Analysis using fluorescence polarization immunoassay for unbound teicoplanin concentration in serum

Objectives:  The aim of this study was to develop a simpler and more rapid analytical method for unbound teicoplanin in serum.
Methods:  A new analytical method was developed by modifying an existing fluorescence polarization immunoassay (FPIA) method. The validation of the developed FPIA method was compared in the quantification of unbound teicoplanin with that of the high-performance liquid chromatography (HPLC) method reported previously. The developed FPIA method was employed for the measurement of 36 clinical samples collected from patients with methicillin-resistant Staphylococcus aureus (MRSA) infection.
Results:  The limits of detection and quantification were 0·5 and 0·8 μg/mL, respectively. The recovery rate was 97·5–106·6%. The developed FPIA method showed better accuracy than the HPLC method. The within-run and interday reproducibility of the assay was good, with relative standard deviation values of 4·76–18·75% (within-run) and 5·68–13·95% (interday). Precision and accuracy of this method were within the acceptable limits defined in the US FDA Guidance for bioanalytical method validation. The correlation between the developed FPIA method and the HPLC method was good ( r ² = 0·87). A positive bias with the FPIA method was observed from the result of the Bland–Altman difference plot.
Conclusion:  We firmly believe that the present method is useful for the adjustment of teicoplanin dosages for patients under various conditions.