Quantification of methyldopa in human plasma by high-performance liquid chromatography–electrospray tandem mass spectrometry: Application to a bioequivalence study

A method based on LC–MS–MS is described for the determination of methyldopa in human plasma using dopa-phenyl-D3 as the internal standard. The method has a chromatographic run time of 5.5 min and was linear in the range of 20–5000 ng/ml. The limit of quantitation was 20 ng/ml, the intra-day precisions were 7.3, 5.4 and 4.3% and the intra-day accuracies were −8.0, −1.3 and −2.0% for 30, 600 and 3000 ng/ml, respectively. The inter-day precisions were 7.7, 0.5 and 0.7% and the inter-day accuracies were 0.2, −1.1 and −2.3%, respectively, for the above concentrations. This method was employed in a bioequivalence study of two tablet formulations of methyldopa.