Determination of memantine in human plasma by liquid chromatography–electrospray tandem mass spectrometry: Application to a bioequivalence study

A simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the quantification of memantine (I) in human plasma is presented. Sample preparation consisted of the addition of amantadine (II) as internal standard (IS), liquid–liquid extraction in basic conditions using a mixture of diethyl ether–chloroform (7:3, v/v) as extracting solvent, followed by centrifugation, solvent evaporation and sample reconstitution in methanol. Both I and II (internal standard) were analyzed using a C18 column and a mobile phase composed of methanol–water–formic acid (80:20:0.1, v/v/v). Eluted compounds were monitored using positive mode electrospray (ES) tandem mass spectrometry. The analyses were carried out by selected reaction monitoring (SRM) using the parent to daughter combinations of m/z 180 > 163 (memantine) and m/z 152 > 135 (amantadine). The peak areas from the analyte and IS were used for quantification of I. The achieved limit of quantification (LOQ) was 0.1 ng/mL; the assay exhibited a linear dynamic range of 0.1–50.0 ng/mL with a determination coefficient (r2) of at least 0.98. Validation results on linearity, specificity, accuracy, precision and stability, as well as on application to the analysis of samples taken up to 320 h after oral administration of 20 mg (two 10 mg capsules) of I in healthy volunteers demonstrated the applicability to bioequivalence studies.