Validated LC-MS/MS method for the simultaneous determination of rotigotine and its prodrug in rat plasma and an application to pharmacokinetics and biological conversion in vitro.

Rotigotine behenate (RGTB), a long chain alkyl ester of the prodrug of rotigotine (RGT), has been synthesized for use in a sustained delivery system. The aim of the present report was to develop and validate a simple, sensitive and reliable LC-MS/MS method for the simultaneous determination of RGT and its prodrug RGTB in rat plasma samples. Detection was performed on a 1290 Infinity UPLC coupled Triple Quad 4500 mass spectrometer operated in positive MRM mode using an Eclipse XDB-CN chromatography column (2.1mm×100mm, 3.5μm) by isocratic elution using a 0.2% formic acid aqueous solution and acetonitrile, with stable isotope labeled RGT as an internal standard. The sample preparation method employed 50μL of a plasma sample and liquid-liquid extraction with a mixture of diethyl ether-dichloromethane (3:2, v/v) as the extraction solvent. The proposed method was fully validated by assessing its specificity, linearity, precision and accuracy, recovery, matrix effects and stability. Good linearity was found within the range of 0.1-10.0ng/mL for both analytes (r>0.996). This method was successfully applied to a pharmacokinetic study of a slow release RGTB formulation in rats following a single intramuscular injection and biological conversion in vitro.