Stereoselective determination of flecainide in human plasma by high-performance liquid chromatography with fluorescence detection.

Enantiomers of a drug may differ in their pharmacological activities or their disposition constants. We now describe a stereoselective analytical method for the determination of the antiarrhythmic agent flecainide in plasma. The resolution of the enantiomers is achieved by high-performance liquid chromatography (HPLC) on a normal phase silica column following derivatization with the optically active reagent (-)-methyl chloroformate. The eluting diastereoisomers are monitored by fluorescence detection at an excitation wavelength of 305 nm and an emission wavelength of 340 nm. The limit of sensitivity for the assay is as low as 2.5 ng/mL for each enantiomer using 1 mL of plasma. A new liquid-liquid extraction procedure with high recovery (greater than 95%) and high selectivity is also reported. The intra- and interassay coefficient of variation for replicated analysis of spiked plasma samples is less than 4.0% and 7.0%, respectively. The method is suitable for single and multiple dose pharmacokinetic studies in healthy volunteers or in patients.