High-performance liquid chromatography of levomepromazine (methotrimeprazine) and its main metabolites

The phenothiazine drug levomepromazine (methotrimeprazine) has five metabolites which previously have been identified in plasma from psychiatric patients. These are formed by sulphoxidation, N-demethylation, O-demethylation and aromatic hydroxylation in two different positions. A high-performance liquid chromatographic system is described for the analysis of levomepromazine and its main metabolites on a Supelcosil C18-DB column, based on ion-pair formation with sodium docecyl sulphate. The effects of variations in pH, buffer concentration, counter-ion concentration, temperature and concentration and composition of the organic solvent were examined. The six components may be analysed in 27.4 min at room temperature using 25 mM sodium dodecyl sulphate in 500 mM ammonium acetate buffer (pH 5.0)-5% v/v tetrahydrofuran in acetonitrile (50:50, v/v) as the mobile phase.