Determination of encainide and its metabolites by high-performance liquid chromatography

Encainide (ENC) and its metabolites O-demethylencainide (ODE), 3-methoxy- O-demethylencainide (MODE), N-demethylencainide (NDE) and bis- N,O-demethylencainide (NODE) have been measured by two HPLC procedures. The method of Mayol using a μPorasil column with ethanol—water—methanesulphonic acid as mobile phase was not able to separately measure NODE and NDE in plasma. A new method is described using a μBondapak Phenyl column with acetonitrile—phosphate buffer (0.05 M, pH 7.5) that yields satisfactory separation of ENC and its metabolites. NODE was not identified as a metabolite in 23 patients analysed.