High-performance liquid chromatographic assay for mexiletine hydroxylation in microsomes of human liver

A simple high-performance liquid chromatographic assay, using fluorescence detection, is described for determining simultaneously the production of the two major hydroxylated metabolites of mexiletine in human liver microsomes. The detection limits of hydroxymethylmexiletine and p-hydroxymexiletine are 0.35 and 0.08 nmol/ml, respectively. The assay is specific, reproducible and allows the simultaneous kinetic characterization of the reactions in small amounts of liver tissue. The assay may be used to acquire a better knowledge of the kinetic behaviour of mexiletine and of its metabolites, and to investigate if the large inter-individual variations of the mexiletine pharmacokinetics are of metabolic origin, due to variations of its hydroxylation processes.