Development and validation of a UPLC–MS/MS method for quantitation of droxidopa in human plasma: Application to a pharmacokinetic study

• A validated UPLC–MS/MS method was reported to determine droxidopa in human plasma for the first time.
• The method has an LLOQ of 5.00 ng/mL.
• Sample preparation was simple and quick with methanol containing formic acid protein precipitation. The separation was achieved on BEH Amide column.

In this study, a simple and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS) method was developed and validated for quantitation of droxidopa in human plasma for the first time. A simple plasma protein precipitation method using methanol containing 3% formic acid was selected, and the separation was achieved by an Acquity UPLC™ BEH Amide column (2.1 mm × 50 mm, 1.7 μm) with a gradient elution using acetonitrile, ammonium formate buffer and formic acid as mobile phase. The detection of droxidopa and benserazide (internal standard, IS) was performed using positive-ion electrospray tandem mass spectrometry via multiple reaction monitoring (MRM). The precursor-to-product ion transitions m/z 214.2 → m/z 152.0 for droxidopa, and m/z 258.1 → m/z 139.1 for IS were used for quantification. A lower limit of quantification of 5.00 ng/mL was achieved and the linear curve range was 5.00–4000 ng/mL using a weighted (1/x2) linear regression model. Intra-assay and inter-assay precision was less than 10.2%, and the accuracy ranged from 0.1% to 2.1%. Stability, recovery and matrix effects were within the acceptance criteria recommended by the regulatory bioanalytical guidelines. The method was successfully applied to a pharmacokinetic study of droxidopa in healthy Chinese volunteers.