LC-ESI-MS/MS method for quantification of ambrisentan in plasma and application to rat pharmacokinetic study.

A sensitive high-performance liquid chromatography-positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of ambrisentan in plasma. The analyte and the internal standard (armodafinil) were extracted from plasma by acetonitrile precipitation and they were separated on a reversed-phase C(18) column with a gradient program. The MS acquisition was performed with multiple reaction monitoring mode using the respective [M + H](+) ions, m/z 379-347 for ambrisentan and m/z 274-167 for the IS. The assay exhibited a linear dynamic range of 1-2000 ng/mL for ambrisentan in plasma. Acceptable precision (<10%) and accuracy (100 ± 8%) were obtained for concentrations over the standard curve range. The method was successfully applied to quantify ambrisentan concentrations in a rodent pharmacokinetic study after a single oral administration of ambrisentan at 2.5 mg/kg to rats. Following oral administration the maximum mean concentration in plasma (C(max) ; 1197 ± 179 ng/mL) was achieved at 1.0 ± 0.9 h (T(max) ), and the area under the curve (AUC) was 6013 ± 997 ng h/mL. Therefore, development of such a simple and sensitive method in rat plasma should translate into a method for ambrisentan in human plasma for clinical trials.