A sensitive LC–MS/MS method for determination of levamisole in human plasma: Application to pharmacokinetic study

A sensitive and rapid LC–MS/MS method was developed and validated for the determination of levamisole in human plasma. The assay was based on liquid–liquid extraction of analytes from human plasma with ethyl ether. Chromatographic separation was carried on an Agilent HC-C8 column (150 mm × 4.6 mm, 5 μm) at 40 °C, with a mobile phase consisting of acetonitrile—10 mM ammonium acetate (70:30, v/v), a flow rate of 0.5 mL/min and a total run time of 6 min. Detection and quantification were performed by mass spectrometry in the multiple reaction monitoring mode with positive electrospray ionization m/z at 205.1 → 178.2 for levamisole, and m/z 296.1 → 264.1 for mebendazole (internal standard). The assay was linear over a concentration range of 0.1–30 ng/mL with a lower limit of quantification of 0.1 ng/mL. The coefficient of variation of the assay precision was less than 8.5%. The assay was successfully used to analyze human plasma samples in a pharmacokinetic study where levamisole was administered as a liniment.