Development and validation of an LC‐MS/MS method for simultaneous quantification of levodopa and MD01 in rat plasma and its application to a pharmacokinetic study of mucuna pruriens extract

Mucuna pruriens, an ancient Indian herbal medicine containing levodopa, is widely used for Parkinson's disease. In order to simultaneously determine levodopa and 1,1‐dimethyl‐3‐carboxy‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline (MD01) in rat plasma, an improved LC‐MS/MS method was developed and validated for a pharmacokinetic study in rats orally administered levodopa or Mucuna pruriens extract (MPE). Elimination of matrix effect and improvement of extraction recovery were achieved through systematic optimization of reversed‐phase and hydrophilic interaction chromatographic conditions together with sample clean‐up procedures. A satisfactory chromatographic performance was obtained with a Thermo Aquasil C₁₈ column (50 × 2.1 mm, 3 µm) using acetonitrile and water containing 0.2% formic acid as mobile phases. Futhermore, sodium metabisulfite and formic acid were used as stabilizers in neat solutions as well as rat plasma. The method was validated in a dynamic range of 20.0–10,000 ng/mL for levodopa and MD01; the intra‐ and inter‐day precision and accuracy were acceptable. The method was successfully utilized to determine the levodopa level in plasma samples of rats administered levodopa or MPE. Pharmacokinetic results showed that an increase in the AUC of levodopa was observed in rats following oral administration of multiple doses of MPE. Copyright © 2016 John Wiley & Sons, Ltd.