Determination of the enantiomers of flecainide and two major metabolites in man by gas chromatography/mass spectrometry using negative ion chemical ionization and stable isotope labelled internal standards

Abstract

The class I antiarrhythmic drug flecainide (1) is used clinically as racemate. In order to study the stereochemical disposition and excretion of 1 an analytical method has been developed based on a deuterated analogue of 1 as internal standard and on measurement with gas chromatography/mass spectrometry (GC/MS) using negative ion chemical ionization (NICI). Several diasteromeric derivatives prepared were separated on an achiral capillary column. All derivatives exhibited negative ion properties forming characteristic fragments: [M  CH2CF3]− and [M  HF]−., respectively. The limit of detection was 1 pmol ml−1 plasma corresponding to 0.41 ng ml−1 of free base. A more convenient and in particular more precise approach was investigated by separating the pentafluoropropionyl (PFP) derivatives on a chiral phase capillary column monitoring the base peak [M  20]−. in NICI mode. This method is not only the most sensitive assay of 1 presently available, but also allows for the determination of the enantiomers of flecainide in biological fluids. In addition, the assay could be applied to the dtermination of the enantiomers of one of the major metabolites of flecainide, the meta-O-dealkylated flecainide (MODF), in human urine. Additionally, a non-sterospecific assay was developed and applied to the quantification of the two major metabolites of flecainide, MODF and the meta-O-dealkylated flecainide lactam in human urine. Deuterated analogues were used as internal standards and measurement of the PFP derivatives with GC/MS using NICI was performed.