Simultaneous determination of amitriptyline, nortriptyline and their respective isomeric 10-hydroxy metabolites in plasma by liquid chromatography.

An ion-pair reversed-phase liquid chromatographic method for the determination of the tricyclic antidepressant amitriptyline, the demethylated metabolite nortriptyline, and their respective cis- and trans-hydroxylated metabolites in plasma is presented. After extraction from 1 ml of plasma, the reconstituted residue was chromatographed on a trimethylsilyl packed column using a mobile phase of acetonitrile and acetate buffer with sodium heptane-sulfonate and triethylamine. Recovery of the drugs and its metabolites from plasma ranged from 56 to 99%. The method is suitable for determining plasma concentrations as low as 5 ng/ml (C.V. less than 9%) for all six compounds. Plasma concentrations of amitriptyline and its metabolites from eleven different patients are presented.