Automated determination of disopyramide and N-monodealkyldisopyramide in plasma by reversed-phase liquid chromatography with a column switching system.

A rapid and simple column liquid chromatographic method involving a column switching system for the determination of disopyramide and its N-monodealkyl metabolite (NMD) in plasma is described. The deproteinized plasma is applied to an automated system. Purification and concentration were performed using a precolumn connected to a six-position valve; analytical separation was done on-line using a cyano reversed-phase column with a mobile phase consisting of 10 mmol/l trimethylamine (pH 2.5, adjusted with phosphoric acid)-acetonitrile-tetrahydrofuran (78:20:2, v/v/v). Absorbance was measured at 265 nm, with a minimum detectable amount of disopyramide and NMD of 0.1 micrograms/ml. The method can be applied to drug monitoring and pharmacokinetic studies.