Determination of methyldopa in plasma using high-performance liquid chromatography with electrochemical detection. Application to pharmacokinetic/bioavailability studies.

The problem of quantitatively measuring methyldopa (a-methyldopa) in biological matrices after applying therapeutic doses to humans is still challenging. Numerous methods have been published but most of them require a tedious, time-consuming sample preparation, are not specific enough or lack the necessary sensitivity. As the basis of conclusive human pharmacokinetic and bioavailability/bioequivalence studies is a validated analytical method, which is reliable, selective, sensitive and able to proceed hundreds or even thousands of samples in a limited time, an assay to fulfill these needs was developed. The present method employs a hiph-performance liquid chromatographic system consisting of a pump, an ODS column, an autosampler and an electrochemical detector. The assay is sensitive down to 50 ng/ml plasma, the calibration curves are linear in a range of 50-2000 ng/ml, the chromatographic peaks are well resolved and the precision and accuracy are excellent. The assay has been successfully used for the determination of very low methyldopa plasma levels during several clinical studies.