Comparison of the Arktm Immunoassay With Hplc-Uv for Therapeutic Drug Monitoring of Linezolid.

BACKGROUND: An enzymatic immunoassay is under development by ARK Diagnostics, Inc. for the quantification of plasma concentrations of linezolid (LZD). In the present study, the authors aimed to assess the performance of this immunoassay using a validated HPLC-UV method as reference.

METHODS: Within- and between-day in vitro inaccuracy and imprecision of the ARK LZD assay were firstly tested using spiked quality controls (QC) provided by the kit manufacture. Subsequently, the performance of the immunoassay was verified in vivo by analyzing 170 trough LZD plasma samples from patients on antibiotic therapy.

RESULTS: Imprecision of the spiked QCs resulted in every instance less than 7.0% and the inaccuracy ranged from -1.5% to 6.6%. The linear correlation between the two methods was documented by the Pearson analysis of plasma samples from patients on LZD therapy (coefficient = 0.9619). By Bland-Altman comparison, 8.2% of the patient samples resulted out of the limits ranging from -27.0% to +33.5%, with the large majority of them having LZD concentrations exceeding 10 mg/L.

CONCLUSIONS: Acceptable analytical performance of the ARK LZD immunoassay has been demonstrated both with spiked QC and patients' samples, making it a viable alternative to HPLC for the TDM of LZD in clinical practice in laboratory hospitals that do not have HPLC equipment.