Determination of the cytotoxic catechol metabolite of etoposide (3'O-demethyletoposide) in human plasma by high-performance liquid chromatography.

The anticancer drug etoposide undergoes O-demethylation in humans. The formed catechol metabolite exhibits significant cytotoxic activity. A simple, rapid, selective, and sensitive reversed-phase high-performance liquid chromatography assay was developed for the measurement of etoposide catechol in plasma of tumour patients. The metabolite was quantified using electrochemical detection. Ascorbic acid was added to each sample to prevent oxidation of etoposide catechol during sample preparation. Linear responses were obtained between 40 ng/ml and 1.25 microg/ml with correlation coefficients exceeding 0.991. The detection limit was 10 ng/ml. Recovery, within-day precision, between-day precision and accuracy were satisfactory. The method has been applied to characterize the concentration-time profile of etoposide catechol in plasma of tumour patients following administration of high-dose etoposide.