Linezolid dosing in critically ill patients undergoing various modalities of renal replacement therapy: a pooled population pharmacokinetic analysis

The altered pharmacokinetics (PK) of linezolid are pronounced in critically ill patients undergoing different modalities of renal replacement therapy (RRT). This study aimed to provide a pooled population PK analysis of linezolid in patients undergoing RRT, and to evaluate the pharmacodynamic target attainment of linezolid standard dosing (600 mg q12h). In total, 414 pooled linezolid concentration observations from 69 patients undergoing intermittent haemodialysis (IHD), sustained low-efficiency dialysis (SLED) or continuous RRT were used to develop the population PK model. The probability of target attainment (PTA) for the efficacy markers of 85% T>minimum inhibitory concentration (MIC) and area under the concentration-time curve (AUC)/MIC >100 was evaluated, and the risk of toxicity was estimated based on Cmin ≥10 mg/L. Linezolid concentration data were described adequately by a two-compartment model. Renal function and body weight were identified as significant modifiers for endogenous clearance of linezolid. Simulations demonstrated that the PTA of 85% T>MIC and AUC/MIC>100 was unacceptably low (0-58.6%, MIC ≥1 mg/L) in RRT patients with preserved renal function, while desirable 85% T>MIC attainment (≥ 90%, MIC ≤2 mg/L) was achieved in anuric RRT patients. The predicted risk of toxicity was negligible (<1.0%) in patients with preserved renal function (regardless of RRT modality), while the probability of reaching Cmin ≥10 mg/L was high (17.9-20.9%) for the anuric patient population undergoing IHD or SLED. In conclusion, standard linezolid dosing is adequate for anuric RRT patients with MIC ≤2 mg/L.

Biofilm formation of Brazilian meticillin-resistant Staphylococcus aureus strains: prevalence of biofilm determinants and clonal profiles

Biofilms plays an important role in medical-device-related infections. This study aimed to determine the factors that influence adherence and biofilm production, as well as the relationship between strong biofilm production and genetic determinants in clinical isolates of meticillin-resistant Staphylococcus aureus (MRSA). Fifteen strains carrying different chromosomal cassettes recovered from hospitalized patients were selected; five SCCmecII, five SCCmecIII and five SCCmecIV. The SCCmec type, agr group and the presence of the virulence genes (bbp, clfA, icaA, icaD, fnbB, bap, sasC and IS256) were assessed by PCR. PFGE and multilocus sequence typing (MLST) techniques were also performed. The initial adhesion and biofilm formation were examined by quantitative assays. The surface tension and hydrophobicity of the strains were measured by the contact angle technique to evaluate the association between these parameters and adhesion ability. SCCmecIII and IV strains were less hydrophilic, with a high value for the electron acceptor parameter and higher adhesion in comparison with SCCmecII strains. Only SCCmecIII strains could be characterized as strong biofilm producers. The PFGE showed five major pulsotypes (A-E); however, biofilm production was related to the dissemination of one specific PFGE clone (C) belonging to MLST ST239 (Brazilian epidemic clonal complex). The genes agrI, fnbB and IS256 in SCCmecIII strains were considered as genetic determinants associated with strong biofilm-formation by an ica-independent biofilm pathway. This study contributes to the understanding of biofilm production as an aggravating factor potentially involved in the persistence and severity of infections caused by multidrug-resistant MRSA belonging to this genotype.

Empiric use of linezolid in febrile hematology and hematopoietic stem cell transplantation patients colonized with vancomycin-resistant Enterococcus spp

OBJECTIVES

We conducted a retrospective study on the impact of the empiric use of linezolid on mortality in vancomycin-resistant Enterococcus spp (VRE)-colonized hematology and hematopoietic stem cell transplantation (HSCT) patients.

METHODS

VRE-colonized inpatients for whom complete data were available (n=100) were divided into two groups: those who received empiric linezolid in the course of fever refractory to broad-spectrum antibiotics, replacing the glycopeptide utilized for the previous 48 h, and those who did not (control group). All patients were followed until hospital discharge or death. The impact of linezolid and risk factors for all-cause mortality were evaluated; variables with p<0.10 were analyzed in a multivariate model. A Kaplan-Meier survival analysis was done to compare survival among febrile patients colonized by VRE who received empiric linezolid with patients who did not receive linezolid.

RESULTS

Patients empirically prescribed linezolid were generally younger (median age 33 vs. 44 years; p=0.008) and more likely to be recipients of an allogeneic HSCT (24 (68.6%) vs. 24 (36.9%); p=0.009) than patients who did not receive the drug. Fourteen (21.5%) VRE bloodstream infections were diagnosed, all in patients who did not receive empiric linezolid (p=0.002). In-hospital mortality was comparable in empiric linezolid and non-linezolid users (19 (54.3%) vs. 27 (41.5%), respectively; p=0.293). The Kaplan-Meier survival analysis showed no significant difference in survival comparing the group that received linezolid to the group that did not (p=0.72). Graft-versus-host disease (GVHD; odds ratio (OR) 5.90, 95% confidence interval (CI) 1.46-23.79; p=0.012) and persistence of neutropenia (OR 6.93, 95% CI 1.72-27.94; p=0.0065) were independent predictors of all-cause in-hospital death in HSCT patients, and persistence of neutropenia in non-HSCT patients (OR 8.12, 95% CI 1.22-53.8; p=0.030).

CONCLUSIONS

The empiric use of linezolid in VRE-colonized hematology patients had no impact on mortality, which appeared rather to be associated with the persistence of neutropenia in general and GVHD in the HSCT group.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Costa Rican children

We collected all Staphylococcus aureus isolates from the National Children's Hospital in Costa Rica to evaluate the prevalence and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA). Of 299 S. aureus isolates, 61% were MRSA. Most MRSA isolates (94.5%) carried SCCmec IV, and 45.6% carried Panton-Valentine leukocidin-encoding genes. The high prevalence of MRSA in this population highlights the need for improvement of antibiotic prescription and infection control measures.

Molecular characterization of methicillin-resistant Staphylococcus aureus isolated from a Brazilian university hospital

The aim of this study was to perform SCCmec typing in Staphylococcus aureus isolates and to characterize the clonal profile of these isolates. Forty-six mecA gene-positive strains isolated between 2002 and 2006 were submitted to antimicrobial resistance testing by the E-test, SCCmec typing by multiplex PCR, and clonal profile analysis by pulsed-field gel electrophoresis. Forty-one (89.1%) isolates were typed as SCCmec III and five (10.9%) as SCCmec IV. Four circulating clones were detected, one of them comprising isolates related to the Brazilian epidemic clone. This clone was detected throughout the study period. The SCCmec III isolates were associated with a high rate of multidrug resistance and clonal dissemination of methicillin-resistant S. aureus in the wards of the University Hospital of the Botucatu School of Medicine, Universidade Estadual Paulista.

Trends in antimicrobial resistance among clinical isolates of enterococci in a Brazilian tertiary hospital: a 4-year study

INTRODUCTION

In the past two decades members of the genus Enterococcus have emerged as important nosocomial pathogens worldwide. This study prospectively analyzed the distribution of species and trends in antimicrobial resistance among clinical isolates of enterococci in a Brazilian tertiary hospital from 2006-2009.

METHODS

Enterococcal species were identified by conventional biochemical tests. The antimicrobial susceptibility profile was performed by disk diffusion in accordance with the Clinical and Laboratory Standards Institute (CLSI). A screening test for vancomycin was also performed. Minimal inhibitory concentration (MIC) for vancomycin was determined using the broth dilution method. Molecular assays were used to confirm speciation and genotype of vancomycin-resistant enterococci (VRE).

RESULTS

A total of 324 non-repetitive enterococcal isolates were recovered, of which 87% were E. faecalis and 10.8% E. faecium. The incidence of E. faecium per 1,000 admissions increased significantly (p < 0.001) from 0.3 in 2006 to 2.3 in 2009. The VRE rate also increased over time from 2.5% to 15.5% (p < 0.001). All VRE expressed high-level resistance to vancomycin (MIC >256 µg/ mL) and harbored vanA genes. The majority (89.5%) of VRE belonged to E. faecium species, which were characteristically resistant to ampicillin and quinolones. Overall, ampicillin resistance rate increased significantly from 2.5% to 21.4% from 2006-2009. Resistance rates for gentamicin, chloramphenicol, tetracycline, and erythromycin significantly decreased over time, although they remained high. Quinolones resistance rates were high and did not change significantly over time.

CONCLUSIONS

The data obtained show a significant increasing trend in the incidence of E. faecium resistant to ampicillin and vancomycin.