Determination of Tedizolid susceptibility interpretive criteria for gram-positive pathogens according to clinical and laboratory standards institute guidelines

A pharmacokinetic-pharmacodynamic (PKPD) model-based analysis of tedizolid against enterococci using the hollow-fibre infection model

BACKGROUND

Tedizolid is a novel oxazolidinone antibiotic. Considering the higher antibacterial effect in immunocompetent compared with immunosuppressed animals, it is not recommended in immunocompromised patients.

OBJECTIVES

In this study, we assessed the 'pure' pharmacokinetic-pharmacodynamic (PKPD) relationship for tedizolid against Enterococcus in the hollow-fibre infection model (HFIM).

METHODS

Unbound plasma concentration time profiles (200-5000 mg/day IV) were simulated in the HFIM over 120 h against an Enterococcus faecalis strain and two clinical isolates of Enterococcus faecium (VRE-vanB and VRE-vanA). Next, a PKPD model describing tedizolid efficacy against bacterial isolates was developed. A population PK model was linked to the developed PKPD model and utilized to predict the bacterial kinetics in plasma and in target tissues [adipose, muscle, epithelial lining fluid (ELF) and sputum] over 120 h of therapy.

RESULTS

The PKPD model adequately described the bacterial kill kinetics for all bacterial populations. At the human recommended dose of 200 mg/day, bacterial growth was predicted in plasma and all tissues, except for ELF. Bacteriostasis was observed only at a higher dose of 1200 mg/day over 120 h. An fAUC/MIC of 80 related to stasis over 120 h. Subpopulations resistant to 3 × MIC were amplified in plasma and target tissues, except for ELF, at doses of 200-800 mg/day.

CONCLUSIONS

The human dose of 200 mg/day was insufficient to suppress bacterial growth in the HFIM, indicating that further components contribute to the clinical effect of tedizolid. This study supports the warning/precaution for tedizolid to limit its use in immunocompromised patients.

Pharmacokinetics and Pharmacodynamics of Tedizolid

Tedizolid is an oxazolidinone antibiotic with high potency against Gram-positive bacteria and currently prescribed in bacterial skin and skin-structure infections. The aim of the review was to summarize and critically review the key pharmacokinetic and pharmacodynamic aspects of tedizolid. Tedizolid displays linear pharmacokinetics with good tissue penetration. In in vitro susceptibility studies, tedizolid exhibits activity against the majority of Gram-positive bacteria (minimal inhibitory concentration [MIC] of ≤ 0.5 mg/L), is four-fold more potent than linezolid, and has the potential to treat pathogens being less susceptible to linezolid. Area under the unbound concentration-time curve (fAUC) related to MIC (fAUC/MIC) was best correlated with efficacy. In neutropenic mice, fAUC/MIC of ~ 50 and ~ 20 induced bacteriostasis in thigh and pulmonary infection models, respectively, at 24 h. The presence of granulocytes augmented its antibacterial effect. Hence, tedizolid is currently not recommended for immunocompromised patients. Clinical investigations with daily doses of 200 mg for 6 days showed non-inferiority to twice-daily dosing of linezolid 600 mg for 10 days in patients with acute bacterial skin and skin-structure infections. In addition to its use in skin and skin-structure infections, the high pulmonary penetration makes it an attractive option for respiratory infections including Mycobacterium tuberculosis. Resistance against tedizolid is rare yet effective antimicrobial surveillance and defining pharmacokinetic/pharmacodynamic targets for resistance suppression are needed to guide dosing strategies to suppress resistance development.

Phenotypic and genotypic characterization of linezolid-resistant Enterococcus faecium from the USA and Pakistan

OBJECTIVES

Linezolid is an important therapeutic option for the treatment of infections caused by VRE. Linezolid is a synthetic antimicrobial and resistance to this antimicrobial agent remains relatively rare. As a result, data on the comparative genomics of linezolid resistance determinants in Enterococcus faecium are relatively sparse.

METHODS

To address this knowledge gap in E. faecium, we deployed phenotypic antibiotic susceptibility testing and Illumina WGS on hospital surface (environmental) and clinical isolates from the USA and Pakistan.

RESULTS

We found complete concordance between isolate source country and mechanism of linezolid resistance, with all the US isolates possessing a 23S rRNA gene mutation and the Pakistan isolates harbouring two to three acquired antibiotic resistance genes. These resistance genes include the recently elucidated efflux-pump genes optrA and poxtA and a novel cfr-like variant. Although there was no difference in the linezolid MIC between the US and Pakistan isolates, there was a significant difference in the geometric mean of the MIC between the Pakistan isolates that had two versus three of the acquired antibiotic resistance genes. In five of the Pakistan E. faecium that possessed all three of the resistance genes, we found no difference in the local genetic context of poxtA and the cfr-like gene, but we identified different genetic contexts surrounding optrA.

CONCLUSIONS

These results demonstrate that E. faecium from different geographical regions employ alternative strategies to counter selective pressure of increasing clinical linezolid use.