Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Vardenafil and Its Application of Bioequivalence

A simple, rapid, and sensitive method of liquid chromatography-tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of vardenafil in rabbit plasma. A simple protein precipitation method with ice-cold acetonitrile was used for plasma extraction. The mass transitions m/z 489 -> 151 and m/z 390 -> 169 were used to measure vardenafil and tadalafil (internal standard), respectively, with a total assay run time of 6 min. The limit of detection was 0.2 ng/mL. The assay was reproducible with intra-assay and interassay precision ranging 1.17%-9.17% and 1.31%-5.86%, respectively. There was also good intra-assay and interassay accuracy between 89.3%-105.3% and 94%-102% of the expected value, respectively. The linearity range was 0.5-60 ng/mL in rabbit plasma (r(2) >= 0.99). The measured AUC from 0 to 24 h (AUG(0-24t)) for the test and reference formulations were 174.38 +/- 95.91 and 176.45 +/- 76.88, respectively. For the test, C-max and T(ma)x were 75.36 +/- 59.53 ng/mL and 1.42 +/- 0.19 h, whereas, for the reference, these were 58.22 +/- 36.11 ng/mL and 2.04 +/- 0.33 h, respectively. The test formulation achieved a slightly lower AUG, 24 , value (p > 0.05), higher C-max values (p > 0.05), faster T-max (p < 0.05), and almost equal bioavailability compared with the reference formulation.