Linezolid for the treatment of resistant gram-positive cocci

A new perspective on the antimicrobial mechanism of linezolid against Staphylococcus aureus revealed by proteomics and metabolomics analysis

Understanding bacterial responses to antimicrobials is crucial for identifying tolerance mechanisms and for developing new therapies. Using mass spectrometry-based metabolomics and proteomics, this study examines the response of Staphylococcus aureus to linezolid (LZD) treatment. Under LZD stress, significant fluctuations were observed in key metabolic pathways such as amino acid biosynthesis and the TCA cycle, alongside a general increase in ribosomal protein complexes. Additionally, LZD disrupted nucleotide metabolism, particularly affecting pyrimidine pathways. Combining LZD with the pyrimidine synthesis inhibitor leflunomide enhanced bactericidal effects both in vitro and in vivo, highlighting the importance of targeting pyrimidine biosynthesis to amplify the antimicrobial efficacy of protein inhibitors. These results underscore downstream metabolic processes as viable targets for synergistic drug combinations, suggesting a strategy to potentially improve the clinical effectiveness of LZD.

Deciphering linezolid-induced hematologic toxicity: Targeting TOP2A and TOP2B via its primary metabolite PNU142586

Linezolid, an oxazolidinone antibiotic, is widely used to treat multidrug-resistant tuberculosis and drug-resistant Gram-positive infections. However, prolonged use is associated with severe hematologic toxicity, the underlying mechanisms of which remain incompletely understood, particularly regarding the role of linezolid metabolites. Our clinical study indicates that elevated exposure to PNU142586, a primary metabolite of linezolid, is associated with an increased risk of linezolid-induced toxicity, even in the absence of renal impairment. To elucidate its mechanism, we identify DNA topoisomerase 2-α (TOP2A) and DNA topoisomerase 2-β (TOP2B) as primary targets of PNU142586 at molecular, cellular, and in vivo levels. PNU142586 disrupts replication and transcription by impeding DNA binding to TOP2A and TOP2B with a favorable conformation for cleavage and by inhibiting adenosine 5'-triphosphate hydrolysis, ultimately leading to antiproliferative and cytotoxic effects, including mitochondrial dysfunction. The present study thus provides mechanistic insight into linezolid-induced hematologic toxicity and offers a foundation for safer antibiotic development and improved clinical monitoring through biomarker identification.

High prevalence and plasmidome diversity of optrA-positive enterococci in a Shenzhen community, China

Background

The emergence of optrA, which can confer resistance to phenicols and oxazolidinones in Enterococcus spp., poses a growing public health threat.

Methods

102 optrA-positive enterococci (OPEs) including various species were isolated from feces of 719 healthy volunteers in a Shenzhen community, China. Antimicrobial susceptibility of these isolates was tested. Whole-genome sequencing and bioinformatics analysis were performed to characterize molecular epidemiology of OPEs.

Results

Compared to optrA-negative enterococci (ONEs), antimicrobial resistance (linezolid, florfenicol, doxycycline, erythromycin and ciprofloxacin) and presence of antimicrobial resistance genes (ARGs) (fexA, cat, tet(M), erm(A), erm(B) and etc) were higher in OPEs. Phylogenetic analysis revealed that high similarly (19-338 SNPs) was observed between the optrA-positive E. faecalis from community and the strains from patients, animals, and environment. In 102 OPEs, the optrA gene was detected on the chromosome (n = 36), on plasmids (n = 62), or both (n = 4). A diverse range of optrA-carrying plasmid types was identified. The rep9-plasmid replicons were widely detected in E. faecalis (44/66), whereas repUS1-plasmid replicons were widely identified in other enterococcal species (7/66). Most of all ARGs harbored by isolates were co-existed on optrA-carrying plasmids, suggesting that the acquisition of optrA-carrying plasmids will pose a greater threat to public health. Notably, the pAD1 (rep9 family) + DOp1-type plasmids should receive more attention for the transfer of optrA given their high prevalence (36.36%), high number of co-located ARGs with optrA (83.87% of total ARGs) and presence in multiple sources. Tn6674, IS1216E, ISEnfa1 and ISEnfa5 are related to the transfer of chromosomal and plasmids-derived optrA, respectively. The bcrABDR gene cluster, fexA, and erm(A) were frequently identified surrounding optrA and may be transferred with optrA via IS1216E or ISEnfa1.

Conclusion

The transfer of optrA gene is related to a variety of mobile elements (including plasmids, insertion sequences, transposons), which will promote the horizontal transfer of optrA. Moreover, many ARGs co-exist with optrA and could co-transfer with optrA. The acquisition of OPEs and optrA-carrying plasmids will pose a greater threat to public health and should be obtained more attention, especially optrA-positive E. faecalis and pAD1 + DOp1-type plasmids.

New 1H-1,2,4-Triazolyl Derivatives as Antimicrobial Agents

New 1H-1,2,4-triazolyl derivatives were synthesized, and six of them were selected based on docking prediction for the investigation of their antimicrobial activity against five bacterial and eight fungal strains. All compounds demonstrated antibacterial activity with MIC lower than that of the ampicillin and chloramphenicol. In general, the most sensitive bacteria appeared to be P. fluorescens, while the plant pathogen X. campestris was the most resistant. The antifungal activity of the compounds was much better than the antibacterial activity. All compounds were more potent (6 to 45 times) than reference drugs ketoconazole and bifonazole with the best activity achieved by compound 4 a. A. versicolor, A. ochraceus, A.niger, and T.viride showed the highest sensitivity to compound 4 b, while, T. viride, P. funiculosum, and P.ochrochloron showed good sensitivity to compound 4 a. Molecular docking studies suggest that the probable mechanism of antibacterial activity involves the inhibition of the MurB enzyme of E. coli, while CYP51 of C. albicans appears to be involved in the mechanism of antifungal activity. It is worth mentioning that none of the tested compounds violated Lipinski's rule of five.

Clinical Experience with Off-Label Intrathecal Administration of Selected Antibiotics in Adults: An Overview with Pharmacometric Considerations

Drain-associated intracerebral infections are life-threatening emergencies. Their treatment is challenging due to the limited penetration of antibiotics to the site of infection, resulting in potentially inadequate exposure. The emergence of multidrug-resistant pathogens might force the use of off-label intrathecal (IT) doses of antibiotics. We reviewed the literature on general aspects determining intrathecal dosing regimen, using pharmacometric knowledge. We summarised clinical experience with IT doses of antibiotics that are usually not used intrathecally, as well as the outcome of the cases and concentrations reached in the cerebrospinal fluid (CSF). Factors determining the IT regimen are the size of the ventricle system and the CSF drainage volume. With regard to pharmacometrics, pharmacokinetic/pharmacodynamic indices are likely similar to those in non-cerebral infections. The following number (N) of cases were described: benzylpenicillin (>50), ampicillin (1), ceftazidime (2), cephaloridine (56), ceftriaxone (1), cefotiam (1), meropenem (57), linezolid (1), tigecycline (15), rifampicin (3), levofloxacin (2), chloramphenicol (3) and daptomycin (8). Many side effects were reported for benzylpenicillin in the 1940-50s, but for the other antibiotics, when administered correctly, all side effects were minor and reversible. These data might help when choosing an IT dosing regimen in case there is no alternative option due to antimicrobial resistance.

Neighborhood-based inference and restricted Boltzmann machine for microbe and drug associations prediction

Background

Efficient identification of microbe-drug associations is critical for drug development and solving problem of antimicrobial resistance. Traditional wet-lab method requires a lot of money and labor in identifying potential microbe-drug associations. With development of machine learning and publication of large amounts of biological data, computational methods become feasible.

Methods

In this article, we proposed a computational model of neighborhood-based inference (NI) and restricted Boltzmann machine (RBM) to predict potential microbe-drug association (NIRBMMDA) by using integrated microbe similarity, integrated drug similarity and known microbe-drug associations. First, NI was used to obtain a score matrix of potential microbe-drug associations by using different thresholds to find similar neighbors for drug or microbe. Second, RBM was employed to obtain another score matrix of potential microbe-drug associations based on contrastive divergence algorithm and sigmoid function. Because generalization ability of individual method is poor, we used an ensemble learning to integrate two score matrices for predicting potential microbe-drug associations more accurately. In particular, NI can fully utilize similar (neighbor) information of drug or microbe and RBM can learn potential probability distribution hid in known microbe-drug associations. Moreover, ensemble learning was used to integrate individual predictor for obtaining a stronger predictor.

Results

In global leave-one-out cross validation (LOOCV), NIRBMMDA gained the area under the receiver operating characteristics curve (AUC) of 0.8666, 0.9413 and 0.9557 for datasets of DrugVirus, MDAD and aBiofilm, respectively. In local LOOCV, AUCs of 0.8512, 0.9204 and 0.9414 were obtained for NIRBMMDA based on datasets of DrugVirus, MDAD and aBiofilm, respectively. For five-fold cross validation, NIRBMMDA acquired AUC and standard deviation of 0.8569 ± -0.0027, 0.9248 ± -0.0014 and 0.9369 ± -0.0020 on the basis of datasets of DrugVirus, MDAD and aBiofilm, respectively. Moreover, case study for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) showed that 13 out of the top 20 predicted drugs were verified by searching literature. The other two case studies indicated that 17 and 17 out of the top 20 predicted microbes for the drug of ciprofloxacin and minocycline were confirmed by identifying published literature, respectively.

Mobile Oxazolidinone Resistance Genes in Gram-Positive and Gram-Negative Bacteria

Seven mobile oxazolidinone resistance genes, including cfr, cfr(B), cfr(C), cfr(D), cfr(E), optrA, and poxtA, have been identified to date. The cfr genes code for 23S rRNA methylases, which confer a multiresistance phenotype that includes resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A compounds. The optrA and poxtA genes code for ABC-F proteins that protect the bacterial ribosomes from the inhibitory effects of oxazolidinones. The optrA gene confers resistance to oxazolidinones and phenicols, while the poxtA gene confers elevated MICs or resistance to oxazolidinones, phenicols, and tetracycline. These oxazolidinone resistance genes are most frequently found on plasmids, but they are also located on transposons, integrative and conjugative elements (ICEs), genomic islands, and prophages. In these mobile genetic elements (MGEs), insertion sequences (IS) most often flanked the cfr, optrA, and poxtA genes and were able to generate translocatable units (TUs) that comprise the oxazolidinone resistance genes and occasionally also other genes. MGEs and TUs play an important role in the dissemination of oxazolidinone resistance genes across strain, species, and genus boundaries. Most frequently, these MGEs also harbor genes that mediate resistance not only to antimicrobial agents of other classes, but also to metals and biocides. Direct selection pressure by the use of antimicrobial agents to which the oxazolidinone resistance genes confer resistance, but also indirect selection pressure by the use of antimicrobial agents, metals, or biocides (the respective resistance genes against which are colocated on cfr-, optrA-, or poxtA-carrying MGEs) may play a role in the coselection and persistence of oxazolidinone resistance genes.

LINEZOLID-INDUCED MITOCHONDRIAL TOXICITY PRESENTING AS RETINAL NERVE FIBER LAYER MICROCYSTS AND OPTIC AND PERIPHERAL NEUROPATHY IN A PATIENT WITH CHRONIC GRANULOMATOUS DISEASE

PURPOSE

To report a case with unique changes in the retinal nerve fiber layer observed on optical coherence tomography in a 22-year-old patient on chronic linezolid therapy for recurrent pyogenic liver abscesses with underlying chronic granulomatous disease.

METHODS

History and clinical examination, laboratory evaluation, fluorescein angiography, and optical coherence tomography.

RESULTS

The patient presented with best-corrected visual acuity of 20/200 in the right eye and 20/125 in the left eye. He had moderate optic disk edema and superotemporal field defects bilaterally. Swept-source optical coherence tomography revealed the presence of retinal nerve fiber layer microcystic spaces. Laboratory tests showed no positive findings except for an elevated lactic acid level. Linezolid-induced optic neuropathy was suspected, and the drug was discontinued. Six weeks after termination of oral linezolid therapy, the optic disk edema and the microcystic spaces in the retinal nerve fiber layer resolved, and the best-corrected visual acuity improved to 20/50 in the right and 20/40 in the left eye, respectively.

CONCLUSION

Linezolid is a widely used antibiotic with broad-spectrum action. However, chronic use can lead to mitochondrial toxicity that may have protean manifestations. Ocular examination, particularly of the optic nerve and nerve fiber layer using multimodal imaging, is critical in diagnosing such toxicity.

Characterization of oxazolidinone and phenicol resistance genes in non-clinical enterococcal isolates from Korea

OBJECTIVES

To investigate the distribution and genetic characteristics of linezolid-resistant enterococci.

METHODS

Enterococcus faecalis and Enterococcus faecium strains were isolated from pigs, equipment, grounds, and employees of 19 Korean swine farms in 2017. Antimicrobial susceptibility testing was then performed and linezolid resistance genes were detected via PCR. For genetic epidemiological characterization, multilocus sequence typing and whole-genome sequencing data were analysed.

RESULTS

Twenty-eightE. faecalis and five E. faecium strains were isolated from 1026 samples obtained from the 19 farms. Ten sequence types were identified among the E. faecalis strains, of which ST256 (42.9%) and ST86 (25%) were the most abundant. The oxazolidinone and phenicol resistance genes poxtA, optrA, and fexA were detected in isolates of E. faecalis (100%, 85.7%, and 67.9%, respectively) and E. faecium (100%, 60%, and 80%, respectively). The minimum inhibitory concentrations of linezolid in these isolates ranged from 2 mg/L to 12 mg/L. The whole-genome sequencing data indicated that fexA was located upstream of poxtA.

CONCLUSIONS

This is the first study to report the detection of poxtA in isolates that were both susceptible and resistant to linezolid in Korea. These results demonstrate the importance of antimicrobial resistance monitoring programmes, including regular antimicrobial susceptibility testing and resistance gene expression analysis, to facilitate the control of the spread of antibiotic resistance in non-clinical settings in Korea.

Novel linezolid resistance plasmids in Enterococcus from food animals in the USA

Objectives

To sequence the genomes and determine the genetic mechanisms for linezolid resistance identified in three strains of Enterococcus isolated from cattle and swine caecal contents as part of the US National Antimicrobial Resistance Monitoring System (NARMS) surveillance programme.

Methods

Broth microdilution was used for in vitro antimicrobial susceptibility testing to assess linezolid resistance. Resistance mechanisms and plasmid types were identified from data generated by WGS on Illumina® and PacBio® platforms. Conjugation experiments were performed to determine whether identified mechanisms were transmissible.

Results

Linezolid resistance plasmids containing optrA were identified in two Enterococcus faecalis isolates and one Enterococcus faecium. The E. faecium isolate also carried the linezolid resistance gene cfr on the same plasmid as optrA. The linezolid resistance plasmids had various combinations of additional resistance genes conferring resistance to phenicols (fexA), aminoglycosides [spc and aph(3')-III] and macrolides [erm(A) and erm(B)]. One of the plasmids was confirmed to be transmissible by conjugation, resulting in linezolid resistance in the transconjugant.

Conclusions

To the best of our knowledge, this is the first identification of linezolid resistance in the USA in bacteria isolated from food animals. The oxazolidinone class of antibiotics is not used in food animals in the USA, but the genes responsible for resistance were identified on plasmids with other resistance markers, indicating that there may be co-selection for these plasmids due to the use of different antimicrobials. The transmissibility of one of the plasmids demonstrated the potential for linezolid resistance to spread horizontally. Additional surveillance is necessary to determine whether similar plasmids are present in human strains of Enterococcus.

Pharmacokinetics of linezolid during continuous hemodiafiltration: A case report

The pharmacokinetics of linezolid clearance (CL_LZD) during continuous hemodiafiltration (CHDF) has not been comprehensively analyzed. Here, we examined CL_LZD by CHDF in a patient with septic shock and disseminated intravascular coagulation due to methicillin-resistant Staphylococcus aureus. The extraction ratio of LZD by CHDF was 22.6%, and the protein-binding rate was 17.9% ± 7.7%. In addition, it was determined that the calculated total body clearance of LZD was 30.2 mL/min, plasma elimination half-life was 8.66 h, and the CL_LZD by the dialyzer used for CHDF was 23.0 mL/min. From the obtained pharmacokinetics, the CL_LZD of patients continuing CHDF was estimated to be approximately half of the reported CL_LZD for healthy subjects. In addition, the LZD concentration of the sepsis patient who underwent CHDF remained higher than the minimum inhibitory concentration and was similar to the LZD concentrations reported in normal renal function patients. Although further studies are warranted, when LZD is administered to patients treated with CHDF, the present findings suggest that dose regulation is not required.

Synthesis of Linezolid Metabolites PNU-142300 and PNU-142586 toward the Exploration of Metabolite-Related Events

Linezolid (1) is an oxazolidinone antibiotic that is partially metabolized in vivo via ring cleavage of its morpholine moiety to mainly form two metabolites, PNU-142300 (2) and PNU-142586 (3). It is supposed that accumulation of 2 and 3 in patients with renal insufficiency may cause thrombocytopenia, one of the adverse effects of linezolid. However, the poor availability of 2 and 3 has hindered further investigation of the clinical significance of the accumulation of these metabolites. In this paper, we synthesized metabolites 2 and 3 via a common synthetic intermediate, 4; this will encourage further exploration of events related to these metabolites and lead to improved clinical use of linezolid.

Intrathecal/Intraventricular Linezolid in Multidrug-Resistant Enterococcus faecalis Ventriculitis

Background The use of intrathecal antibiotic therapy for the treatment of ventriculitis and/or meningitis has demonstrated efficacy especially when sterilization of the cerebrospinal fluid is not possible with intravenous antibiotics alone. Case Description We describe the successful treatment of Enterococcus faecalis ventriculitis utilizing intrathecal linezolid in a 32-year-old female patient with severe allergy to vancomycin, prohibitive bacterial susceptibilities, and failure of previous attempts to sterilize the cerebrospinal fluid despite multimodal treatment. Conclusion Intrathecal linezolid is a useful treatment in the setting of multidrug-resistant bacterial ventriculitis. We present a useful dosing regimen for the administration of intrathecal linezolid.

Appropriateness of antibiotic usage for gastrointestinal disorders in a tertiary care hospital

OBJECTIVE

To assess antibiotic usage in gastrointestinal disorders with respect to appropriateness, pattern of resistance, and incidence of adverse drug reactions (ADRs).

METHODOLOGY

Antibiotic prescribing in the gastroenterology department of a tertiary care hospital was evaluated using the Gyssens criteria and also by assessing drug related problems (DRPs) using the Pharmaceutical Care Network Europe V.6.2. A total of 173 patients were studied prospectively by a team of clinical pharmacists. Antibiotic susceptibility was prospectively studied; in addition, retrospective data on culture and sensitivity reports of commonly isolated organisms from 1 October 2012 to 30 September 2014 were collected to determine the resistance pattern in previous years. ADRs were evaluated using the Naranjo scale.

RESULTS

Antibiotic therapy was appropriate in 60% of patients and inappropriate in the remaining patients due to incorrect decision, choice, and use. A total of 184 DRPs and 30 ADRs of antibiotics were identified. In the study patients, the most commonly isolated organism was Escherichia coli (27.3%) followed by Klebsiella pneumoniae (16.7%). Both E coli and K pneumoniae exhibited 100% resistance towards cefotaxime. There was an increase in the resistance of E coli and K pneumoniae against various antibiotics tested in 2013-2014 as compared to the previous year. An empirical antibiotic policy was developed which was endorsed by the gastroenterology department.

CONCLUSIONS

Although antibiotic therapy was appropriate in the majority of patients, irrational use occurred due to incorrect choice, improper dosage, and improper duration of therapy. E coli and K pneumoniae isolates showed an increase in resistance towards various antibiotics tested.

Thrombocytopenia Associated with Linezolid Therapy in Solid Organ Transplant Recipients: A Retrospective Cohort Study

BACKGROUND

Linezolid is associated infrequently with bone marrow suppression in immunocompetent patients, but hematologic complications from linezolid in transplant recipients are understudied. This study evaluated the hematologic safety of linezolid in solid organ transplant recipients.

METHODS

We performed a retrospective study of inpatients at our institution treated with linezolid from June 1, 2009 until June 6, 2012. The solid organ transplant cohort (TP) was compared with the non-transplant cohort (NTP) using parameters related to linezolid safety. Outcomes included incidences of leukopenia or thrombocytopenia at the end of linezolid treatment (EOT), lengths of stay, and blood product requirements.

RESULTS

The TP cohort included 110 patients; the NTP cohort included 583 patients. Baseline parameters were similar between the TP and NTP cohorts. Non-transplant patients were more likely to have methicillin-resistant Staphylococcus aureus (MRSA), whereas TP patients received more doses of linezolid (17.0 vs. 11.3, p<0.001) and were more likely to receive other drugs associated with thrombocytopenia (91.7% vs. 11.3%, p<0.0001). Transplant patients with normal platelet counts at baseline were more likely to have EOT thrombocytopenia (29.3% vs. 10.7%, p=0.005), and multivariable regression analysis confirmed only a beginning platelet count less than 150,000 platelets per micoliter to be significantly different between groups: 43% TP versus 26.9% NTP (p=0.0009) making it the only independent predictor of EOT thrombocytopenia. Finally, TP patients were more likely to require platelet transfusions compared with the NTP cohort.

CONCLUSIONS

Transplant patients who received linezolid had a higher incidence of EOT thrombocytopenia and platelet transfusions, compared with NTP. Transplant patients who are thrombocytopenic at baseline are at the greatest risk. These findings may relate to more frequent use of drugs associated with marrow suppression or greater linezolid exposure in the TP cohort. Clinicians caring for transplant patients should take into account this higher risk of thrombocytopenia and need for platelets when considering use of linezolid in this population.

Ceftaroline - a cause for neutropenia

WHAT IS KNOWN AND OBJECTIVE

The US Food and Drug Administration approved ceftaroline in 2010 for the treatment of community-acquired pneumonia and skin and soft-tissue infections. The most common adverse reactions are diarrhoea, nausea and rash. To present the first case of neutropenia directly related to ceftaroline.

CASE SUMMARY

A 90-year-old female was given ceftaroline for treatment of a pneumonia complicated by methicillin-resistant Staphylococcus aureus bacteraemia and possible vertebral osteomyelitis. After 25 days of ceftaroline, she developed neutropenia. Ceftaroline was discontinued and her white blood cell count returned to normal within one week.

WHAT IS NEW AND CONCLUSION

Although neutropenia is a potential cephalosporin class effect, we present the first case of neutropenia directly related to ceftaroline. Agranulocytosis and neutropenia are rare, yet potentially life-threatening adverse effects of cephalosporins. Healthcare providers should be aware of the potential for ceftaroline to cause neutropenia, particularly in patients treated for greater than two weeks.

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.

Clinical pharmacokinetic/pharmacodynamic profile of linezolid in severely ill intensive care unit patients

Severely ill Intensive Care Unit (ICU) patients have an increased risk of developing multiresistant Gram-positive infections, largely due to the inappropriate use of antimicrobials. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) profile of linezolid, an antibiotic against Gram-positive infections, was characterised in eight critically ill patients admitted to the ICU. Remarkable variation amongst patients in the PK parameters of linezolid was observed, including a 5-7-fold difference in peak serum concentration (C(max)) (mean±standard deviation 15.70±6.58 mg/L) and 12-h area under the serum concentration-time curve (AUC(0-12)) (96.73±56.45 mg h/L), although the minimum inhibitory concentration (MIC) was similar amongst patients. In particular, variation amongst patients was found in the ratio of AUC(0-24)/MIC (range 31.66-216.82, mean 96.73) and the percentage of time that the serum concentration exceeded the MIC (T>MIC) (range 53.4-100%), two parameters used to predict linezolid efficacy. These variations highlight the importance of individual monitoring of linezolid PK/PD properties in critically ill patients. Furthermore, it was observed that regardless of AUC(0-24)/MIC and T>MIC values, the clinical and microbiological responses of patients were primarily affected by the individual's pathophysiological condition. In summary, these findings point to highly variable PK/PD properties of linezolid in severely ill patients, providing the rationale for targeting linezolid dosage to each individual patient's specific properties. An optimal dosage regimen based on individual PK/PD properties and pathophysiological conditions will help reduce the occurrence of resistance in Gram-positive bacteria.

Treatment of meningitis caused by vancomycin-resistant Enterococcus faecium: high-dose and combination daptomycin therapy

OBJECTIVE

To report 3 successful treatments of vancomycin-resistant Enterococcus faecium meningitis in adults using daptomycin and either linezolid or gentamicin.

CASE SUMMARY

Three case reports involving males (aged 58-78 years) are presented; in each case (trigeminal nerve microvascular decompression and subdural hygroma; paraspinal abscess; and hydrocephalus with subsequent craniotomy and ventriculo-peritoneal shunt placement) CSF examination revealed vancomycin-resistant Enterococcus (VRE) susceptible to daptomycin, gentamicin, and/or linezolid. Threeto four-week treatment regimens with daptomycin 6-12 mg/kg and either gentamicin or linezolid led to clinical resolution and microbiological clearance of infection.

DISCUSSION

Daptomycin has previously been shown to be successful in treating methicillin-resistant Staphylococcus aureus-associated meningitis and other serious VRE and enterococcal infections. Higher than approved doses of daptomycin were used in 2 cases where in theory higher CSF concentrations would thus be obtained. Gentamicin and linezolid were added to daptomycin therapy based on in vitro data synergy results and because of documented successful treatment for VRE meningitis, respectively.

CONCLUSIONS

The difficulty in treating VRE CSF infections involves both drug kinetics and microbial resistance factors, as well as external factors such as foreign bodies like shunts. This report highlighted 3 cases where daptomycin use in concert with either gentamicin or linezolid was successful in treating this infection. Additional controlled trials will be helpful in identifying the best strategies when using daptomycin to treat CSF infections.

[GEIPC-SEIMC (Study Group for Infections in the Critically Ill Patient of the Spanish Society for Infectious Diseases and Clinical Microbiology) and GTEI-SEMICYUC ( Working Group on Infectious Diseases of the Spanish Society of Intensive Medicine, Critical Care, and Coronary Units) recommendations for antibiotic treatment of gram-positive cocci infections in the critical patient]

In recent years, an increment of infections caused by gram-positive cocci has been documented in nosocomial and hospital-acquired-infections. In diverse countries, a rapid development of resistance to common antibiotics against gram-positive cocci has been observed. This situation is exceptional in Spain but our country might be affected in the near future. New antimicrobials active against these multi-drug resistant pathogens are nowadays available. It is essential to improve our current knowledge about pharmacokinetic properties of traditional and new antimicrobials to maximize its effectiveness and to minimize toxicity. These issues are even more important in critically ill patients because inadequate empirical therapy is associated with therapeutic failure and a poor outcome. Experts representing two scientific societies (Grupo de estudio de Infecciones en el Paciente Crítico de la SEIMC and Grupo de trabajo de Enfermedades Infecciosas de la SEMICYUC) have elaborated a consensus document based on the current scientific evidence to summarize recommendations for the treatment of serious infections caused by gram-positive cocci in critically ill patients.

Recomendaciones GEIPC-SEIMC y GTEI-SEMICYUC para el tratamiento antibiótico de infecciones por cocos grampositivos en el paciente crítico

In recent years, an increment of infections caused by gram-positive cocci has been documented in nosocomial and hospital-acquired infections. In diverse countries, a rapid development of resistance to common antibiotics against gram-positive cocci has been observed. This situation is exceptional in Spain but our country might be affected in the near future. New antimicrobials active against these multi-drug resistant pathogens are nowadays available. It is essential to improve our current knowledge about pharmacokinetic properties of traditional and new antimicrobials to maximize its effectiveness and to minimize toxicity. These issues are even more important in critically ill patients because inadequate empirical therapy is associated with therapeutic failure and a poor outcome. Experts representing two scientific societies (Grupo de estudio de Infecciones en el Paciente Critico de la SEIMC and Grupo de trabajo de Enfermedades Infecciosas de la SEMICYUC) have elaborated a consensus document based on the current scientific evidence to summarize recommendations for the treatment of serious infections caused by gram-positive cocci in critically ill patients.

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.

Pharmacoeconomic evaluation of linezolid versus teicoplanin in bacteremia by Gram-positive microorganisms

OBJECTIVE

The objective of this study was to compare the efficiency of linezolid versus teicoplanin in the treatment of bacteremia produced by Gram-positive microorganisms through a pharmacoeconomic analysis based on clinical results obtained from a previous clinical trial.

METHODS

We applied an analysis of cost-effectiveness elaborated through a pharmacoeconomic model. We defined each unit of effectiveness as 'each successfully cured of infections with bacteremia.' We used the program Pharma-Decision (version Hospital 1.1) that allows to build interactive pharmacoeconomic models. Effectiveness data of both antibiotics were obtained from a published clinical trial, while resources consumed were obtained from the same source and from a consensus provided by a local expert panel. Only direct costs were included in the analysis without taking into consideration indirect costs. The perspective chosen was hospital assistance and the time horizon was set to 28 days. All costs are expressed in Euros.

RESULTS

Linezolid demonstrated a better clinical outcome with less associated costs compared to teicoplanin (88.5 versus 56.7% of cured patients and 5,557.04 versus 6,327.43 per treated patient, respectively), thus resulting in a lower cost-effectiveness ratio for linezolid versus teicoplanin (6,279.1 versus 11,159.5 per cured patient with a 95% CI of 5,960.2-6,510.4 and 10,865.2-12,647.3, respectively) which results in a the dominant position for linezolid. The sensitivity analysis showed that linezolid was always the most efficient option even when modifying the value of variables with higher uncertainty.

CONCLUSIONS

Linezolid is a more efficient option than teicoplanin because it presents higher rate of effectiveness with lower consumption of resources, thus being a dominant alternative in the treatment of Gram-positive infection with bacteremia.

Human vitreous distribution of linezolid after a single oral dose

PURPOSE

To evaluate the relationship between vitreous linezolid concentrations versus both time and serum concentrations after a single 600 mg oral dose.

METHODS

Two groups of six subjects undergoing a pars plana vitrectomy indicated by macular pucker or full thickness macular hole were given a single tablet of linezolid before surgery. The early group underwent vitrectomy at random times before the time of maximum serum linezolid concentration (i.e., 77 minutes) and the late group underwent vitrectomy at random times afterward. Each patient had a serum sample drawn shortly before and after vitrectomy and the vitreous specimen was sampled at the initiation of surgery.

RESULTS

The early group and late group had mean vitreous linezolid concentrations of 0.06 mcg/mL and 1.25 mcg/mL, respectively. The vitreous linezolid concentration showed a strong correlation to the interpolated serum concentration (R2 = 0.74, P < 0.01) at the time of vitrectomy.

CONCLUSION

The study demonstrates that linezolid penetrates the blood-retina barrier in noninflamed eyes. Because the vitreous concentrations appeared to exponentially trend upward with time and 33% of the late group achieved sufficient MIC90 levels for the common pathogens found in postoperative endophthalmitis, adequate concentrations might be achieved with an altered dosing regimen to achieve higher serum steady state levels. Further study is warranted.

Ramoplanin: a lipoglycodepsipeptide antibiotic

OBJECTIVE

To review the pharmacology, antimicrobial activity, pharmacokinetics, clinical applications, and safety of ramoplanin, a lipoglycodepsipeptide antibiotic.

DATA SOURCES

Information was obtained from MEDLINE and BIOSIS databases (1984-August 2004) and Oscient Pharmaceuticals using the key words ramoplanin, A 16686, A 16686A, and MDL 62198.

STUDY SELECTION AND DATA EXTRACTION

Available English-based articles and abstracts were reviewed, along with information from Oscient Pharmaceuticals.

DATA SYNTHESIS

Ramoplanin exerts its bactericidal activity against gram-positive aerobic and anaerobic bacteria by blocking peptidoglycan synthesis via lipid II. In vitro susceptibility reports have demonstrated efficacy against antibiotic-resistant gram-positive pathogens. Cross-resistance has not been documented with vancomyin and other glycopeptides. Clinical trials are investigating ramoplanin's oral administration for treatment of Clostridium difficile-associated diarrhea. Previous clinical trials had evaluated the suppression of colonization of vancomycin-resistant Enterococcus with ramoplanin. Adverse effects are minimal, and drug-drug interactions have not been documented.

CONCLUSIONS

The completion of clinical trials will determine whether ramoplanin has a promising role as a treatment option for diarrhea due to C. difficile.

Treatment of Vancomycin-Resistant Enterococcus with Quinupristin/Dalfopristin and High-Dose Ampicillin

OBJECTIVE:

To report the successful treatment of vancomycin-resistant Enterococcus (VRE) bacteremia using the combination of quinupristin/dalfopristin and high-dose ampicillin.

CASE SUMMARY:

A 38-year-old African American woman with relapsed acute myeloid leukemia and neutropenic fever developed VRE bacteremia following 3 successive courses of vancomycin for methicillin-resistant staphylococcal infections. Treatment with linezolid was initiated; however, after 9 days of therapy, blood cultures continued to reveal VRE and the patient became febrile. The patient was subsequently switched to quinupristin/dalfopristin and high-dose ampicillin. The fever resolved and all subsequent blood cultures were negative after the initiation of combination therapy.

DISCUSSION:

The emergence of VRE infections presents a treatment challenge in immunocompromised patients. When treating VRE infections in this patient population, the effectiveness of linezolid and quinupristin/dalfopristin is limited by their bacteriostatic activity when used as monotherapy. Recent in vitro data suggest synergistic activity with quinupristin/dalfopristin when used in combination with other antimicrobials in selected isolates of VRE.

CONCLUSIONS:

Persistent VRE bacteremia was successfully treated in this neutropenic patient using the combination of high-dose ampicillin and quinupristin/dalfopristin. Case reports and in vitro data suggest that concomitant therapy with high-dose ampicillin may be an effective treatment alternative for VRE infections not responding to standard therapy.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.

Prevention and management of antibacterial resistance for primary care patients with respiratory tract infections

This review examines the problem of increasing antibacterial resistance among the pathogens commonly associated with community-acquired respiratory tract infections, particularly Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The increases in morbidity, mortality, and treatment cost associated with increased resistance to available antibiotics are challenging prescribers to find more effective therapeutic strategies. A MEDLINE search of the literature from 1966 to the present was performed to seek data relevant to the issue of resistance, especially the negative effects on patient outcomes and costs of therapy. Several observations and conclusions emerged. Data are lacking on local resistance patterns, broad-spectrum agents are overprescribed when narrower-spectrum choices would be more appropriate, a need exists for educational programs to encourage restricting drug use and changing prescribing habits, and there is a need for new antibiotic choices. The best antibiotic options are agents with a tailored spectrum of activity that are targeted at particular respiratory tract pathogens and have low potential to select for resistant organisms.

[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.

Osteomyelitis attributable to vancomycin-resistant enterococci

Vancomycin-resistant enterococcus first was described in 1988, and has become a major problem in nosocomial infections. This is a retrospective review of 10 patients, seen at the authors' hospital during a 2-year period, with confirmed vancomycin-resistant enterococcal osteomyelitis: four patients had total joint arthroplasty infections, one patient had an infected tibial nail, three patients had infections associated with external fixators, and two patients had osteomyelitis of the femur. Four of the 10 patients had underlying medical illnesses (diabetes mellitus, systemic lupus erythematosus, human immunodeficiency virus infection); four of the 10 patients were intravenous drug users. Two patients had vancomycin-resistant enterococci on admission, and the other eight patients were admitted to the hospital for a mean of 21.3 days (range, 3-73 days) before vancomycin-resistant enterococci were identified in the bone. Eight of the 10 patients had monomicrobial infections with vancomycin-resistant enterococci. Patients were treated by surgical debridement, removal of hardware, and antibiotics (chloramphenicol in eight patients, quinupristin and dalfopristin (Synercid) in two patients). All patients initially improved with therapy, but one patient had a recurrence of vancomycin-resistant enterococcal osteomyelitis and died of bacteremia. Bone infections with vancomycin-resistant enterococcus still may be uncommon, but with time and selective antibiotic pressures, vancomycin-resistant enterococci may become a more prominent entity in orthopaedic infections.

Spectrum and potency evaluation of a new oxazolidinone, linezolid: report from the SENTRY Antimicrobial Surveillance Program, 1998-2000

Resistance (R) among Gram-positive cocci has escalated in the last two decades to levels necessitating the development and use in the newer drug classes, oxazolidinones (linezolid) and streptogramins (quinupristin/dalfopristin [Q/D]). The SENTRY Antimicrobial Surveillance Program has monitored these classes before, during and after their release by various regulatory agencies. Over 30,000 Gram-positive strains were tested against >30 drugs by reference broth microdilution methods between 1998-2000 in four geographic regions (Asia-Western Pacific [APAC], Europe [EU], Latin America [LA], North America [NA]). The tested strains were 23,188 staphylococci; 5,103 enterococci and 2,045 streptococci. Among staphylococci, linezolid was active against all isolates (MICs, < or =4 microg/ml) regardless of susceptibility patterns of other antimicrobial agents. Similar results were noted for vancomycin (includes one VISA from Hong Kong), teicoplanin, and Q/D (<1% R). Gatifloxacin had the widest spectrum among fluoroquinolones (FQ) against Staphylococcus aureus (1.5-9.2% R) and coagulase-negative staphylococci (0.8-4.0%). Linezolid was also active against all enterococci (MIC50 and (90,) 2 microg/ml). Q/D was active against only 75.3% of vancomycin-resistant enterococci (VRE). The VRE rate was highest in NA (12.4%) > EU (3.2%) > LA (1.6%) > APAC (1.3%). Among streptococci, linezolid was consistently active (MIC(90,) 1 microg/ml) as were the glycopeptides and Q/D. Variable penicillin-R (MIC, > or = 2 microg/ml) was observed among regions: EU (32.5%) > APAC (15.1%) > LA (13.8%) > NA (9.6%), and macrolide-R was higher in EU (40.3%). Ciprofloxacin-R at > or =4 microg/ml in streptococcal strains was noted world wide highest in viridans group streptococci (18.4-25.6%). Linezolid remained active (MIC, < or =4 microg/ml) against all Gram-positive species strains tested in the SENTRY Program (1998-2000). Q/D, glycopeptides and newer FQ compounds were generally less effective in vitro. It remains a prudent practice to continue surveillance programs to detect emerging resistance patterns and recognize significant regional variations in the oxazolidinone susceptibilities.