Determination of silodosin in human plasma by liquid chromatography-tandem mass spectrometry.

A rapid, sensitive and specific liquid chromatography-tandem mass spectrometric (LC-MS/MS) method has been developed and validated for the determination of silodosin in human plasma. Silodosin and internal standard (IS) were extracted from human plasma by liquid-liquid extraction using methyl t-butyl ether and analyzed on an Agilent C(8) column with the mobile phase of acetonitrile-10 mM ammonium acetate (40:60, v/v) adjusted to pH 4.5 with acetic acid. Detection was carried out by MS/MS using TurboIonSpray (TIS) ionization and multiple reaction monitoring (MRM) in the positive-ion mode. The mass transitions monitored were m/z 496.3-->261.4 and m/z 440.4-->259.3 for silodosin and IS, respectively. The standard curve was linear in the range of 0.50-50.0 ng/ml with intra- and inter-day precision of 3.2-7.2% and 2.0-7.5%, respectively. The lower limit of quantification (LLOQ) for silodosin was 0.50 ng/ml using 500 microl plasma sample. This method was successfully applied to the pharmacokinetic study in healthy volunteers.