Abstract
A rapid, sensitive, and simple ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC/MS/MS) method for the determination of udenafil and its active metabolite, DA‐8164, in human plasma and urine using sildenafil as an internal standard (IS) was developed and validated. Udenafil, DA‐8164 and IS from a 100 µL aliquot of biological samples were extracted by protein precipitation using acetonitrile. Chromatographic separation was carried on an Acquity UPLC BEH C~18~ column (50 × 2.1 mm, i.d., 1.7 µm) with an isocratic mobile phase consisting of acetonitrile and containing 0.1% formic acid (75:25, v/v) at flow rate of 0.4 mL/min, and total run time was within 1 min. Detection and quantification was performed by the mass spectrometer using multiple reaction‐monitoring mode at m/z 517 → 283 for udenafil, m/z 406 → 364 for DA‐8164 and m/z 475 → 100 for IS. The assay was linear over a concentration range of 1–600 ng/mL with a lower limit of quantification of 1 ng/mL in both human plasma and urine. The coefficient of variation of this assay precision was less than 13.7%, and the accuracy exceeded 92.0%. This method was successfully applied for pharmacokinetic study after oral administration of udenafil 100 mg to healthy Korean male volunteers. Copyright © 2008 John Wiley & Sons, Ltd.