predominant organisms involved in both nosocomial and community-acquired infections. Since the 1980s, vancomycin has been the first-line antibiotic used to treat methicillin- resistant S aureus. However, allergy and intolerance to vancomycin, the increasing number of vancomycin clinical failures and the existence of vancomycin intermediate-susceptible isolates of S aureus suggest that new antibiotics are needed. This paper reports the only known case of a successful clinical outcome with long term oral linezolid and rifampin therapy in the management of recurrent and persistent methicillin-resistant S aureus bacteremia with metastatic infections despite prolonged vancomycin use. More than two years since the initiation of linezolid and rifampin, the study patient has been clinically well with no evidence of adverse drug reactions including cytopenia and hepatic toxicities. Physicians must be aware of the novel developments in antibiotic therapy to treat drug-resistant bacterial infections.

Nosocomial methicillin-resistant Staphylococcus aureus (MRSA) pneumonia: linezolid or vancomycin? - Comparison of pharmacology and clinical efficacy

The incidence of nosocomial pneumonia involving methicillin-resistant Staphylococcus aureus strains (MRSA) is on the rise worldwide. For years, vancomycin has been used as the drug of choice in the treatment of MRSA infections and was recommended as such by clinical guidelines. There is growing evidence that vancomycin, despite low resistance rates is a suboptimal therapeutic option in critically ill patients, particularly in patients with pneumonia. Disadvantages of vancomycin are i) slow bactericide action, ii) poor penetration into pulmonary tissue, iii) the globally slowly increasing vancomycin MICs ("creep") that result in increased clinical failure despite being susceptible according to defined break points and iv) nephrotoxicity. In contrast to other novel antibiotics with MRSA activity, Linezolid is currently approved for the treatment of nosocomial pneumonia in the USA and Europe. Several studies have compared vancomycin with linezolid for nosocomial pneumonia with conflicting results. This review compares both substances regarding pharmacodynamics, resistance, safety and clinical efficacy and discusses preliminary data of the ZEPHyR study. This study compared linezolid versus vancomycin in patients with proven MRSA pneumonia and was the largest trial ever conducted in this population.

Intra- and extracellular activity of linezolid against Staphylococcus aureus in vivo and in vitro

BACKGROUND AND AIMS

Treatment of Staphylococcus aureus infections remains problematic (slow responses and frequent recurrences). Intracellular persistence of the S. aureus could explain those difficulties because of impaired intracellular efficacy of antibiotics. Our aim was to study linezolid for its intracellular activity.

METHODS

(i) Pharmacodynamic (PD) analysis of intracellular activity using in vitro (THP-1 macrophages) and in vivo (mouse peritonitis) models with determination of key dose-response parameters [maximal relative efficacy (E(max)), relative potency (EC(50)) and static concentration (C(static))] towards methicillin-susceptible S. aureus (ATCC 25923; clinical isolate) with linezolid MICs of 4 mg/L; (ii) pharmacokinetic (PK) analysis in uninfected mice for determination of C(max), AUC and half-life for total and free drug; and (iii) determination of the predictive PK/PD parameter (fT > MIC, fAUC(24)/MIC or fC(max)/MIC) for therapeutic outcome.

RESULTS

In vitro, linezolid showed an E(max) of approximately 1 log(10) cfu reduction compared with initial inoculum both intra- and extracellularly and an approximately 3-fold increased relative potency (lower EC(50) and C(static)) intracellularly. In vivo, the efficacy of linezolid was impaired (<0.5 log(10) reduction extracellularly; failure to reduce the cfu to less than the initial load intracellularly) with, however, an increased intracellular potency (lower EC(50)). Infection outcome correlated better with the fAUC(24)/MIC (R(2) = 55%) than with the fT > MIC parameter (R(2) = 51%) for the extracellular compartment, but no parameter emerged as significant for the intracellular compartment.

CONCLUSIONS

Linezolid exerts only a weak intracellular activity against the strains of S. aureus tested, even though, in contrast to most other antibiotics, its potency does not appear impaired in comparison with the extracellular activity.

Successful Treatment of Disseminated Cerebritis Complicating Methicillin-resistant Staphylococcus aureus Endocarditis Unresponsive to Vancomycin Therapy with Linezolid

A unique case of community acquired methicillin resistant Staphylococcus aureus (MRSA) sepsis, with endocardial and cerebral metastatic seeding, caused by a strain representative of the Italian clone, is described. The patient was a 47-y-old man without apparent risk factors for endocarditis and for MRSA infection who developed coma with multiple cerebritis lesions under vancomycin plus amikacin therapy. He was eventually cured with the addition of linezolid to the initial antimicrobial regimen. This observation seems to confirm previous reports of the efficacy of linezolid for the treatment of central nervous system infections caused by multidrug resistant Gram-positive bacteria. To our knowledge, this is the first report of MRSA disseminated cerebritis, a nearly always fatal disease, cured with this oxazolidinone drug. The increase in community acquired MRSA may have some impact on empirical treatment of serious infections caused by this organism.

[Use of antibiotics for the treatment of multiresistant gram positive cocci infections in critical patients]

INTRODUCTION

This study has been designed to know the use of these antibiotics (ATB) in Intensive Care Units (ICUs).

DESIGN AND PATIENTS

A multicentric, prospective, observational study was conducted. In cluded as cases were the indications of vancomycin (VAN), teicoplanin (TPN), quinupristin/dalfopristin (Q/D) and linezolid (LZD).

RESULTS

A total of 826 indications (VAN 52.1%, TPN 36.6%, LZD 11.6% and Q/D 0%) were analyzed, 793 (96%) as treatment and 33 (4%) as prophylaxis in 818 patients. Serious sepsis or septic should occurred in 55.9% of the patients treated. The most common infections were pneumonia and catheter-related bacteremia, 48.3% of all the infections being acquired in ICUs. LZD was used mostly in mechanical-ventilation related pneumonia (p = 0.001), VAN in community Central Nervous System infections (p = 0.01) and in catheter-related bacteremia (p = 0.001), TPN in community pneumonia (p = 0.01) and in catheter-related bacteremia (p = 0.001). Treatments were empirical in 65.8% and diagnosis of gram positive cocci was confirmed in 48.3% of them. Staphylococcus aureus was isolated more in the LZD-treated group. Initial treatment was modified 224 times, this occurring more frequently in the VAN-treated group. The reason for this change was clinical failure 59 times, this being more frequent in the TPN group and less frequent in the patients treated with LZD, which was the drug used the most in rescue therapies (43/69, 62.3%). Adverse events, probably related to the ATB, were identified in 36/826 (4.4%) cases.

CONCLUSIONS

The most common use of this ATB was to treat ICU-acquired infections. VAN was the most frequently used drug. Treatments with LZD were modified less frequently for clinical failure and this drug was the one most used in rescue therapies. This information indicates an appropriate use of these ATB in an important percentage of critically patients.

Antimicrobial activity of the ornamental species Salvia corrugata, a potential new crop for extractive purposes

As a part of our search for biologically active compounds from cultivated Salvia spp. we investigated Salvia corrugata Vahl. The activity of two isolated icetaxane diterpene quinones, fruticuline A and demethylfruticuline A, was assessed against 46 bacterial pathogens, mostly resistant to several primary antibiotics. The MIC for all the inhibited Gram-positive pathogens tested showed a very narrow distribution and ranged from 32 to 64 mg/L, regardless of their resistance patterns to other antibiotics. Demethylfruticuline A was shown to be highly bactericidal (>3 log(10) CFU decrease within 24 h) against Staphylococcus aureus and S. epidermidis and bacteriostatic against Enterococcus faecalis and E. faecium. Fruticuline A manifested bacteriostatic activity against all tested strains. S. corrugata can be viewed as an interesting source for these diterpenes, which, if well tolerated in vivo, may represent new medical agents useful for the treatment of serious infections caused by resistant Gram-positive pathogens.

Chiral analysis using the kinetic method with optimized fixed ligands: applications to some antibiotics

A new version of the kinetic method for chiral analysis, which employs a fixed (nondissociating) ligand as well as the usual analyte and chiral reference ligands, is introduced to simplify the kinetics of this experiment. Singly charged clusters containing the divalent transition metal ion MnII, a peptide which serves as a fixed ligand, an amino acid chiral reference, and the analyte 4-benzyl-2-oxazolidinone were generated by electrospray ionization (ESI). The cluster ion of interest was mass-selected, and the kinetics of its competitive unimolecular dissociations was investigated in an ion trap mass spectrometer. The chiral selectivity (R(fixed)chiral), the ratio of the two fragment ion abundances when the cluster contains one pure enantiomer of the analyte expressed relative to that for the other enantiomer, varies with increasing size of the fixed peptide ligands. The metal-ligand and the ligand-ligand interactions that produce chiral discrimination are optimized in the tetrapeptide fixed ligand Gly-Gly-Ala-Gly, as shown by data for 15 fixed ligands. The difference in the free energies of activation for the two competitive reactions is estimated to be approximately 7 kJ/mol for this particular fixed ligand. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity (intrinsic to the kinetic method) allows mixtures to be analyzed for as little as 1% enantiomeric excess (ee), by simply recording the ratios of fragment ion abundances in a tandem mass spectrum. These features are demonstrated in the case of the pharmacologically important 4-benzyl-2-oxazolidinones and in the case of penicillamine.

Linezolid: pharmacokinetic characteristics and clinical studies

Linezolid is an oxazolidinone indicated in the treatment of nosocomial and community-acquired pneumonia, complicated and uncomplicated skin and skin structure infections and vancomycin-resistant Enterococcus infections. The drug is also approved for use in complicated skin infections and nosocomial pneumonia caused by methicillin-resistant Staphylococcus aureus, concurrent bacteremia associated with vancomycin-resistant Enterococcus faecium and concurrent bacteremia associated with community-acquired pneumonia caused by penicillin-susceptible Streptococcus pneumoniae.