Continuous intravenous monitoring of levodopa and 3-O-methyldopa by microdialysis and high-performance liquid chromatography with electrochemical detection.

Microdialysis, in association with ion-pair reversed-phase high-performance liquid chromatography with electrochemical detection, was applied in vitro for the determination and quantification of levodopa and 3-O-methyldopa in blank spiked plasma and blood. The method presented gave accurate results; the calibration graphs for plasma were linear over the range of the expected values for both compounds. When using a dialysis probe with a membrane length of 1.6 cm at a 5 microliters min-1 perfusion speed, the recovery rate in plasma for levodopa was 30.1% and 68.5% for 3-O-methyldopa. However, less reproducible results were obtained for plasma levodopa levels in the range of 0.5 microliter ml-1 and lower. The microdialysis technique was subsequently successfully applied for the continuous intravenous monitoring of levodopa and 3-O-methyldopa in a levodopa-treated dogs.