A validated high-performance liquid chromatographic method for the determination of levodopa in rat plasma & its application in pharmacokinetic studies

Levodopa (l-dopa), the metabolic precursor of dopamine, has primarily been used for the treatment of Parkinson's disease (PD). A reversed phase high performance liquid chromatography (RP-HPLC) method with UV-detection at room temperature has been developed for analysis of levodopa. The method entailed direct injection of rat plasma sample after deproteinization using acetonitrile — propanol (1:1). The mobile phase comprises a mixture of water and acetonitrile containing 0.1% trifloroacetic acid. The flow rate was set at 1.0 ml/min with detector operating at 280nm and utilizes C18 (150 mm × 4.6 mm i.d. column) for the chromatographic separation. Under these conditions, the method was validated with respect to linearity, recovery, specificity, accuracy, precision, and stability. The described method was linear over a range of 0.39–200 μg/ml with mean correlation coefficient of 0.999. The percentage mean recovery was found to be 98.4%, while the coefficient of variation of within-day and between-day measurements were all less than 8%. The limit of quantification (LOQ) and limit of detection (LOD) of the method were 0.39 μg/ml and 0.19 μg/ml, respectively. This validated method was applied to determine the pharmacokinetic profiles of levodopa in rat plasma after its intestinal administration.