Determination of bicuculline in rat plasma by liquid chromatography mass spectrometry and its application in a pharmacokinetic study

• Development and validation of an LC–MS method for the determination of bicuculline in rat plasma.
• The method successfully applied to pharmacokinetic study of bicuculline after gavage administration.
• A simple one-step protein precipitation procedure without further cleanup was developed.

Bicuculline, a phthalide isoquinoline alkaloid is of current interest as an antagonist of gamma-aminobutyric acid (GABA). A simple and sensitive liquid chromatography mass spectrometry method for determination of bicuculline in rat plasma was developed over the range of 5–500 ng/mL. After addition of midazolam as internal standard, protein precipitation with acetonitrile–methanol (9:1, v/v) was used as sample preparation. Chromatographic separation was achieved on a Zorbax SB–C18 (2.1 mm × 150 mm, 5 μm) column with acetonitrile −0.1% formic acid in water as mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used for quantification using target fragment ions m/z 368 for bicuculline and m/z 326 for the IS. Linear calibration was obtained with correlation coefficients r > 0.99. The CV of the precision measurements was less than 13%. The accuracy of the method ranged from 93.6% to 100.5%. Mean recoveries of bicuculline in plasma were in the range of 80.5–91.8%. The method was successfully applied to the pharmacokinetic study after gavage administration of 15 mg/kg bicuculline in rats.