A new validated HPLC method for the determination of levodopa: Application to study the impact of ketogenic diet on the pharmacokinetics of levodopa in Parkinson's participants

: A simple, accurate, and reproducible HPLC-UV method has been developed and validated for the quantification of levodopa (l-Dopa) in human plasma. The method involves a simple protein precipitation procedure to extract both l-Dopa and methyldopa, the internal standard. The chromatographic analysis was achieved on a Shimadzu LC 20A HPLC system equipped with a Zorbax Eclipse XDB C18 column and an isocratic mobile phase consisting of 20 mm KH2 PO4 (pH 2.5) and methanol (95:5, v/v) run at a flow rate of 1 mL/min. The UV detection wavelength was set at 230 nm. The method exhibited good linearity (R2  > 0.999) over the assayed concentration range (0.1-10 μg/mL) and demonstrated good intra- and inter-day precision and accuracy (relative standard deviations and the deviation from predicted values were <15%). This method was also successfully applied for studying the potential effect of ketogenic diet on the pharmacokinetics of l-Dopa in Parkinson's participants. Our data analysis indicates that ketogenic diet does not significantly affect the pharmacokinetics of l-Dopa.