A sensitive and validated HPLC-UV method for the quantitative determination of the new antifungal drug isavuconazole in human plasma

Isavuconazole is a broad‐spectrum triazole antifungal drug recently approved for the therapy of both invasive aspergillosis and mucormycosis. To support a widespread therapeutic drug monitoring of isavuconazole, a simple, sensitive, and precise high‐performance liquid chromatography method with UV detection was developed and fully validated for the quantification of this drug in human plasma. The method involved a combined protein precipitation−solid‐phase extraction and a chromatographic separation on a Waters XTerra RP18 (150 × 4.6 mm, 3.5 μm) column using an isocratic mobile phase of ammonium acetate buffer (pH 8.0, 10 mm) and acetonitrile (45:55, v/v). The UV detection was performed at 285 nm. This method was linear (correlation coefficients ≥0.998), specific (no interference with plasma components or various potentially co‐administrated drugs), sensitive (lower limit of quantification of 0.025 μg/mL), reproducible (coefficients of variation were ≤7.9%) and accurate (deviations ranged from −5.0 to 8.0%) over the range of 0.025–10 μg/mL. The method fulfilled all of the US Food and Drug Administration guidelines validation criteria and performed well in an international proficiency testing program. The assay was also successfully applied to routine therapeutic drug monitoring of patients and to drug stability investigations under various conditions.