Determination of aniracetam's main metabolite, N-anisoyl-GABA, in human plasma by LC-MS/MS and its application to a pharmacokinetic study

A simple and rapid high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for the determination of 4-p-anisamidobutyric acid (ABA; or N-anysoyl-γ-aminobutiryc acid, N-anisoyl-GABA), a major active metabolite of aniracetam, in human plasma. After protein precipitation of plasma sample with methanol, ABA and the internal standard lisinopril were separated on a Venusil ASB C₁₈ column at 25 °C. The mobile phase consisted of methanol-ammonium acetate (10 mmol/L) (30:70, v/v). The detection was performed on a triple quadrupole tandem mass spectrometer with an ESI source in negative ion mode. Multiple reaction monitoring (MRM) using the precursor→product ion combinations of m/z 235.8→m/z 106.6, and m/z 403.8→m/z 113.6 was used to quantify ABA and lisinopril, respectively. This is the first LC-MS/MS method for ABA with advantages of short analysis time (4.5 min per sample run) and high selectivity attributable to the MRM detection and optimized HPLC conditions. The response was linear in a concentration range of 0.0485-19.4 μg/mL in plasma. The extraction recovery of ABA was between 89.1% and 100.7%. The precision (RSD) and accuracy (RE) of the method were evaluated to be within 7.3% and from 2.5% to 6.9%. The validated method has been applied to the pharmacokinetic study after a single oral administration of aniracetam dispersible tablets to human beings.