Improved detection and determination of carbamazepine and oxcarbazepine and their metabolites by high-performance liquid chromatography.

An HPLC assay for carbamazepine or oxcarbazepine (OXC) and six of their metabolites in one run was applied to 35 clinical samples from patients receiving monotherapy. This rapid and economical method, utilizing a simple one-step extraction with methyl tert.-butyl ether before the run, showed recoveries of 77-108%, except for 43% for 10,11-trans-dihydroxy-10,11-dihydrocarbamazepine, from 500-microliters samples, with detection limits of 8-12 ng/ml and limits of quantification of 14-55 ng/ml depending on the compound. Indication of a new OXC metabolite, 3-hydroxycarbamazepine, was found in 2/12 patients.