A Liquid Chromatographic Method for Quantifying Unbound Micafungin in Human Plasma and the Relationship between the Concentrations of Unbound and Total Micafungin in Plasma

This report describes a modified method for the quantitative determination of unbound micafungin (MCFG) in human plasma that is unrelated to chemical methods currently in use, and the relationship between the concentration of unbound and total MCFG in plasma of the patients. The mobile phase consisted of 50 mM phosphate buffer:tetrahydrofuran (65:35, v/v). Samples were fractionated on a C-18 column. The fluorescence detection wavelengths of excitation and emission were set at 273 nm and 464 nm, respectively. The retention times of MCFG and 1-hydroxy-2-naphtoeic acid (internal standard: IS) were 10.5 min and 7.3 min, respectively. For each concentration of MCFG/IS, the peak height ratio on a 5-point calibration curve was linear from 0.004 to 0.08 μg/mL (r=0.999, p