Improved method for the determination of 4'-epidoxorubicin and seven metabolites in plasma by high-performance liquid chromatography.

4'-Epidoxorubicin, its seven metabolites and doxorubicin, as internal standard, were efficiently extracted from plasma using C18 Sep-Pak cartridges. The recoveries ranged from 58% for doxorubicin aglycone up to 98% for 4'-epidoxorubicin glucuronide. The anthracyclines were separated by reversed-phase high-performance liquid chromatography within 9 min and analysed by fluorescence. The assay was sensitive to 3 X 10(-10) M for the glucuronides up to 12 X 10(-10) M for 7-deoxydoxorubicin aglycone. The peak-height ratio of the fluorescence intensities of the anthracyclines versus doxorubicin showed a linear correlation with the concentration from the detection limit up to 2.5 X 10(-7) M (correlation coefficient r2 greater than 0.99). Within-day and between-day precision of the assay were in the ranges 2-14% (n = 6) and 2-11% (n = 6), respectively.