Simultaneous determination of mexiletine and four hydroxylated metabolites in human serum by high-performance liquid chromatography and its application to pharmacokinetic studies.

A high-performance liquid chromatographic method has been developed for the simultaneous determination of mexiletine and its four hydroxylated metabolites in human serum. The method involves a single-step extraction of mexiletine, hydroxymethylmexiletine, p-hydroxymexiletine and their corresponding alcohols with diisopropyl ether-dichloromethane-propan-2-ol (2.5:1.5:0.5, v/v). Separation of the compounds on a deactivated Supelcosil LC8-DB column is accomplished by high-performance liquid chromatography with ultraviolet detection at 203 nm. Overall the recovery of each compound is reproducible and greater than 75%. The lower limit of detection is 2 ng/ml for mexiletine and its metabolites. The application of the method is shown by measuring the concentrations in serum of mexiletine and its metabolites over 24 h in a healthy volunteer after a single intravenous injection of the drug and by monitoring serum concentrations in patients receiving long-term treatment by mouth of the drug.